Abstract
Solar interpretations of the recent XENON1T excess events, such as axion or dark photon emissions from the sun, are thought to be at odds with stellar cooling bounds from the horizontal branch stars and red giants. We propose a simple effective field theory of a dark photon in which a $Z_2$ symmetry forbids a single dark photon emission in the dense stars, thereby evading the cooling bounds, while the $Z_2$ is spontaneously broken in the vacuum and sun, thereby explaining the XENON1T excess. The scalar responsible for the $Z_2$ breaking has an extremely flat potential, but the flatness can be maintained under quantum corrections. The UV completion of the EFT generally requires the existence of new electrically charged particles with sub-TeV masses with $O(1)$ couplings to the dark photon, offering the opportunity to test the scenario further and opening a new window into the dark sector in laboratory experiments.
Highlights
The XENON1T experiment has recently reported excess events with more than 3σ significance [1]
We propose a simple effective field theory of a dark photon in which a Z2 symmetry forbids a single dark photon emission in the dense stars, thereby evading the cooling bounds, while the Z2 is spontaneously broken in the vacuum and Sun, thereby explaining the XENON1T excess
An attractive explanation is that a new light particle, such as an axionlike particle (ALP) or a dark photon, with a coupling to the electron is produced in the Sun and absorbed by the XENON detector [2]
Summary
The XENON1T experiment has recently reported excess events with more than 3σ significance [1]. The solar interpretations of the excess, are inconsistent with various stellar cooling bounds [3,4,5,6,7,8], because the very interaction that produces the new particle in the Sun and allows it to be detected by the XENON1T experiment produces it in other stars, such as horizontal branch (HB) stars and red giants (RG). In a denser environment such as the core of a HB or RG star, where the electron number density ne exceeds a critical value nc, ε vanishes and takes us out of the stellar cooling bounds, as indicated by the downward arrow We realize this scenario by promoting ε to a dynamical operator φðxÞ=Λ0 with some mass scale Λ0 and a scalar field φ whose expectation value depends on ne. IV, focusing on the stability of the flat potential under quantum corrections
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