Flavour anomalies on the eve of the Run-2 verdict

Abstract

The RK measurement by LHCb suggests non-standard lepton-universality violation (LUV) to occur in b to s l+ l- decays, with effects in muons rather than electrons. It is intriguing that a number of other measurements of b to s l+ l- transitions by LHCb and B-factories are consistent in magnitude and sign with the RK effect, and fit a coherent effective-theory picture. Further indications of non-standard LUV are provided by the long-standing discrepancies in b to c tau nu transitions via the ratios R(D) and R(D^*). We review in detail the experimental situation and its rich outlook, the theoretical efforts -- and their challenges -- towards convincing dynamics beyond the effective-theory level, and discuss the many directions of further investigation that propagate from the current situation.

14 pages. Preprint of invited short review for MPLA (World Scientific). Matches journal version. See http://www.worldscientific.com/worldscinet/mpla

References in corpus (18)

• Big-Bang Nucleosynthesis
• Test of lepton universality using $B^{+}\to K^{+}{\ell }^{+}{\ell }^{-}$ decays
• On the B to D* tau nu Sensitivity to New Physics
• Angular Distributions of B -> K ll Decays
• $R_K$ and future $b\to s\ell \ell$ BSM opportunities
• Confronting lepton flavor universality violation in B decays with high-$p_T$ tau lepton searches at LHC
• Simultaneous Explanation of the $R_K$ and $R(D^{(\ast )})$ Puzzles
• Lepton Flavor Violation in B Decays?
• $SU(2)\times U(1)$ gauge invariance and the shape of new physics in rare $B$ decays
• Leptoquark model to explain the $B$-physics anomalies, $R_K$ and $R_D$
• On the impact of power corrections in the prediction of B->K*mu+mu- observables
• Hint of Lepton Flavour Non-Universality in $B$ Meson Decays
• B -> D tau nu Branching Ratios: Opportunity for Lattice QCD and Hadron Colliders
• Diagnosing lepton-nonuniversality in $b\to s\ell \ell$
• Resonances gone topsy turvy - the charm of QCD or new physics in $b\to s{\ell }^{+}{\ell }^{-}$?
• Measurement of the phase difference between short- and long-distance amplitudes in the $B^{+}\to K^{+}{\mu }^{+}{\mu }^{-}$ decay
• Constrained Flavor Breaking
• Rare radiative leptonic B-decays

Cited by in corpus (8)

• $R_2$ as a single leptoquark solution to $R_{D^{(\ast )}}$ and $R_{K^{(\ast )}}$
• Search for the lepton-flavour violating decays $B_{(s)}^0\to e^{\pm }{\mu }^{\mp }$
• Unified SU(4) theory for the $R_{D^{(\ast )}}$ and $R_{K^{(\ast )}}$ anomalies
• Rare FCNC radiative leptonic $B_{s,d}\to \gamma l^{+}{l}^{-}$ decays in the Standard Model
• Performance of the ATLAS Level-1 topological trigger in Run 2
• $B_s^0\to {\ell }^{+}{\ell }^{-}\gamma$ as a Test of Lepton Flavor Universality
• Rare decays of the $B_s-$meson into four charged leptons in the framework of the Standard Model
• Long-distance QCD effects in FCNC $B\to \gamma l^{+}{l}^{-}$ decays