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Impact of Non-Thermal Leptogenesis with Early Matter Domination on Gravitational Waves from First-order Phase Transition

Dilip Kumar Ghosh, Anish Ghoshal, Koustav Mukherjee, Nimmala Narendra, Nobuchika Okada

TL;DR

This work probes a high-scale, non-thermal leptogenesis scenario in which a heavy scalar φ dominates the early Universe and decays to heavy right-handed neutrinos (RHNs), whose out-of-equilibrium decays generate the observed baryon asymmetry via sphalerons. Simultaneously, φ-driven early matter domination and associated entropy production modify the gravitational-wave spectrum produced by a strong first-order phase transition, leading to a damped, altered-frequency signal whose features depend on the φ decay width Γ_φ. The authors solve coupled Boltzmann equations for φ, RHNs, radiation, and B−L, showing how the BAU can be achieved with $T_{RH}<M_N$ and how the GW spectrum is shaped by the MD epoch, using a model-independent GW analysis with parameters $\alpha$, $\beta/H_*$, $T_*$, and $v_w$. They demonstrate that regions of parameter space yield BAU-consistent leptogenesis and GW signals within the reach of future detectors such as ET, DECIGO, and BBO, offering an indirect probe of high-scale leptogenesis and the thermal history of the early Universe.

Abstract

We study the impact of non-thermal leptogenesis on the spectrum of gravitational waves (GWs) produced by a strong first-order phase transition in the early Universe. We consider a scenario in which a heavy scalar field, $φ$, dominates the energy density of the early Universe and decays into heavy right-handed neutrinos (RHNs). The subsequent decay of RHNs generates a lepton asymmetry, which is partially converted into the observed baryon asymmetry via the sphaleron process. The $φ$-dominated era and the entropy injection from the decays of $φ$ and RHNs leave characteristic imprints on the GW spectrum, such as damping and modified frequency dependence, that distinguish it from the standard cosmological evolution. We identify the parameter space in which non-thermal leptogenesis is successful, leading to distinctive GW spectral features. We show that these GW signals can fall within the sensitivity ranges of future detectors such as ET, DECIGO and BBO. If observed, they would provide valuable insights into the thermal history and dynamics of the early Universe.

Impact of Non-Thermal Leptogenesis with Early Matter Domination on Gravitational Waves from First-order Phase Transition

TL;DR

This work probes a high-scale, non-thermal leptogenesis scenario in which a heavy scalar φ dominates the early Universe and decays to heavy right-handed neutrinos (RHNs), whose out-of-equilibrium decays generate the observed baryon asymmetry via sphalerons. Simultaneously, φ-driven early matter domination and associated entropy production modify the gravitational-wave spectrum produced by a strong first-order phase transition, leading to a damped, altered-frequency signal whose features depend on the φ decay width Γ_φ. The authors solve coupled Boltzmann equations for φ, RHNs, radiation, and B−L, showing how the BAU can be achieved with and how the GW spectrum is shaped by the MD epoch, using a model-independent GW analysis with parameters , , , and . They demonstrate that regions of parameter space yield BAU-consistent leptogenesis and GW signals within the reach of future detectors such as ET, DECIGO, and BBO, offering an indirect probe of high-scale leptogenesis and the thermal history of the early Universe.

Abstract

We study the impact of non-thermal leptogenesis on the spectrum of gravitational waves (GWs) produced by a strong first-order phase transition in the early Universe. We consider a scenario in which a heavy scalar field, , dominates the energy density of the early Universe and decays into heavy right-handed neutrinos (RHNs). The subsequent decay of RHNs generates a lepton asymmetry, which is partially converted into the observed baryon asymmetry via the sphaleron process. The -dominated era and the entropy injection from the decays of and RHNs leave characteristic imprints on the GW spectrum, such as damping and modified frequency dependence, that distinguish it from the standard cosmological evolution. We identify the parameter space in which non-thermal leptogenesis is successful, leading to distinctive GW spectral features. We show that these GW signals can fall within the sensitivity ranges of future detectors such as ET, DECIGO and BBO. If observed, they would provide valuable insights into the thermal history and dynamics of the early Universe.

Paper Structure

This paper contains 9 sections, 53 equations, 5 figures, 1 table.

Table of Contents

  1. Introduction
  2. Non-Thermal Leptogenesis from Heavy Scalar Decay
  3. The Boltzmann Equations
  4. Gravitational Waves from FOPT
  5. GW spectral shape analysis
  6. Imprints of $\phi$-domination on the GW signal
  7. Results: Leptogenesis and the Gravitational Waves
  8. GW Detection prospects with interferometers
  9. Conclusions and Discussion

Figures (5)

  • Figure 1: The abundances of $\phi$(Blue), RHN (Orange), $Y_{B}$ (Green) and radiation (Red). The Black dotted line is the observed baryon asymmetry of the Universe. The parameter choices are as follows: $M_{\phi}=10^{14}$ GeV, $M_{N}=10^{13}$ GeV, $\Gamma_{\phi}^{NN}=4.7\times10^{-3}$ GeV, $\Gamma_{\phi}^{R}=7.95\times10^{-16}$ GeV, $\epsilon_{1}=1.6\times10^{-4}$.
  • Figure 2: The GW spectrum with EMD (Solid Black curve) and without EMD (Black Dashed Curve), along with the reaches of the future observations and the region already excluded. The parameter choice are: $\,\alpha=100,\,\beta/H_{*}=10,\, \kappa_{\text{col}}=0.999$, $f_{*}=10^{-3}$, $M_{\phi}=10^{12} \,\text{GeV},$$M_{N_1}=10^{10}\, \text{GeV},\, \lambda=10^{-10}$ with $\Gamma_\phi /H_{*}\sim10^{-2}$.
  • Figure 3: The GW spectrum with EMD (Black solid curve) and with RD (Red dotted curve), along with the reaches of the future observations and the region already excluded. The parameter choices are: $\,\alpha=100,\,\beta/H_{*}=10 \, (\text{EMD}), 35\, (\text{RD}),\, \kappa_{\text{col}}=0.999$, $f_{*}=10^{-3}$, $M_{\phi}=10^{12} \,\text{GeV},$$M_{N_1}=10^{10}\, \text{GeV},\, \lambda=10^{-10}\,(\text{EMD}),\,6.3\times 10^{-9}\,(\text{RD})$ with $\Gamma_\phi /H_{*}=10^{-2}(\text{EMD})$.
  • Figure 4: The GW spectrum with EMD: The parameter choices are: $\,\alpha=100,\,\beta/H_{*}=10,\, \kappa_{\text{col}}=0.999,$$\, f_{*}=10^{-3},$$M_{\phi}=10^{13} \,\text{GeV},\text{(solid)} ,$$M_{\phi}=10^{12} \,\text{GeV}\,\text{(dashed)},$$M_{\phi}=10^{11} \, \text{GeV} \,\text{(dotted)},$$M_{N_1}=10^{10}\, \text{GeV},\, \lambda=10^{-10}$, with $\Gamma_\phi/H_{*}= 10^{-1}\,\text{(solid)},\,10^{-2}\,\text{(dashed)},\,10^{-3}\,\text{(dotted)}$.
  • Figure 5: The GW spectrum, which is compatible with the BAU. The solid line corresponds to BPs given in Table \ref{['table_BPs']}. Solid, dashed and dotted lines correspond to $\Gamma_{\phi}/H_{*}\sim 10^{-1},\,10^{-2}, {\rm and}\,10^{-3}$ respectively.