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Sign-Locked Gravitational Baryogenesis from Bulk Viscosity and Cosmological Particle Creation

Yakov Mandel

Abstract

We study a concrete realization of gravitational baryogenesis in which a small bulk-viscous deformation of an otherwise radiation-dominated early universe generates a sign-definite curvature source. The key point is thermodynamic irreversibility: positive entropy production makes the driving term monotonic and therefore avoids the freeze-out cancellation that suppresses rapidly oscillating or sign-changing sources. Motivated by a simple first-order transfer-function diagnostic, we analyze the standard curvature-current operator $\mathcal{L}_{\rm int}=(c/M^2)\,\partial_μR\,J^μ_{B-L}$ in a near-radiation background with effective pressure $p_{\rm eff}=p-3ζH$ and $ζ=ξρ/H$. For $ξ>0$ one finds $R\neq 0$, $\dot R>0$, and a baryon asymmetry $η\propto ξT_D^5/(M^2 \bar M_{\rm Pl}^3)$. We derive the viable $(T_D,M,ξ)$ region, include entropy dilution from a finite viscous epoch, and show that the observed $η_{\rm obs}\simeq 8.6\times10^{-11}$ can be reproduced in a parameter region consistent with current cosmological bounds while maintaining EFT control. The highest-scale benchmarks should be read conditionally on a very high reheating scale in view of current tensor limits. A particle-creation sector of heavy GUT-scale fields then provides a phenomenological motivation for the required range $ξ\sim10^{-4}$--$10^{-3}$. We also discuss the known higher-derivative instability of gravitational baryogenesis and the role of stabilized or completed embeddings.

Sign-Locked Gravitational Baryogenesis from Bulk Viscosity and Cosmological Particle Creation

Abstract

We study a concrete realization of gravitational baryogenesis in which a small bulk-viscous deformation of an otherwise radiation-dominated early universe generates a sign-definite curvature source. The key point is thermodynamic irreversibility: positive entropy production makes the driving term monotonic and therefore avoids the freeze-out cancellation that suppresses rapidly oscillating or sign-changing sources. Motivated by a simple first-order transfer-function diagnostic, we analyze the standard curvature-current operator in a near-radiation background with effective pressure and . For one finds , , and a baryon asymmetry . We derive the viable region, include entropy dilution from a finite viscous epoch, and show that the observed can be reproduced in a parameter region consistent with current cosmological bounds while maintaining EFT control. The highest-scale benchmarks should be read conditionally on a very high reheating scale in view of current tensor limits. A particle-creation sector of heavy GUT-scale fields then provides a phenomenological motivation for the required range --. We also discuss the known higher-derivative instability of gravitational baryogenesis and the role of stabilized or completed embeddings.

Paper Structure

This paper contains 18 sections, 39 equations, 3 figures, 1 table.

Table of Contents

  1. Introduction
  2. Relation to Previous Work
  3. Freeze-Out Suppression as a Transfer-Function Diagnostic
  4. Bulk Viscosity, Entropy Production, and a Sign-Locked Curvature Source
  5. Entropy production
  6. Curvature trace and the sign of Rdot
  7. Curvature-Current Baryogenesis
  8. Finite Viscous Epoch and the Parameter Window
  9. Phenomenological Handles
  10. Comparison with Current Cosmological Constraints
  11. Baryon-abundance target.
  12. Effective number of relativistic species.
  13. Tensor bound and reheating scale.
  14. Particle Creation as a Microphysical Motivation for xi
  15. Caveat: Higher-Derivative Instability and Stabilized Completions
  16. ...and 3 more sections

Figures (3)

  • Figure 1: Transfer-function diagnostic for a time-dependent baryogenesis source under smooth freeze-out. A sign-locked source corresponds to $x=\omega\tau_{\rm off}\approx0$, while rapidly oscillating sources with $x\gg1$ are adiabatically suppressed.
  • Figure 2: Parameter space reproducing $\eta_{\rm obs}$ for $\Delta_S\simeq1$, $c=g_b=1$, and $g_*=106.75$. Solid curves correspond to fixed $\xi$. The dashed line is the EFT boundary $M=T_D$; viable points lie above it. Stars mark the benchmark points of Table \ref{['tab:bench']}, including their actual $\Delta_S$ corrections.
  • Figure 3: Left: entropy dilution factor $\Delta_S$ as a function of the duration of the viscous phase, expressed through $T_D/T_{\rm off}$. Right: suppression factor $\Delta_S^{-4/3}$ for a decoupled radiation component as a function of $\xi$ for the illustrative choice $T_D/T_{\rm off}=10^4$. Benchmark points B--D are marked for orientation.