Unified Models for Dark Matter and Dark Energy

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Unified Models for Dark Matter and Dark Energy

• G. J. Mathews - Univ. Notre Dame

VIth Rencontres du Vietnam August 7-11, 2006
Hanoi
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Premise of this talk

• It is an amazing coincidence that the dark energy
  and dark matter contribute comparable amounts of
  mass energy
• This begs the question as to whether they could
  be different aspects of the same physical
  phenomenon

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Alternative ViewsDark Matter produces Dark
Energy

• Unified/Interacting Dark Matter
• Relativistic/Inhomogeneous Corrections to
  Friedmann Cosmology
• Chaplygin Gas p -A??
• Viscous/ Decaying Dark Matter
• Appearing Dark Matter

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Appearing Dark Matter in Brane Cosmology

• G. J. Mathews, Univ. Notre Dame
• K. Umezu, K. Ichiki, T. Kajino, Tokyo Univ./NAOJ
• M. Yahiro, Kyushu Univ. PRD 73, (2006) 063527
  astro-ph/0507227

• The universe is described as an effective
  3-brane
• Embedded in a large 5 dimensional anti-deSitter
  space (AdS5).

• Standard-model particles are dynamically
  confined to the 3-brane
• The possibility exists for particles to reside in
  the bulk

m0
Bulk Dimension
z
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The flow of particles from the bulk to the brane
produces an accelerating cosmology
Kiritsis et al., hep-th/0207060, Tetradis
hep-th/0211200, Umezu et al. astro-ph/0507227

• The flow of matter from the bulk into the
  3-brane will appear as spontaneous matter
  creation
• ? H constant
• ? acceleration
• This mimics a cosmological constant even for ?4
  0

m0
m0
m0
Bulk Dimension
Z
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Modified Cosmic Expansion
- Static Bulk/Expanding 3-space

• ds2 -?2 dt2 a(t,y)?ijdxidxj dz2
• TAB(?P)UAUB?ABP U5 -Hl
• TAB (bulk)(?DM PDM)U5 T05-Hl?
• TAB (brane)(?(z)/b)diag(-?-?, -?p, -?p,
  -?p,0)
• TAB (vacuum) diag( -?5, -?5, -?5, -?5, -?5 )

• E Dark Radiation or Electric part of the bulk
  Weyl tensor

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Modified Equation of state
Parametrize EOS in Bulk

• T05 -(? H/2)(? /aq)

• q 3 Normal matter,
• q 4 Relativistic matter
• q 1 Strings
• q 0 Dark energy

• Only works if q lt 3

Best fit ? 7.6, q 1.0, ?DM ?E 0.26 ?DM
3.1 , ?0
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Accelerating Cosmology
E
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Equivalently fit with ?0 or ?CDM
Fit to SNIa Data
Umezu, et al. (2006)
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CMB Power Spectrum
Diminished power for the lowest multipoles
Umezu, et al. (2006)
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Matter Power Spectrum
Less power on the scales near the horizon
Umezu, et al. (2006)
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Bulk Viscosity and Decaying Dark MatterG. J.
Mathews C. Kolda and N. Q. Lan, Univ. Notre
DameJ. R. Wilson, LLNLG. M. Fuller, UC San
Diego

• Decaying dark matter leads to dissipative bulk
  viscosity in the cosmic fluid
• This viscosity may account for some or all of the
  apparent cosmic acceleration

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Viscous Dark MatterWeinberg (1971)
Bulk Viscosity
Negative pressure gt Dark Energy
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Bulk Viscosity can fit the SNIa redshift relation
Fabris et al. 2005 astro-ph/0503362
A 8?G ?/H0
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Need a Physical Model for Bulk Viscosity
If a gas is out of pressure equilibrium as it
expands or contracts a bulk viscosity is generated
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Particle decay

• Pressureless DM ? relativistic particles P ?/3
• Out of temperature and pressure equilibrium
• Dissipation Bulk Viscosity

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During decay matter and relativistic particles
are out of pressure and temperature equilibrium

• 3 ? h?eq(1/3) - (?P/ ??
• ?eq ?/(1 3 ? H)

Weinberg (1971)
Need (?P/ ??) P/ ? ? 1/3
P (?l ??)/3
? ?DM ?b ?h ?? ?l
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Candidates for Decaying Dark Matter

• sneutrino ? ? g??e
• Gauge mediated supersymmetry breaking
• ? ? ?R ?R
• Decaying massive sterile neutrino
• ?S ? ?es

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Particle decay
SNIa
?CDM
?M 1.0
BV ? 10
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Why this does not work
?tot falls off too rapidly with time Need
constant ?tot
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How to fix this?

• Late decays
• Cascading decays Sterile neutrinos
• ?1? ?2? ?3? ?4? ?5? ?6? regular neutrinos
• Late decays due to time varying mass or a late
  phase transition

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Late Decaying Particles
Accelerating
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Late Decaying Particles
SNIa
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Cascading particle Decays ?1? ?2? ?3? ?4? ?5? ?6?
SNIa
?CDM
Delayed BV ? 10
?M 1.0
BV ? 10
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Conclusions

• Appearing dark matter
• Can fit CMB, SNIa, and matter power spectrum
  constraints if EOS (q ?1)
• Can test by observations CMB supression/P(k)
• DM decay
• Can produce a bulk viscosity but its effect is
  too small
• Can account for some dark energy if particle
  decay is delayed by a cascade or a late phase
  transition/time-dependent mass

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Bulk Viscosity from Particle Decay
First Law
Entropy density
Entropy from decay
Conservation Eq.
gt
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Conclusions

• Growing dark matter can fit CMB, SNIa, and matter
  power spectrum constraints if
• Matter in the bulk has a different EOS (q ?1)
• Dark matter is offset by dark radiation
• Can test by observations

• There should be an excess density of the dark
  matter particles compared to a standard cosmology
• There should be diminished power for the largest
  structures near the scale of the horizon

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ISW effect suppresses low multipoles
Potentials Slowly varying