UV-complete theory for T^2 CPT-violating background

Construct a UV-complete quantum field theory that yields a temperature-dependent CPT-violating background field b0(T) proportional to T^2, producing electron–positron mass asymmetries at Big Bang Nucleosynthesis energies while ensuring CPT violation vanishes as T→0 to satisfy present-day experimental bounds.

Background

The paper presents three toy constructions—(i) a cubic-potential vector model, (ii) a scalar–vector coupling with a temperature-driven phase transition, and (iii) a PT-symmetric model—that can realize b0(T)∝T2, enabling sizeable early-universe CPT violation while evading low-temperature constraints.

Although these examples demonstrate feasibility at an effective or phenomenological level, the authors note that embedding such mechanisms in a complete, radiatively stable UV theory consistent with the Standard Model and cosmology remains unresolved and is needed to provide a fundamental basis for the proposed temperature-dependent CPT violation.

References

Together, these examples serve as existence proofs that the mass asymmetries constrained by BBN can be realized in theoretically reasonable frameworks, though a complete UV-complete theory remains an open question for future work.

— Temperature-Dependent CPT Violation: Constraints from Big Bang Nucleosynthesis  (2601.06259 - Barenboim et al., 9 Jan 2026) in Section 4, Theoretical Mechanisms for Temperature-Dependent CPT Violation (opening paragraph)