We speculate about the possible interpretations of the recently observed excess in the h → τμ decay. We derive a robust lower bound on the Higgs boson coupling strength to a tau and a muon, even in presence of the most general new physics affecting other Higgs properties. Then we reevaluate complementary indirect constraints coming from low energy observables as well as from theoretical considerations. In particular, the tentative signal should lead to τ → μγ at rates which could be observed at Belle II. In turn we show that, barring fine-tuned cancellations, the effect can only be accommodated within models with an extended scalar sector. These general conclusions are demonstrated using a number of explicit new physics models. Finally we show how, given the h → τμ signal, the current and future searches for μ → eγ and μ → e nuclear conversions unambiguously constrain the allowed rates for h → τe.

A bstractWe investigate the phenomenology of flavored dark matter (DM). DM stability is guaranteed by an accidental Z3$$ {\mathcal{Z}}_3 $$ symmetry, a subgroup of the standard model (SM) flavor group that is not broken by the SM Yukawa interactions. We consider an explicit realization where the quark part of the SM flavor group is fully gauged. If the dominant interactions between DM and visible sector are through flavor gauge bosons, as we show for Dirac fermion flavored DM, then the DM mass is bounded between roughly 0.5 TeV and 5 TeV if the DM multiplet mass is split only radiatively. In general, however, no such relation exists. We demonstrate this using scalar flavored DM where the main interaction with the SM is through the Higgs portal. For both cases we derive constraints from flavor, cosmology, direct and indirect DM detection, and collider searches.

We analyze the bounds on the Higgs pseudo-observables following from electroweak constraints, under the assumption that the Higgs particle is the massive excitation of an $SU(2)_L$ doublet. Using such bounds, detailed predictions for $h\to 4\ell$ decay rates, dilepton spectra, and lepton-universality ratios are presented.

We analyze the bounds on the Higgs pseudo-observables following from electroweak constraints, under the assumption that the Higgs particle is the massive excitation of an $$\text {SU}(2)_L$$SU(2)L doublet. Using such bounds, detailed predictions for $$h\rightarrow 4\ell $$h→4ℓ decay rates, dilepton spectra, and lepton-universality ratios are presented.

We define a set of pseudo-observables characterizing the properties of Higgs decays in generic extensions of the Standard Model with no new particles below the Higgs mass. The pseudo-observables can be determined from experimental data, providing a systematic generalization of the “κ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\kappa $$\end{document}-framework” so far adopted by the LHC experiments. The pseudo-observables are defined from on-shell decay amplitudes, allow for a systematic inclusion of higher-order QED and QCD corrections, and can be computed in any Effective Field Theory (EFT) approach to Higgs physics. We analyze the reduction of the number of independent pseudo-observables following from the hypotheses of lepton universality, CP invariance, custodial symmetry, and linearly realized electroweak symmetry breaking. We outline the importance of kinematical studies of h→4ℓ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$h\rightarrow 4\ell $$\end{document} decays for the extraction of such parameters and present their predictions in the linear EFT framework.

A bstractWe speculate about the possible interpretations of the recently observed excess in the h → τμ decay. We derive a robust lower bound on the Higgs boson coupling strength to a tau and a muon, even in presence of the most general new physics affecting other Higgs properties. Then we reevaluate complementary indirect constraints coming from low energy observables as well as from theoretical considerations. In particular, the tentative signal should lead to τ → μγ at rates which could be observed at Belle II. In turn we show that, barring fine-tuned cancellations, the effect can only be accommodated within models with an extended scalar sector. These general conclusions are demonstrated using a number of explicit new physics models. Finally we show how, given the h → τμ signal, the current and future searches for μ → eγ and μ → e nuclear conversions unambiguously constrain the allowed rates for h → τe.

Anomalous couplings of the Z boson to top quarks are only marginally constrained by direct searches and are still sensitive to new particle dynamics at the TeV scale. Employing an effective field theory approach we consider the dimension-six operators which generate deviations from the standard-model vector and axial-vector interactions. We show that rare B and K meson decays together with electroweak precision observables provide strong constraints on these couplings. We also consider constraints from t-channel single-top production.

We define a set of pseudo-observables characterizing the properties of Higgs decays in generic extensions of the Standard Model with no new particles below the Higgs mass. The pseudo-observables can be determined from experimental data, providing a systematic generalization of the “$$\kappa $$κ-framework” so far adopted by the LHC experiments. The pseudo-observables are defined from on-shell decay amplitudes, allow for a systematic inclusion of higher-order QED and QCD corrections, and can be computed in any Effective Field Theory (EFT) approach to Higgs physics. We analyze the reduction of the number of independent pseudo-observables following from the hypotheses of lepton universality, CP invariance, custodial symmetry, and linearly realized electroweak symmetry breaking. We outline the importance of kinematical studies of $$h\rightarrow 4\ell $$h→4ℓ decays for the extraction of such parameters and present their predictions in the linear EFT framework.

A bstractAnomalous couplings of the Z boson to top quarks are only marginally constrained by direct searches and are still sensitive to new particle dynamics at the TeV scale. Employing an effective field theory approach we consider the dimension-six operators which generate deviations from the standard-model vector and axial-vector interactions. We show that rare B and K meson decays together with electroweak precision observables provide strong constraints on these couplings. We also consider constraints from t-channel single-top production.

We study the LHC phenomenology of flavor changing Yukawa couplings between the top quark, the Higgs boson, and either an up or charm quark. Such tuh or tch couplings arise for instance in models in which the Higgs sector is extended by the existence of additional Higgs bosons or by higher dimensional operators. We emphasize the importance of anomalous single top plus Higgs production in these scenarios, in addition to the more widely studied t → hj decays. By recasting existing CMS searches in multilepton and diphoton plus lepton final states, we show that bounds on ℬ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \mathrm{\mathcal{B}} $$\end{document}(t → hu) are improved by a factor of 1.5 when single top plus Higgs production is accounted for. We also recast the CMS search for vector boson plus Higgs production into new, competitive constraints on tuh and tch couplings, setting the limits of ℬ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \mathrm{\mathcal{B}} $$\end{document}(t → hu) < 0.7% and ℬ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \mathrm{\mathcal{B}} $$\end{document}(t → hc) < 1.2%. We then investigate the sensitivity of future searches in the multilepton channel and in the fully hadronic channel. In multilepton searches, studying the lepton rapidity distributions and charge assignments can be used to discriminate between tuh couplings, for which anomalous single top production is relevant, and tch couplings, for which it is suppressed by the parton distribution function of the charm quark. An analysis of fully hadronic t + h production and t → hj decay can be competitive with the multilepton search at 100 fb−1 of 13 TeV data if jet substructure techniques are employed to reconstruct boosted top quarks and Higgs bosons. To show this we develop a modified version of the HEPTopTagger algorithm, optimized for tagging t → hj decays. Our sensitivity estimates on ℬ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \mathrm{\mathcal{B}} $$\end{document}(t → hu) (ℬ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$ \mathrm{\mathcal{B}} $$\end{document}(t → hc)) at 100 fb−1 of 13 TeV data for multilepton searches, vector boson plus Higgs search and fully hadronic search are 0.22% (0.33%), 0.15% (0.19%) and 0.36% (0.48%), respectively.

We study implications of large lepton-quark-leptoquark couplings for direct leptoquark searches at Large Hadron Collider. We present all existing flavor constraints on the strength of these couplings assuming that leptoquarks under consideration interact exclusively with charged leptons and quarks of the same generation. We find that these leptoquarks can have sizeable couplings to the Standard Model fermions. This insures a self consistency of our study. We discuss the leptoquark production mechanisms at LHC and demonstrate the importance of inclusion of a t-channel pair production and, in particular, a single leptoquark production through a recast of an existing CMS search at LHC for the second generation leptoquark. Our recast yields the best direct limit on Yukawa coupling of the second generation leptoquark that couples to a muon and a strange quark to date.

A bstractWe study the LHC phenomenology of flavor changing Yukawa couplings between the top quark, the Higgs boson, and either an up or charm quark. Such tuh or tch couplings arise for instance in models in which the Higgs sector is extended by the existence of additional Higgs bosons or by higher dimensional operators. We emphasize the importance of anomalous single top plus Higgs production in these scenarios, in addition to the more widely studied t → hj decays. By recasting existing CMS searches in multilepton and diphoton plus lepton final states, we show that bounds on ℬ$$ \mathrm{\mathcal{B}} $$(t → hu) are improved by a factor of 1.5 when single top plus Higgs production is accounted for. We also recast the CMS search for vector boson plus Higgs production into new, competitive constraints on tuh and tch couplings, setting the limits of ℬ$$ \mathrm{\mathcal{B}} $$(t → hu) < 0.7% and ℬ$$ \mathrm{\mathcal{B}} $$(t → hc) < 1.2%.We then investigate the sensitivity of future searches in the multilepton channel and in the fully hadronic channel. In multilepton searches, studying the lepton rapidity distributions and charge assignments can be used to discriminate between tuh couplings, for which anomalous single top production is relevant, and tch couplings, for which it is suppressed by the parton distribution function of the charm quark. An analysis of fully hadronic t + h production and t → hj decay can be competitive with the multilepton search at 100 fb−1 of 13 TeV data if jet substructure techniques are employed to reconstruct boosted top quarks and Higgs bosons. To show this we develop a modified version of the HEPTopTagger algorithm, optimized for tagging t → hj decays. Our sensitivity estimates on ℬ$$ \mathrm{\mathcal{B}} $$(t → hu) (ℬ$$ \mathrm{\mathcal{B}} $$(t → hc)) at 100 fb−1 of 13 TeV data for multilepton searches, vector boson plus Higgs search and fully hadronic search are 0.22% (0.33%), 0.15% (0.19%) and 0.36% (0.48%), respectively.

We perform an analysis of Higgs portal models of dark matter (DM), where DM is light enough to contribute to invisible Higgs decays. Using effective field theory we show that DM can be a thermal relic only if there are additional light particles present with masses below a few 100 GeV. We give three concrete examples of viable Higgs portal models of light DM: (i) the SM extended by DM scalar along with an electroweak triplet and a singlet, (ii) a Two Higgs Doublet Model of type II with additional scalar DM, (iii) SM with DM and an extra scalar singlet that is lighter than DM. In all three examples the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$ \mathcal{B} $\end{document}(h → invisible) constraint is not too restrictive, because it is governed by different parameters than the relic abundance. Additional light particles can have implications for flavor violation and collider searches.