New physics searches at kaon and hyperon factories

Rare meson decays are among the most sensitive probes of both heavy and light new physics. Among them, new physics searches using kaons benefit from their small total decay widths and the availability of very large datasets. On the other hand, useful complementary information is provided by hyperon decay measurements. We summarize the relevant phenomenological models and the status of the searches in a comprehensive list of kaon and hyperon decay channels. We identify new search strategies for under-explored signatures, and demonstrate that the improved sensitivities from current and next-generation experiments could lead to a qualitative leap in the exploration of light dark sectors.

Optimized lepton universality tests in B → V ℓ ν ¯ decays

We propose improved lepton flavor universality (LFU) ratios in semileptonic P → V ℓ ν ¯ decays, when comparing μ and τ modes, that minimize the theoretical form-factor uncertainties. These optimized ratios are obtained with simple cuts or reweighting of the dilepton mass distributions, which imply a minimum loss of signal on the rare tauonic modes while maximizing the cancellation of theoretical uncertainties among the two modes. We illustrate the usefulness of these observables inB c → J / ψ ,B c → ψ ( 2 S ) , B → D ∗ andB s → D s ∗ transitions, showing that in all cases we can reach O ( 1 % ) uncertainties on the SM predictions of the improved LFU ratios employing conservative form-factor uncertainties.

Lepton flavor violation and dilepton tails at the LHC

Starting from a general effective Lagrangian for lepton flavor violation (LFV) in quark-lepton transitions, we derive constraints on the effective coefficients from the high-mass tails of the dilepton processes p p → ℓ k ℓ l (with k ≠ l ). The current (projected) limits derived in this paper from LHC data with 36 fb - 1 ( 3 ab - 1 ) can be applied to generic new physics scenarios, including the ones with scalar, vector and tensor effective operators. For purely left-handed operators, we explicitly compare these LHC constraints with the ones derived from flavor-physics observables, illustrating the complementarity of these different probes. While flavor physics is typically more constraining for quark-flavor violating operators, we find that LHC provides the most stringent limits on several flavor-conserving ones. Furthermore, we show that dilepton tails offer the best probes for charm-quark transitions at current luminosities and that they provide competitive limits for tauonic b → d transitions at the high-luminosity LHC phase. As a by-product, we also provide general numerical expressions for several low-energy LFV processes, such as the semi-leptonic decays K → π ℓ k ± ℓ l ∓ , B → π ℓ k ± ℓ l ∓ and B → K ( ∗ ) ℓ k ± ℓ l ∓ .