Speaker
Description
New light scalar fields with a negative quadratic coupling to Standard Model fermions can be sourced in large, dense objects. Finite density contributions to the potential result in the displacement of the field from its vacuum value. This situation arises, for example, for a lighter-than-usual QCD axion. The sourcing of the scalar field leads to a reduction of the fermion masses, which, depending on the scalar field's coupling and mass, can result in a first-order phase transition or a new ground state of matter.
White dwarfs are well understood and therefore provide ideal laboratories to observe these effects. The presence of a new ground state predicts a gap in the possible radii of white dwarfs, which is inconsistent with observational data. Including finite temperature effects gives access to further observables, which allows us to also constrain first-order phase transitions arising from new scalar fields. This excludes large regions of parameter space without the necessity for the new scalar field to be dark matter.
