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Abstract |
In this study, we explore temperature-dependent CPT violation during big bang nucleosynthesis (BBN) through electron-positron mass asymmetries parametrized by b0(T) 1/4 alpha T2. The T2 scaling naturally evades stringent laboratory bounds at zero temperature while allowing for significant CPT violation at MeV scales in the early Universe [S. Navas et al. (Particle Data Group), Phys. Rev. D 110, 030001 (2024)]. Using a modified version of the BBN code PRyMordial with dynamically-solved chemical potentials and appropriate finite-mass corrections, we constrain electron-positron mass differences from observed abundances of helium-4, deuterium, and Neff. We find that alpha must be greater than or approximately equal to 10-6 GeV-1 for keV-scale mass differences at BBN. All three observables show no simultaneous 1 sigma overlap, though pairwise combinations allow for constrained regions of parameter space. We present two toy models demonstrating how b0(T) proportional to T2 arises from field-theoretic mechanisms, including temperature-driven phase transitions. These results provide the most stringent constraints on early-Universe CPT violation in this regime, probing parameter space inaccessible to laboratory experiments. |
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