Stellar limits on scalars from electron-nucleus bremsstrahlung

Abstract

We revisit stellar energy-loss bounds on the Yukawa couplings g B,L of baryophilic and leptophilic scalars ϕ. The white-dwarf luminosity function yields g B ≲ 7 × 10-13 and g L ≲ 4 × 10-16, based on bremsstrahlung from 12C and 16O collisions with electrons. In models with a Higgs portal, this also implies a bound on the scalar-Higgs mixing angle sinθ ≲ 2 × 10-10. Our new bounds apply for mϕ ≲ 1 keV and are among the most restrictive ones, whereas for mϕ ≲ 0.5 eV, long-range force measurements dominate. Besides a detailed calculation of the bremsstrahlung rate for degenerate and semi-relativistic electrons, we prove with a simple argument that non-relativistic bremsstrahlung by the heavy partner is suppressed relative to that by the light one by their squared-mass ratio. This large reduction was overlooked in previous much stronger bounds on g B. In an appendix, we provide fitting formulas (few percent precision) for the bremsstrahlung emission of baryophilic and leptophilic scalars as well as axions for white-dwarf conditions, i.e., degenerate, semi-relativistic electrons and ion-ion correlations in the “liquid” phase.

Evaporation barrier for dark matter in celestial bodies

“…We also show astrophysical constraints for scalar mediators based on stellar cooling of RG and HB stars [199] (see also ref. [200] for similar constraints from white dwarfs), and SN1987A [201,202], as well as cosmological constraints based on BBN deuterium abundances for leptophilic mediators [146,203]. For vector mediators, these limits are in general weaker in the light mass end than the scalar bounds shown in figure 4.…”

Astrophysical Axion Bounds: The 2024 Edition

“…Axion cooling proceeds through electron bremsstrahlung and can show up in a modified WD luminosity function (WDLF), the distribution of galactic WDs per brightness interval, or in the cooling speed of individual WDs that can be measured for variable WDs by a drift of the pulsation period-for a recent review see Ref. [219] that also covers several non-axion cases and and see also a recent application to scalar interactions [220].…”

Production rates of dark photons and Z' in the Sun and stellar cooling bounds

“…Hot and dense astrophysical environments can be used to probe light and weakly-coupled particles if they are copiously produced via frequent collisions of medium particles. In well-modeled stars such as the Sun, the additional energy loss caused by the emission of such new particles has been used to impose one of the most restrictive bounds on them in certain mass ranges [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39]. In supernovae and neutron stars, new particles of higher masses could be probed [24][25][26][40][41][42][43][44][45][46][47][48], though the astrophysical models have more diverse and larger uncertainties.…”