Abstract

Scalar fields are ubiquitous in fundamental theories of the early universe. Axions, for example, are theoretically well-motivated, providing an elegant solution to the strong CP problem, while a plethora of other axion-like fields arise naturally in theories with extra dimensions. Such fields have couplings to the electromagnetic sector, offering an exciting opportunity to constrain high-energy physics using astrophysical photons in the late universe. I will discuss how distance determinations in cosmology (coming from supernova observations, measurements of cosmic expansion, and baryon acoustic oscillations) can be used to place strong constraints on axion-like particles through distance duality tests. Similar techniques apply to any scalar field coupling to photons, including dark energy. I will point out additional effects of scalar-photon couplings on the CMB temperature evolution, that could be used to break degeneracies in dark energy parameter estimations.