Overview

While the LHC has not directly observed any new particles, in the last years several flavor experiments including LHCb have found very strong indications for the violation of lepton flavor universality in semi-leptonic B-meson decays. Additionally, much interest has been focused on anomalies in individual rare decays involving flavor-changing neutral currents. However, in many cases, the significance of the observation crucially depends on hadronic form factors, with profound consequences for the interpretation of the experimental measurements and their impact on BSM models. The primary goal of the program is to address the hadronic input, bringing together experts from lattice QCD (LQCD), light-cone sum rules (LCSR), and effective field theories, and evaluate the impact on BSM model building.

Background

• Apart from R(K^(*)), the SM predictions for the various observables in b → s ℓ⁺ℓ^- transitions, such as B → K^(*) ℓ⁺ℓ^-, B_s → ϕ ℓ⁺ℓ^-, and the related Λ_b → Λ ℓ⁺ ℓ^-, depend on hadronic form factors and the same is true concerning b → c τ ν transitions. Furthermore, considering in the future b → d ℓ⁺ℓ^- and b → u τ ν one is facing the same (or even bigger) problems.

• Available methods typically cover parts of the required kinematics, e.g. LQCD is best suited for high invariant lepton masses and LCSR for low ones. In addition, each method comes with its own set of systematic uncertainties, e.g. related to the unstable nature of the K^* resonance in LQCD or to the continuum threshold and Borel parameter in LCSR. Further, non-factorizable corrections from c c resonances may play a role. However, control over the ensuing QCD uncertainties is critical to gain confidence in the observed B anomalies.

• There have been long-standing discrepancies between exclusive and inclusive determinations of |V_cb| and |V_ub|, which in turn affect the SM prediction for K → π ν ν and B_s → μ⁺μ^-. Improved measurements of the exclusive decay modes of B_(s) and Λ_b decays at LHCb have the potential to resolve this issue, but again control over the hadronic input is critical.

• The B decay modes in which anomalies have been reported possess analogs in b → d and b → u transitions as well as in kaon and D meson decays. In particular, while in general the operators are independent, many models that explain the B-physics anomalies lead to effects in kaon decays that are potentially observable in forthcoming experiments.

Program format

We plan to host a workshop in the second week of the program (August 19-23) on "Heavy-Quark Physics and Fundamental Symmetries: Interplay between theory and experiment." A workshop registration fee of $40 will apply. The registration fee includes participation in the workshop, lectures, and coffee breaks. Otherwise, we will follow the standard INT-program format of one or two daily talks with plenty of time for discussions and collaborations.