A post-inflationary kinetic axion

A bstract We present a novel realization of axion kinetic misalignment, triggered by a Hubble-induced phase transition during a post-inflationary stiff (kination) era. A negative Ricci scalar flips the sign of the mass term of a non-minimally coupled complex field Φ, driving its radial mode to large amplitudes through a tachyonic instability. At large |Φ|, higher-dimensional U (1)-breaking operators become relevant and impart a kick in the angular direction, generating a conserved U (1) charge that sustains rotation as the symmetry is approximately restored. Because phases randomize across causally disconnected regions, multiple domains with distinct charges form. The subsequent axion potential converts the domain charges into an axion abundance, yielding dark matter even when the net global charge vanishes. We analyze the dynamics using a linear, domain-averaged treatment and identify two thermal histories: (i) Ricci reheating via saxion decays into Higgs bosons; (ii) external reheating with efficient damping of saxion energy through Higgs/fermion scatterings. The mechanism populates regions that are underabundant in standard misalignment and are accessible to next-generation axion searches.