Microscopic calculation of baryon transmission through Peccei–Quinn domain walls

Derive the microscopic quark reflection and transmission probabilities through Peccei–Quinn domain walls, including the resulting capture efficiency for baryon sweeping and trapping during primordial quark pellet formation.

Background

The formation scenario assumes efficient baryon concentration by contracting Peccei–Quinn domain walls and adopts an effective capture efficiency of approximately 0.84, inferred from cosmological baryon-number accounting rather than from a first-principles dynamical calculation. The relevant microscopic process is the reflection or transmission of relativistic quarks and baryons through the domain-wall barrier, whose efficiency depends on the wall profile, the axion decay constant, and the particle kinetic energy.

The paper estimates that barrier penetration may be exponentially suppressed using a simplified square-well profile and the WKB approximation, but explicitly leaves a detailed particle-level treatment unresolved. Such a calculation is needed to determine whether the assumed capture efficiency is dynamically realized.

References

The present work does not attempt a microscopic calculation of quark reflection or transmission through PQ domain walls. Instead, it investigates the cosmological implications of efficient baryon concentration, leaving the detailed particle-level dynamics for future work.

— Seeding baryonic dark matter  (2608.17395 - Espriu, 18 Aug 2026) in Section 2.4, subsection “Minimum and maximum masses”