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Abstract

We scrutinize the XENON1T electron recoil excess in the
scalar-singlet-extended dark matter effective field theory. We confront it with
various astrophysical and laboratory constraints both in a general setup and in
the more specific, recently proposed, variant with leptophilic $Z_2$-odd
mediators. The latter also provide mass to the light leptons via suppressed
$Z_2$ breaking, a structure that is well fitting with the nature of the
observed excess and the discrete symmetry leads to non-standard dark-matter
interactions. We find that the excess can be explained by neutrino--electron
interactions, linked with the neutrino and electron masses, while
dark-matter--electron scattering does not lead to statistically significant
improvement. We analyze the parameter space preferred by the anomaly and find
severe constraints that can only be avoided in certain corners of parameter
space. Potentially problematic bounds on electron couplings from Big-Bang
Nucleosynthesis can be circumvented via a late phase transition in the new
scalar sector.