$D^0 -_s13gt_s19 gamma gamma$ and $D^0 -_s13gt_s19 mu^_s16 mu^-$ Rates on an Unlikely Impact of the Littlest Higgs Model with T-Parity

Abstract

The decays D^0 -> gamma gamma, $mu^_s16 mu^- are highly suppressed in the Standard Model (SM) with the lion_s14s share of the rate coming from long distance dynamics_s19 D^0 -> mu^_s16 mu^- is driven predominantly by D^0 -> gamma gamma -> mu^_s16 mu^-. Their present experimental bounds are small, yet much larger than SM predictions. New Physics models like the Littlest Higgs models with T parity (LHT) can induce even large indirect CP violation in D^0 transitions. One would guess that LHT has a `fighting chance_s14 to affect these D^0 -> gamma gamma, mu^_s16 mu^- rates in an observable way. We have found LHT contributions can be much larger than short distance SM amplitude by orders of magnitude. Yet those can barely compete with the long distance SM effects. If D^0 -> gamma gamma, mu^_s16 mu^- modes are observed at greatly enhanced rates, LHT scenarios will not be candidates for generating such signals. LHT-like frameworks will not yield larger D^0 rightarrow gamma gamma/mu^_s16 mu^- rates as they are constrained by B and K rare decays.