Improved supernova bounds on CP-even scalars: cooling and decay constraints

Abstract

Supernovae provide among the most powerful probes of weakly-coupled new particles in the MeV mass range, where laboratory experiments lose sensitivity. In this work, we derive improved supernova constraints on CP-even scalars mixing with the Higgs boson, combining an updated production rate calculation, which improves the cooling bound by more than an order of magnitude, with new decay-based constraints from the galactic 511~keV positron flux and energy deposition in low-energy Type~II-P supernovae. Together, these constraints probe mixing angles as small as $\sinθ\sim 10^{-9}$, more than five orders of magnitude below existing collider bounds. We also extend our analysis to a hadrophilic scalar model, constraining Yukawa couplings down to $y_N \sim 10^{-10}$. Our results demonstrate that the combination of astrophysical and collider probes covers over nine orders of magnitude in coupling for these classes of models, probing a large region of parameter space motivated by dark matter considerations.

Figures (8)

• Figure 1: Feynman diagrams showing production of scalar fields via t-channel nucleon-nucleon bremsstrahlung. $N = n, p$.
• Figure 2: Density and Temperature profile of the SN at $t=1$s post bounce. The violet curve represents the hotter profile LS220-s20.0 with progenitor mass $20 \odot$ , and the pink curve represents the colder profile SFHo-18.8 with progenitor mass $18.8 \odot$.
• Figure 3: Lifetime of scalar $S$ as a function of their mass $m_s$ for mixing angle $\sin\theta = 10^{-7}$.
• Figure 4: SN cooling bound on scalar $S$. The shaded region represents the bounds using the colder profile, whereas the region inside the dotted line represents the bounds using the hotter profile.
• Figure 5: Low-energy supernova explosion bound on scalar $S$.