A dark matter candidate from extra dimensions

A dark matter

candidate from extra dimensions1 Regis Marco (SISSA, Trieste)

9/28/06 DESY WORKSHOP “The Dark Universe”

OUTLINE:

● The Model● Z

2 symmetry

● Dark matter candidate● Coannihilation process● Resonant channels● Results

Collaboration with M. Serone and P. Ullio


Regis Marco (SISSA, Trieste) 2

THE MODEL

5D gauge theory on S1/Z2 orbifold

with gauge-Higgs unification

G = SU(3)C

x SU(3)W

x U(1)'

G' = SU(3)C

x SU(2)W

x U(1)Y

In 4D by orbifold projection

MATTER CONTENT :Couples of bulk fermions “UP” in reps “DOWN” in reps

Chiral fermions localized at y = 0: QL, u

R, b

R

Scrucca, Serone, Silvestrini '03Panico, Serone, Wulzer '05Panico, Serone, Wulzer '06


3 Regis Marco (SISSA, Trieste)

,~

( 3,3,1/3)( 3,6,1/3)

-

THE MODEL (2)

● Explicit tree-level breaking of the Lorentz SO(4,1) symmetry

G = SU(3)1,C

x SU(3)2,C

x SU(3)W

x U(1)'1 x U(1)'

2

● Z2 “mirror” symmetry

Lagrangian invariant under the Z2 symmetry 1 2 :



Z2 “MIRROR” SYMMETRY

Boundary conditions:A

1(y ± 2R) = A

2(y) , A

1(-y) = A

2(y) (BC)

● Linear combinations A±= (A

1 ± A

2 )/√2 are periodic / antiperiodic

● Under the mirror symmetry: A±

± A±

Couples charged under G1 and neutral under G

2

Couples charged under G2 and neutral under G

1

Same couplings

Boundary conditions as (BC) ±= (

1 ±

2 )/√2

periodic / antiperiodic



,,

~

~

STABILITY

All SM fields are even under the mirror symmetry

The lightest antiperiodic field is absolutely stable!

If it is neutral and weakly interacting could be a good dark matter candidate (WIMP)

New parity in a ED model different from KK parity can provide the stability of a DM candidate

No need of Universal extra dimensions



WHO IS THE LIGHTEST?

Mass of antiperiodic fields:

Gauge bosons:

Fermions:

Suppose ' < S and ' < k

The n = 0 mode of the gauge boson A_ is the lighest

(with mass ~ 1/2R)



A_ as DM CANDIDATE

It is the analogous of the first kk mode of the hypercharge gauge boson in UED

A_ is the gauge boson of the abelian gauge group U(1)_

Coupling only with bulk fermions.

But SM fermions are a mixture of bulk and boundary fermions

Annihilation cross section is (highly) reduced

At the scale allowed from EW bound (i.e. 1/R ~ 4-5 TeV)

A_ overcloses the Universe!



“STRONG” COANNIHILATIONS

Is it possible to have a WIMP with Multi-TeV mass?Yes, if the DM candidate coannihilates with strong interacting particles (i.e. gluons or colored fermions)

MUED example:B(1) - COANNIHILATION WITH g(1)

Burnell, Kribs '05Kong, Matchev '05



h2

COANNIHILATION WITH g_(without resonances)

● The mass splitting is given by the ratio s / '

● The production of quark pairs in s-channel do not suffer of the suppression due to the fermion localization● The dominant cross section comes from the process g_+g_ g

SM+g

SM

● The running of s is negligible

A_ can be a good DM candidate!



h2

RESONANCES

g+

(1)g_

(0)

g_

(0)

This process can occur since:

Localized fermions

KK number violation at tree level

(at loop level in UED)

And it is resonant because:

g+

(1) mass = 2 g-(0) mass at tree level



Kakizaki, Matsumoto, Sato, Senami '05

q

q_

COANNIHILATION WITH g_(including resonances)

The decay rate of g+

(1) q + q is significantly higher than the

mass splitting induced by radiative corrections.

The resonance highly increases the thermally averaged cross section!



_

h2

CONCLUSIONS

● A new Z2 symmetry (different from KK parity)

can guarantee the stability for a DM candidate.● The Multi-Tev mass region for a WIMP is not excluded since “strong” coannihilations and resonances.● There is a significant fraction of parameter space in which A_ is a DM candidate with the correct relic density.● Need of a fine-tuning estimation (and possible other coannihilation processes) to have a better judgment of the results.

13


Regis Marco (SISSA, Trieste)

A dark matter candidate from extra dimensions

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