Speaker
Description
Light, weakly coupled new particles are produced efficiently in the hot and dense interior of stars. The resulting effects on stellar evolution can have distinct observable impacts on stellar populations, leading to some of the strongest bounds on new light particles. We revisit stellar bounds on electrophilic scalars arising from the tip of the red-giant branch (TRGB) of globular clusters, and set new bounds stronger by more than an order of magnitude in the coupling squared. We improve upon previous constraints, which relied on a rescaling of neutrino emission rates, by self-consistently simulating the effects of stellar energy loss using the MESA stellar evolution code, accounting for relevant backreaction processes. We also account for all the in-medium production channels of light scalars more accurately, including both resonant and continuous emission. We find that scalar emission leads to a significantly brighter TRGB, and set bounds by comparing our predictions to bolometric luminosity observations of 14 globular clusters from the Gaia database.