What can the CMB tell about cosmic reheating? · WHAT CAN THE CMB TELL ABOUT COSMIC REHEATING?...

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WHAT CAN THE CMB TELL ABOUT COSMIC REHEATING? Marco Drewes TU München based on JCAP 1603 (2016) no.03, 013 arXiv:1511.03280 [astro-ph.CO] April 29th 2016 XI. Kosmologietag, Bielefeld, Gremany 1 / 13 WHAT CAN THE CMB TELL ABOUT COSMIC REHEATING?

Transcript of What can the CMB tell about cosmic reheating? · WHAT CAN THE CMB TELL ABOUT COSMIC REHEATING?...

WHAT CAN THE CMB TELL ABOUT COSMIC REHEATING?

Marco DrewesTU München

based onJCAP 1603 (2016) no.03, 013

arXiv:1511.03280 [astro-ph.CO]

April 29th 2016XI. Kosmologietag, Bielefeld, Gremany

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2 / 13WHAT CAN THE CMB TELL ABOUT COSMIC REHEATING?

Inflation and Reheating

0.1 0.2 0.5 1 2

0.3

0.4

0.5

0.6

0.7

0.80.9

ϕ

V(ϕ)

Inflation Era Reheating Era

explains homogeneity, isotropyand flatness of the universe

explains origin of densityfluctuations from blown-upquantum fluctuations

ϕ+ (3H + Γϕ)ϕ+ ∂ϕV(ϕ) = 0

effective potential V(ϕ) governs the dynamics of inflation

effective dissipation rate Γϕ leads to reheating

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How reheating affects the CMB

0.1 0.5 1 5 10 50

1

5

10

t

a

Inflation Era Reheating Era Radiation Era

equation of state p = wρ during reheating is neither that of inflation(w < −1/3) nor that of radiation (w = 1/3)

that affects the rate of cosmic expansion via H = −4π(1 + w)ρ/m2P

⇒ affects relation between observed angular size of perturbationsand size at their generation

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How to quantify this effect

1 + zend =areh

aend(1 + zreh) =

areh

aend

(ρreh

ργ

)1/4

=areh

aend

ρ1/4reh

ρ1/4end

ρ1/4end

ρ1/4γ

≡ 1Rrad

(ρend

ργ

)1/4

0.1 0.5 1 5 10 50

1

5

10

t

a

Inflation Era Reheating Era Radiation Era

Rrad parameterises the effect ofthe reheating era on the expan-sion history. Martin/Ringeval 2010

Rrad = 1 if reheating were instan-taneous

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The parameter Rrad

One can express

ln Rrad =1− 3wreh

12 (1 + wreh)ln(ρreh

ρend

)wreh, ρend are governed by V(ϕ)ρreh is governed by Γϕ and V(ϕ)(reheating stops when Γϕ > H)

1) Can one constrain Rrad from observations?

2) Can one learn anything about the inflaton couplings from that?

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Constraining Rrad Ireheating happened after inflation,

ρreh < ρend,

and before big bang nucleosynthesis,

ρBBN < ρreh.

If V(ϕ) ∝ (ϕ/MP)p, then wreh = p−2p+2 and

Rrad =

(ρreh

ρend

) 4−p12p

and (ρBBN

ρend

) 4−p12p

≷ Rrad ≷ 1 for p ≷ 4,

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Constraining Rrad IIRrad can be treated as a free parameter in addition to those inV(ϕ) and those of the ΛCDM model when constraininginflationary models with CMB data.

Martin/Ringeval/Vennin 2016

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Use Rrad to constrain inflaton couplings ?

ln Rrad =1− 3wreh

12 (1 + wreh)ln(ρreh

ρend

)depends on V(ϕ) via wreh, ρend, ρreh and on Γϕ via ρreh

⇒ For given V(ϕ) one can constrain Γϕ⇒ Γϕ is given by inflaton coupling(s) λ⇒ allows to constrain inflaton couplng λ!

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Backreaction and parametric resonanceTime dependence of Γϕ is not given by inflaton coupling λ alone,but depends on coupling constants α of the produced particles .

resonance→ complicated far from equilibrium dynamics→ no meaningful bound on λ or α from Rrad.

Example: Lint = λmφφχ2 + α

4!χ4

induced transitions Γϕ ' Γ0[1 + 2fχ(mφ/2)]

can lead to resonant production of χ-particlesefficiency depends on how quickly χ-particles rescatter into othermodes

⇒ depends on α

large effective χ-masses in the plasma modify particle kinematics⇒ depends on α

But what if λ� 1 and there is no resonance?

10 / 13WHAT CAN THE CMB TELL ABOUT COSMIC REHEATING?

Backreaction and parametric resonanceTime dependence of Γϕ is not given by inflaton coupling λ alone,but depends on coupling constants α of the produced particles .

resonance→ complicated far from equilibrium dynamics→ no meaningful bound on λ or α from Rrad.

Example: Lint = λmφφχ2 + α

4!χ4

induced transitions Γϕ ' Γ0[1 + 2fχ(mφ/2)]

can lead to resonant production of χ-particlesefficiency depends on how quickly χ-particles rescatter into othermodes

⇒ depends on α

large effective χ-masses in the plasma modify particle kinematics⇒ depends on α

But what if λ� 1 and there is no resonance?

10 / 13WHAT CAN THE CMB TELL ABOUT COSMIC REHEATING?

Backreaction and parametric resonanceTime dependence of Γϕ is not given by inflaton coupling λ alone,but depends on coupling constants α of the produced particles .

resonance→ complicated far from equilibrium dynamics→ no meaningful bound on λ or α from Rrad.

Example: Lint = λmφφχ2 + α

4!χ4

induced transitions Γϕ ' Γ0[1 + 2fχ(mφ/2)]

can lead to resonant production of χ-particlesefficiency depends on how quickly χ-particles rescatter into othermodes

⇒ depends on α

large effective χ-masses in the plasma modify particle kinematics⇒ depends on α

But what if λ� 1 and there is no resonance?10 / 13

WHAT CAN THE CMB TELL ABOUT COSMIC REHEATING?

Perturbative reheating

1 100 104 106 108 1010

0.001

0.100

10

1000

a

T

TR

Tmax

Reheating Era Radiation Era

MaD 2014thermal history without backreactionthermal history with backreactionbackreaction affects themal history, but not expansionhistory⇒ leaves ρreh unaffected!⇒ backreaction does not affect Rrad!

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Constraining the inflaton coupling: Example

Lint = λmφφχ2 + α

4!χ4

Γ0 ' λ2mφ/(16π)

V(ϕ) = 12 m2

φϕ2 → wreh = 0, ρend ' m2

φm2P/2

ρreh/ρend can be determined from Γϕ = H at ρ = ρreh

This yields

Rrad 'λ1/3

2and

TR '√

mφmP

g1/4∗

R3rad

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Conclusions

the CMB is sensitive to the expansion history during reheating

this effect can be parameterised by a single number Rrad

Rrad can be constrained from CMB data

in absence of a parametric resonance, a constraint on Rrad can betranslated into a constraint on the inflaton coupling(s) andreheating temperature

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