The Cosmological Energy Density of Neutrinos from Oscillation

MeasurementsKev Abazajian

Fermilab

June 10, 2003

NuFact 03 – Fifth International Workshop on Neutrino Factories & Superbeams

WMAP: Measurement of 10-5 fluctuations on the entire sky to ~0.25°

The photon last scattering surface

ee

Number density from thermodynamic equilibrium:

Primordial Soup of Neutrinos, etc.

baryonnn

nNn

Tn

10

3

332

10

cm34011

3

cm410)3(2

ee

2eV8.93 h

mnm i

crit

ii

0.003 < m < 0.15

Neutrino Dark Matter:

Big Bang Nucleosynthesis

►concordance of light element abundances with standard theory

WMAP

►Consistency with baryon density at 300,000 years later, at CMB decoupling

Neutrino energy density beyond the standard model (assumption)

1. Neutrino Asymmetry:

2. Extra Neutrino Flavors: s, s’, s’’ …

Models: 2+2, 3+1, 3+2, 3+N …

1)/exp(

1),(

Tppf

3.4 3.2 3.0

BBNBBN: From a baryometerbaryometer to a calorimetercalorimeter

The primordial He abundance:

Yp = 0.238 ± 0.002 ± 0.005 (Olive, Steigman & Skillman 1997; Fields & Olive 1998)

Yp = 0.244 ± 0.002 (Izotov & Thuan 1998)

Gives precision measurement of the energy density of the universe at ~ 1 sec!

Constrains new neutrino physics

nNn

11

3

BBN Allowed

BBN Allowed

Orito et al ’02astro-ph/0203352

CMB

CMB

Allowed

Using the observed

abundances of D, 4He,

and 7Li alone,

BBN is very pliable to

allow large neutrino

asymmetries

Due to cancelling

effects

between and e, and

baryon

density, bh2

“Degenerate” Big Bang Nucleosynthesis

Vacuum Oscillation

e+/- / +/- background

Thermal Potential

(finite temperature effects)

Neutrino Self-Potential

Evolution of Neutrino Asymmetries in the Early Universe

)(cm113

)()3(2

11

3

23

23

2

Fn

FTn

LMA solar + maximal ATM

Any chemical potential will alter the 4He abundance.

<<1

Generally:

13 flavorcm113

n

number density of neutrinos

(Dolgov et al, hep-ph/0201287 ; Abazajian, Beacom, Bell astro-ph/0203442 ; Wong hep-ph/0203180 )

Transformation of neutrino asymmetries

Dolgov et al.

Neutrino Flavor Momentum Synchronization…

Abazajian, Beacom & Bellastro-ph/0203442

The Synchronized “Magnetic” Dipole of Neutrino Flavor

Allowed

Allowed

The Death of Degenerate BBN and New Constraints…

CMB

Allowed

Allowed: B

BN + LMA+Atm

Atmospheric, 23

LMA Solar, 12

13

The cosmological neutrino density from sol

(Maltoni)

Non-zero: 13 > 10-10

m2atm

m2sol1

2

3

Normal Hierarchy

Inverted Hierarchy

m2atm

m2sol

1

2

3

Light Sterile Neutrinos

4-Neutrino Mass-modelling

Maltoni, Schwetz, & Valle 2001, 2002; Päs, Song & Weiler 2002

“3+1”

m2atm

m2sol

m2LSND

1

2

3

4

“2+2”

m2sol

m2atm

m2LSND

4

3

1

2

Constraining Sterile Neutrino Mixing

• Collisions decohere neutrino gas and populate sterile neutrinos

• Requiring that s are not equilibrated (N<4)

The relevant amplitude is simply:

Application to all 4 neutrino models:K. Abazajian, Astropart. Phys., astro-ph/0205238; P. Di Bari, PRD 65, 043509 (2002)

Original 2-neutrino limits:Langacker 1989;Barbieri & Dolgov 1990;Enqvist, Kainulainen, Thomson 1992;Shi, Schramm & Fields 1993

3+1

Indirect -> e

Along with unitarity, forces large amplitude mixing with large m2, violating BBN bound

“3+1”

m2atm

m2sol

m2LSND

1

2

3

4

K. Abazajian, Astropart. Phys., astro-ph/0205238

2+2

Both solar (SNO) – neutral current signal of D breakup and capture

and atmospheric (Super-K) – enhanced neutral current component and matter effects

experiments are now effectively appearance experiments, and disfavor large sterile components

Sterile must be split between upper and lower doublet

“2+2”

m2sol

m2atm

m2LSND

4

3

1

2

K. Abazajian, Astropart. Phys., astro-ph/0205238

Assuming Standard Big Bang Nucleosynthesis

Something more precise than “optimistic” and “pessimistic” limits

And using only:

1. The Baryon Density:● from the deuterium abundance:D/H = (3.0 ± 0.4) x 10-5

bh2 = 0.020 ± 0.002 (95% CL)(Burles, Nollet & Turner 2000; Burles & Tytler 1998)● from the CMB:bh2 = 0.022(+0.004)(-0.003)(DASI+DMR) + (BOOMerANG)

2. The primordial helium abundance:Yp = 0.241± 0.002 ± 0.006 (Olive, Steigman & Skillman 1997; Fields & Olive 1998)(Izotov & Thuan 1998)

Constraint Evasion & New Physics

1. Pre-existing lepton number (L ~ 105 B)2. A fifth mass eigenstate, mostly sterile

may dynamically generate lepton number (Foot, Thomson & Volkas, 1996) sufficiently early

3. Generation of majoron fields (Berezinsky & Bento 2001)4. Low reheating temperature (3 active neutrinos are not

thermalized)5. Baryon-Antibaryon inhomogeneities: N < 7 (Giovannini, Kurki-

Suonio & Sihvola 2002)6. Extended quintessence (“dark radiation”) (Chen, Scherrer &

Steigman 2001)7. CPT violating Neutrinos (Murayama & Yanagida 2001; Barenboim,

Borrisov, Lykken & Smirnov 2001)

5

The MiniBooNE Experiment… see Ion Stancu’s talk (next)

Summary…Summary…

• Future measurements of LMA and 13 will further constrain the cosmological neutrino density

• Big bang nucleosynthesis and the CMB (in the future) is – Best probe of relic neutrino asymmetries– And has consequences for four neutrino models,

or vice-versa