Charge transfer between rotating complex scalar fields

TL;DR

This paper investigates how charge density transfers between complex scalar fields in a cosmological setting, emphasizing the role of symmetry breaking and thermal effects in facilitating efficient charge redistribution with implications for dark matter and baryogenesis.

Contribution

It demonstrates the conditions under which charge transfer between scalar fields is efficient, highlighting the impact of symmetry breaking and thermal bath interactions in cosmological contexts.

Findings

Charge transfer is highly efficient without additional symmetries.

Symmetry breaking to a single U(1) enables charge redistribution.

Implications for axion dark matter and baryogenesis are discussed.

Abstract

We consider the transfer of a U(1) charge density between Bose-Einstein condensates of complex scalar fields coupled to a thermal bath, focusing on the case of a homogeneous Affleck-Dine field transmitting the charge stored in its angular motion to an axion field. We demonstrate that in the absence of additional symmetries this charge transfer, aided by cosmic expansion as well as the thermal effective potential of the Affleck-Dine field, can be very efficient. The charge redistribution between the scalar fields becomes possible if the interactions with the thermal bath break the original U(1) x U(1) symmetry down to a single U(1) symmetry; the charge distribution between the two fields is then determined by minimizing the free energy. We discuss implications for cosmological setups involving complex scalars, with applications to axion dark matter, baryogenesis, kination domination, and gravitational wave production.