New Physics in $B$ decays

Abstract

While the LHC did not observe direct evidence for physics beyond the standard model, indirect hints for new physics were uncovered in the flavour sector in the decays $B\to K^{\ast }{\mu }^{+}{\mu }^{-}$, $B\to K{\mu }^{+}{\mu }^{-}/B\to K{e}^{+}{e}^{-}$, $B_s\to \varphi {\mu }^{+}{\mu }^{-}$, $B\to D^{(\ast )}\tau \nu$ and $h\to {\tau }^{\pm }{\mu }^{\mp }$. Each observable deviates from the SM predictions at the $2-3\sigma$ level only, but combining all $b\to s{\mu }^{+}{\mu }^{-}$ data via a global fit, one finds $4-5\sigma$ difference for NP compared to the SM and combining $B\to D^{\ast }\tau \nu$ with $B\to D\tau \nu$ one obtains $3.9\sigma$. While $B\to D^{(\ast )}\tau \nu$ and $h\to \tau \mu$ can be naturally explained by an extended Higgs sector, the $b\to s{\mu }^{+}{\mu }^{-}$ anomalies point at a $Z^{\prime }$ gauge boson. However, it is also possible to explain $B\to D^{(\ast )}\tau \nu$ and $b\to s{\mu }^{+}{\mu }^{-}$ simultaneously with leptoquarks while their effect in $h\to {\tau }^{\pm }{\mu }^{\mp }$ is far too small to account for current data. Combining a 2HDM with a gauged $L_{\mu }-L_{\tau }$ symmetry allows for explaining the $b\to s{\mu }^{+}{\mu }^{-}$ anomalies in combination with $h\to {\tau }^{\pm }{\mu }^{\mp }$, predicting interesting correlations with $\tau \to 3\mu$. In the light of these deviations from the SM we also discuss the possibilities of observing lepton flavour violating $B$ decays (e.g. $B\to K^{(\ast )}{\tau }^{\pm }{\mu }^{\mp }$ and $B_s\to {\tau }^{\pm }{\mu }^{\mp }$).

Comments: 9 pages, 6 figures, proceedings for "Flavour changing and conserving processes" 2015, references added