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 annihilation
cross 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 !
Thanks !
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