Stellar Signals of a Baryon-Number-Violating Long-Range Force

We entertain the novel possibility that long range forces may lead to violations of accidental symmetries, in particular baryon number. Employing an ultralight scalar, with a mass $\ll$ eV, we illustrate that this scenario can lead to vastly disparate nucleon lifetimes, in different astronomical objects. Such a long range interaction can yield a number of potentially observable effects, such as a flux of neutrinos at $\gtrsim 10$ MeV from the Sun and heating of old neutron stars. We examine the prospects for constraining this scenario, with current and future astrophysical data, and find that neutron star heating provides the strongest present and near term bounds. Simple extensions of our setup allow for the ultralight scalar to constitute the dark matter of the Universe. This suggests that matter-enhanced baryon number violation can be a signal of ultralight dark matter, which has apparently been overlooked, so far.