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We revisit stellar constraints on dark photons. We undertake dynamicalstellar evolution simulations which incorporate the resonant and off-resonantproduction of transverse and longitudinal dark photons. We compare our resultswith observables derived from measurements of globular cluster populations,obtaining new constraints based on the luminosity of the tip of the red-giantbranch (RGB), the ratio of populations of RGB to horizontal branch (HB) stars(the $R$-parameter), and the ratio of asymptotic giant branch to HB stars (the$R_2$-parameter). We find that previous bounds derived from static stellarmodels do not capture the effects of the resonant production of light darkphotons leading to overly conservative constraints, and that they over-estimatethe effects of heavier dark photons on the RGB-tip luminosity. This leads todifferences in the constraints of up to an order of magnitude in the kineticmixing parameter.

Constraining Dark Photons with Self-consistent Simulations of Globular Cluster Stars