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Probing reheating temperature of the universe with gravitational wave background

Kazunori Nakayama, Shun Saito, Yudai Suwa, Jun'ichi Yokoyama

TL;DR

Addresses the unknown reheating epoch after inflation by linking the reheating temperature $T_R$ to the shape of the inflationary stochastic gravitational wave background around $f \sim 1$ Hz. The paper derives the spectrum including reheating and late-time entropy production, showing that future space-based detectors such as DECIGO and BBO could determine $T_R$ (or place a lower bound) for $T_R$ in the range $10^{5}-10^{9}$ GeV depending on the tensor-to-scalar ratio $r$ and dilution factor $F$. It discusses implications for particle physics, including gravitino production in SUSY models and baryogenesis via leptogenesis, highlighting how a GW measurement of $T_R$ can constrain high-energy theories. Overall, the work demonstrates that a direct gravitational wave probe can reveal the thermal history of the early Universe prior to BBN and provide concrete targets for upcoming GW experiments.

Abstract

Thermal history of the universe after big-bang nucleosynthesis (BBN) is well understood both theoretically and observationally, and recent cosmological observations also begin to reveal the inflationary dynamics. However, the epoch between inflation and BBN is scarcely known. In this paper we show that the detection of the stochastic gravitational wave background around 1Hz provides useful information about thermal history well before BBN. In particular, the reheating temperature of the universe may be determined by future space-based laser interferometer experiments such as DECIGO and/or BBO if it is around 10^{6-9} GeV, depending on the tensor-to-scalar ratio $r$ and dilution factor $F$.

Probing reheating temperature of the universe with gravitational wave background

TL;DR

Addresses the unknown reheating epoch after inflation by linking the reheating temperature to the shape of the inflationary stochastic gravitational wave background around Hz. The paper derives the spectrum including reheating and late-time entropy production, showing that future space-based detectors such as DECIGO and BBO could determine (or place a lower bound) for in the range GeV depending on the tensor-to-scalar ratio and dilution factor . It discusses implications for particle physics, including gravitino production in SUSY models and baryogenesis via leptogenesis, highlighting how a GW measurement of can constrain high-energy theories. Overall, the work demonstrates that a direct gravitational wave probe can reveal the thermal history of the early Universe prior to BBN and provide concrete targets for upcoming GW experiments.

Abstract

Thermal history of the universe after big-bang nucleosynthesis (BBN) is well understood both theoretically and observationally, and recent cosmological observations also begin to reveal the inflationary dynamics. However, the epoch between inflation and BBN is scarcely known. In this paper we show that the detection of the stochastic gravitational wave background around 1Hz provides useful information about thermal history well before BBN. In particular, the reheating temperature of the universe may be determined by future space-based laser interferometer experiments such as DECIGO and/or BBO if it is around 10^{6-9} GeV, depending on the tensor-to-scalar ratio and dilution factor .

Paper Structure

This paper contains 10 sections, 30 equations, 8 figures.

Table of Contents

  1. Introduction
  2. Primordial gravitational wave spectrum
  3. Prospects for the determination of $T_R$ with future space-based laser interferometer experiments
  4. Late-time entropy production
  5. Implications on particle physics
  6. Supersymmetric models
  7. Thermally produced gravitinos
  8. Non-thermally produced gravitinos
  9. Baryogenesis mechanism
  10. Conclusions and discussion

Figures (8)

  • Figure 1: A schematic picture of evolution of the Hubble horizon scale $H^{-1}$ and physical wave length of some modes. $\phi$.D., R.D., M.D. and $\Lambda$.D. denote the inflaton oscillation dominated era, radiation dominated era, matter dominated era, and cosmological constant dominated era, respectively.
  • Figure 2: $\Omega_{\rm gw}(f)$ at $f=0.1$Hz for $\eta =0.01,0,-0.01$ from upper to lower.
  • Figure 3: Primordial gravitational wave spectrum for $T_R = 10^9$ GeV and $T_R=10^5$ GeV are shown by thin and thick lines for $r=0.1$ and $0.001$. Also shown are expected sensitivity of DECIGO (green dashed), correlated analysis of DECIGO (blue dot-dashed), ultimate-DECIGO (purple dashed) and correlated analysis of ultimate-DECIGO (red dotted), from upper to lower.
  • Figure 4: In the outer light shaded region the gravitational wave background can be detected, and the inner blue shaded region shows the region where $T_R$ can be determined with signal-to-noise ratio 5 by correlated analysis of DECIGO, ultimate-DECIGO (single) and ultimate-DECIGO (correlation) from upper to lower.
  • Figure 5: A schematic picture of evolution of the Hubble horizon scale $H^{-1}$ and physical wave length in the presence of late-time entropy production from $\chi$. $\chi.$D. represents $\chi$-dominated era.
  • ...and 3 more figures