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Primordial Dirac Leptogenesis

Aqeel Ahmed, Juan P. Garcés, Manfred Lindner

TL;DR

This work addresses the baryon asymmetry of the universe (BAU) by proposing a Dirac leptogenesis mechanism realized during the post-inflation reheating phase. The authors introduce a minimal model with an inflaton, an inert Higgs doublet, and right-handed neutrinos under a Z2 symmetry, where CP-violating inflaton decays generate a chiral Higgs asymmetry that is transferred to neutrinos and partially converted into a baryon asymmetry by electroweak sphalerons; global lepton number remains conserved, and light neutrino masses arise from SM Yukawas. A drift–and–decay analysis yields a simple relation $Y_B \approx 1.2\times 10^{-2} \lambda_5 \sin(2\theta)$, linking the BAU to the quartic coupling $\\lambda_5$ and CP phase $\\theta$, with the observed $Y_B$ fixing parameter combinations. The scenario also predicts a measurable contribution to $\\Delta N_{\\rm eff}$ from light right-handed neutrinos, providing cosmological tests that complement collider probes and neutrino experiments. Overall, the paper establishes a testable bridge between inflationary reheating dynamics and the origin of the baryon asymmetry, with a concrete minimal realization and clear observational consequences.

Abstract

We present a novel realization of Dirac leptogenesis based on the post-inflationary reheating phase of the early universe. An asymmetry generated within the scalar sector via CP-violating and out-of-equilibrium inflaton decays is transferred to chiral neutrinos through Yukawa interactions and then to baryons via electroweak sphalerons. We describe in detail a minimal realization of this mechanism that naturally accommodates small neutrino Yukawa couplings and results in contributions to the effective number of relativistic species, $N_{\text{eff}}$, testable in upcoming cosmological observations.

Primordial Dirac Leptogenesis

TL;DR

This work addresses the baryon asymmetry of the universe (BAU) by proposing a Dirac leptogenesis mechanism realized during the post-inflation reheating phase. The authors introduce a minimal model with an inflaton, an inert Higgs doublet, and right-handed neutrinos under a Z2 symmetry, where CP-violating inflaton decays generate a chiral Higgs asymmetry that is transferred to neutrinos and partially converted into a baryon asymmetry by electroweak sphalerons; global lepton number remains conserved, and light neutrino masses arise from SM Yukawas. A drift–and–decay analysis yields a simple relation , linking the BAU to the quartic coupling and CP phase , with the observed fixing parameter combinations. The scenario also predicts a measurable contribution to from light right-handed neutrinos, providing cosmological tests that complement collider probes and neutrino experiments. Overall, the paper establishes a testable bridge between inflationary reheating dynamics and the origin of the baryon asymmetry, with a concrete minimal realization and clear observational consequences.

Abstract

We present a novel realization of Dirac leptogenesis based on the post-inflationary reheating phase of the early universe. An asymmetry generated within the scalar sector via CP-violating and out-of-equilibrium inflaton decays is transferred to chiral neutrinos through Yukawa interactions and then to baryons via electroweak sphalerons. We describe in detail a minimal realization of this mechanism that naturally accommodates small neutrino Yukawa couplings and results in contributions to the effective number of relativistic species, , testable in upcoming cosmological observations.

Paper Structure

This paper contains 6 sections, 34 equations, 1 figure.

Table of Contents

  1. Introduction
  2. A minimal realization
  3. From scalar to baryon asymmetry
  4. Testability
  5. Summary and conclusions
  6. Acknowledgments---

Figures (1)

  • Figure 1: Schematic illustration of Primordial Dirac Leptogenesis. The inflaton decays produce an initial chiral neutrino asymmetry (ⓟ), which is partially converted into a baryon asymmetry via weak sphalerons (ⓢ). Left-right equilibration of neutrinos (ⓔ) occurs at much lower temperatures, ensuring the freeze-out of the baryon asymmetry.