WIMPless Miracle and Relics in Hidden Sectors
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Transcript of WIMPless Miracle and Relics in Hidden Sectors
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WIMPless Miracle and Relics in Hidden Sectors
Hai-Bo YuUniversity of California, Irvine
Talk given at KITPC 09/16/2008
with Jonathan L. Feng and Huitzu Tu arXiv:0808.2318 [hep-ph]
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Outline
• Review of WIMPless miracle• Thermal relics in hidden sectors• Issues related to small structure formation • Gravitino problem?• Summary
For experimental signals, see
Feng, Kumar and Strigari arXiv:0806.3746 [hep-ph] Feng, Kumar, Learned and Strigari arXiv:0808.4151 [hep-ph]
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Expect new physics at TeV scale
• Gauge hierarchy problem weak scale vs. Planck scale
• Dark Matter ~20% of total mass budget of the Universe
WIMP miracle:
g~gw, m~mw, Ωh^2~0.11
Supersymmetry• Weak scale is stabilized by SUSY.• MSSM has new particles (LSPs) for dark matter candidate.
Kolb and Tuner (1990)
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Hidden sectors?
• But what do we really know about dark matter? ---Gravitational ---No strong, EM interactions ---Dark matter could be SM neutral, i.e. hidden.
• The idea of hidden sector has long history. Lee, Yang (1956); Gross, Harvey, Martinec, Rohm (1985), Schabinger, Wells (2005); Patt,
Wilczek (2006); Strassler, Zurek (2006); Georgi (2007); Kang, Luty (2008), March-Russell, West, Cumberbatch, Hooper (2008); McDonald, Sahu (2008); Kim, Lee, Shin (2008); Krolikowski (2008); Foot (2008); …
• Hidden sector dark matter? ---WIMP miracle? ---connection to the gauge hierarchy problem? ---prediction?
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WIMPless Miracle• the ratio is important
• SUSY partner mass of GMSB
• The ratio is determined solely by the SUSY breaking factor
Feng, Kumar (2008)
One can rescale (mx, gx) simultaneously while keep the ratio unchanged.
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Thermal relics in the hidden sectors
• A GMSB-inspired concrete model for hidden sector DM.
• BBN and CMB constraints on the hidden sectors.
• Thermal dynamics with two independent thermal baths in the expanding universe.
• Lower mass limit from the thermal consideration.
• Kinetic decoupling and small structure formation (Feng, Tu, Kaplinghat and Yu, work in progress).
• Provide a possible solution for the gravitino problem. (Feng, Tu and Yu, work in progress).
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A GMSB-inspired model• SM gauge group SU(3)×SU(2)×U(1)
• One generation of matter fields, flavor-free model
• Assume gauge coupling unification
• 2mx: others 1.5mx: Z mx: stau (DM candidate), Massless: photon, (anti-)neutrino, gluon,
• Model parameters:
Note there is no good DM candidate in the usual MSSM with GMSB. This scenario also works for AMSB. No good DM candidate in the MSSM with AMSB.
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BBN constraints on light degree of freedom
A, B
C, D
Cyburt et al (2004)
---Very small number of light degree of freedom if two sectors have the same T at BBN.
---Hidden sector is colder at BBN. Two ways: colder reheating temperature; more light d.o.f in the hidden sector. Feng, Tu and Yu (2008)
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CMB constraints
C’, D’
C”, D”
Feng, Tu and Yu (2008)
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Temperature evolution of hidden sectors
Assume entropy is conserved in both sector independently
Feng, Tu and Yu (2008)
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Boltzman equations with two thermal baths
---Both sectors have contributions to the Hubble expansion rate.
---The thermally-averaged product of cross section and Moller velocity and the number density are only determined by the hidden sector temperature.
Use visible sector T as “Clock”
Sit in the hidden sector
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Annihilation Channels
---Photon channel has overall ½ smaller than photon Z channel due to the identical final states.
---Neutrino channel is P-wave suppressed. Not surprise.
---Accuracy of the dimensional analysis
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Approximation formulas
---Set xi to 0, we get formulas for one thermal bath case.---delta takes 0.2-0.5 from the fitting.---This approximation yields agreements typically better than 3%.
Feng, Tu and Yu (2008)
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Freezeout behavior with different hidden sector temperature
For different reheating temperature, averaged cross section is nearly the same due to S-wave dominance.
Feng, Tu and Yu (2008)
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Sit in the hidden sector
Inconsistent?
Feng, Tu and Yu (2008)
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Freezeout with different mass
---Larger mass, smaller number density at present time, freezout occurs later, larger coupling.
Feng, Tu and Yu (2008)
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Relics in the hidden sector
Numerically solving Boltzman equations to get (mx, gx).
---Two solid contours essentially follow the scaling relation mx~gx^2.
---The parameters that give correct relic density are those that give weak scale MSSM masses (WIMPless miracle).
---The dimensional analysis is confirmed in this concrete model.
---Colder hidden sector requires smaller coupling to get correct relic abundance for given mass.
Feng, Tu and Yu (2008)
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Lower mass limit ---The lower mass limit is derived by requiring freezeout xfh=mx/Th>3 and correct relic abundance.
---Lower mass limit goes up with colder hidden sector.
---The WIMPless framework may be valid at least down to dark matter masses of mx~keV.
WIMP scenario mass range (100GeV, TeV)
WIMPless scenario mass range (keV, TeV)
Feng, Tu and Yu (2008)
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Kinetic equilibrium
• After freezeout, the DM particle still keep contact with thermal bath through elastic scattering with the relativistic degree of freedom.
• Elastic scattering does not change the number density of DM particle while transfers momentum to DM and keep it in the kinetic equilibrium.
• When the Universe cools down, the kinetic decoupling occurs, DM particle begins free-streaming.
• Decoupling temperature is critical for small structure formation.
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Kinetic decoupling
• Processes keep stau in the kinetic equilibrium
• Decoupling occurs when
decoupling temperature
• Kinetic decoupling happens in two stages,
neutrino process decouples first, then photon process.
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Decoupling temperature
---Larger mass, decouple earlier.
---Neutrino channel decouples earlier.
---Colder hidden sector, decoupling occurs earlier.
---Free-streaming length which sets more correct lower mass bound.
Feng, Tu, Kaplinghat and Yu, in preparation
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Gravitino problem
• In MSSM with GMSB, the gravitino mass should be smaller than a few GeV to avoid FCNC.
• If the reheating temperature is too high, it may produce too many gravitinos which cause the Universe over-close.
• The thermal leptogenesis prefers high reheating temperature.
Bolz, Brandenburg Buckmuller (2000)
Moroi, Murayama and Yamaguchi, (1993)
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A solution from hidden sectors
• Gravitino mass is set by the visible sector (gravitino is the LSP in usual MSSM with GMSB)
• However, gravitino mass can be larger than the hidden sector particle
• Gravitino can decay to hidden sector particles without upsetting BBN.
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Summary
• DM particle can be hidden. WIMPless framework keeps WIMP miracle for hidden sector DM.
• Two thermal baths have interesting implications on thermal behaviors of the DM particle .
• It has cosmological implications on small structure formation.
• This model provides a solution for the gravitino problem.