Hoernisa Iminniyaz- Relic density of cold dark matter in nonstandard cosmological scenarios

8/3/2019 Hoernisa Iminniyaz- Relic density of cold dark matter in nonstandard cosmological scenarios

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Relic density of cold dark

matter in nonstandardcosmological scenarios

Hoernisa Iminniyaz

University of Bonn

Mitsuru Kakizaki

Manuel Drees


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Contents

MotivationThe relic density of cold dark matter in the standardcosmological scenario in which particles were inthermal equilibrium in the early universe, WIMP:

weakly interacting massive particlessemi-analytic formulae for the relic density of colddark matter in nonstandard cosmological scenario inwhich particles can't reach thermal equilibrium in the

early universeThe relic density including the decay of heavierparticles into dark matter in nonstandard cosmolo-gical scenario

Conclusion


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MotivationSeveral observations indicate existence of non-lumin-

ous dark matter, e.g. WMAP: 4 % baryonic matter,23% non-baryonic cold dark matter, 73% dark energy

Challenge: searching the nature of the cold dark mat-ter particle, calculating its relic density

The need for nonstandard cosmological scenario: highrelic density in the standard cosmological scenario insome case, seeking scenarios predicting smaller relicdensity


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The relic density in the Stand-

ard cosmological scenario

: the generic dark matter particle

: its number density

Time evolution of the particle number density is determined byBoltzmann equation

n

The particles: in thermal equilibrium in the early universe

decouple: when it was non-relativistic

(The Early Universe, by Edward W.Kolb, Michael S.Turner)


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For WIMP

For radiation dominated era :

Using

When species were in thermal equilibrium,at late times, the equilibrium number density droppedexponentially,


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Equation (1)

In non-relativistic limit

(6)

The approximate solution to the equation (4) :

x=m/T

(Theory and Phenomenology of SparticlesM. Drees, Rohini M.Godbole, Probir Roy)

(5)


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Todays relic density

h is the scaled Hubble parameter,

where

(9)

(7)

(10)

(8)


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Semi-analytic calculation of the relicdensity in the nonstandard cosmo-

logical scenario the particles never reach thermal equilibrium

because of the low reheating temperature after

inflation

From the big bangnucleosynthesis

SUSY dark matter in equilibrium,


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Simplified Boltzmann equation

The figure based on this assumption and comparisonwith the old result

(11)


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(2) At late times,

(1) At early times,

(12)

(14)

(13)


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(3) When both the annihilation term and the production termare important

When is small

(15)

(16)

(17)

(18)


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When Rewriting Eq. (19)

(19)

(20)


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comparison with the numerical result

Figure 1. with zero initial value

Figure 2. with non-zero initial value

R li d it i l di th d f


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Relic density including the decay ofheavier particles

Dark matter particles are produced through thedecay of heavier particles, e.g. WIMP

can be obtained by the decay of moduli fields orgravitino

(21)

n

: are the decay rate and the number density ofheavier particles


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The Boltzmann equation including the decay of heavier particles

is the solution when the equation includes only the production term

(22)

(23)

(1) At early times,

The solution

(24)


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(3) When both the production term and annihilation term are important

When is small

let

(25)

(2) At late times, there is only annihilation term, the solution issame with the case without the decay of heavier particles


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(26)


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Conclusions

Review of the calculation of the relic density

in the standard cosmological scenarioThe relic abundance of the dark matter insemi-analytic way in the nonstandard cosmo-logical scenarios

The relic density including the decay of heav-ier particles into dark matter particles in non-standard cosmological scenario

Documents

Hoernisa Iminniyaz- Relic density of cold dark matter in nonstandard cosmological scenarios