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Leptogenesis in exponential $f(R)$ gravity model

Suhail Khan, Ajay Bassi, Rathin Adhikari

TL;DR

The paper investigates gravitational baryogenesis in an expanding universe within the exponential $f(R)$ gravity framework, augmented by axion dark matter. By incorporating a dynamical CPT-violating coupling $({\partial_{\mu} R}) J^{\mu}$, it derives a lepton asymmetry that depends on the time derivative of the Ricci scalar, the decoupling temperature $T_D$, and the gravity parameter $\beta$, while ensuring consistency with late-time acceleration. It analyzes both non-SUSY and SUSY lepton-number-violating decays (heavy right-handed neutrinos and sneutrinos), deriving expressions for $T_D$ and the resulting baryon asymmetry $\eta_b$, and finds an upper bound $\beta<2$ with a best-fit near $0.8$, compatible with axion dark matter. The results show that the observed baryon asymmetry can be achieved in this setup, and the framework links early-universe baryogenesis to the modified gravity sector that governs late-time cosmic acceleration, though SUSY scenarios may face gravitino-related constraints at high $T_D$.

Abstract

We show that gravitational leptogenesis with dynamical $CPT$ breaking in an expanding universe can be reconciled with the exponential $f(R)$ gravity model, which introduces only one additional parameter $β$ compared to the standard $Λ$CDM cosmology. This model incorporated axions as cold dark matter. For $L$ violating interactions, we consider both a non-supersymmetric model with heavy right-handed neutrino decay and a supersymmetric model with sneutrino decay. For both cases, we have shown that the required baryonic asymmetry could be obtained. We have also shown the variation of decoupling temperature for lepton number violating interactions with the $β$ parameter in exponential $f(R)$ gravity. Lepton number-violating model parameters are constrained with the $β$ through the decoupling temperature. An upper bound on the $β$ parameter of the exponential $f(R)$ gravity is also obtained.

Leptogenesis in exponential $f(R)$ gravity model

TL;DR

The paper investigates gravitational baryogenesis in an expanding universe within the exponential gravity framework, augmented by axion dark matter. By incorporating a dynamical CPT-violating coupling , it derives a lepton asymmetry that depends on the time derivative of the Ricci scalar, the decoupling temperature , and the gravity parameter , while ensuring consistency with late-time acceleration. It analyzes both non-SUSY and SUSY lepton-number-violating decays (heavy right-handed neutrinos and sneutrinos), deriving expressions for and the resulting baryon asymmetry , and finds an upper bound with a best-fit near , compatible with axion dark matter. The results show that the observed baryon asymmetry can be achieved in this setup, and the framework links early-universe baryogenesis to the modified gravity sector that governs late-time cosmic acceleration, though SUSY scenarios may face gravitino-related constraints at high .

Abstract

We show that gravitational leptogenesis with dynamical breaking in an expanding universe can be reconciled with the exponential gravity model, which introduces only one additional parameter compared to the standard CDM cosmology. This model incorporated axions as cold dark matter. For violating interactions, we consider both a non-supersymmetric model with heavy right-handed neutrino decay and a supersymmetric model with sneutrino decay. For both cases, we have shown that the required baryonic asymmetry could be obtained. We have also shown the variation of decoupling temperature for lepton number violating interactions with the parameter in exponential gravity. Lepton number-violating model parameters are constrained with the through the decoupling temperature. An upper bound on the parameter of the exponential gravity is also obtained.
Paper Structure (6 sections, 48 equations, 3 figures)

This paper contains 6 sections, 48 equations, 3 figures.

Table of Contents

  1. Introduction
  2. Field equations
  3. Gravitational Baryogenesis with Exponential $f(R)$ Gravity
  4. Decoupling Temperature $T_D$ for non SUSY model
  5. Decoupling Temperature $T_D$ for SUSY model
  6. Discussion and conclusion

Figures (3)

  • Figure 1: The plot shows the variation of decoupling temperature $T_D$ with $\beta$ at a cut-off scale of $M_* =M_P$ GeV.
  • Figure 2: The plots show the variation between neutrino mass $M$ and Yukawa coupling $\lambda$ with different $\beta$ values at a cut-off scale of $M_*=10^{15}$ GeV ( upper) and $M_*=M_P$ GeV ( lower), respectively.
  • Figure 3: The plots show the variation between sneutrino mass $M$ and trilinear SUSY breaking parameter $A$ with different $\beta$ values at a cut-off scale of $M_*=10^{15}$ GeV ( upper) and $M_*=M_P$ GeV ( lower), respectively.