Gravitational Baryogenesis Mechanisms in Cosmology

Gravitational baryogenesis proposes that the observed predominance of matter over antimatter arises from interactions between the evolving geometry of the early Universe and baryonic currents. In these frameworks, a time-varying curvature scalar or related gravitational invariants couples to a baryon current, generating an effective chemical potential under CPT violation and out-of-equilibrium conditions. Various realisations extend beyond the Ricci scalar to include torsion and non-metricity scalars, boundary terms and higher-order invariants such as the Gauss–Bonnet term. These approaches are often explored within modified theories of gravity, which provide additional degrees of freedom that can amplify the baryon-to-entropy ratio while remaining consistent with cosmic microwave background and big-bang nucleosynthesis constraints. Gravitational baryogenesis thus bridges fundamental particle physics and cosmology, offering testable predictions for model parameters and with implications for the thermal history and global evolution of the Universe.

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Gravitational Baryogenesis Mechanisms in Cosmology publication trend

The graph below shows the total number of articles in gravitational baryogenesis mechanisms in cosmology across all publications each year (not limited to Nature Index journals).

Technical terms

Baryon-to-entropy ratio: the number density of baryons divided by the entropy density, a key observational measure of matter–antimatter asymmetry.

Non-metricity scalar (Q): a measure of how the metric tensor varies under parallel transport, central to f(Q) gravity theories.

Torsion scalar (T): a quantity describing the antisymmetric part of the connection in torsion-based gravity models.

Ricci scalar (R): the trace of the Ricci curvature tensor, representing the simplest curvature invariant of spacetime.

Gauss–Bonnet term: a specific combination of curvature invariants that yields second-order field equations in four dimensions when coupled appropriately.

QCD phase transition: the epoch when quarks became confined into hadrons, around 150 MeV temperature, with potential non-equilibrium effects for baryogenesis.

CPT violation: the breakdown of combined charge, parity and time-reversal symmetries, necessary for generating a net baryon number from symmetric initial conditions.

References

1. QCD preheating: New frontier of baryogenesis. Physical Review D (2023).
2. Compatibility of gravitational baryogenesis in f(Q, C) gravity. European Physical Journal C (2024).
3. Constraining f ( T , T ) gravity with gravitational baryogenesis. Physics Letters B (2023).
4. Gauss–Bonnet gravitational baryogenesis. Physics Letters B (2016).