Energy transfer by feebly interacting particles in supernovae: the trapping regime

Abstract

Feebly interacting particles, such as sterile neutrinos, dark photons, and axions, can be abundantly produced in the proto-neutron star (PNS) formed in core-collapse supernovae (CCSNe). These particles can decay into photons or charged leptons, depositing energy outside the PNS. Strong bounds on new particles can thus be derived from the observed luminosity of CCSNe, with even tighter bounds obtained from low-energy SNe observations. For the first time we highlight that, at sufficiently large couplings, particle production \textit{outside} the PNS must also be considered. Using the prototypical case of axions coupling to two photons, we show that at large couplings the energy transfer from PNS to its surroundings is diffusive rather than ballistic, substantially reducing the deposited energy. Our findings have implications for the parameter space of particles probed in beam dump experiments and for dark matter models involving a sub-GeV mediator.

Figures (3)

• Figure 1: Energy deposited outside the PNS across different regimes of interaction strength. We choose an axion mass $m_a=80\,\rm MeV$ and a progenitor radius $R_1=3\times 10^{12}\,\rm cm$. The thin line accounts only for axions produced within the PNS (Eq. \ref{['eq:wrong_eq_1']}), the thick line includes production outside of the PNS (Eq. \ref{['eq:e_dep_correct']}). CCSNe can constrain $E_{\rm dep}\gtrsim 1\,\rm B$; above $E^{\rm tot}_\nu$, the total energy emitted in neutrinos Fiorillo:2022cdq, post-processing the SN model is certainly unphysical. The top axis shows the decay length for an axion with energy $E_a=300\,\rm MeV$.
• Figure 2: Schematic geometry of the diffusive heat transfer in the trapping regime: axions are nearly in thermal equilibrium outside the PNS, with a small diffusive flux driven by the temperature gradient; at the axiosphere, where $R\sim \lambda$, they decay, dissipating all the energy locally into heat.
• Figure 3: Energy-deposition and cooling constraints on axion-photon coupling. Similarly to Ref. Caputo:2022mah, energy-deposition constraints are shown both for a large progenitor ($R_{\rm prog}=5\times 10^{13}\,\rm cm$) with an explosion energy $E_{\rm dep}=0.1\,\rm B=10^{50} \, erg$, and for a smaller progenitor ($R_{\rm prog}=3\times 10^{12}\, \rm cm$) with an explosion energy $E_{\rm dep}=1\,\rm B$. For the latter, we also show with a dashed line the constraints that would be drawn using Eq. \ref{['eq:wrong_eq_1']}, neglecting particle production outside of the PNS. Previous Earth-based CHARM:1985anbRiordan:1987awBlumlein:1990ayNA64:2020qwqDolan:2017ospCapozzi:2023ffu and astrophysical Jaeckel:2017tudHoof:2022xbeDiamond:2023ctoDiamond:2023scc constraints are shown in gray.