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Gravitational waves from supermassive right-handed neutrinos produced at preheating

Shinya Kanemura, Kunio Kaneta, Dibyendu Nanda

Abstract

The post-inflationary production of supermassive particles can have profound implications for the thermal history of the universe and may leave observable imprints in the gravitational wave (GW) background. In scenarios where the inflaton couples predominantly to heavy fields, say right-handed neutrino (RHN), non-perturbative mechanisms such as parametric resonance can lead to their efficient production, even when their masses exceed the inflaton mass. Once produced, the RHNs emit gravitons through bremsstrahlung as they decay into the Standard Model (SM) particles via $N\rightarrow \ell + H$, enabled by the unavoidable minimal coupling to gravity, sourcing a stochastic GW background. We study this mechanism within the framework of $α-$attractor inflationary models, highlighting how the resulting GW spectrum carries indirect imprints of the heavy sector and the post-inflationary dynamics. This offers an observational window into otherwise inaccessible supermassive particles and provides a powerful probe of high-scale physics beyond the SM.

Gravitational waves from supermassive right-handed neutrinos produced at preheating

Abstract

The post-inflationary production of supermassive particles can have profound implications for the thermal history of the universe and may leave observable imprints in the gravitational wave (GW) background. In scenarios where the inflaton couples predominantly to heavy fields, say right-handed neutrino (RHN), non-perturbative mechanisms such as parametric resonance can lead to their efficient production, even when their masses exceed the inflaton mass. Once produced, the RHNs emit gravitons through bremsstrahlung as they decay into the Standard Model (SM) particles via , enabled by the unavoidable minimal coupling to gravity, sourcing a stochastic GW background. We study this mechanism within the framework of attractor inflationary models, highlighting how the resulting GW spectrum carries indirect imprints of the heavy sector and the post-inflationary dynamics. This offers an observational window into otherwise inaccessible supermassive particles and provides a powerful probe of high-scale physics beyond the SM.

Paper Structure

This paper contains 7 sections, 38 equations, 6 figures.

Table of Contents

  1. Introduction
  2. Production of super heavy right handed neutrinos at preheating
  3. Connection to CMB-observables
  4. Production of matter-antimatter asymmetry
  5. Gravitational wave spectrum
  6. Conclusion and Discussions
  7. Derivation of the abundance of the GW energy density

Figures (6)

  • Figure 1: Inflation field value normalised by the reduced Planck mass ($M_P$) as a function of scale factor.
  • Figure 2: Number density of heavy RHNs during preheating as a function of the scale factor.
  • Figure 3: Prediction of CMB spectral index ($n_s$) as a function of the reheating temperature ($T_{\rm RH}$) for different values of $\alpha$ and $n=3$.
  • Figure 4: Evolution of energy densities of different species in the early universe for fixed benchmark values of the parameters. The inflationary parameters are taken as $n=3$ and $\alpha=1$, the asymmetry parameter $\varepsilon_{\ell} = 0.1$, the mass of the RHNs are $M_1\approx M_2 = 10^{15} \text{ GeV and } M_3=10^{16} \text{ GeV}$, and the decay widths of the RHNs are $\Gamma_{N_{1,2}}= 10^{10} \text{ GeV}$ and $\Gamma_{N_3} = 10^{-12} \text{ GeV}$.
  • Figure 5: Feynman diagram representing the bremsstrahlung production of graviton.
  • ...and 1 more figures