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Probing Right Handed Neutrino assisted Reheating with Gravitational Waves and Leptogenesis

Arghyajit Datta, Shaaban Khalil, Rajat Kumar Mandal, Arunansu Sil

TL;DR

The authors propose a renormalisable inflaton-RHN coupling that drives a two-stage, perturbative extended reheating in which RHN decays reheat the Universe and generate the baryon asymmetry via leptogenesis. Gravitational waves arise from both inflaton decay via bremsstrahlung and inflaton annihilation, producing a spectrum that redshifts through the reheating and radiation-dominated eras and may be probed by resonant cavity experiments. Neutrino masses are accommodated by the type-I seesaw, with the Casas-Ibarra parametrisation used to fit oscillation data while satisfying BAU constraints, notably limiting the lightest RHN mass to 10^9–10^13 GeV in the benchmark scenarios. The study identifies k=2 as the viable inflaton potential near its minimum, yielding a reheating temperature in the 10^7–10^8 GeV range for the benchmarks and predicting GW features that could serve as a distinctive signature of non-instantaneous reheating and RHN dynamics.

Abstract

We investigate a non-instantaneous reheating period in the early Universe, where the inflaton field decays exclusively to right-handed neutrinos (RHNs). The subsequent decay of these RHNs into Standard Model particles not only drives the transition to a radiation-dominated era but also generates the baryon asymmetry of the Universe via leptogenesis. In this typical reheating scenario, gravitational waves (GWs) can be produced during inflaton decay, both through bremsstrahlung and inflaton scattering processes. While GW production via bremsstrahlung dominates near the end of the reheating phase, inflaton scattering leads to a non-negligible GW contribution near the maximum temperature of the Universe. The combined GW spectrum from both decay and scattering processes lies within the sensitivity range of proposed resonant cavity experiments. This framework thus offers a compelling and unified approach to addressing neutrino mass generation, the baryon asymmetry of the Universe via leptogenesis, and probing the dynamics of a non-instantaneous reheating era.

Probing Right Handed Neutrino assisted Reheating with Gravitational Waves and Leptogenesis

TL;DR

The authors propose a renormalisable inflaton-RHN coupling that drives a two-stage, perturbative extended reheating in which RHN decays reheat the Universe and generate the baryon asymmetry via leptogenesis. Gravitational waves arise from both inflaton decay via bremsstrahlung and inflaton annihilation, producing a spectrum that redshifts through the reheating and radiation-dominated eras and may be probed by resonant cavity experiments. Neutrino masses are accommodated by the type-I seesaw, with the Casas-Ibarra parametrisation used to fit oscillation data while satisfying BAU constraints, notably limiting the lightest RHN mass to 10^9–10^13 GeV in the benchmark scenarios. The study identifies k=2 as the viable inflaton potential near its minimum, yielding a reheating temperature in the 10^7–10^8 GeV range for the benchmarks and predicting GW features that could serve as a distinctive signature of non-instantaneous reheating and RHN dynamics.

Abstract

We investigate a non-instantaneous reheating period in the early Universe, where the inflaton field decays exclusively to right-handed neutrinos (RHNs). The subsequent decay of these RHNs into Standard Model particles not only drives the transition to a radiation-dominated era but also generates the baryon asymmetry of the Universe via leptogenesis. In this typical reheating scenario, gravitational waves (GWs) can be produced during inflaton decay, both through bremsstrahlung and inflaton scattering processes. While GW production via bremsstrahlung dominates near the end of the reheating phase, inflaton scattering leads to a non-negligible GW contribution near the maximum temperature of the Universe. The combined GW spectrum from both decay and scattering processes lies within the sensitivity range of proposed resonant cavity experiments. This framework thus offers a compelling and unified approach to addressing neutrino mass generation, the baryon asymmetry of the Universe via leptogenesis, and probing the dynamics of a non-instantaneous reheating era.

Paper Structure

This paper contains 19 sections, 77 equations, 9 figures, 1 table.

Table of Contents

  1. Introduction
  2. The Era of Extended Reheating with RHNs
  3. Evolution of Energy Densities during Reheating
  4. Estimating Reheating Temperature Embedded in RHN-Assisted Reheating
  5. Gravitational Wave Generation during RHN-Assisted Reheating
  6. Production of GWs from Decay of the Inflaton
  7. Production of GWs from Inflaton Annihilation
  8. Estimating Effective Gravitational Wave Spectrum
  9. Leptogenesis during RHN-Assisted Reheating
  10. Gravitational Wave Spectrum and Leptogenesis
  11. Phenomenology of Leptogenesis during Reheating
  12. Combined GW Spectrum for $k=2$
  13. Case with $k=4$
  14. Conclusion
  15. Acknowledgement
  16. ...and 4 more sections

Figures (9)

  • Figure 1: Feynman diagram for graviton production from three body decay of inflaton.
  • Figure 2: Feynman diagrams for inflaton annihilation
  • Figure 3: Evolution of energy densities of different components w.r.t. renormalised scale factor $\mathcal{A}=a/a_{{\rm end}}$ for BP1 (left panel) and BP3) (right panel) respectively.
  • Figure 4: Evolution of Temperature of the Universe for BP1 ($M_{1}=10^{11}\text{ GeV}$) and BP3 ($M_{1}=10^{9}\text{ GeV}$) (from left to right) respectively.
  • Figure 5: Evolution of $M_{N_1}(t)$ (left panel) and $Y_{B-L}=n_{B-L}/s$ (right panel) for BP1($M_{1}=10^{11}\text{ GeV}$).
  • ...and 4 more figures