Title: Degenerate Stars as Laboratories: Probing Axions and Ultralight Scalars.

Host: Csaba Csaki

Abstract: Ultralight scalar fields, the most famous example being the QCD axion, are common in beyond the standard model physics. In particular, if their leading interaction with the Standard Model is quadratic, direct experimental searches become very challenging. Astrophysics, especially scalar sourcing - where the scalar field develops a classical expectation value at finite density - provides an exciting alternative avenue to test these theories. 

In this talk, I will discuss how the backreaction of scalar sourcing on stellar remnants can be used to probe such models.

Generic light scalar fields coupling to electrons or nucleons can turn white dwarfs into $\phi$-dwarfs, leading to drastic changes in their mass-radius relation. Similarly, neutron stars can lose their heat blanketing envelope due to scalar sourcing, which results in stringent constraints on lighter-than-usual QCD axions.