Search

Di-Higgs couplings to fermions of the form h 2 f ‾ f are absent in the Standard Model, however, they are present in several physics Beyond Standard Model (BSM) extensions, including those with vector-like fermions. In Effective Field Theories (EFTs), such as the Standard Model Effective Field Theory (SMEFT) and the Higgs Effective Field Theory (HEFT), these couplings appear at dimension 6 and can in general, be flavour-violating (FV). In the present work, we employ a bottom-up approach to investigate the FV in the lepton and quarks sectors through the di-Higgs effective couplings. We assume that all FV arises from this type of couplings and assume that the Yukawa couplings Y i j are given by their SM values, i.e. Y i j = 2 m i δ i j / v. In the lepton sector, we set upper limits on the Wilson coefficients C l l ′ from l → 3 l ′ decays, l → l γ decays, muonium oscillations, the (g − 2) μ anomaly, LEP searches, muon conversion in nuclei, FV Higgs decays, and Z decays. We also make projections on some of these coefficients from Belle II, the Mu2e experiment and the LHC's High Luminosity (HL) run. In the quark sector, we set upper limits on the Wilson coefficients C q q ′ from meson oscillations and from B -physics searches. A key takeaway from this study is that current and future experiments should set out to measure the effective di-Higgs couplings C f f ′ , whether these couplings are FV or flavour-conserving. We also present a matching between our formalism and the SMEFT operators and show the bounds in both bases. [ABSTRACT FROM AUTHOR]

A primary goal of present and future colliders is measuring the Higgs couplings to Standard Model (SM) particles. Any observed deviation from the SM predictions for these couplings is a sign of new physics whose energy scale can be bounded from above by requiring tree-level unitarity. In this paper, we extend previous work on unitarity bounds from the Higgs cubic coupling to Higgs couplings to vector bosons and top quarks. We find that HL-LHC measurements of these couplings compatible with current experimental bounds may point to a scale that can be explored at the HL-LHC or a next-generation collider. Our approach is completely model-independent: we assume only that there are no light degrees of freedom below the scale of new physics, and allow arbitrary values for the infinitely many couplings beyond the SM as long as they are in agreement with current measurements. We also extend and clarify the methodology of this analysis, and show that if the scale of new physics is above the TeV scale, then the deviations can be described by the leading higher-dimension gauge invariant operator, as in the SM effective field theory. [ABSTRACT FROM AUTHOR]

Measuring the Higgs couplings accurately at colliders is one of the best routes for finding physics Beyond the Standard Model (BSM). If the measured couplings deviate from the SM predictions, then this would give rise to energy-growing processes that violate tree-level unitarity at some energy scale, indicating new physics. In this paper, we extend previous work on unitarity bounds from the Higgs potential and the Higgs couplings to vector bosons, the top quark, γγ and γZ ; to the Higgs coupling to gg. We show that the scale of new physics could be as low as ∼10 TeV, which although beyond the reach of the LHC, is well within the reach of the future 100-TeV collider, and can also be probed indirectly in the High Luminosity LHC (HL-LHC). [ABSTRACT FROM AUTHOR]

Inspired by the Contino-Pomarol-Rattazzi mechanism we explore scenarios with a very light (1 keV to 10 GeV) radion which could be associated with the suppression of the electroweak contribution to vacuum energy. We construct explicit, realistic models that realize this mechanism and explore the phenomenological constraints on this class of models. Compared with axion-like particles in this mass range, the bounds from SN 1987a and from cosmology can be much weaker, depending on the mass of the radion and its coupling to other particles. With couplings suppressed by a scale lower than 100 TeV, much of the mass window from 100 keV to 10 GeV is still open. [ABSTRACT FROM AUTHOR]