We present a comprehensive analysis of low-energy signals of hypothetical scalar leptoquark interactions in lepton and kaon transitions. We derive the most general effective four-fermion Lagrangian induced by tree-level scalar leptoquark exchange and identify the Wilson coefficients predicted by the five possible types of scalar leptoquarks. The current constraints on the leptoquark Yukawa couplings arising from lepton and kaon processes are worked out, including also loop-induced transitions with only leptons (or quarks) as external states. In the presence of scalar leptoquark interactions, we also derive the differential distributions for flavour-changing neutral-current transitions in semileptonic kaon modes, including all known effects within the Standard Model. Their interference with the new physics contributions could play a significant role in future improvements of those constraints that are currently hampered by poorly-determined non-perturbative parameters. *

It is a challenging task to explain, in terms of a simple and compelling new physics scenario, the intriguing discrepancies between the standard model expectations and the data for the neutralcurrent observables RK and RK * , as well as the charged-current observables R(D) and R(D * ). We show that this can be achieved in an effective theory with only two unknown parameters. In addition, this class of models predicts some interesting signatures in the context of both B decays as well as high-energy collisions.Introduction and the data -Several recent hints of discrepancies in a few charged-as well as neutral-current semileptonic decays of B-mesons have intrigued the community. Unlike the case for fully hadronic decay modes that suffer from large (and, in some cases, not-so-well understood) strong interaction corrections, the theoretical uncertainties in semileptonic decays are much better controlled. Even these uncertainties are removed to a great extent in ratios of similar observables. While, individually, none of the observables, militate against the standard model (SM), viewed together, they strongly suggest that some new physics (NP) is lurking around the corner [1,2]. The pattern also argues convincingly for the violation of lepton-flavor universality.With the ratios of partial widths being particularly clean probes of physics beyond the SM, on account of the cancellation of the leading uncertainties, let us focus on R(D) and R(D * ) defined as

Analyzing the neutrino Yukawa effect in the freeze-out process of a generic dark matter candidate with right-handed neutrino portal, we identify the parameter regions satisfying the observed dark matter relic density as well as the current Fermi-LAT and H.E.S.S. limits and the future CTA reach on gamma-ray signals. In this scenario the dark matter couples to the Higgs boson at one-loop level and thus could be detected by spin-independent nucleonic scattering for a reasonable range of the relevant parameters.

Motivated by the persistent anomalies reported in the b → cτν data, we perform a general model-independent analysis of these transitions, in the presence of light right-handed neutrinos. We adopt an effective field theory approach and write a low-energy effective Hamiltonian, including all possible dimension-six operators. The corresponding Wilson coefficients are determined through a numerical fit to all available experimental data. In order to work with a manageable set of free parameters, we define eleven wellmotivated scenarios, characterized by the different types of new physics that could mediate these transitions, and analyse which options seem to be preferred by the current measurements. The data exhibit a clear preference for new-physics contributions, and good fits to the data are obtained in several cases. However, the current measurement of the longitudinal D * polarization in B → D * τν cannot be easily accommodated within its experimental 1σ range. A general analysis of the three-body B → Dτν and four-body B → D * (→ Dπ)τν angular distributions is also presented. The accessible angular observables are studied in order to assess their sensitivity to the different new physics scenarios. Experimental information on these distributions would help to disentangle the dynamical origin of the current anomalies.