Ze-Peng Liu, Yue-Liang Wu and Yu-Feng Zhou

Kavli Institute for Theoretical Physics China,Institute of Theoretical Physics, Chinese Academy of SciencesarXiv:1101.4148[hep-ph]

Enhancement of dark matter relic density from the late time dark matter conversions

海峡两岸粒子与宇宙学研讨会 2011.04.01-06, 新竹

Outline Introduction:

evidences of DM from observations DM candidates: WIMPs recent experimental results

Thermal evolution of interacting multi-DM Generic case with multiple component DM models Boost factor in two-component DM model

Numerical results and a simple model Conclusions

DM revealed from gravitational effects

Gravitational curves

Strong lensing

Weak lensing

Large scale structure

CMB

Bullet clusters

What we know about DM Massive: from gravitational interactions. Stable: lifetime longer than the age of the Universe Electro-magnetic and color neutral: dark, but can annihilate into

photons Non-baryonic

MACHOs: disfavored by micro-lensing survey MOND: disfavored by bullet clusters D/H from BBN: CMB:

Non-relativistic motion ( from N-body simulations ) Cold DM： substructure, halo core Warm DM ?

A big challenge to the standard model of particle physics !

Stability: symmetry + kinematics

Symmetries important for keeping particle stableelectron: U(1) em. symmetry, lightest charged particleproton: U(1) B-L symmetry, lightest baryonneutrino: Lorentz symmetry, lightest fermion

DM protected by symmetriesKnown examples

SUSY: R-parity, LSPUED: KK-parity, LKPLittle Higgs: T-parity

LR model: P and CP parity W.L. Guo, L.M.Wang, Y.L. Wu, YFZ, C. Zhuang Phys.Rev.D79:055015,2009

W.L.Guo, Y.L. Wu, YFZ, Phys.Rev.D82:095004,2010W.L.Guo, Y.L. Wu, YFZ, Phys.Rev.D81:075014,2010

DM stability

DM relic density: The WIMPs miracle

Thermal freeze out: the origin of species

Weakly Interacting Massive Particles (WIMPs)• Particle physics independently predicts WIMPs• WIMPs have just the right relic density• WIMPs are testable by the current exp.

Search for non-gravitational effects ?

Satellite

underground

Cherenkov telescope balloon

collider

Hint of DM ? Positron fraction

if interpreted as DM signal Large annihilation cross section now, boost

factor problem. Sommerfeld enhancement ? Resonance enhancement ? Non-thermal DM ? DM may slightly decay ?

Mainly annihilation/decay into leptons,not quarks Light final states <1GeV ? Leptophilic interaction ?

background

PAMELA

Nature 458, 607 (2009)

Hint of DM? electrons plus positrons

ATIC/PPB-BETS Excess in the total flux peak at ~600 GeV rapid drop below 800GeV

Fermi LAT Spectrum harder than

expected background with power index around ~3.

Nature, 456, 2008,362-365

Phys.Rev.Lett.102:181101,2009

Direct searches

CRESST

EDELWEISS-II

EDELWEISS-II, arXiv:1103.4070.

The boost factor problem

The std. WIMP annihilationcross section is too small to account for the PAMELA/Fermi data

Positron flux

Boost factor

Need a large boost factor B~100-1000

Bergstrom, Edsjo, Zaharijas, PRL103,031103,09’

Boot factor for DM annihilation Local clumps

Via Lactea II: in subhalo? B~ 4-15, Temperature-dependent ann. cross section

Sommerfeld enhancement

Resonance enhancement

Possible origins of boost factor

Diemand, et al, 0805.1244, Nature

Sommerfeld, Ann. Phy 403, 257 (1931).J. Hisano, S. Matsumoto and M. M. Nojiri, Phys. Rev. D 67 (2003)

Phys. Rev. Lett. 92, 031303 (2004)

Feldman, Liu, Nath, 09Ibe, Murayama, Yanagida, 09

Guo, Wu, 09

Other mechanism: DM decay, non-thermal DM ….

Constraints from relic density

Other constraints

•Halo shape

•CMB, protohalo

Refined analysis at freeze-out

• Cut-off of resonance, recoupling• Force-carrier production & decay rates• Kinetic decoupling

• Self-interaction efficiency, non-thermality

J. Zavala, M. Vogelsberger and S. D. M. White, Phys. Rev. D 81, 083502 (2010)M. Kamionkowski and S. Profumo, Phys. Rev. Lett. 101,261301 (2008)

J. L. Feng, M. Kaplinghat and H. B. Yu, Phys. Rev. Lett. 104, 151301 (2010)arXiv:1005.4678

Boost factor in multi-component DM models

Large boost requires1. Large annihilation cross

section2. Still the correct relic density

Impossible for one-component thermal DM?

Multi-component DM Models with hidden sectors

naturally have multi-DM DM may have SUSY partners Neutrinos are already (tiny)

part of DM

boost from simply mixed thermal multi-DM ? (No)

Boost factor from interacting multi-DM ?(Possible)

For thermal relic large cross section Always reduces signal

Z.P.Liu, Y.L.Wu and YFZ, arXiv:1101.4148

Thermal evolution of interacting multi-DM

The components can be converted Thermal evolution for interacting DM

Use common variable

the DM conversion process

Maintain thermal equilibrium between the DM components, after decoupling from the SM thermal bath

Convert the heavy DM into the light

Thermal evolution of the total density

The total density at equilibrium

The total density evolves like an ordinary WIMP at early time

effective cross section is temperature-dependent

The effective cross section

A interesting limit

Approximate form

The two-component case

Thermal evolution for two-component DM

1. Thermal equilibrium with SM

2. Decouple from SM, but still in equilibrium with each other

3. Late time DM conversion at large z Slow conversion characterized by r(z) Crossing point

4. Complete decouple (freeze-out) after Freeze-out condition

Y1(z) increased eventually

Numerical results

Equilibrium• Equilibrium density Y2

Numerical results

Equilibrium• Equilibrium density Y2• Equilibrium density Y1

Numerical results

Equilibrium• Equilibrium density Y2• Equilibrium density Y1If no conversion• Decoupling of Y2

Numerical results

Equilibrium• Equilibrium density Y2• Equilibrium density Y1If no conversion• Decoupling of Y2• Decoupling of Y1

Numerical results

Equilibrium• Equilibrium density Y2• Equilibrium density Y1If no conversion• Decoupling of Y2• Decoupling of Y1With conversion• Evolution of Y2

Numerical results

Equilibrium• Equilibrium density Y2• Equilibrium density Y1If no conversion• Decoupling of Y2• Decoupling of Y1With conversion• Evolution of Y2• Evolution of Y1

Numerical results

Equilibrium• Equilibrium density Y2• Equilibrium density Y1If no conversion• Decoupling of Y2• Decoupling of Y1With conversion• Evolution of Y2• Evolution of Y1• Evolution of Y1+Y2

Numerical results

B vs mass difference B vs relative cross sections

Conditions for a large boost factor

• Large internal degree of freedom of Y2: • Small mass difference:

• Cross sections satisfy:

Approximate expression for the boost factor

A simple 2dm model

Add to the SM

Cross sections

Summary

In multi-DM models, DM conversion can significantly modify the thermal evolution of each DM component.

The relic density of the DM component may not always inversely proportional to it’s annihilation cross section. Through conversions from heavier DM components, the relic density of light DM can be enhanced, leading to large boost factors.

The boost factor is independent of DM velocity. For generic models with large conversion rate the boost fact can reach ~100-1000.

Thank You !

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