Self-interacting neutrinos: solution to Hubble tension versus
  experimental constraints
  Exotic self-interactions among the Standard-Model neutrinos have been
proposed as a potential reason behind the tension in the expansion rate, H0, of
the universe inferred from different observations. We constrain this proposal
using electroweak precision observables, rare meson decays, and neutrinoless
double-\{beta} decay. In contrast to previous works, we emphasize the
importance of carrying out this study in a framework with full Standard-Model
gauge invariance. We implement this first by working with a relevant set of
Standard- Model-Effective-Field-Theory operators and subsequently by
considering a UV completion in the inverse See-Saw model. We find that the
scenario in which all flavors of neutrinos self-interact universally is
strongly constrained, disfavoring a potential solution to the H0 problem in
this case. The scenario with self-interactions only among tau neutrinos is the
least constrained and can potentially be consistent with a solution to the H0
problem.
