[Paper Review] Baryogenesis through baryon capture by black holes

A. D. Dolgov, N. A. Pozdnyakov|arXiv (Cornell University)|Sep 9, 2020

Cosmology and Gravitation Theories1 references4 citations

TL;DR

This paper proposes a novel mechanism for cosmological baryogenesis via selective capture of baryons and antibaryons by primordial black holes (PBHs), operating in thermal equilibrium without requiring baryon number violation. The asymmetry arises from CP- and C-breaking interactions that induce different scattering cross-sections for X and X̄ particles, leading to preferential capture of antibaryons and generating a net baryon asymmetry proportional to the CP-violating splitting in cross sections.

ABSTRACT

A novel mechanism of cosmological baryogenesis through baryon capture by primordial black holes is suggested. In contrast to the conventional scenarios it does not demand non-conservation of baryonic number in particle physics and can proceed in thermal equilibrium. For implementation of this mechanism a heavy superweakly interacting particle a with non-zero baryon number is necessary.

Motivation & Objective

• To propose a new mechanism for cosmological baryogenesis that does not require baryon number non-conservation.
• To explore how primordial black holes (PBHs) could generate a baryon asymmetry through differential capture of baryons and antibaryons.
• To investigate whether baryogenesis can occur in thermal equilibrium, contrary to the standard Sakharov conditions.
• To identify the necessary particle physics conditions—specifically CP- and C-violating interactions with non-degenerate cross-sections—for this mechanism to function.

Proposed method

• Modeling the equations of motion for X and X̄ particles near PBHs, including gravitational, electromagnetic, and scattering forces.
• Deriving capture velocity differences between X and X̄ particles using fluid velocity equations that include momentum transfer and scattering cross-sections.
• Estimating the CP-violating splitting in scattering cross-sections via one-loop radiative corrections, with the difference proportional to α.
• Using a supersymmetry-inspired model where a heavy H particle mediates X + q → H + 2q̄, enabling asymmetric cross-sections.
• Analyzing the total cross-sections for X and X̄ scattering, showing that differences arise when final states exclude the initial particle.
• Demonstrating that the asymmetry grows with decreasing Hubble expansion rate, favoring slower expansion (larger Planck mass).

Experimental results

Research questions

• RQ1 Can baryogenesis occur without baryon number violation in thermal equilibrium?
• RQ2 What conditions are required for PBHs to preferentially capture antibaryons over baryons?
• RQ3 How can CP and C violation lead to different scattering cross-sections for particles and antiparticles in this context?
• RQ4 What role do radiative corrections play in generating the necessary asymmetry in cross-sections?
• RQ5 Why does the baryon asymmetry increase with larger Planck mass in this model?

Key findings

• The mechanism generates a baryon asymmetry in thermal equilibrium, bypassing the standard requirement of departure from thermal equilibrium.
• The asymmetry arises from a small CP- and C-violating splitting in the scattering cross-sections of X and X̄ particles, estimated as δ ∝ α.
• The cross-section difference is driven by one-loop corrections involving virtual Y-particles, leading to distinct mobilities of X and X̄ in the plasma.
• The asymmetry is proportional to the CP-violating parameter in the scattering amplitude and grows with decreasing Hubble expansion rate.
• The model predicts that larger Planck mass (slower expansion) enhances the baryon asymmetry, opposite to standard baryogenesis.
• Proton decay via virtual black hole formation is suppressed, with lifetime τ_p ∼ 10^45 years, ensuring proton stability.