Searching for lepton flavor universality violation and collider signals from a singly charged scalar singlet

In recent years, evidence for lepton flavor universality violation beyond the Standard Model has been accumulated. In this context, a singly charged SU(2)(L) singlet scalar (phi(+/-)) is very interesting, as it can only have flavor off-diagonal couplings to neutrinos and charged leptons therefore necessarily violating lepton flavor (universality). In fact, it gives a (necessarily constructive) tree-level effect in l -> l'nu nu processes, while contributing to charged lepton flavor violating only at the loop level. Therefore, it can provide a common explanation of the hints for new physics in tau -> mu nu nu/tau(mu) -> e nu nu and of the Cabibbo Angle Anomaly. Such an explanation predicts Br[tau -> e gamma] to be of the order of a few times 10(-11), while Br[tau -> e mu mu] can be of the order of 10(-9) for order one couplings and therefore in the reach of forthcoming experiments. Furthermore, we derive a novel coupling-independent lower limit on the scalar mass of approximate to 200 GeV by recasting LHC slepton searches. In the scenario preferred by low energy precision data, the lower limit is even strengthened to approximate to 300 GeV, showing the complementary between LHC searches and flavor observables. Furthermore, we point out that this model can be tested by reinterpreting dark matter monophoton searches at future e(+)e(-) colliders.

Automated summary

Recent research has shown evidence of lepton flavor universality violation beyond the Standard Model. A specific scalar model can provide explanations for experimental hints of new physics and predictions for forthcoming experiments. The model's parameters and predictions can be tested in future experiments to further understand lepton flavor universality.