Supernova bound on axionlike particles coupled with electrons

Axionlike particles (ALPs) coupled with electrons would be produced in a supernova (SN) via electron-proton bremsstrahlung and electron-positron fusion. We evaluate the ALP emissivity from these processes by taking into account the ALP mass and thermal effects on electrons in the strongly degenerate and relativistic SN plasma. Using a state-of-the-art SN simulation, we evaluate the SN 1987A cooling bound on ALPs for masses in the range 1--200 MeV, which excludes currently unprobed regions down to g₀₄2. 510^-10 at m₀120 MeV.