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A Benchmark Approach to Quantitative Finance

Eckhard PlatenSchool of Finance and Economics and Department of Mathematical Sciences

University of Technology, Sydney

Lit: Platen, E. & Heath, D.: A Benchmark Approach to Quantitative Finance

Springer Finance, 700 pp., 199 illus., Hardcover, ISBN-10 3-540-26212-1 (2006).

Platen, E.: A benchmark approach to finance. Mathematical Finance16(1), 131-151 (2006).

Buhlmann, H. & Platen, E.: A discrete time benchmark approach for insurance and finance

ASTIN Bulletin33(2), 153-172 (2003).

Contents1 Asset Pricing 1

2 Continuous Financial Markets 55

3 Portfolio Optimization 91

4 Modeling Stochastic Volatility 107

5 Minimal Market Model 154

6 Stylized Multi-Currency MMM 214

7 Valuing Guaranteed Minimum Death Benefits 219

8 Markets with Event Risk 273

References 337

1 Asset Pricing

Law of One Price

“All replicating portfolios of a payoff have the same price!”

Debreu (1959), Sharpe (1964), Lintner (1965),

Merton (1973a, 1973b), Ross (1976), Harrison & Kreps (1979),

Cochrane (2001),. . .

will be, in general, violated under the benchmark approach.

c© Copyright Eckhard Platen 10 BA - Toronto C 1 1

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1930 1940 1950 1960 1970 1980 1990 2000

time

ln(savings bond)ln(fair zero coupon bond)

ln(savings account)

Figure 1.1: Logarithms of savings bond, fair zero coupon bondand savings

account.c© Copyright Eckhard Platen 10 BA - Toronto C 1 2

Financial Market

• jth primary security account

Sjt

j ∈ 0, 1, . . . , d

• savings account

S0t

t ≥ 0

c© Copyright Eckhard Platen 10 BA - Toronto C 1 3

• strategy

δ = δt = (δ0t , δ1t , . . . , δ

dt )⊤, t ≥ 0

predictable

• portfolio

Sδt =

d∑

j=0

δjt S

jt

• self-financing

dSδt =

d∑

j=0

δjt dS

jt

c© Copyright Eckhard Platen 10 BA - Toronto C 1 4

• strictly positive portfolio

Sδ0 = x > 0

Sδt ∈ (0,∞) for all t ∈ [0,∞)

=⇒ Sδ ∈ V+x

c© Copyright Eckhard Platen 10 BA - Toronto C 1 5

Numeraire Portfolio

Definition 1.1 Sδ∗ ∈ V+x numeraire portfolioif

Et

Sδt+h

Sδ∗

t+h

Sδt

Sδ∗

t

− 1

≤ 0

for all nonnegativeSδ and t, h ∈ [0,∞).

• Sδ∗ “best” performing portfolio

Long (1990), Becherer (2001), Pl. (2002, 2006),

Buhlmann& Pl. (2003), Goll & Kallsen (2003), Karatzas & Kardaras (2007)

c© Copyright Eckhard Platen 10 BA - Toronto C 1 6

Main Assumption of the Benchmark Approach

Assumption 1.2 There exists a numeraire portfolioSδ∗ ∈ V+x .

c© Copyright Eckhard Platen 10 BA - Toronto C 1 7

EWI

MCI

DWI

WSI

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

1/1/73 28/9/76 25/6/80 22/3/84 18/12/87 15/9/91 12/6/95 9/3/99 4/12/02 31/8/06

$US

Figure 1.2: Constructed MCI, DWI, EWI and WSI. In the long term the WSI

and EWI outperform all other indices, Le& Platen (2006).

c© Copyright Eckhard Platen 10 BA - Toronto C 1 8

• benchmarked value

Sδt =

Sδt

Sδ∗

t

Supermartingale Property

Corollary 1.3 For nonnegativeSδ

Sδt ≥ Et

(

Sδs

)

0 ≤ t ≤ s < ∞

Sδ supermartingale

c© Copyright Eckhard Platen 10 BA - Toronto C 1 9

• long term growth rate

gδ = lim supt→∞

1

tln

(

Sδt

Sδ0

)

Theorem 1.4 For Sδ ∈ V+x

gδ ≤ gδ∗ .

• “pathwise best” in the long run

Karatzas & Shreve (1998), Pl. (2004a),

Karatzas & Kardaras (2007)

c© Copyright Eckhard Platen 10 BA - Toronto C 1 10

Pl. (2004a)

Definition 1.5 Nonnegative portfolioSδ outperforms systematicallySδ if

(i) Sδ0 = Sδ

0 ;

(ii) P(

Sδt ≥ Sδ

t

)

= 1

(iii) P(

Sδt > Sδ

t

)

> 0.

• “relative arbitrage” Fernholz & Karatzas (2005)

c© Copyright Eckhard Platen 10 BA - Toronto C 1 11

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0

1

1930 1940 1950 1960 1970 1980 1990 2000

time

ln(fair zero coupon bond)ln(savings account)

Figure 1.3: Logarithms of fair zero coupon bond and savings account.

c© Copyright Eckhard Platen 10 BA - Toronto C 1 12

Theorem 1.6 Numeraire portfolio cannot be outperformed systematically.

c© Copyright Eckhard Platen 10 BA - Toronto C 1 13

• portfolio ratio

Aδt,h =

Sδt+h

Sδt

• expected growth

gδt,h = Et

(

ln(

Aδt,h

))

t, h ≥ 0

c© Copyright Eckhard Platen 10 BA - Toronto C 1 14

Definition 1.7 Sδ growth optimal if

gδt,h ≤ g

δt,h

for all t, h ≥ 0 and nonnegativeSδ.

• expected log-utility

Kelly (1956)

Hakansson (1971a)

Merton (1973a)

Roll (1973)

Markowitz (1976)

c© Copyright Eckhard Platen 10 BA - Toronto C 1 15

Theorem 1.8 The numeraire portfolio is growth optimal.

c© Copyright Eckhard Platen 10 BA - Toronto C 1 16

Strong Arbitrage

• market participants can only exploit arbitrage

• limited liability

=⇒ nonnegative total wealth of each market participant

Definition 1.9 A nonnegativeSδ is a strong arbitrageif Sδ0 = 0 and

P(

Sδt > 0

)

> 0.

Pl. (2002)-mathematical arguments (super-martingale property)

Loewenstein & Willard (2000)-economic arguments

c© Copyright Eckhard Platen 10 BA - Toronto C 1 17

Theorem 1.10 There isno strong arbitrage.

c© Copyright Eckhard Platen 10 BA - Toronto C 1 18

• Delbaen & Schachermayer (1998)

free lunches with vanishing risk (FLVR)

• Loewenstein & Willard (2000)

free snacks& cheap thrills

=⇒ no-arbitrage pricing makes no sense under BA

c© Copyright Eckhard Platen 10 BA - Toronto C 1 19

-0.2

0

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1

1930 1940 1950 1960 1970 1980 1990 2000

time

Figure 1.4:P (t, T ) minus savings account.

c© Copyright Eckhard Platen 10 BA - Toronto C 1 20

-0.0004

-0.0002

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0.0014

0.0016

0.0018

1920 1922 1924 1926 1928

time

Figure 1.5:P (t, T ) minus savings account.

c© Copyright Eckhard Platen 10 BA - Toronto C 1 21

• Existence of equivalent risk neutral probability measure is

more amathematical conveniencethan an economic necessity.

• Basing quantitative methods on classical risk neutral pricing is

restrictive.

• Trends are ignored under

Fundamental Theorem of Asset Pricing

Delbaen & Schachermayer (1998)

c© Copyright Eckhard Platen 10 BA - Toronto C 1 22

• Equivalent to risk neutral pricing are pricing via:

stochastic discount factor, Cochrane (2001);

deflator, Duffie (2001);

pricing kernel , Constantinides (1992);

state price density, Ingersoll (1987);

numeraire portfolio as in Long (1990)

All ignore trends !

c© Copyright Eckhard Platen 10 BA - Toronto C 1 23

• One needs consistent pricing concept that exploits trends

• All benchmarked nonnegative securities are supermartingales

(no upward trend)

c© Copyright Eckhard Platen 10 BA - Toronto C 1 24

Definition 1.11 Price is fair if, when benchmarked, forms martingale

(no trend)

Sδt = Et

(

Sδs

)

0 ≤ t ≤ s < ∞.

c© Copyright Eckhard Platen 10 BA - Toronto C 1 25

Lemma 1.12 Theminimal nonnegative supermartingale that reaches a

given benchmarked contingent claimis a martingale.

see Pl.& Heath (2006)

c© Copyright Eckhard Platen 10 BA - Toronto C 1 26

0

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1930 1940 1950 1960 1970 1980 1990 2000

time

benchmarked savings bondbenchmarked fair zero coupon bond

Figure 1.6: Benchmarked savings bond and benchmarked fair zero coupon

bond.c© Copyright Eckhard Platen 10 BA - Toronto C 1 27

Law of the Minimal Price

Pl. (2008)

Theorem 1.13 If a fair portfolio replicates a nonnegative payoff, then this

represents the minimal replicating portfolio.

• least expensive

• minimal hedge

• economically correct price in a competitive market

c© Copyright Eckhard Platen 10 BA - Toronto C 1 28

• contingent claim

HT

E0

(

HT

Sδ∗

T

)

< ∞

• SδH

t fair if

SδH

t =SδH

t

Sδ∗

t

= Et

(

HT

Sδ∗

T

)

Link with real economy !

c© Copyright Eckhard Platen 10 BA - Toronto C 1 29

Law of the Minimal Price =⇒

Corollary 1.14

Minimal price for replicableHT is fair and given by

real world pricing formula

SδH

t = Sδ∗

t Et

(

HT

Sδ∗

T

)

.

c© Copyright Eckhard Platen 10 BA - Toronto C 1 30

• most pricing concepts are unified and generalized by real world pricing

=⇒

actuarial pricing

risk neutral pricing

pricing with stochastic discount factor

pricing with numeraire change

pricing with deflator

pricing with state pricing density

pricing with pricing kernel

pricing with numeraire portfolio

c© Copyright Eckhard Platen 10 BA - Toronto C 1 31

WhenHT independentof Sδ∗

T

=⇒ rigorous derivation of

• actuarial pricing formula

SδH

t = P (t, T )Et(HT )

with zero coupon bond

P (t, T ) = Sδ∗

t Et

(

1

Sδ∗

T

)

c© Copyright Eckhard Platen 10 BA - Toronto C 1 32

• real world pricing formula =⇒

SδH

0 = E0

(

ΛT

S00

S0T

HT

)

Λt =S0

t

S00

supermartingale

1 = Λ0 ≥ E0(ΛT )

=⇒

SδH

0 ≤E0

(

ΛTS0

0

S0T

HT

)

E0(ΛT )

similar for any numeraire (hereS0 savings account)

c© Copyright Eckhard Platen 10 BA - Toronto C 1 33

0

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20

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40

50

60

70

80

90

100

1930 1940 1950 1960 1970 1980 1990 2000

time

Figure 1.7: Discounted S&P500 total return index.

c© Copyright Eckhard Platen 10 BA - Toronto C 1 34

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Radon-Nikodym derivativeTotal RN-Mass

Figure 1.8: Radon-Nikodym derivative and total mass of putative risk neutral

measure.c© Copyright Eckhard Platen 10 BA - Toronto C 1 35

• special case whensavings account is fair:

=⇒ ΛT = dQ

dPforms martingale; E0(ΛT ) = 1;

equivalent risk neutral probability measureQ exists;

Bayes’ formula =⇒risk neutral pricing formula

SδH

0 = EQ0

(

S00

S0T

HT

)

Harrison & Kreps (1979), Ingersoll (1987),

Constantinides (1992), Duffie (2001), Cochrane (2001),. . .

• otherwise “risk neutral price”≥ real world price

c© Copyright Eckhard Platen 10 BA - Toronto C 1 36

-1

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9

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time

ln(index)ln(savings account)

Figure 1.9: ln(S&P500 accumulation index) and ln(savings account).

c© Copyright Eckhard Platen 10 BA - Toronto C 1 37

Extreme Maturity Bond

• short rate deterministic

• savings bond

P ∗(t, T ) =S0

t

S0T

• index S1 as numeraire portfolioSδ∗

c© Copyright Eckhard Platen 10 BA - Toronto C 1 38

• fair zero coupon bond

Law of the Minimal Price

=⇒ real world pricing formula

P (t, T ) = Sδ∗

t Et

(

1

Sδ∗

T

)

• benchmarked fair zero coupon bond

P (t, T ) =P (t, T )

Sδ∗

t

martingale

c© Copyright Eckhard Platen 10 BA - Toronto C 1 39

• discounted numeraire portfolio

Sδ∗

t =Sδ∗

t

S0t

numeraire portfolio for continuous market:

dSδ∗

t = αt dt+

Sδ∗

t αt dWt

time transformed squared Bessel process

c© Copyright Eckhard Platen 10 BA - Toronto C 1 40

• model the drift of discounted index as

αt = α expη t=⇒

Sδ∗

t time transformed squared Bessel process of dimension four

=⇒ Minimal Market Model

MMM, see Pl.& Heath (2006)

• net growth rate

η ≈ 0.054 with R2 of 0.89

c© Copyright Eckhard Platen 10 BA - Toronto C 1 41

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5

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time

ln(discounted index)trendline

Figure 1.10: Logarithm of discounted S&P500 and trendline.

c© Copyright Eckhard Platen 10 BA - Toronto C 1 42

• normalized index

Yt =Sδ∗

t

αt

dYt = (1 − η Yt) dt+√

Yt dWt

• quadratic variation of√Yt

d√

Yt = . . .+1

2dWt

it∑

ℓ=1

(

Ytℓ−√

Ytℓ−1

)2

≈[√Y]

t=t

4

• scaling parameter α ≈ 0.01468 with R2 of 0.995

c© Copyright Eckhard Platen 10 BA - Toronto C 1 43

0

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10

15

20

25

30

1930 1940 1950 1960 1970 1980 1990 2000

time

[sqrt Y]trendline

Figure 1.11: Quadratic Variation of√Yt.

c© Copyright Eckhard Platen 10 BA - Toronto C 1 44

• fair zero coupon bond

P (t, T ) = P ∗(t, T )

(

1 − exp

− 2 η Sδ∗

t

α (expη T − expη t)

)

• initial prices

P ∗(0, T ) = 0.0335

P (0, T ) = 0.00077

P (0,T )P ∗(0,T )

< 0.023 =⇒ 2.3%

no strong arbitrage

c© Copyright Eckhard Platen 10 BA - Toronto C 1 45

0

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time

benchmarked savings bondbenchmarked fair zero coupon bond

Figure 1.12: Benchmarked savings bond and benchmarked fair zero coupon

bond.c© Copyright Eckhard Platen 10 BA - Toronto C 1 46

0

0.1

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1

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time

savings bondfair zero coupon bond

savings account

Figure 1.13: Savings bond, fair zero coupon bond and savings account.

c© Copyright Eckhard Platen 10 BA - Toronto C 1 47

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time

ln(savings bond)ln(fair zero coupon bond)

Figure 1.14: Logarithms of fair zero coupon bond and savings account.

c© Copyright Eckhard Platen 10 BA - Toronto C 1 48

• savings account isoutperformed systematically

by fair zero coupon bond

c© Copyright Eckhard Platen 10 BA - Toronto C 1 49

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time

ln(fair zero coupon bond)ln(savings account)

Figure 1.15: Logarithms of fair zero coupon bond and savings account.

c© Copyright Eckhard Platen 10 BA - Toronto C 1 50

• self-financing hedge portfoliohedge ratio

δ∗t =

∂P (t, T )

∂Sδ∗

t

= P ∗(0, T ) exp

−2 η Sδ∗

t

α (expη T − expη t)

× 2 η

α (expη T − expη t)

c© Copyright Eckhard Platen 10 BA - Toronto C 1 51

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time

ln(zero coupon bond)ln(self financing hedge portfolio)

Figure 1.16: Logarithm of zero coupon bond and self-financinghedge port-

folio.c© Copyright Eckhard Platen 10 BA - Toronto C 1 52

-2e-005

-1e-005

0

1e-005

2e-005

3e-005

4e-005

5e-005

6e-005

7e-005

1930 1940 1950 1960 1970 1980 1990 2000

time

Figure 1.17: Benchmarked profit and loss.

c© Copyright Eckhard Platen 10 BA - Toronto C 1 53

0

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time

Figure 1.18: Fraction invested in the index.

c© Copyright Eckhard Platen 10 BA - Toronto C 1 54

2 Continuous Financial Markets

• d sources of continuoustraded uncertainty

independent standard Wiener processes

W 1,W 2, . . . ,W d, d ∈ 1, 2, . . .

c© Copyright Eckhard Platen 10 BA - Toronto C 2 55

Primary Security Accounts

Sjt - jth primary security account at timet,

j ∈ 0, 1, . . . , d

cum-dividend share value or savings account value,

dividends or interest are accumulated, reinvested

• vector process of primary security accounts

S = St = (S0t , . . . , S

dt )⊤, t ∈ [0, T ]

c© Copyright Eckhard Platen 10 BA - Toronto C 2 56

• assumeunique strong solutionof SDE

dSjt = Sj

t

(

ajt dt+

d∑

k=1

bj,kt dW k

t

)

t ∈ [0,∞), Sj0 > 0, j ∈ 1, 2, . . . , d

• predictable, integrable appreciation rate processesaj

• predictable, square integrable volatility processesbj,k

c© Copyright Eckhard Platen 10 BA - Toronto C 2 57

• savings account

S0t = exp

∫ t

0

rs ds

predictable, integrable short rate process

r = rt, t ∈ [0,∞)

c© Copyright Eckhard Platen 10 BA - Toronto C 2 58

• Market price of risk

The unique invariant of the market

θt = (θ1t , θ

2t , . . . , θ

dt )⊤

solution of relation

bt θt = at − rt 1

where

at = (a1t , a

2t , . . . , a

dt )

1 = (1, 1, . . . , 1)⊤

c© Copyright Eckhard Platen 10 BA - Toronto C 2 59

Assumption 2.1

Volatility matrixbt = [bj,kt ]dj,k=1 is invertible

=⇒• market price of risk equals

θt = b−1t (at − rt 1)

c© Copyright Eckhard Platen 10 BA - Toronto C 2 60

• rewritejth primary security account SDE

dSjt = Sj

t

rt dt+d∑

k=1

bj,kt (θk

t dt+ dW kt )

t ∈ [0,∞), j ∈ 1, 2, . . . , d

c© Copyright Eckhard Platen 10 BA - Toronto C 2 61

• strategy

δ = δt = (δ0t , . . . , δdt )⊤, t ∈ [0, T ]

predictable andS-integrable,

δjt number of units ofjth primary security account

• portfolio

Sδt =

d∑

j=0

δjt S

jt

c© Copyright Eckhard Platen 10 BA - Toronto C 2 62

• Sδ self-financing⇐⇒

dSδt =

d∑

j=0

δjt dS

jt

changes in the portfolio value only due to gains from trading,

self-financing in each denomination

c© Copyright Eckhard Platen 10 BA - Toronto C 2 63

• jth fraction

πjδ,t = δj

t

Sjt

Sδt

j ∈ 0, 1, . . . , d

d∑

j=0

πjδ,t = 1

c© Copyright Eckhard Platen 10 BA - Toronto C 2 64

• portfolio SDE

dSδt = Sδ

t

(

rt dt+

d∑

k=1

bkδ,t

(

θkt dt+ dW k

t

)

)

with kth portfolio volatility

bkδ,t =

d∑

j=1

πjδ,t b

j,kt

c© Copyright Eckhard Platen 10 BA - Toronto C 2 65

• logarithm of strictly positive portfolio

d ln(Sδt ) = gδ

t dt+

d∑

k=1

bkδ,t dW

kt

with growth rate

gδt = rt +

d∑

k=1

bkδ,t

(

θkt − 1

2bk

δ,t

)

c© Copyright Eckhard Platen 10 BA - Toronto C 2 66

Numeraire Portfolio Sδ∗ = Growth Optimal Portfolio

=⇒ maximize the growth rate

gδt = rt +

d∑

k=1

d∑

j=1

πjδ,t b

j,kt

(

θkt − 1

2

d∑

ℓ=1

πℓδ,t b

ℓ,kt

)

=⇒ for eachj ∈ 1, 2, . . . , d

0 =

d∑

k=1

bj,kt

(

θkt −

d∑

ℓ=1

πℓδ∗,t b

ℓ,kt

)

=⇒θ⊤

t = π⊤δ∗,t bt

c© Copyright Eckhard Platen 10 BA - Toronto C 2 67

Sincebt invertible=⇒

πδ∗,t = (π1δ∗,t, . . . , π

dδ∗,t)

= (b−1t )⊤ θt

=⇒ NP

dSδ∗

t = Sδ∗

t

([

rt +

d∑

k=1

(θkt )2

]

dt+

d∑

k=1

θkt dW

kt

)

finite NP exists

c© Copyright Eckhard Platen 10 BA - Toronto C 2 68

Benchmarked Portfolios

Sδt =

Sδt

Sδ∗

t

dSδt = Sδ

t

rt dt+

d∑

k=1

d∑

j=0

πjδ,t b

j,kt

(

θkt dt+ dW k

t

)

dSδ∗

t = Sδ∗

t

(

rt dt+d∑

k=1

θkt

(

θkt dt+ dW k

t

)

)

dSδt = −Sδ

t

d∑

k=1

d∑

j=0

πjδ,t s

j,kt dW k

t

driftless =⇒ local martingale =⇒ supermartingalewhen nonnegative

c© Copyright Eckhard Platen 10 BA - Toronto C 2 69

Theorem 2.2 Any nonnegative benchmarked portfolio is an

(A, P )-supermartingale(no upward trend).

c© Copyright Eckhard Platen 10 BA - Toronto C 2 70

=⇒ NP is numeraire portfolio

use NP asbenchmark for investment and asnumeraire for pricing

• markets have thousands of primary security accounts

c© Copyright Eckhard Platen 10 BA - Toronto C 2 71

Example of a Multi-Asset BS Model

• jth primary security account

dSjt = Sj

t

[

(

r + σ2

(

1 +1√d

))

dt+σ√d

d∑

k=1

dW kt + σ dW j

t

]

t ∈ [0, T ], j ∈ 1, 2, . . . , d, σ > 0

general market risk, specific market risk

c© Copyright Eckhard Platen 10 BA - Toronto C 2 72

• NP fractions

πjδ∗,t =

(√d(

1 +√d))−1

j ∈ 1, 2, . . . , d

π0δ∗,t =

(

1 +√d)−1

• NP SDE

dSδ∗

t = Sδ∗

t

(

(

r + σ2)

dt+σ√d

d∑

k=1

dW kt

)

• simulate overT = 32 yearsd = 50 risky primary security accounts

σ = 0.15, r = 0.05

c© Copyright Eckhard Platen 10 BA - Toronto C 2 73

0

5

10

15

20

25

0 5 10 15 20 25 30 35

time

Figure 2.1: Simulated primary security accounts.

c© Copyright Eckhard Platen 10 BA - Toronto C 2 74

0

1

2

3

4

5

6

7

8

9

10

0 5 10 15 20 25 30 35

time

GOPB

Figure 2.2: Simulated NP and savings account.

c© Copyright Eckhard Platen 10 BA - Toronto C 2 75

Diversified Portfolios

Fundamental phenomenon ofdiversification leads naturally toNP:

diversified =⇒ fractions “small”

Definition 2.3 A strictly positive portfolioSδ is adiversified portfolio if

∣πj

δ,t

∣≤ K2

d12+K1

a.s. for allj ∈ 0, 1, . . . , d andt ∈ [0, T ] for K1,K2 ∈ (0,∞) and

K3 ∈ 1, 2, . . ., independent ofd ∈ K3,K3 + 1, . . ..

c© Copyright Eckhard Platen 10 BA - Toronto C 2 76

• jth benchmarked primary security account

Sjt =

Sjt

Sδ∗

t

dSjt = −Sj

t

d∑

k=1

sj,kt dW k

t

• (j, k)th specific volatility

sj,kt = θk

t − bj,kt

measuresspecific market risk of Sj with respect toW k

• θkt measuresgeneral market risk with respect toW k

c© Copyright Eckhard Platen 10 BA - Toronto C 2 77

• kth total specific absolute volatility

skt =

d∑

j=0

|sj,kt |

regular =⇒ variance of specific returns “bounded”

Definition 2.4 A market is calledregular if

E(

(

skt

)2)

≤ K5.

c© Copyright Eckhard Platen 10 BA - Toronto C 2 78

Tracking Rate

Variance of benchmarked portfolio returns

Rdδ(t) =

d∑

k=1

d∑

j=0

πjδ,t s

j,kt

2

Rdδ(t) - quantifies distance betweenSδ and Sδ∗

benchmarked NP constant=⇒

Rdδ∗

(t) = 0

c© Copyright Eckhard Platen 10 BA - Toronto C 2 79

Approximate NP

tracking rate “small”

Definition 2.5 A strictly positive portfolioSδ is an approximate NP if

for all t ∈ [0, T ] and ε > 0

limd→∞

P(

Rdδ(t) > ε

)

= 0.

c© Copyright Eckhard Platen 10 BA - Toronto C 2 80

Diversification Theorem

Theorem 2.6 In a regular market

any diversified portfolio is an approximate NP.

• model independent

• similarity to CLT

c© Copyright Eckhard Platen 10 BA - Toronto C 2 81

Equal Weighted Index (EWI)

SδEWI holds equal fractions

πjδEWI,t

=1

d+ 1

j ∈ 0, 1, . . . , d

• tracking rate for multi-asset BS example:

RdδEWI

(t) =

d∑

k=1

(

1

d+ 1

(

θkt − bk,k

t

)

)2

= d

(

1

d+ 1

(

σ√d

− σ

))2

≤ σ2

(d+ 1)→ 0

c© Copyright Eckhard Platen 10 BA - Toronto C 2 82

0

1

2

3

4

5

6

7

8

9

10

0 5 10 15 20 25 30 35

time

GOPEWI

Figure 2.3: Simulated NP and EWI.

c© Copyright Eckhard Platen 10 BA - Toronto C 2 83

0

1

2

3

4

5

6

7

8

9

10

0 5 10 15 20 25 30 35

time

GOPindex

Figure 2.4: Simulated diversified accumulation index and NP.

c© Copyright Eckhard Platen 10 BA - Toronto C 2 84

0

20,000

40,000

60,000

80,000

100,000

120,000

1/1/73 28/9/76 25/6/80 22/3/84 18/12/87 15/9/91 12/6/95 9/3/99 4/12/02 31/8/06

Figure 2.5: World industry sector stock market indices as primary security

accounts.

c© Copyright Eckhard Platen 10 BA - Toronto C 2 85

EWI

MCI

DWI

WSI

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

1/1/73 28/9/76 25/6/80 22/3/84 18/12/87 15/9/91 12/6/95 9/3/99 4/12/02 31/8/06

$US

Figure 2.6: Constructed MCI, DWI, EWI and WSI. In the long term the WSI

and EWI outperform all other indices, Le& Platen (2006).

c© Copyright Eckhard Platen 10 BA - Toronto C 2 86

0

50

100

150

200

250

300

350

400

450

0 5 9 14 18 23 27 32

Figure 2.7: Primary security accounts under the MMM.

c© Copyright Eckhard Platen 10 BA - Toronto C 2 87

0

10

20

30

40

50

60

0 5 9 14 18 23 27 32

Figure 2.8: Benchmarked primary security accounts.

c© Copyright Eckhard Platen 10 BA - Toronto C 2 88

0

10

20

30

40

50

60

70

80

90

100

0 5 9 14 18 23 27 32

EWI

GOP

Figure 2.9: NP and EWI.

c© Copyright Eckhard Platen 10 BA - Toronto C 2 89

0

10

20

30

40

50

60

70

80

90

100

0 5 9 14 18 23 27 32

Market index

GOP

Figure 2.10: NP and market index.

c© Copyright Eckhard Platen 10 BA - Toronto C 2 90

3 Portfolio Optimization

• NP best long term investment

Kelly (1956), Latane (1959), Breiman (1961),

Hakansson (1971b), Thorp (1972)

• optimal portfolio separated into two funds

Tobin (1958), Sharpe (1964)

c© Copyright Eckhard Platen 10 BA - Toronto C 3 91

• mean-variance efficient portfolio

Markowitz (1959)

• intertemporal capital asset pricing model

Merton (1973a)

c© Copyright Eckhard Platen 10 BA - Toronto C 3 92

Expected Utility Maximization

• utility function U(·), U ′(·) > 0 U ′′(·) < 0

• examples

power utility

U(x) =1

γxγ

for γ 6= 0 andγ < 1

log-utility

U(x) = ln(x)

c© Copyright Eckhard Platen 10 BA - Toronto C 3 93

5 10 15 20x

-15

-10

-5

5

U

Figure 3.1: Examples for power utility (upper graph) and log-utility (lower

graph).

c© Copyright Eckhard Platen 10 BA - Toronto C 3 94

• assumeS0 is scalar diffusion

• maximize expected utility

vδ = maxSδ∈V+

S0

E0

(

U(

SδT

))

V+S0

strictly positive, discounted, fair portfolios

Sδ0 = S0 > 0

c© Copyright Eckhard Platen 10 BA - Toronto C 3 95

Theorem 3.1

Benchmarked, expected utility maximizing portfolio:

Sδt = u(t, S0

t ) = Et

(

U ′−1(

λ S0T

)

S0T

)

,

λ s.t. S0 = Sδ0 S

δ∗

0 = u(0, S0)Sδ∗

0

two fund separation with risk aversion coefficient

J δt =

1

1 − S0t

u(t,S0t )

∂u(t,S0t )

∂S0t

=⇒ invest 1

J δt

of wealth in NP and remainder in savings account

c© Copyright Eckhard Platen 10 BA - Toronto C 3 96

• log-utility function U(x) = ln(x)

U ′(x) =1

x

U ′−1(y) =1

y

U ′′(x) = − 1

x2

utility concave

u(t, S0t ) = Et

(

U ′−1(

λ S0T

)

S0T

)

= Et

(

1

λ S0T

S0T

)

=1

λ

Lagrange multiplier

c© Copyright Eckhard Platen 10 BA - Toronto C 3 97

λ =Sδ∗

0

S0

risk aversion coefficient

J δt = 1

• expected log-utility

vδ = E0

(

ln(

Sδ∗

T

))

= ln(λ) + ln(S0) +1

2

∫ T

0

E0

(

(

θ(s, Sδ∗

s ))2)

ds

if local martingale part forms a martingale

c© Copyright Eckhard Platen 10 BA - Toronto C 3 98

• power utility

U(x) =1

γxγ

for γ < 1, γ 6= 0

U ′(x) = xγ−1

U ′−1(y) = y1

γ−1

U ′′(x) = (γ − 1)xγ−2

concave

u(t, S0t ) = Et

(

λ

Sδ∗

T

)1

γ−11

Sδ∗

T

= λ1

γ−1 Et

(

(

Sδ∗

T

1−γ

)

c© Copyright Eckhard Platen 10 BA - Toronto C 3 99

Sδ∗ geometric Brownian motion

u(t, S0t ) = λ

1γ−1

(

Sδ∗

t

)

γ1−γ

×Et

(

exp

γ

1 − γ

(

θ2

2(T − t) + θ (WT −Wt)

))

= λ1

γ−1(

Sδ∗

t

)

γ1−γ exp

θ2

2

γ

(1 − γ)2(T − t)

c© Copyright Eckhard Platen 10 BA - Toronto C 3 100

Lagrange multiplier

λ = Sγ−10 Sδ∗

0 exp

θ2

2

γ

1 − γT

S0t = (Sδ∗

t )−1

∂u(t, S0t )

∂S0=u(t, S0

t )

S0t

γ

γ − 1

=⇒ risk aversion coefficient

J δt = 1 − γ

expected utility

vδ = E0

(

1

γ

(

SδT

)γ)

= exp

−θ2

2

γ

1 − γT

(S0)γ

c© Copyright Eckhard Platen 10 BA - Toronto C 3 101

Utility Indifference Pricing

discounted payoff H = HS0

T

(not perfectly hedgable)

vδε,V = E0

(

U

(

(S0 − ε V )Sδ

T

S0

+ ε H

))

• assumeS0 is scalar diffusion

Definition 3.2 utility indifference price V s.t.

limε→0

vδε,V − vδ

0,V

ε= 0

Davis (1997)

c© Copyright Eckhard Platen 10 BA - Toronto C 3 102

• Taylor expansion

vδε,V ≈ E0

(

U(

SδT

)

+ εU ′(

SδT

)

(

H − V SδT

S0

))

= vδ0,V + εE0

(

U ′(

SδT

)

H)

− V εE0

(

U ′(

SδT

) SδT

S0

)

SδT = Sδ

T /S0T = U ′−1

(

λ S0T

)

=⇒

vδε,V − vδ

0,V = ε

(

E0

(

λ S0T H

)

− V E0

(

λ S0T

SδT

S0

))

c© Copyright Eckhard Platen 10 BA - Toronto C 3 103

=⇒• utility indifference price

V =E0

(

λ

Sδ∗

T

H)

E0

(

λ

Sδ∗

T

SδT

S0

) =E0

(

H

Sδ∗

T

)

1S0

S0

Sδ∗

0

independent ofU and of given model =⇒

• real world pricing formula

V = Sδ∗

0 E0

(

H

Sδ∗

T

)

c© Copyright Eckhard Platen 10 BA - Toronto C 3 104

Hedging

• benchmarked derivative price

UH(t) = Et

(

H

Sδ∗

T

)

• real world martingale representation

H

Sδ∗

T

= UH(t) +

d∑

k=1

∫ T

t

xkH(s) dW k

s +MH(t)

MH -orthogonal martingale

E([

MH ,Wk]

t

)

= 0

Follmer-Schweizer decomposition, Follmer & Schweizer (1991)

least square projection

c© Copyright Eckhard Platen 10 BA - Toronto C 3 105

Theorem 3.3 Derivative price

SδH

t = Sδ∗

t Et

(

H

Sδ∗

T

)

fractions

πδH(t) =

(

bδH(t)⊤ b−1

t

)⊤

with portfolio volatilities

bkδH

(t) =1

UH(t)

d∑

j=0

δjH(t) Sj

t bj,kt =

xkH(t)

UH(t)+ θk

t .

c© Copyright Eckhard Platen 10 BA - Toronto C 3 106

4 Modeling Stochastic Volatility

• consider well diversified accumulation index≈ NP

dSδ∗

t = Sδ∗

t

(

rt dt+ |θt|(

|θt| dt+ dWt

))

d ln(

Sδ∗

t

)

=

(

rt dt+1

2|θt|2

)

dt+ |θt| dWt

• volatility

|θt| =

d

dt[ln (Sδ∗)]t

c© Copyright Eckhard Platen 10 BA - Toronto C 4 107

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

1982 1992 2002

time

Figure 4.1: Estimated volatility of WSI from 1973–2004.

c© Copyright Eckhard Platen 10 BA - Toronto C 4 108

Log-Returns of a Stock Index

-10 -5 0 5 10

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Figure 4.2: Histogram for S&P500 hourly deseasonalized log-returns.

fitted Gaussian density, much fatter tails

c© Copyright Eckhard Platen 10 BA - Toronto C 4 109

Implied Volatilities

• European call for Black-Scholes model

cτ,K(0, S, σ)

maturity τ ∈ [0, T ]

strike priceK > 0

underlying indexS > 0

volatility σ

c© Copyright Eckhard Platen 10 BA - Toronto C 4 110

• observed European call option price

Vc,τ,K(0, S0)

• implied volatility

σcallBS (0, S0, τ,K)

obtained such that

Vc,τ,K(0, S0) = cτ,K

(

0, S0, σcallBS (0, S0, τ,K)

)

by some root finding method

c© Copyright Eckhard Platen 10 BA - Toronto C 4 111

100

200

300

time 0.6

0.8

1

1.2

1.4

moneyness

20

40

60

100

200

300

time

Figure 4.3: Implied volatilities for S&P500 three month options.

c© Copyright Eckhard Platen 10 BA - Toronto C 4 112

implied volatility surface

0.5

0.75

1

1.25

1.5

KS

0.20.4

0.60.8

11.2

1.41.6T

0.22

0.24

0.26

0.28

0.5

0.75

1

1.25KS

0.20.4

0.60.8

11.2

1.4

Figure 4.4: Average S&P500 implied volatility surface.

c© Copyright Eckhard Platen 10 BA - Toronto C 4 113

A Modified Constant Elasticity of Variance Model

• CEV Model

Cox (1975), Cox & Ross (1976)

Andersen & Andreasen (2000)

Lewis (2000)

Lo, Yuen & Hui (2000)

Brigo & Mercurio (2005)

Heath& Pl. (2005b)

c© Copyright Eckhard Platen 10 BA - Toronto C 4 114

• classical risk neutral CEV

Beckers (1980)

Schroder (1989)

Delbaen & Shirakawa (2002)

certain problems in risk neutral pricing of derivatives

c© Copyright Eckhard Platen 10 BA - Toronto C 4 115

Modified CEV Model

Heath& Pl. (2005b)

• savings account

dS0t = r S0

t dt

total market price for risk process

θt ≥ 0, t ∈ [0, T ]

• drifted Wiener process

dWθ(t) = θt dt+ dWt

c© Copyright Eckhard Platen 10 BA - Toronto C 4 116

• NP

dSδ∗

t = Sδ∗

t (rt dt+ θt dWθ(t))

• NP volatility

θt = (Sδ∗

t )a−1 ψ

exponenta ∈ (−∞,∞)

scaling parameterψ > 0

stochastic fora 6= 1

c© Copyright Eckhard Platen 10 BA - Toronto C 4 117

• hypothetical risk neutral CEV dynamics

dSδ∗

t = Sδ∗

t rt dt+ (Sδ∗

t )a ψ dWθ(t)

Wθ - Wiener process under a hypothetical risk neutral measurePθ

• If a = 1 =⇒ BS model

=⇒ equivalent risk neutral probability measurePθ

with market price of riskθt = ψ

c© Copyright Eckhard Platen 10 BA - Toronto C 4 118

• real world CEV dynamics

dSδ∗

t =(

Sδ∗

t rt +(

Sδ∗

t

)2a−1ψ2)

dt+(

Sδ∗

t

)aψ dWt

modified CEV model remains fora < 1 strictly positive

this isnot the case for its “risk neutral” dynamics

c© Copyright Eckhard Platen 10 BA - Toronto C 4 119

• squared Bessel process

Xt =(

Sδ∗

t

)2 (1−a)

for a 6= 1 with SDE

dXt =(

2(1 − a) rtXt + ψ2 (1 − a) (3 − 2a))

dt

+2ψ (1 − a)√

Xt dWt

anddimension

δ =3 − 2 a

1 − a

c© Copyright Eckhard Platen 10 BA - Toronto C 4 120

• Radon-Nikodym derivative process

Λθ = Λθ(t), t ∈ [0, T ](state price density)

• hypothetical risk neutral measurePθ

dPθ

dP= Λθ(T )

Λθ(t) =Sδ∗

0

Sδ∗

t

S0t =

(

X0

Xt

)q

S0t

q =1

2 (1 − a)

c© Copyright Eckhard Platen 10 BA - Toronto C 4 121

• squared Bessel process

dXt =(

2 (1 − a) rtXt + ψ2 (1 − a)(1 − 2 a))

dt

+2ψ (1 − a)√

Xt dWθ(t)

dimension

δθ =1 − 2 a

1 − a

c© Copyright Eckhard Platen 10 BA - Toronto C 4 122

• dimension

risk neutral

δθ =1 − 2 a

1 − a

real world

δ =3 − 2 a

1 − a

• if a < 1 =⇒ δ > 2 andδθ < 2

if a > 1 =⇒ δ < 2 andδθ > 2

c© Copyright Eckhard Platen 10 BA - Toronto C 4 123

-1 0 1 2 3

-4

-2

0

2

4

6

8

Risk Neutral

Real World

Figure 4.5: Dimensionsδ andδθ as a function of the exponenta.

c© Copyright Eckhard Platen 10 BA - Toronto C 4 124

• hypothetical risk neutral probability

Pθ(A) =

A

dPθ(ω) =

A

dPθ(ω)

dP (ω)dP (w)

=

A

Λθ(T ) dP (ω)

=⇒

Pθ(Ω) =

Ω

Λθ(T ) dP (ω) = E0 (Λθ(T ))

c© Copyright Eckhard Platen 10 BA - Toronto C 4 125

• for a < 1 =⇒ δθ < 2

=⇒ Λθ is strict supermartingale =⇒

Pθ(Ω) < Λθ(0) = 1

=⇒ Pθ is not a probability measure

c© Copyright Eckhard Platen 10 BA - Toronto C 4 126

• for a 6= 1 P andPθ are not equivalent

=⇒ modified CEV model doesnot haveequivalent risk neutral

probability measure

• consider onlya < 1 since fora > 1 NP explodes

c© Copyright Eckhard Platen 10 BA - Toronto C 4 127

Real World Pricing

• contingent claim

Hτ = Hτ (Sδ∗

τ ), E

(

Sδ∗

τ

)

< ∞

• fair price

uHτ(t, Sδ∗

t ) = Sδ∗

t uHτ(t, Sδ∗

t )

benchmarked price

uHτ(t, Sδ∗

t ) = Et

(

Hτ (Sδ∗

τ )

Sδ∗

τ

)

c© Copyright Eckhard Platen 10 BA - Toronto C 4 128

Martingale Representation

Sδ∗

τ

= uHτ(τ, Sδ∗

τ )

= uHτ(t, Sδ∗

t ) +

∫ τ

t

(

Sδ∗

s

)aψ∂uHτ

(s, Sδ∗

s )

∂Sδ∗

dWs

c© Copyright Eckhard Platen 10 BA - Toronto C 4 129

Stochastic Volatility Models

• volatility function of underlying diffusion=⇒ LV model

• volatility as separate, possibly correlated process

Hull & White (1987, 1988)Johnson & Shanno (1987)Scott (1987)Wiggins (1987)Chesney & Scott (1989)Melino & Turnbull (1990)Stein & Stein (1991)Hofmann, Pl.& Schweizer (1992)Heston (1993),. . .

c© Copyright Eckhard Platen 10 BA - Toronto C 4 130

Empirical Evidence on Log-Returns

• Markowitz & Usmen (1996)

daily S&P500 → Studentt(4.5)

• Hurst & Platen (1997)

daily stock market indices→ Studentt(4)

• Fergusson& Pl. (2006), Pl.& Rendek (2008)

daily WSI, EWI104s with high accuracy→ Studentt(4)

• Breymann, Dias & Embrechts (2003)

copula of joint distribution of log-returns of exchange rates →Studentt copula with roughly four degrees of freedom

c© Copyright Eckhard Platen 10 BA - Toronto C 4 131

−10 −5 0 5 10

10−4

10−3

10−2

10−1

Figure 4.6: Log-histogram of the EWI104s log-returns and Studentt density

with four degrees of freedom.c© Copyright Eckhard Platen 10 BA - Toronto C 4 132

0

0.5

1

1.5

2

−5−4

−3−2.15

−10

1 2

34

5

−2.94

−2.92

−2.9

−2.88

−2.86

−2.84

αλ

Estimated λ

Estimated LLF

× 105

Figure 4.7: Log-likelihood function based on the EWI104s.

c© Copyright Eckhard Platen 10 BA - Toronto C 4 133

Country Student-t NIG Hyperbolic VG ν

Australia 0.000000 76.770817 150.202282 181.632971 4.281222

Austria 0.000000 39.289103 77.505683 102.979330 4.725907

Belgium 0.000000 31.581622 60.867570 83.648470 4.989912

Brazil 2.617693 5.687078 63.800349 60.078395 2.713036

Canada 0.000000 47.506215 79.917741 104.297607 5.316154

Denmark 0.000000 41.509921 87.199686 114.853658 4.512101

Finland 0.000000 28.852844 68.677271 88.553080 4.305638

France 0.000000 26.303544 57.639325 80.567283 4.722787

Germany 0.000000 27.290205 52.667918 71.120798 5.005856

Greece 0.000000 60.432172 104.789463 125.601499 4.674626

Hong.Kong 0.000000 42.066531 100.834255 122.965326 3.930473

India 0.000000 74.773701 163.594078 198.002956 3.998713

Ireland 0.000000 77.727856 136.505582 170.013644 4.761519

Italy 0.000000 25.196598 55.185625 75.481897 4.668983

Japan 0.000000 37.630363 77.163656 102.967380 4.649745

Korea.S. 0.000000 120.904983 304.829431 329.854620 3.289204

c© Copyright Eckhard Platen 10 BA - Toronto C 4 134

Malaysia 0.000000 79.714054 186.013963 221.061290 3.785195

Netherlands 0.000000 26.832761 51.625813 71.541627 5.084056

Norway 0.000000 42.243851 89.012090 115.059003 4.472349

Portugal 0.000000 61.177624 137.681039 165.689683 3.984860

Singapore 0.000000 36.379685 77.600590 98.124375 4.251472

Spain 0.000000 56.694545 109.533768 138.259224 4.517153

Sweden 0.000000 77.618384 143.420049 178.983373 4.546640

Taiwan 0.000000 41.162560 96.283628 115.186585 3.914719

Thailand 0.000000 78.250621 254.590254 267.508143 3.032038

UK 0.000000 26.693076 55.937248 80.678494 4.952843

USA 0.000000 40.678242 79.617362 100.901197 4.636661

Table 1:Ln test statistic of the EWI104s for different currency denominations

c© Copyright Eckhard Platen 10 BA - Toronto C 4 135

Index Log-returns

• Student t distributed with about 4 degrees of freedom

• clustering

Find corresponding stationary volatility processes !

Kessler (1997), Prakasa Rao (1999)

c© Copyright Eckhard Platen 10 BA - Toronto C 4 136

• normal mixing

log-return conditionally Gaussian distributed

with stochastic variance process

for small time step sizeh > 0

∆ ln(Sδ∗

t ) = ln

(

Sδ∗

t+h

Sδ∗

t

)

∼ N(

θ2t

2h, θ2

t h

)

whenθ2t has inverse gamma stationary density

=⇒ estimated log-return appears to be Studentt distributed

c© Copyright Eckhard Platen 10 BA - Toronto C 4 137

A Class of Continuous Stochastic Volatility Models

• discounted NP

Sδ∗

t =Sδ∗

t

S0t

dSδ∗

t = Sδ∗

t (θ2t dt+ θt dWt)

c© Copyright Eckhard Platen 10 BA - Toronto C 4 138

Particular Stochastic Volatility Models

• Hull and White’87 model

Hull & White (1987)

dθ2t = µ θ2

t dt+ ξ θ2t dWt

squared volatility does not have a stationary dynamics

c© Copyright Eckhard Platen 10 BA - Toronto C 4 139

• Heston model

Hull & White (1988), Heston (1993)

mean reverting dynamics

k, θ andγ are positive constants

=⇒

dθ2t = k (θ2 − θ2

t ) dt+ γ |θt| dWt

θ20 > 0, κ

γ2 ≥ 12

=⇒ has as stationary density gamma density

c© Copyright Eckhard Platen 10 BA - Toronto C 4 140

• Scott model

Scott (1987)

Stein & Stein (1991)

Ornstein-Uhlenbeck process

k, θ, γ positive constants

dθt = k (θ − θt) dt+ γ dWt

θ0 ∈ ℜ

=⇒ θ2t has as stationary density a gamma density

c© Copyright Eckhard Platen 10 BA - Toronto C 4 141

• Wiggins model

Wiggins (1987)

Chesney & Scott (1989)

Melino & Turnbull (1990)

d ln(θt) = k(

ln(θ) − ln(θt))

dt+ γ dWt

θ0 > 0

θ2t has as stationary density a log-normal density

c© Copyright Eckhard Platen 10 BA - Toronto C 4 142

• inverted gamma distribution

pθ2(y) =(12ν)

12 ν

ε2 Γ(12ν)

(

y

ε2

)− 12 ν−1

exp

−12ν ε2

y

y > 0, degrees of freedomν > 0, scaling parameterε

c© Copyright Eckhard Platen 10 BA - Toronto C 4 143

• SDE for squared volatility

dθ2t = k θ

4(ξ−1)t (θ2 − θ2

t ) dt+ γ θ2 ξt dWt

degree of freedom

ν =2 (2 ξ − 1)

1 − ε2

θ2

=⇒ stationary density inverted gamma

c© Copyright Eckhard Platen 10 BA - Toronto C 4 144

•32

volatility model

ξ = 32

Pl. (1997), Lewis (2000), Pl. (2001)

dθ2t = k θ2

t (θ2 − θ2t ) dt+ γ θ3

t dWt

c© Copyright Eckhard Platen 10 BA - Toronto C 4 145

• ARCH diffusion

ξ = 1

Engle (1982), Nelson (1990) and Frey (1997)

dθ2t = k (θ2 − θ2

t ) dt+ γ θ2t dWt

continuous time limit of innovation process

GARCH(1,1) and NGARCH(1,1)

c© Copyright Eckhard Platen 10 BA - Toronto C 4 146

Implied Volatilities for the ARCH Diffusion Model

Hurst (1997), Lewis (2000), Heath, Hurst& Pl. (2001)

GARCH(1,1) of Bollerslev (1986) whenW andW are independent

continuous time limit of NGARCH(1, 1) model of Engle & Ng (1993)

two-factor model

c© Copyright Eckhard Platen 10 BA - Toronto C 4 147

80

90

100

110

120K 0.2

0.4

0.6

0.8

1

T

0.2

0.21

0.22

80

90

100

110

120K

Figure 4.8: Implied volatility surface for zero correlation.

c© Copyright Eckhard Platen 10 BA - Toronto C 4 148

80

90

100

110

120K -0.4

-0.2

0

0.2

0.4

rho

0.18

0.2

0.22

80

90

100

110

120K

Figure 4.9: Effect of changing correlation on implied volatilities.

c© Copyright Eckhard Platen 10 BA - Toronto C 4 149

8090

100

110

120K

5

10

15

20

k

0.1950.1975

0.2

0.2025

0.205

8090

100

110

120K

Figure 4.10: Effect of changing speed of adjustment on implied volatilities.

c© Copyright Eckhard Platen 10 BA - Toronto C 4 150

8090

100

110

120K

0.5

1

1.5

2

gamma

0.19

0.2

0.21

8090

100

110

120K

Figure 4.11: Effect of changing volatility of the squared volatility on implied

volatilities.

c© Copyright Eckhard Platen 10 BA - Toronto C 4 151

Moneyness

Opt

ion

Pric

e D

iffer

ence

-0.3 -0.2 -0.1 0.0 0.1 0.2 0.3

-0.1

5-0

.10

-0.0

50.

00.

05

GLMRHestonBlack-Scholes

Figure 4.12: Option price differences between the ARCH diffusion (GLMR),

Heston and Black-Scholes models, with time to maturity of three months.

c© Copyright Eckhard Platen 10 BA - Toronto C 4 152

Moneyness

Impl

ied

Vol

atili

ty

-0.3 -0.2 -0.1 0.0 0.1 0.2 0.3

0.14

0.16

0.18

0.20

GLMRHestonBlack-Scholes

Figure 4.13: Implied volatilities of the ARCH diffusion (GLMR), Heston

and Black-Scholes models, with time to maturity of three months.

c© Copyright Eckhard Platen 10 BA - Toronto C 4 153

5 Minimal Market Model

• search for parsimonious one-factor model

• Diversification Theorem =⇒

well diversified stock market index approximates NP

• discounted NP

dSδ∗

t = Sδ∗

t |θt| (|θt| dt+ dWt),

where

dWt =1

|θt|d∑

k=1

θkt dW

kt

c© Copyright Eckhard Platen 10 BA - Toronto C 5 154

0

10

20

30

40

50

60

70

80

90

100

1930 1940 1950 1960 1970 1980 1990 2000

time

Figure 5.1: Discounted S&P500 total return index.

c© Copyright Eckhard Platen 10 BA - Toronto C 5 155

-2

-1

0

1

2

3

4

5

1930 1940 1950 1960 1970 1980 1990 2000

time

Figure 5.2: Logarithm of discounted S&P500.

c© Copyright Eckhard Platen 10 BA - Toronto C 5 156

• logarithm of discounted NP

• is not a transformed Wiener process

• is not a process with independent increments

• has somefeedback effect

c© Copyright Eckhard Platen 10 BA - Toronto C 5 157

Drift Parametrization

• discounted NP drift

αt = Sδ∗

t |θt|2

strictly positive, predictable

=⇒• volatility

|θt| =

αt

Sδ∗

t

leverage effect creates naturalfeedbackunder independent drift

c© Copyright Eckhard Platen 10 BA - Toronto C 5 158

• discounted NP

dSδ∗

t = αt dt+

Sδ∗

t αt dWt

drift has economic meaning,

fundamental value

• transformed time

ϕt =1

4

∫ t

0

αs ds

c© Copyright Eckhard Platen 10 BA - Toronto C 5 159

• squared Bessel process of dimension four

Xϕt= Sδ∗

t

dW (ϕt) =√αt dWt

dXϕ = 4 dϕ+ 2√

Xϕ dW (ϕ)

Revuz & Yor (1999)

economically founded dynamics inϕ-time

still no specific dynamics int-time

c© Copyright Eckhard Platen 10 BA - Toronto C 5 160

Time Transformed Bessel Process

d

Sδ∗

t =3αt

8

Sδ∗

t

dt+1

2

√αt dWt

• quadratic variation

[√

Sδ∗

]

t=

1

4

∫ t

0

αs ds

• transformed time

ϕt =[√

Sδ∗

]

t

observable

c© Copyright Eckhard Platen 10 BA - Toronto C 5 161

0

1

2

3

4

5

6

7

8

9

10

1930 1940 1950 1960 1970 1980 1990 2000

time

Figure 5.3: Empirical quadratic variation of the square rootof the discounted

NP.c© Copyright Eckhard Platen 10 BA - Toronto C 5 162

Stylized Minimal Market Model

Pl. (2001, 2002, 2006)

• assumediscounted NP drift as

αt = α exp η t

• initial parameter α > 0

• net growth rate η

c© Copyright Eckhard Platen 10 BA - Toronto C 5 163

• transformed time

ϕt =α

4

∫ t

0

exp η z dz

4 η(exp η t − 1)

c© Copyright Eckhard Platen 10 BA - Toronto C 5 164

0

1

2

3

4

5

6

7

8

9

10

1930 1940 1950 1960 1970 1980 1990 2000

time

[sqrt(discounted index)]theoretical variation

Figure 5.4: Fitted and observed transformed time.

c© Copyright Eckhard Platen 10 BA - Toronto C 5 165

• normalized NP

Yt =Sδ∗

t

αt

dYt = (1 − η Yt) dt+√

Yt dWt

square root process of dimension four

=⇒ parsimonious model, long term viability

c© Copyright Eckhard Platen 10 BA - Toronto C 5 166

=⇒• discounted NP

Sδ∗

t = Yt αt

• NP

Sδ∗

t = S0t S

δ∗

t = S0t Yt αt

• scaling parameterα0 = 0.01468

• net growth rateη = 0.054

• reference level1η

= 18.5

• speed of adjustmentη

• half life time of major displacement ln(2)η

≈ 13 years

c© Copyright Eckhard Platen 10 BA - Toronto C 5 167

0

10

20

30

40

50

60

70

80

90

1930 1940 1950 1960 1970 1980 1990 2000

time

Figure 5.5: Normalized NP.

c© Copyright Eckhard Platen 10 BA - Toronto C 5 168

• logarithm of discounted NP

ln(Sδ∗

t ) = ln(Yt) + ln(α0) + η t

• no need for extra volatility process in MMM

• realistic long term dynamics

c© Copyright Eckhard Platen 10 BA - Toronto C 5 169

Volatility of NP under the stylized MMM

|θt| =1√Yt

• squared volatility

d|θt|2 = d

(

1

Yt

)

= |θt|2 η dt− (|θt|2)

32 dWt

3/2 volatility model

Platen (1997), Lewis (2000)

c© Copyright Eckhard Platen 10 BA - Toronto C 5 170

0.1

0.15

0.2

0.25

0.3

0.35

1930 1940 1950 1960 1970 1980 1990 2000

time

Figure 5.6: Volatility of the NP under the stylized MMM.

c© Copyright Eckhard Platen 10 BA - Toronto C 5 171

Transition Density of Stylized MMM

• transition density ofdiscounted NP Sδ∗

p(s, x; t, y) =1

2 (ϕt − ϕs)

(

y

x

)12

exp

− x+ y

2 (ϕt − ϕs)

× I1

( √x y

ϕt − ϕs

)

ϕt =α

4 η(expη t − 1)

I1(·) modified Bessel function of the first kind

c© Copyright Eckhard Platen 10 BA - Toronto C 5 172

• non-central chi-squaredistributed random variable:

y

ϕt − ϕs

=Sδ∗

t

ϕt − ϕs

with δ = 4 degrees of freedom andnon-centrality parameter:

x

ϕt − ϕs

=Sδ∗

s

ϕt − ϕs

c© Copyright Eckhard Platen 10 BA - Toronto C 5 173

80

90

100

110

120

y0.1

0.2

0.3

0.4

0.5

t

0

0.05

0.1

0.15

80

90

100

110y

Figure 5.7: Transition density of squared Bessel process forδ = 4.

c© Copyright Eckhard Platen 10 BA - Toronto C 5 174

Zero Coupon Bond under the stylized MMM

• zero coupon bond

P (t, T ) = Sδ∗

t Et

(

1

Sδ∗

T

)

= P ∗T (t)Et

(

Sδ∗

t

Sδ∗

T

)

with savings bond

P ∗T (t) = exp

−∫ T

t

rs ds

c© Copyright Eckhard Platen 10 BA - Toronto C 5 175

δ = 4 =⇒

P (t, T ) = P ∗T (t)

(

1 − exp

− Sδ∗

t

2 (ϕT − ϕt)

)

< P ∗T (t)

for t ∈ [0, T ), Platen (2002)

with time transform

ϕt =α

4 η(expη t − 1)

P (0, T ) = 0.00077

P ∗T (0) = 0.0335

P (0,T )P ∗

T (0)≈ 0.023

c© Copyright Eckhard Platen 10 BA - Toronto C 5 176

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1930 1940 1950 1960 1970 1980 1990 2000

time

savings bondfair zero coupon bond

savings account

Figure 5.8: Savings bond, fair zero coupon bond and savings account.

c© Copyright Eckhard Platen 10 BA - Toronto C 5 177

-8

-7

-6

-5

-4

-3

-2

-1

0

1

1930 1940 1950 1960 1970 1980 1990 2000

time

ln(savings bond)ln(fair zero coupon bond)

Figure 5.9: Logarithms of savings bond and fair zero coupon bond.

c© Copyright Eckhard Platen 10 BA - Toronto C 5 178

Forward Rates under the MMM

• forward rate

f(t, T ) = − ∂

∂Tln(P (t, T ))

= rT + n(t, T )

c© Copyright Eckhard Platen 10 BA - Toronto C 5 179

• market price of risk contribution

n(t, T ) = − ∂

∂Tln

(

1 − exp

− Sδ∗

t

2(ϕT − ϕt)

)

=1

(

exp

Sδ∗

t

2(ϕT −ϕt)

− 1)

Sδ∗

t

(ϕT − ϕt)2

αT

8

limT →∞

n(t, T ) = η

Pl. (2005a), Miller& Pl. (2005)

c© Copyright Eckhard Platen 10 BA - Toronto C 5 180

0.020.04

0.06

0.08

0.1

eta

20

40

60

80

T

0

0.025

0.05

0.075

0.1

0.020.04

0.06

0.08eta

Figure 5.10: Market price of risk contribution in dependence on η andT .

c© Copyright Eckhard Platen 10 BA - Toronto C 5 181

Free Snack from Savings Bond

• potential existence of weak form of arbitrage?

borrow amountP (0, T ) from savings account

Sδt = P (t, T ) − P (0, T ) expr t

such thatSδ0 = 0

SδT = 1 − P (0, T ) expr T > 0

lower bound

Sδt ≥ −P (0, T ) expr t

c© Copyright Eckhard Platen 10 BA - Toronto C 5 182

• sinceSδt may become negative

allowed by strong arbitrage concept

• cheap thrills may exist

Loewenstein & Willard (2000)

MMM doesnot admit an equivalent risk neutral probability measure

=⇒there is afree lunch with vanishing risk

Delbaen & Schachermayer (2006)

c© Copyright Eckhard Platen 10 BA - Toronto C 5 183

Absence of an Equivalent Risk Neutral Probability Measure

• fair zero coupon bond has a lower price than the savings bond

P (t, T ) < P ∗T (t) = exp

−∫ T

t

rs ds

=S0

t

S0T

• Radon-Nikodym derivative

Λt =S0

t

S00

=Sδ∗

0

Sδ∗

t

strict (A, P )-supermartingaleunder MMM

c© Copyright Eckhard Platen 10 BA - Toronto C 5 184

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

1930 1940 1950 1960 1970 1980 1990 2000

time

Radon-Nikodym derivativeTotal RN-Mass

Figure 5.11: Radon-Nikodym derivative and total mass of putative risk neu-

tral measure.c© Copyright Eckhard Platen 10 BA - Toronto C 5 185

• hypothetical risk neutral measure

total mass:

Pθ,T (Ω) = E0 (ΛT ) = 1 − exp

− Sδ∗

0

2ϕT

< Λ0 = 1

Pθ is not a probability measure

c© Copyright Eckhard Platen 10 BA - Toronto C 5 186

European Call Options under the MMM

real world pricing formula =⇒

cT,K(t, Sδ∗

t ) = Sδ∗

t Et

(

(Sδ∗

T −K)+

Sδ∗

T

)

= Et

(

Sδ∗

t − K Sδ∗

t

Sδ∗

T

)+

= Sδ∗

t

(

1 − χ2(d1; 4, ℓ2))

−K exp−r (T − t) (1 − χ2(d1; 0, ℓ2))

χ2(·; ·, ·) non-central chi-square distribution

c© Copyright Eckhard Platen 10 BA - Toronto C 5 187

with

d1 =4 ηK exp−r (T − t)

S0t αt (expη (T − t) − 1)

and

ℓ2 =2 η Sδ∗

t

S0t αt (expη (T − t) − 1)

Hulley, Miller & Pl. (2005)

Hulley & Pl. (2008)

Miller & Pl. (2008)

c© Copyright Eckhard Platen 10 BA - Toronto C 5 188

0.6

0.8

1

1.2K2

4

6

8

10

T

0.2

0.225

0.25

0.275

0.6

0.8

1

1.2K

Figure 5.12: Implied volatility surface for the stylized MMM.

c© Copyright Eckhard Platen 10 BA - Toronto C 5 189

• implied volatility

in BS-formula adjust short rate to

r = − 1

T − tln(P (t, T ))

otherwise put and call implied volatilities do not match

c© Copyright Eckhard Platen 10 BA - Toronto C 5 190

European Put Options under the MMM

• fair put-call parity relation

pT,K(t, Sδ∗

t ) = cT,K(t, Sδ∗

t ) − Sδ∗

t +K P (t, T )

• European put option formula

pT,K(t, Sδ∗

t ) = −Sδ∗

t

(

χ2(d1; 4, ℓ2))

+K exp−r (T − t)(χ2(d1; 0, ℓ2) − exp −ℓ2)

Hulley, Miller & Pl. (2005)

c© Copyright Eckhard Platen 10 BA - Toronto C 5 191

• put-call paritybreaks down if one uses the savings bondP ∗T (t)

pT,K(t, Sδ∗

t ) < cT,K(t, Sδ∗

t ) − Sδ∗

t +K exp−r (T − t)

for t ∈ [0, T )

c© Copyright Eckhard Platen 10 BA - Toronto C 5 192

• excellent hedge performance for extreme maturities

Hulley & Pl. (2008)

European calls

European puts

barrier options

c© Copyright Eckhard Platen 10 BA - Toronto C 5 193

Comparison to Hypothetical Risk Neutral Prices

• hypothetical risk neutral price c∗T,K(t, Sδ∗

t )

of a European call option on the NP

• benchmarked hypothetical risk neutral call price

c∗T,K(t, Sδ∗

t ) =c∗

T,K(t, Sδ∗

t )

Sδ∗

t

local martingale

c∗T,K(·, ·) uniformly bounded

c© Copyright Eckhard Platen 10 BA - Toronto C 5 194

=⇒ c∗T,K martingale =⇒

c∗T,K(t, Sδ∗

t ) = cT,K(t, Sδ∗

t )

=⇒c∗

T,K(t, Sδ∗

t ) = cT,K(t, Sδ∗

t )

c© Copyright Eckhard Platen 10 BA - Toronto C 5 195

• hypothetical risk neutral put-call parity

p∗T,K(t, Sδ∗

t ) = c∗T,K(t, Sδ∗

t ) − Sδ∗

t +K P ∗T (t)

sinceP ∗T (t) > P (t, T ) =⇒

pT,K(t, Sδ∗

t ) < p∗T,K(t, Sδ∗

t )

t ∈ [0, T )

c© Copyright Eckhard Platen 10 BA - Toronto C 5 196

Difference in Asymptotic Put Prices

• hypothetical risk neutral prices can become extreme if NP value tends

towards zero

• asymptotic fair zero coupon bond

limS

δ∗

t →0PT (t, T )

a.s.= 0

for t ∈ [0, T )

• asymptotic fair European call

limS

δ∗

t →0cT,K(t, Sδ∗

t )a.s.= lim

Sδ∗

t →0Sδ∗

t cT,K(t, Sδ∗

t ) = 0

c© Copyright Eckhard Platen 10 BA - Toronto C 5 197

• asymptotic fair putfair put-call parity =⇒

limS

δ∗

t →0pT,K(t, Sδ∗

t )a.s.= 0

• asymptotic hypothetical risk neutral puthypothetical risk neutral put-call parity =⇒

limS

δ∗

t →0p∗

T,K(t, Sδ∗

t )

a.s.= lim

Sδ∗

t →0

(

pT,K(t, Sδ∗

t ) +KS0

t

S0T

exp

− Sδ∗

t

2(ϕT − ϕt)

)

a.s.= K

S0t

S0T

> 0

dramatic differences can arise

c© Copyright Eckhard Platen 10 BA - Toronto C 5 198

0

2

4

6

8

1930 1940 1950 1960 1970 1980 1990 2000

time

ln(K*savings bond)ln(risk neutral put)

ln(put)

Figure 5.13: Logarithms of savings bond timesK, risk neutral put and fair

put.c© Copyright Eckhard Platen 10 BA - Toronto C 5 199

MMM with Random Market Activity

• squared Bessel process with dimensionδ = 4

Sδ∗ = Sδ∗

t , t ∈ [0,∞)

dSδ∗

t = αt dt+

αt Sδ∗

t dWt

c© Copyright Eckhard Platen 10 BA - Toronto C 5 200

• NP

Sδ∗

t = S0t S

δ∗

t

• volatility

|θt| =

αt

Sδ∗

t

• discounted NP drift

αt to be modeled

c© Copyright Eckhard Platen 10 BA - Toronto C 5 201

0.6

0.8

1

1.2K2

4

6

8

10

T

0.2

0.225

0.25

0.275

0.6

0.8

1

1.2K

Figure 5.14: Implied volatility surface for the stylized MMM.

c© Copyright Eckhard Platen 10 BA - Toronto C 5 202

0.5

0.75

1

1.25

1.5

KS

0.20.4

0.60.8

11.2

1.41.6T

0.22

0.24

0.26

0.28

0.5

0.75

1

1.25KS

0.20.4

0.60.8

11.2

1.4

Figure 5.15: Average S&P500 implied volatility surface.

c© Copyright Eckhard Platen 10 BA - Toronto C 5 203

100

200

300

time 0.6

0.8

1

1.2

1.4

moneyness

20

40

60

100

200

300

time

Figure 5.16: Implied volatilities for S&P500 three month options.

c© Copyright Eckhard Platen 10 BA - Toronto C 5 204

100

200

300

time 0.6

0.8

1

1.2

1.4

moneyness

1020304050

100

200

300

time

Figure 5.17: Implied volatilities for S&P500 one year options.

c© Copyright Eckhard Platen 10 BA - Toronto C 5 205

• market activity mt

Breymann, Kelly& Pl. (2006)

Pl. & Rendek (2008)

αt = ξtmt

with

ξt = ξ0 exp η t

dmt = k(mt)β2 dt+ βmt

(

dWt +√

1 − 2 dWt

)

- correlation parameter

activity volatility β > 0

W - independent Wiener process

c© Copyright Eckhard Platen 10 BA - Toronto C 5 206

Example:

• drift

k(mt) = (p− gmt)mt

2

• stationary density

pm(y) =gp−1

Γ(p− 1)yp−2 exp−g y

gamma density with meanp−1g

and variance1g

for p > 1 andg > 0

c© Copyright Eckhard Platen 10 BA - Toronto C 5 207

0.5

1

1.5y

10

20

30

40

50

g

0

1

2

0.5

1

1.5y

Figure 5.18: Stationary density of market activitymt = y as function ofy

and speed of adjustment parameterg.c© Copyright Eckhard Platen 10 BA - Toronto C 5 208

Zero Coupon Bond

• benchmarked zero coupon bond

PT (t, Sδ∗

t ,mt) = Et

(

1

Sδ∗

T

)

= Et

(

1

S0T S

δ∗

T

)

• zero coupon bond

PT (t, Sδ∗

t ,mt) = Sδ∗

t PT (t, Sδ∗

t ,mt) = S0t S

δ∗

t PT (t, Sδ∗

t ,mt)

c© Copyright Eckhard Platen 10 BA - Toronto C 5 209

European Options on a Market Index

• put option price

pT,K(t, Sδ∗

t ,mt) = S0t S

δ∗

t Et

(

K

S0T S

δ∗

T

− 1

)+

effect of random market time on implied volatilities

curvature for the short dated implied volatility surface

Heath& Pl. (2005a)

c© Copyright Eckhard Platen 10 BA - Toronto C 5 210

80

90

100

110

120

K 0.2

0.4

0.6

0.8

1

T

0.30.32

0.34

0.36

80

90

100

110K

Figure 5.19: Implied volatilities for put options on index asa function of

strikeK and maturityT .c© Copyright Eckhard Platen 10 BA - Toronto C 5 211

80

90

100

110

120

K

2

4

6

8

10

g

0.3

0.32

0.34

80

90

100

110K

Figure 5.20: Implied volatilities for put options as a function of strikeK and

speed of adjustmentg.

c© Copyright Eckhard Platen 10 BA - Toronto C 5 212

80

100

120K 2

4

6

8

10

T

0.30.3250.35

0.375

0.4

80

100

120K

Figure 5.21: Implied volatilities for long dated put optionsas a function of

strikeK and maturityT .

c© Copyright Eckhard Platen 10 BA - Toronto C 5 213

6 Stylized Multi-Currency MMM

Pl. (2001)

Heath& Pl. (2005a)

d+ 1 currencies

Sδ∗

i (t) NP in ith currency

rit - ith short rate

θki (t) - market price of risk

Sδ∗

i (t) = αit Y

it S

ii(t)

c© Copyright Eckhard Platen 10 BA - Toronto C 6 214

αit = αi

0 expηi t

Sii(t) = expri t

• ith normalized NP

dY it =

(

1 − ηi Y it

)

dt+

Y it

d+1∑

k=1

qi,k dW kt

scaling levelsqi,k

d+1∑

k=1

(qi,k)2 = 1

c© Copyright Eckhard Platen 10 BA - Toronto C 6 215

• (i, j)th exchange rate

Xi,jt =

Sδ∗

i (t)

Sδ∗

j (t)=Y i

t αit S

ii(t)

Y jt α

jt S

jj (t)

dXi,jt = Xi,j

t

(ri − rj) dt+

d+1∑

k=1

qi,k

Y it

− qj,k

Y jt

(

qi,k

Y it

dt+ dW kt

)

c© Copyright Eckhard Platen 10 BA - Toronto C 6 216

• jth savings account inith currency

Sji (t) = Xi,j

t Sjj (t)

dSji (t) = Sj

i (t)

ri dt+

d+1∑

k=1

qi,k

Y it

− qj,k

Y jt

(

qi,k

Y it

dt+ dW kt

)

c© Copyright Eckhard Platen 10 BA - Toronto C 6 217

• stochastic market price of risk

θki (t) =

qi,k

Y it

• (j, k)th volatility

bj,ki (t) = θk

i (t) − θkj (t)

equity prices

commodity prices

c© Copyright Eckhard Platen 10 BA - Toronto C 6 218

7 Valuing Guaranteed Minimum Death Benefits

• variable annuitiesfund-linked

tax-deferred

guarantees

• guaranteed minimum death benefits(GMDBs)

roll-ups:

original investment accrued at a pre-defined interest rate

ratchets:

death benefit based upon the highest anniversary account value

embedded options:

hedging against market downturn occurrence of death

c© Copyright Eckhard Platen 10 BA - Toronto C 7 219

• GMDB put, floating put and/or look-back put option

long maturities of contracts

standard option pricing theory ?

no obvious best choice for price:

IFRS Phase II

CFO-Forum (2008)

CRO-Forum (2008)

Solvency II

Verheugen & Hines (2008)

c© Copyright Eckhard Platen 10 BA - Toronto C 7 220

• pricing and hedging of GMDBs

benchmark approachin

Pl. (2002, 2004b), Pl.& Heath (2006)

Buhlmann& Pl. (2003)

best performing portfolio isbenchmark

doesnot require

existence of an equivalent risk neutral probability measure

uniquefair price is theminimal price

may provide significantly lower prices

c© Copyright Eckhard Platen 10 BA - Toronto C 7 221

Financial Model

• underlying risky security (unit)

dSt = (µt − γ)Stdt+ σtSt dWt

γ ≥ 0 management fee rates

Wt - Brownian motion

• savings account

dBt = rtBt dt

c© Copyright Eckhard Platen 10 BA - Toronto C 7 222

• market price of risk

θt =µt − γ − rt

σt

• risky asset

dSt

St

= rt dt+ σtθt dt+ σt dWt

c© Copyright Eckhard Platen 10 BA - Toronto C 7 223

• self-financing portfolio

Vt = δ0tBt + δ1tSt

dVt = δ0t dBt + δ1t dSt

• fractions

π0t = δ0t

Bt

Vt

, π1t = δ1t

St

Vt

π0t + π1

t = 1

c© Copyright Eckhard Platen 10 BA - Toronto C 7 224

• instantaneous portfolio return

dVt

Vt

= π0t

dBt

Bt

+ π1t

dSt

St

= rt dt+ π1tσt(θt dt+ dWt)

c© Copyright Eckhard Platen 10 BA - Toronto C 7 225

• numeraire portfolio (NP) as benchmark

Long (1990)

V ∗ is best performing in several ways

• is growth optimal portfolio

Kelly (1956)

V ∗ = maxE(log VT )

π1∗t =

µt − γ − rt

σ2t

=θt

σt

dV ∗t

V ∗t

= rt dt+ θt(θt dt+ dWt)

Merton (1992)

c© Copyright Eckhard Platen 10 BA - Toronto C 7 226

• NP best performing portfolio

lim supT →∞

1

Tlog

(

V ∗T

V ∗0

)

≥ lim supT →∞

1

Tlog

(

VT

V0

)

global well diversified index≈ NP

Pl. (2005b)

c© Copyright Eckhard Platen 10 BA - Toronto C 7 227

0

10

20

30

40

50

60

70

80

90

100

1930 1940 1950 1960 1970 1980 1990 2000

time

Figure 7.1: Discounted S&P500 total return index.

c© Copyright Eckhard Platen 10 BA - Toronto C 7 228

-2

-1

0

1

2

3

4

5

1930 1940 1950 1960 1970 1980 1990 2000

time

Figure 7.2: Logarithm of discounted S&P500.

c© Copyright Eckhard Platen 10 BA - Toronto C 7 229

• benchmarked price

Ut = Ut

V ∗

t

U nonnegative =⇒

Ut ≥ Et

(

Us

)

t ≤ s

supermartingales (no upward trend)

Pl. (2002)

no strong arbitrage

c© Copyright Eckhard Platen 10 BA - Toronto C 7 230

• benchmarked securities that form martingales are calledfair.

Ut = Et

(

Us

)

t ≤ s

c© Copyright Eckhard Platen 10 BA - Toronto C 7 231

• Law of the Minimal Price

Pl. (2008)

Fair prices are minimal prices

V nonnegative fair portfolio

V ′ nonnegative portfolio

VT = V ′T

supermartingale property

=⇒Vt ≤ V ′

t

t ∈ [0, T ],

c© Copyright Eckhard Platen 10 BA - Toronto C 7 232

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

1930 1940 1950 1960 1970 1980 1990 2000

time

benchmarked savings bondbenchmarked fair zero coupon bond

Figure 7.3: Benchmarked savings bond and benchmarked fair zero coupon

bond.c© Copyright Eckhard Platen 10 BA - Toronto C 7 233

• real world pricing formulafor

Et

(

HT

V ∗T

)

< ∞

UH(t) = V ∗t Et

(

HT

V ∗T

)

t ∈ [0, T ]

no risk neutral probability needs to exist

c© Copyright Eckhard Platen 10 BA - Toronto C 7 234

• actuarial pricing formula

whenHT is independent ofV ∗T

=⇒UH(t) = P (t, T )Et(HT )

zero coupon bond

P (t, T ) = V ∗t Et

(

1

V ∗T

)

c© Copyright Eckhard Platen 10 BA - Toronto C 7 235

• standard risk neutral pricing

Ross (1976), Harrison & Pliska (1983)

complete market

candidate Radon-Nikodym derivative

Λt =dQ

dP

At

=BtV

∗0

B0V∗

t

supermartingale =⇒

1 = Λ0 ≥ E0 (ΛT )

c© Copyright Eckhard Platen 10 BA - Toronto C 7 236

=⇒

UH(0) = E

(

V ∗0

V ∗T

HT

)

= E

(

ΛT

B0

BT

HT

)

≤E(

ΛTB0

BTHT

)

E(ΛT )

c© Copyright Eckhard Platen 10 BA - Toronto C 7 237

Only in the special case whenΛT martingale

=⇒ risk neutral pricing formula:

UH(0) = EQ

(

B0

BT

HT

)

Ignores any real trend !

c© Copyright Eckhard Platen 10 BA - Toronto C 7 238

• Trends ignored also when using:

stochastic discount factor, Cochrane (2001);

deflator, Duffie (2001);

pricing kernel , Constantinides (1992);

state price density, Ingersoll (1987);

NP as Long (1990)

c© Copyright Eckhard Platen 10 BA - Toronto C 7 239

• Example zero coupon bond

benchmarked fair zero coupon

P (t, T ) =P (t, T )

V ∗t

= Et

(

1

V ∗T

)

martingale (no trend)

for rt - deterministic

P (t, T ) = V ∗t Et

(

1

V ∗T

)

= exp

−T∫

t

rs ds

Et

(

V ∗t

V ∗T

)

,

V ∗t =

V ∗

t

Bt- discounted NP

c© Copyright Eckhard Platen 10 BA - Toronto C 7 240

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

1930 1940 1950 1960 1970 1980 1990 2000

time

benchmarked savings bondbenchmarked fair zero coupon bond

Figure 7.4: Benchmarked savings bond and benchmarked fair zero coupon

bond.c© Copyright Eckhard Platen 10 BA - Toronto C 7 241

=⇒ downward trend reflects equity premium

=⇒ Λ strict supermartingale (downward trend), then

P (t, T ) < exp

−T∫

t

rs ds

=Bt

BT

c© Copyright Eckhard Platen 10 BA - Toronto C 7 242

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

1930 1940 1950 1960 1970 1980 1990 2000

time

Radon-Nikodym derivativeTotal RN-Mass

Figure 7.5: Radon-Nikodym derivative and total mass of putative risk neutral

measure.c© Copyright Eckhard Platen 10 BA - Toronto C 7 243

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

1930 1940 1950 1960 1970 1980 1990 2000

time

savings bondfair zero coupon bond

savings account

Figure 7.6: Savings bond, fair zero coupon bond and savings account.

c© Copyright Eckhard Platen 10 BA - Toronto C 7 244

-8

-7

-6

-5

-4

-3

-2

-1

0

1

1930 1940 1950 1960 1970 1980 1990 2000

time

ln(savings bond)ln(fair zero coupon bond)

Figure 7.7: Logarithms of savings bond and fair zero coupon bond.

c© Copyright Eckhard Platen 10 BA - Toronto C 7 245

-2

-1

0

1

2

3

4

5

1930 1940 1950 1960 1970 1980 1990 2000

time

Figure 7.8: Logarithm of discounted S&P500.

c© Copyright Eckhard Platen 10 BA - Toronto C 7 246

• discounted NP

V ∗t =

V ∗t

Bt

dV ∗t = V ∗

t θt (θt dt+ dWt)

= αt dt+

αt V∗

t dWt

c© Copyright Eckhard Platen 10 BA - Toronto C 7 247

• discounted NP drift

αt := V ∗t θ

2t

=⇒ volatility

θt =

αt

V ∗t

reflects leverage effect

c© Copyright Eckhard Platen 10 BA - Toronto C 7 248

• minimal market model

Pl. (2001, 2002)

MMM

discounted NP drift

assume

αt = α0 expηt

α0 > 0

net growth rateη > 0

=⇒ MMM

c© Copyright Eckhard Platen 10 BA - Toronto C 7 249

-2

-1

0

1

2

3

4

5

1930 1940 1950 1960 1970 1980 1990 2000

time

ln(discounted index)trendline

Figure 7.9: Logarithm of discounted S&P500 and trendline.

c© Copyright Eckhard Platen 10 BA - Toronto C 7 250

• normalized NP

Yt =V ∗

t

αt

dYt = (1 − ηYt) dt+√

Yt dWt

square root process of dimension four

Only one parameter !

c© Copyright Eckhard Platen 10 BA - Toronto C 7 251

• volatility of NP

θt =1√Yt

=

αt

V ∗t

c© Copyright Eckhard Platen 10 BA - Toronto C 7 252

• Zero coupon bond under the MMM

rt - deterministic

P (t, T ) = exp

−T∫

t

rs ds

(

1 − exp

− V ∗t

2(ϕ(T ) − ϕ(t))

)

Explicit formula !

c© Copyright Eckhard Platen 10 BA - Toronto C 7 253

-8

-7

-6

-5

-4

-3

-2

-1

0

1

1930 1940 1950 1960 1970 1980 1990 2000

time

ln(savings bond)ln(fair zero coupon bond)

Figure 7.10: Logarithms of savings bond and fair zero coupon bond.

c© Copyright Eckhard Platen 10 BA - Toronto C 7 254

0

0.2

0.4

0.6

0.8

1

1930 1940 1950 1960 1970 1980 1990 2000

time

Figure 7.11: Fraction invested in the savings account.

c© Copyright Eckhard Platen 10 BA - Toronto C 7 255

-2e-005

-1e-005

0

1e-005

2e-005

3e-005

4e-005

5e-005

6e-005

7e-005

1930 1940 1950 1960 1970 1980 1990 2000

time

Figure 7.12: Benchmarked profit and loss.

c© Copyright Eckhard Platen 10 BA - Toronto C 7 256

since

Et

(

ΛT

Λt

)

= Et

(

V ∗t

V ∗T

)

=

(

1 − exp

− V ∗t

2(ϕ(T ) − ϕ(t))

)

=⇒ P (t, T ) < Bt

BT

Overpricing by savings bond

no equivalent risk neutral probability measure

c© Copyright Eckhard Platen 10 BA - Toronto C 7 257

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

1930 1940 1950 1960 1970 1980 1990 2000

time

Radon-Nikodym derivativeTotal RN-Mass

Figure 7.13: Radon-Nikodym derivative and total mass of putative risk neu-

tral measure.c© Copyright Eckhard Platen 10 BA - Toronto C 7 258

• European put option under the MMM

Hulley, Miller & Pl. (2005)

p(t, V ∗t , T,K, r) = V ∗

t Et

(

(K − V ∗τ )+

V ∗τ

)

p(t, V ∗t , T,K, r) = −V ∗

t χ2(d1; 4, l2)

+Ke−r(T −t)(

χ2(d1; 0, l2) − exp −l2/2)

c© Copyright Eckhard Platen 10 BA - Toronto C 7 259

with

d1 =4ηK exp−r(T − t)

Btαt(expη(T − t) − 1)

and

l2 =4ηV ∗

t

Btαt(expη(T − t) − 1)

c© Copyright Eckhard Platen 10 BA - Toronto C 7 260

χ2(x;n, l) non-central chi-square distribution function

n ≥ 0 degrees of freedom

non-centrality parameterl > 0

χ2(x;n, l) =

∞∑

k=0

exp− l

2

(

l2

)k

k!

1 −Γ(

x2; n+2k

2

)

Γ(

n+2k2

)

c© Copyright Eckhard Platen 10 BA - Toronto C 7 261

• putative risk neutral price

p(t, V ∗t , T,K, r) = p(t, V ∗

t , T,K, r)+Ke−r(T −t) exp

− V ∗t

2(ϕ(T ) − ϕ(t))

risk neutral is overpricing

for V ∗t → 0 =⇒ p(t, V ∗

t , T,K, r) → 0

and

p(t, V ∗t , T,K, r) → K e−r(T −t) > 0

risk neutral ignores trends

c© Copyright Eckhard Platen 10 BA - Toronto C 7 262

0

2

4

6

8

1930 1940 1950 1960 1970 1980 1990 2000

time

ln(K*savings bond)ln(risk neutral put)

ln(put)

Figure 7.14: Logarithms of savings bond timesK, risk neutral put and fair

put.c© Copyright Eckhard Platen 10 BA - Toronto C 7 263

Guaranteed Minimum Death Benefit (GMDB)

• payout to the policyholder

max(egτV0, Vτ )

time of deathτ

g ≥ 0 is the guaranteed instantaneous growth rate

V0 is the initial account value

Vτ is the unit value of the policyholder’s account at time of death τ

c© Copyright Eckhard Platen 10 BA - Toronto C 7 264

• insurance chargesξ ≥ 0

=⇒ policyholder’s unit value

Vt = e−ξtV ∗t

=⇒

max(egτV0, Vτ ) = max(egτV0, e−ξτV ∗

τ )

= e−ξτ max(e(g+ξ)τV0, V∗

τ )

c© Copyright Eckhard Platen 10 BA - Toronto C 7 265

insurance company invests the entire fund valueV in the NP V ∗

=⇒ payoff

HT = GMDBT = e−ξT[

(e(g+ξ)TV ∗0 − V ∗

T )+ + V ∗T

]

c© Copyright Eckhard Platen 10 BA - Toronto C 7 266

fair valueGMDB0 of the total claim

real world pricing formula

GMDB0 = V ∗0 E

(

GMDBT

V ∗T

)

= e−ξT(

p(0, V ∗0 , T, e

(g+ξ)TV ∗0 , r) + V ∗

0

)

c© Copyright Eckhard Platen 10 BA - Toronto C 7 267

0 5 10 15 20 25 300.8

0.85

0.9

0.95

1

1.05

1.1

MMM

T

GM

DB

0

0 5 10 15 20 25 300.8

0.85

0.9

0.95

1

1.05

1.1

risk neutral

T

GM

DB

0

0 5 10 15 20 25 300.8

0.85

0.9

0.95

1

1.05

1.1

1.15Black Scholes

T

GM

DB

0

0 5 10 15 20 25 300.9

0.95

1

1.05

1.1

1.15MMM

T

GM

DB

0

0 5 10 15 20 25 300.9

0.95

1

1.05

1.1

1.15risk neutral

T

GM

DB

0

0 5 10 15 20 25 300.9

0.95

1

1.05

1.1

1.15Black Scholes

T

GM

DB

0g=0.025

g=0

g=0.025g=0.025

g=0g=0

Figure 7.15:Present value of the GMDB under the real world pricing formula (left),

the risk neutral pricing formula (middle) and the Black Scholes formula (right) for

η = 0.05,α0 = 0.05, r = 0.05, ξ = 0.01 andY0 = 20.

c© Copyright Eckhard Platen 10 BA - Toronto C 7 268

• lifetime τ is stochastic

GMDB0 = V ∗0 E

(

E

(

GMDBτ

V ∗τ

))

GMDB0 =

∫ T

0

(

p(0, V ∗0 , t, e

(g+ξ)tV ∗0 , r) + V ∗

0

)

e−ξtfτ (t) dt

fτ (·) - mortality density

c© Copyright Eckhard Platen 10 BA - Toronto C 7 269

0 20 40 60 80 100 12010

−5

10−4

10−3

10−2

10−1

100

Age x

log(

q x)

malefemale

Figure 7.16: German mortality data

c© Copyright Eckhard Platen 10 BA - Toronto C 7 270

rational investors will lapse when embedded put-option outof the moneyGMDBs have stochastic maturityTitanic options, Milevsky & Posner (2001)

• roll-up GMDB payoff

Ht =

(1 − βt)V∗

t , if lapsed at timet,

max(egτV0, V∗

τ ), if death occurs at timet = τ

surrender chargeβt

βt =

(8 − ⌈t⌉)%, t ≤ 7,

0, t > 7

no credit riskno accumulation phase

c© Copyright Eckhard Platen 10 BA - Toronto C 7 271

20 30 40 50 60 70 801

1.05

1.1

1.15

Age x

GM

DB

0

malefemale

Figure 7.17: Value of the GMDB under the MMM for male and female pol-

icyholders agedx, assuming an irrational lapsation ofl = 1%.

c© Copyright Eckhard Platen 10 BA - Toronto C 7 272

8 Markets with Event Risk

Jump Diffusion Markets

• filtered probability space(Ω,A,A, P )

• continuous trading uncertainty

m ∈ 1, 2, . . . , d

Wiener processesW k = W kt , t ∈ [0,∞), k ∈ 1, 2, . . . ,m

c© Copyright Eckhard Platen 10 BA - Toronto C 8 273

• events

counting processpk = pkt , t ∈ [0,∞)

intensity hk = hkt , t ∈ [0,∞)

hkt > 0

∫ t

0

hks ds < ∞

• jump martingale

dqkt =

(

dpkt − hk

t dt) (

hkt

)− 12

k ∈ 1, 2, . . . , d−m

c© Copyright Eckhard Platen 10 BA - Toronto C 8 274

E

(

(

qkt+∆ − qk

t

)2 ∣∣

∣At

)

= ∆

• trading uncertainty

W = W t = (W 1t , . . . , W

mt , q1

t , . . . , qd−mt )⊤, t ∈ [0,∞)

c© Copyright Eckhard Platen 10 BA - Toronto C 8 275

Primary Security Accounts

dSjt = Sj

t−

(

ajt dt+

d∑

k=1

bj,kt dW k

t

)

j ∈ 1, 2, . . . , d

c© Copyright Eckhard Platen 10 BA - Toronto C 8 276

Assumption 8.1

bj,kt ≥ −

hk−mt

for all t ∈ [0,∞), j ∈ 1, 2, . . . , d andk ∈ m+ 1, . . . , d.

Assumption 8.2 bt is invertible

c© Copyright Eckhard Platen 10 BA - Toronto C 8 277

• market price of risk

θt = (θ1t , . . . , θ

dt )⊤ = b−1

t [at − rt 1]

at = (a1t , . . . , a

dt )

1 = (1, . . . , 1)⊤

=⇒

dSjt = Sj

t−

(

rt dt+

d∑

k=1

bj,kt (θk

t dt+ dW kt )

)

j ∈ 0, 1, . . . , d

c© Copyright Eckhard Platen 10 BA - Toronto C 8 278

• strategy

δ = δt = (δ0t , . . . , δdt )⊤, t ∈ [0,∞)

• portfolio

Sδt =

d∑

j=0

δjt S

jt

• self-financing if

dSδt =

d∑

j=0

δjt dS

jt

c© Copyright Eckhard Platen 10 BA - Toronto C 8 279

Growth Optimal Portfolio

• fraction

πjδ,t = δj

t

Sjt

Sδt

πδ,t = (π1δ,t, . . . , π

dδ,t)

dSδt = Sδ

t−

rt dt+ π⊤δ,t− bt (θt dt+ dW t)

strictly positive ⇐⇒

d∑

j=1

πjδ,t b

j,kt > −

hk−mt

k ∈ m+ 1, . . . , d

c© Copyright Eckhard Platen 10 BA - Toronto C 8 280

d ln(Sδt ) = gδ

t dt+

m∑

k=1

d∑

j=1

πjδ,t b

j,kt dW k

t

+d∑

k=m+1

ln

1 +d∑

j=1

πjδ,t−

bj,kt

hk−mt

hk−mt dW k

t

• growth rate

gδt = rt +

m∑

k=1

d∑

j=1

πjδ,t b

j,kt θk

t − 1

2

d∑

j=1

πjδ,t b

j,kt

2

+

d∑

k=m+1

d∑

j=1

πjδ,tb

j,kt

(

θkt −

hk−mt

)

+ln

1+

d∑

j=1

πjδ,t

bj,kt

hk−mt

hk−mt

c© Copyright Eckhard Platen 10 BA - Toronto C 8 281

Assumption 8.3√

hk−mt > θk

t

k ∈ m+ 1, . . . , d

c© Copyright Eckhard Platen 10 BA - Toronto C 8 282

• fractions of candidate benchmark

πδ∗,t = (π1δ∗,t, . . . , π

dδ∗,t)

⊤ =(

c⊤t b

−1t

)⊤

ckt =

θkt for k ∈ 1, 2, . . . ,m

θkt

1−θkt (h

k−mt )−

12

for k ∈ m+ 1, . . . , d

if θkt

hk−mt

≪ 1

=⇒ ckt ≈ θk

t

c© Copyright Eckhard Platen 10 BA - Toronto C 8 283

• candidate benchmark

dSδ∗

t = Sδ∗

t−(

rt dt+ c⊤t (θt dt+ dW t)

)

= Sδ∗

t−

(

rt dt+

m∑

k=1

θkt (θk

t dt+ dW kt )

+

d∑

k=m+1

θkt

1 − θkt (hk−m

t )− 12

(θkt dt+ dW k

t )

c© Copyright Eckhard Platen 10 BA - Toronto C 8 284

Definition 8.4 Sδ ∈ V+ NP if gδt ≤ g

δt for all Sδ ∈ V+.

=⇒

Sδ∗ is a NP.

=⇒

gδ∗

t = rt+1

2

m∑

k=1

(θkt )2−

d∑

k=m+1

hk−mt

ln

1 +θk

t√

hk−mt − θk

t

+θk

t√

hk−mt

c© Copyright Eckhard Platen 10 BA - Toronto C 8 285

for θkt

hk−mt

≪ 1 asymptotically

gδ∗

t ≈ rt +1

2

d∑

k=1

(θkt )2 = rt +

|θt|22

d ln(Sδ∗

t ) ≈ gδ∗

t dt+

d∑

k=1

θkt dW

kt

dSδ∗

t ≈ Sδ∗

t

(

rt +

d∑

k=1

θkt

(

θkt dt+ dW k

t

)

)

c© Copyright Eckhard Platen 10 BA - Toronto C 8 286

• jump diffusion market (JDM) SJD(d) = S, a, b,~r, h,A, P

• benchmarked portfolio

Sδt =

Sδt

Sδ∗

t

dSδt =

m∑

k=1

d∑

j=1

δjt S

jt b

j,kt − Sδ

t θkt

dW kt

+

d∑

k=m+1

d∑

j=1

δjt S

jt− b

j,kt

1 − θkt

hk−mt

− Sδt− θ

kt

dW kt

driftless

c© Copyright Eckhard Platen 10 BA - Toronto C 8 287

• benchmarked savings account

dS0t = −S0

t−

d∑

k=1

θkt dW

kt

driftless

c© Copyright Eckhard Platen 10 BA - Toronto C 8 288

benchmarked portfolioSδ driftless =⇒ (A, P )-local martingale

Ansel & Stricker (1994)

=⇒

Theorem 8.5 In a JDM a nonnegativeSδ is an (A, P )-supermartin-

gale

Sδt ≥ E

(

Sδτ

∣At

)

τ ∈ [0,∞) andt ∈ [0, τ ].

c© Copyright Eckhard Platen 10 BA - Toronto C 8 289

A nonnegative portfolio is a strongarbitrage if it can get out of zero.

Corollary 8.6

A JDM does not allow nonnegative portfolios that permit strong arbitrage.

c© Copyright Eckhard Platen 10 BA - Toronto C 8 290

Law of the Minimal Price

Corollary 8.7 Aτ -measurable payoffH withE( H

Sδ∗

τ

|A0) < ∞. If

there exists a fair nonnegative portfolioSδ that replicates the payoff

Sδτ = H,

then this is the minimal nonnegative replicating portfolio.

=⇒• fair portfolios provide the cheapest hedge

c© Copyright Eckhard Platen 10 BA - Toronto C 8 291

H Aτ -measurable payoff, withE( H

Sδ∗

τ

) < ∞

=⇒

real world pricing formula

UH(t) = Sδ∗

t E

(

H

Sδ∗

τ

At

)

• equivalent to riskneutral pricing as long as candidate Radon-Nikodym

derivative S0t

S00

forms(A, P )-martingale

c© Copyright Eckhard Platen 10 BA - Toronto C 8 292

• zero coupon bond

P (t, T ) = E

(

Sδ∗

t

Sδ∗

T

At

)

• benchmarked zero coupon bond

P (t, T ) = P (t,T )

Sδ∗

t

dP (t, T ) = −P (t−, T )

d∑

k=1

σk(t, T ) dW kt

c© Copyright Eckhard Platen 10 BA - Toronto C 8 293

=⇒

ln(P (t, T )) = ln(P (0, T )) −m∑

k=1

(∫ t

0

σk(s, T )dW ks +

1

2

∫ t

0

(σk(s, T ))2 ds

)

+

d∑

k=m+1

(

∫ t

0

σk(s, T )√

hk−ms ds+

∫ t

0

ln

(

1 − σk(s, T )√

hk−ms

)

dpks

)

c© Copyright Eckhard Platen 10 BA - Toronto C 8 294

• forward rate

f(t, T ) = − ∂

∂Tln(P (t, T )) = − ∂

∂Tln(P (t, T ))

=⇒• forward rate equation

f(t, T ) = f(0, T ) +

m∑

k=1

∫ t

0

(

∂Tσk(s, T )

)

(

σk(s, T ) ds+ dW ks

)

+

d∑

k=m+1

∫ t

0

1

1 − σk(s,T )√h

k−ms

∂Tσk(s, T )

(

σk(s, T ) ds+ dW ks

)

similar to HJM equation

c© Copyright Eckhard Platen 10 BA - Toronto C 8 295

Sequences of Diversified Portfolios

Sequence(Sδ(d))d∈N is a sequence of DPs if

∣πj

δ,t

∣≤ K2

d12+K1

for all j ∈ 0, 1, . . . , d, t ∈ [0,∞) and d ∈ d0, d0 + 1, . . ..

c© Copyright Eckhard Platen 10 BA - Toronto C 8 296

• benchmarked primary security account

dSj

(d)(t) = −Sj

(d)(t−)

d∑

k=1

σj,k

(d)(t) dWkt

• kth total specific volatility

σk(d)(t) =

d∑

j=0

|σj,k

(d)(t)|

c© Copyright Eckhard Platen 10 BA - Toronto C 8 297

Sequence of JDMsregular if

E

(

(

σk(d)(t)

)2)

≤ K5

for all t ∈ [0,∞), d ∈ N and k ∈ 1, 2, . . . , d.

c© Copyright Eckhard Platen 10 BA - Toronto C 8 298

Sequence of Approximate NPs

• tracking rate

Rδ(d)(t) =

d∑

k=1

d∑

j=0

πjδ,t σ

j,k

(d)(t)

2

Sδ(d) is NP ⇐⇒ Sδ

(d) ≡ constant

⇐⇒Rδ

(d)(t) = 0

c© Copyright Eckhard Platen 10 BA - Toronto C 8 299

(Sδ(d))d∈N is a sequence ofapproximate NPsif

limd→∞

Rδ(d)(t)

P= 0

• expected tracking rate

eδ(d)(t) = E

(

Rδ(d)(t)

)

(Sδ(d))d∈N has vanishing expected tracking rate, if

limd→∞

eδ(d)(t) = 0

=⇒

c© Copyright Eckhard Platen 10 BA - Toronto C 8 300

limd→∞

P(

Rδ(d)(t) > ε

)

≤ limd→∞

1

εeδ(d)(t) = 0

Lemma 8.8 For a sequence of JDMs, any sequence of strictly positive

portfolios with vanishing expected tracking rate is a sequence of approximate

NPs.

c© Copyright Eckhard Platen 10 BA - Toronto C 8 301

Diversification Theorem

Platen (2005a)

For a regular sequence of JDMs(SJD(d))d∈N , each sequence(Sδ

(d))d∈N

of DPs is a sequence of approximate NPs. Moreover

eδ(d)(t) ≤ (K2)

2K5

d2K1.

c© Copyright Eckhard Platen 10 BA - Toronto C 8 302

Diversification in an MMM Setting

• savings account

S0(d)(t) = expr t

• discounted NP drift

αδ∗

t = α0 expη t

• jth benchmarked primary security account

Sj

(d)(t) =1

Y jt α

δ∗

t

c© Copyright Eckhard Platen 10 BA - Toronto C 8 303

• SR process

dY jt =

(

1 − η Y jt

)

dt+

Y jt dW

jt

• NP

Sδ∗

(d)(t) =S0

(d)(t)

S0(d)(t)

• jth primary security account

Sj

(d)(t) = Sj

(d)(t)Sδ∗

(d)(t)

c© Copyright Eckhard Platen 10 BA - Toronto C 8 304

0

50

100

150

200

250

300

350

400

450

0 5 9 14 18 23 27 32

Figure 8.1: Primary security accounts under the MMM.

c© Copyright Eckhard Platen 10 BA - Toronto C 8 305

0

10

20

30

40

50

60

0 5 9 14 18 23 27 32

Figure 8.2: Benchmarked primary security accounts.

c© Copyright Eckhard Platen 10 BA - Toronto C 8 306

0

10

20

30

40

50

60

70

80

90

100

0 5 9 14 18 23 27 32

EWI

GOP

Figure 8.3: NP and EWI.

c© Copyright Eckhard Platen 10 BA - Toronto C 8 307

0

10

20

30

40

50

60

70

80

90

100

0 5 9 14 18 23 27 32

Market index

GOP

Figure 8.4: NP and market index.

c© Copyright Eckhard Platen 10 BA - Toronto C 8 308

Real World Pricing for Two Market Models

Specifying a Continuous NP

market prices of event risks are zero

θkt = 0

NP

dSδ∗

t = Sδ∗

t

(

rt dt+

m∑

k=1

θkt

(

θkt dt+ dW k

t

)

)

Sδ∗

0 = 1

c© Copyright Eckhard Platen 10 BA - Toronto C 8 309

Benchmarked Primary Security Accounts

dSjt = −Sj

t−

d∑

k=1

σj,kt dW k

t

Sjt = Sj

0 exp

−1

2

∫ t

0

m∑

k=1

(

σj,ks

)2ds−

m∑

k=1

∫ t

0

σj,ks dW k

s

× exp

∫ t

0

d∑

k=m+1

σj,ks

hk−ms ds

d∏

k=m+1

pk−mt∏

l=1

1 −σj,k

τkl −

hk−m

τkl −

pivotal objects of study

c© Copyright Eckhard Platen 10 BA - Toronto C 8 310

• simplifying notation:

|σjt | =

m∑

k=1

(

σj,kt

)2

• aggregate continuous noise processes

W jt =

m∑

k=1

∫ t

0

σj,ks

|σjs|dW k

s

c© Copyright Eckhard Platen 10 BA - Toronto C 8 311

• generalized volatility matrix bt = [bj,kt ]dj,k=1 invertible

bj,kt = θk

t − σj,kt

for k ∈ 1, 2, . . . ,m

bj,kt = −σj,k

t

k ∈ m+ 1, . . . , d

c© Copyright Eckhard Platen 10 BA - Toronto C 8 312

• constant intensities

hkt = hk > 0

σj,kt = σj,k ≤

√hk−m

• benchmarkedjth primary security account:

Sjt = Sj,c

t Sj,dt

c© Copyright Eckhard Platen 10 BA - Toronto C 8 313

• continuous part

Sj,ct = Sj

0 exp

−1

2

∫ t

0

|σjs|2 ds−

∫ t

0

|σjs| dW j

s

• compensated jump part

Sj,dt = exp

d∑

k=m+1

σj,k√hk−m t

d∏

k=m+1

(

1 − σj,k

√hk−m

)pk−mt

c© Copyright Eckhard Platen 10 BA - Toronto C 8 314

Merton Model

rt = r, σj,kt = σj,k

Sj,ct = Sj

0 exp

−1

2|σj|2 t− |σj| W j

t

Girsanov’s theorem, see Section 9.5

c© Copyright Eckhard Platen 10 BA - Toronto C 8 315

A Minimal Market Model with Jumps

Hulley, Miller & Pl. (2005)

• discounted NP drift

αj(t) = αj0 expηjt

ηj - net growth rate

c© Copyright Eckhard Platen 10 BA - Toronto C 8 316

• jth square root process

dY jt =

(

1 − ηjY jt

)

dt+

Y jt dW

jt

• continuous part

Sj,ct =

1

αj(t)Y jt

c© Copyright Eckhard Platen 10 BA - Toronto C 8 317

• time transformation

ϕj(t) = ϕj0 +

1

4

∫ t

0

αj(s) ds

• squared Bessel process of dimension four

Xj

ϕj(t)= αj(t)Y j

t =1

Sj,ct

S0 is a strict local martingale

c© Copyright Eckhard Platen 10 BA - Toronto C 8 318

Zero Coupon Bonds

P (t, T ) = Sδ∗

t E

(

1

Sδ∗

T

At

)

=1

S0t

E

(

exp

−∫ T

t

rs ds

S0T

At

)

• MM case

P (t, T ) = exp−r(T−t) 1

S0t

E(

S0T

∣At

)

= exp−r(T−t)

c© Copyright Eckhard Platen 10 BA - Toronto C 8 319

• MMM case

λjt =

1

Sjt (ϕ

j(t) − ϕj(T ))

S0T = S0,c

T

P (t, T ) = E

(

exp

−∫ T

t

rs ds

At

)

1

S0t

E(

S0T

∣At

)

= E

(

exp

−∫ T

t

rs ds

At

)

(

1 − exp

−1

2λ0

t

)

c© Copyright Eckhard Platen 10 BA - Toronto C 8 320

Forward Contracts

Sδ∗

t E

(

F j(t, T ) − SjT

Sδ∗

T

At

)

= 0

forward price

F j(t, T ) =Sδ∗

t E(

SjT

∣At

)

Sδ∗

t E(

1

Sδ∗

T

∣At

) =

Sjt

P (t,T )1

Sjt

E(

SjT

∣At

)

if Sjt > 0

0 if Sjt = 0

c© Copyright Eckhard Platen 10 BA - Toronto C 8 321

• MM caseF j(t, T ) = Sj

t expr(T − t)standard expression

• MMM case

1

Sjt

E(

SjT

∣At

)

=1

Sj,ct

E(

Sj,cT

∣At

) 1

Sj,dt

E(

Sj,dT

∣At

)

= 1 − exp

−1

2λj

t

forward price

F j(t, T ) = Sjt

1 − exp

−12λj

t

1 − exp−1

2λ0

t

(

E

(

exp

−∫ T

t

rs ds

At

))−1

c© Copyright Eckhard Platen 10 BA - Toronto C 8 322

Asset-or-Nothing Binaries

Ingersoll (2000), Buchen (2004) and Buchen & Konstandatos (2005)

rt = r

c© Copyright Eckhard Platen 10 BA - Toronto C 8 323

Aj,k(t, T,K) = Sδ∗

t E

(

1SjT ≥K

SjT

Sδ∗

T

At

)

=Sj

t

Sjt

E(

1SjT ≥K(S0

T )−1S0T S

jT

∣At

)

=Sj

t

Sj,ct

E

(

1Sj,cT ≥g(p

k−m

T −pk−mt )S0

T

× exp

σj,k√hk−m (T − t)

(

1 − σj,k

√hk−m

)pk−m

T −pk−mt

Sj,cT

At

c© Copyright Eckhard Platen 10 BA - Toronto C 8 324

Aj,k(t, T,K) =

=

∞∑

n=0

exp−hk−m(T − t)

(hk(T − t))n

n!exp

σj,k√hk−m(T − t)

×(

1 − σj,k

√hk−m

)nSj

t

Sj,ct

E(

1Sj,cT ≥g(n)S0

T Sj,cT

∣At

)

for all t ∈ [0, T ], where

g(n) =K

S0t S

j,dt

exp

−(

r + σj,k√hk−m

)

(T − t)

(

1 − σj,k

√hk−m

)−n

for all n ∈ N

c© Copyright Eckhard Platen 10 BA - Toronto C 8 325

MM case

Aj,k(t, T,K) =∞∑

n=0

exp−hk−m (T − t)

(hk−m (T − t))n

n!

× exp

σj,k√hk−m (T − t)

(

1 − σj,k

√hk−m

)n

Sjt N(d1(n))

for all t ∈ [0, T ], where

d1(n) =

ln(

Sjt

K

)

+

r + σj,k√hk−m + n

ln

(

1− σj,k√hk−m

)

T −t+ 1

2

(

σ0,j)2

(T − t)

σ0,j√T − t

c© Copyright Eckhard Platen 10 BA - Toronto C 8 326

σi,j =√

|σi|2 − 2 i,j |σi| |σj| + |σj|2

i,j - correlation

c© Copyright Eckhard Platen 10 BA - Toronto C 8 327

MMM case

S0 and Sj,c are independent

Aj,k(t, T,K) =

∞∑

n=0

exp−hk−m(T − t)

(hk−m(T − t))n

n!

× exp

σj,k√hk−m(T − t)

(

1 − σj,k

√hk−m

)n

×Sjt

(

G′′0,4

(ϕ0(T ) − ϕ0(t)

g(n);λj

t , λ0t

)

− exp

−1

2λj

t

)

c© Copyright Eckhard Platen 10 BA - Toronto C 8 328

G′′0,4(x;λ, λ

′) equals probabilityP ( ZZ′

≤ x)

non-central chi-square distributed random variableZ ∼ χ2(0, λ)

non-central chi-square distributed random variableZ′ ∼ χ2(4, λ′)

c© Copyright Eckhard Platen 10 BA - Toronto C 8 329

Bond-or-Nothing Binaries

MM case

Bj,k(t, T,K) =

∞∑

n=0

exp−hk−m (T − t)(hk−m (T − t))n

n!

×K exp−r(T − t)N(d2(n))

for all t ∈ [0, T ], where

d2(n) =

ln(

Sjt

K

)

+

(

r + σj,k√hk−m + n

ln(1− σj,k√hk−m

)

T −t− 1

2

(

σ0,j)2

)

(T − t)

σ0,j√T − t

= d1(n) − σ0,j√

T − t

c© Copyright Eckhard Platen 10 BA - Toronto C 8 330

MMM case

Bj,k(t, T,K)

=

∞∑

n=0

exp−hk−m(T − t)(hk−m (T − t))n

n!

×K exp−r(T − t)(

1 −G′′0,4

(

(ϕj(T ) − ϕj(t))g(n);λ0t , λ

jt

))

c© Copyright Eckhard Platen 10 BA - Toronto C 8 331

European Call Options

cj,kT,K(t) = Sδ∗

t E

(

SjT −K

)+

Sδ∗

T

At

= Sδ∗

t E

(

1SjT ≥K

SjT −K

Sδ∗

T

At

)

= Aj,k(t, T,K) −Bj,k(t, T,K)

c© Copyright Eckhard Platen 10 BA - Toronto C 8 332

MM case

cj,kT,K(t) =

∞∑

n=0

exp−hk−m(T − t)(hk−m(T − t))n

n!

×(

exp

σj,k√hk−m (T − t)

(

1 − σj,k

√hk−m

)n

Sjt N(d1(n))

−K exp−r(T − t)N(d2(n))

)

c© Copyright Eckhard Platen 10 BA - Toronto C 8 333

MMM case

cj,kT,K(t) =

∞∑

n=0

exp−hk−m(T − t)(hk−m(T − t))n

n!

×[

exp

σj,k√hk−m (T − t)

(

1 − σj,k

√hk−m

)n

×Sjt

(

G′′0,4

((

ϕ0(T ) − ϕ0(t)

g(n)

)

;λjt , λ

0t

)

− exp

−1

2λj

t

)

−K exp−r(T − t)(

1 −G′′0,4

(

(ϕj(T ) − ϕj(t))g(n);λ0t , λ

jt

))

]

c© Copyright Eckhard Platen 10 BA - Toronto C 8 334

Defaultable Zero Coupon Bonds

maturityT

defaults at the first jump timeτk−m1 of pk−m

zero recovery

P k−m(t, T ) = Sδ∗

t E

(

1τk−m1 >T Sδ∗

T

At

)

= Sδ∗

t E

(

1

Sδ∗

T

At

)

E(

1τk−m1 >T

∣At

)

= P (t, T )P (pk−mT = 0

∣At)

c© Copyright Eckhard Platen 10 BA - Toronto C 8 335

• conditional probability of survival

P(

pk−mT = 0

∣At

)

= E(

1pk−mt =0 1p

k−m

T −pk−mt =0

∣At

)

= 1pk−mt =0 P

(

pk−mT − pk−m

t = 0∣

∣At

)

= 1pk−mt =0E

(

exp

−∫ T

t

hk−ms ds

At

)

c© Copyright Eckhard Platen 10 BA - Toronto C 8 336

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