Search

Abstract The observation of Higgs boson production in association with a top quark pair (t t ¯ H), based on the analysis of proton–proton collision data at a centre-of-mass energy of 13 TeV recorded with the ATLAS detector at the Large Hadron Collider, is presented. Using data corresponding to integrated luminosities of up to 79.8 fb−1, and considering Higgs boson decays into b b ¯ , W W ⁎ , τ + τ − , γγ , and Z Z ⁎ , the observed significance is 5.8 standard deviations, compared to an expectation of 4.9 standard deviations. Combined with the t t ¯ H searches using a dataset corresponding to integrated luminosities of 4.5 fb−1 at 7 TeV and 20.3 fb−1 at 8 TeV, the observed (expected) significance is 6.3 (5.1) standard deviations. Assuming Standard Model branching fractions, the total t t ¯ H production cross section at 13 TeV is measured to be 670 ± 90 (stat.) − 100 + 110 (syst.) fb, in agreement with the Standard Model prediction. [ABSTRACT FROM AUTHOR]

We study the next-to-leading order electroweak corrections to Higgs processes from dimension-six top-quark operators in the Standard Model Effective Field Theory approach. We consider the major production channels, including W H, ZH, and VBF production at the LHC, and ZH, VBF production at future lepton colliders, as well as the major decay channels including H → γγ, γZ, Wlν, Zll, b¯b, μμ, τ τ . The results show that within the current constraints, top-quark operators can shift the signal strength of the loop-induced processes, i.e. H → γγ, γZ, by factors of ∼ O(1)- O(10), and that of the tree-level processes, i.e. all remaining production and decay channels, by ∼ 5 - 10% at the LHC, and up to ∼ 15% at future lepton colliders. This implies that essentially all Higgs channels have started to become sensitive to top-quark couplings, and in particular, Higgs observables at high luminosity LHC as well as future lepton colliders, even below the tt¯ threshold, will improve our knowledge of top-quark couplings. We derive the sensitivities of Higgs measurements to top-quark operators at the high luminosity LHC, using projections for both inclusive and differential measurements. We conclude that treating the dimensionsix top-quark sector and the Higgs/electroweak sector separately may not continue to be a good strategy. A global analysis combining Higgs and top-quark measurements is desirable, and our calculation and implementation provide an automatic and realistic simulation tool for this purpose. [ABSTRACT FROM AUTHOR]

We study the sensitivity to the shape of the Higgs potential of single, double, and triple Higgs production at future e+e- colliders. Physics beyond the Standard Model is parameterised through the inclusion of higher-dimensional operators (Φ†Φ-v2/2)n/Λ(2n-4) with n=3,4, which allows a consistent treatment of independent deviations of the cubic and quartic self couplings beyond the tree level. We calculate the effects induced by a modified potential up to one loop in single and double Higgs production and at the tree level in triple Higgs production, for both Z boson associated and W boson fusion production mechanisms. We consider two different scenarios. First, the dimension six operator provides the dominant contribution (as expected, for instance, in a linear EFT); we find in this case that the corresponding Wilson coefficient can be determined at O(10%) accuracy by just combining accurate measurements of single Higgs cross sections at ŝ--√=240-250 GeV and double Higgs production in W boson fusion at higher energies. Second, both operators of dimension six and eight can give effects of similar order, i.e., independent quartic self coupling deviations are present. Constraints on Wilson coefficients can be best tested by combining measurements from single, double and triple Higgs production. Given that the sensitivity of single Higgs production to the dimension eight operator is presently unknown, we consider double and triple Higgs production and show that combining their information colliders at higher energies will provide first coarse constraints on the corresponding Wilson coefficient. [ABSTRACT FROM AUTHOR]

Future Higgs factories can reach impressive precision on Higgs property measurements. In this paper, instead of conventional focus of Higgs precision in certain interaction bases, we explore its sensitivity to new physics models at the electron-positron colliders. In particular, we study two categories of new physics models, Standard Model (SM) with a real scalar singlet extension, and Two Higgs Double Model (2HDM) as examples of weakly-interacting models, Minimal Composite Higgs Model (MCHM) and three typical patterns of the more general operator counting for strong interacting models as examples of strong dynamics. We perform a global fit to various Higgs search channels to obtain the 95% C.L. constraints on the model parameter space. In the SM with a singlet extension, we obtain the limits on the singlet-doublet mixing angle sin θ, as well as the more general Wilson coefficients of the induced higher dimensional operators. In the 2HDM, we analyze tree level effects in tan β vs. cos( β − α) plane, as well as the one-loop contributions from the heavy Higgs bosons in the alignment limit to obtain the constraints on heavy Higgs masses for different types of 2HDM. In strong dynamics models, we obtain lower limits on the strong dynamics scale. In addition, once deviations of Higgs couplings are observed, they can be used to distinguish different models. We also compare the sensitivity of various future Higgs factories, namely Circular Electron Positron Collider (CEPC), Future Circular Collider (FCC)-ee and International Linear Collider (ILC). [ABSTRACT FROM AUTHOR]

A search for heavy resonances decaying to a W or Z boson and a Higgs boson in the q q ¯ ( ′ ) b b ¯ final state is described. The search uses 36.1 fb − 1 of proton–proton collision data at s = 13 TeV collected by the ATLAS detector at the CERN Large Hadron Collider in 2015 and 2016. The data are in agreement with the Standard Model expectations, with the largest excess found at a resonance mass of 3.0 TeV with a local (global) significance of 3.3 (2.1) σ . The results are presented in terms of constraints on a simplified model with a heavy vector triplet. Upper limits are set on the production cross-section times branching ratio for resonances decaying to a W ( Z ) boson and a Higgs boson, itself decaying to b b ¯ , in the mass range between 1.1 and 3.8 TeV at 95% confidence level; the limits range between 83 and 1.6 fb (77 and 1.1 fb) at 95% confidence level. [ABSTRACT FROM AUTHOR]

We describe ColliderBit, a new code for the calculation of high energy collider observables in theories of physics beyond the Standard Model (BSM). ColliderBit features a generic interface to BSM models, a unique parallelised Monte Carlo event generation scheme suitable for large-scale supercomputer applications, and a number of LHC analyses, covering a reasonable range of the BSM signatures currently sought by ATLAS and CMS. ColliderBit also calculates likelihoods for Higgs sector observables, and LEP searches for BSM particles. These features are provided by a combination of new code unique to ColliderBit, and interfaces to existing state-of-the-art public codes. ColliderBit is both an important part of the GAMBIT framework for BSM inference, and a standalone tool for efficiently applying collider constraints to theories of new physics. [ABSTRACT FROM AUTHOR]

New physics coupling to the Higgs sector of the Standard Model can lead to dangerously large corrections to the Higgs mass. We investigate this problem in the type II seesaw model for neutrino mass, where a weak scalar triplet is introduced. The interplay of direct and indirect constraints on the type II seesaw model with its contribution to the Higgs mass is analyzed. The focus lies on testable triplet masses and (sub) eV-scale triplet vacuum expectation values. We identify scenarios that are testable in collider and/or lepton flavor violation experiments, while satisfying the Higgs naturalness criterion. [ABSTRACT FROM AUTHOR]

Models with non-minimal Higgs sectors represent a mainstream direction in theoretical exploration of physics opportunities beyond the Standard Model. Extended scalar sectors help alleviate difficulties of the Standard Model and lead to a rich spectrum of characteristic collider signatures and astroparticle consequences. In this review, we introduce the reader to the world of extended Higgs sectors. Not pretending to exhaustively cover the entire body of literature, we walk through a selection of the most popular examples: the two- and multi-Higgs-doublet models, as well as singlet and triplet extensions. We will show how one typically builds models with extended Higgs sectors, describe the main goals and the challenges which arise on the way, and mention some methods to overcome them. We will also describe how such models can be tested, what are the key observables one focuses on, and illustrate the general strategy with a subjective selection of results. [ABSTRACT FROM AUTHOR]

We investigate the prospects for producing new, light, hidden states at a future e e collider in a Higgsed dark U(1) model, which we call the Double Dark Portal model. The simultaneous presence of both vector and scalar portal couplings immediately modifies the Standard Model Higgsstrahlung channel, e e → Zh, at leading order in each coupling. In addition, each portal leads to complementary signals which can be probed at direct and indirect detection dark matter experiments. After accounting for current constraints from LEP and LHC, we demonstrate that a future e e Higgs factory will have unique and leading sensitivity to the two portal couplings by studying a host of new production, decay, and radiative return processes. Besides the possibility of exotic Higgs decays, we highlight the importance of direct dark vector and dark scalar production at e e machines, whose invisible decays can be tagged from the recoil mass method. [ABSTRACT FROM AUTHOR]

We estimate the possible accuracies of measurements at the proposed CLIC e e collider of Higgs and W W production at centre-of-mass energies up to 3 TeV, incorporating also Higgsstrahlung projections at higher energies that had not been consid-ered previously, and use them to explore the prospective CLIC sensitivities to decoupled new physics. We present the resulting constraints on the Wilson coefficients of dimension-6 operators in a model-independent approach based on the Standard Model effective field theory (SM EFT). The higher centre-of-mass energy of CLIC, compared to other projects such as the ILC and CEPC, gives it greater sensitivity to the coefficients of some of the operators we study. We find that CLIC Higgs measurements may be sensitive to new physics scales $$ \Lambda =\mathcal{O}(10) $$ TeV for individual operators, reduced to $$ \mathcal{O}(1) $$ TeV sensitivity for a global fit marginalising over the coefficients of all contributing operators. We give some examples of the corresponding prospective constraints on specific scenarios for physics beyond the SM, including stop quarks and the dilaton/radion. [ABSTRACT FROM AUTHOR]

We analyze an extension of the Standard Model with an additional SU(2) hypercolor gauge group keeping the Higgs boson as a fundamental field. Vectorlike interactions of new hyperquarks with the intermediate vector bosons are explicitly constructed. We also consider pseudo-Nambu–Goldstone bosons caused by the symmetry breaking SU(4)→Sp(4). A specific global symmetry of the model with zero hypercharge of the hyperquark doublets ensures the stability of a neutral pseudoscalar field. Some possible manifestations of the lightest states at colliders are also examined. [ABSTRACT FROM AUTHOR]

One item on the agenda of future colliders is certain to be the Higgs boson. What is it trying to tell us? The primary objective of any future collider must surely be to identify physics beyond the Standard Model, and supersymmetry is one of the most studied options. Is supersymmetry waiting for us and, if so, can LHC Run 2 find it? The big surprise from the initial 13 TeV LHC data has been the appearance of a possible signal for a new boson with a mass 750 GeV. What are the prospects for future colliders if the X(750) exists? One of the most intriguing possibilities in electroweak physics would be the discovery of nonperturbative phenomena. What are the prospects for observing sphalerons at the LHC or a future collider? [ABSTRACT FROM AUTHOR]

The journey in search for the Higgs boson started in earnest with the discovery of the W and Z bosons. The LHC accelerator, the ATLAS and CMS experiments were conceived in the late 1980s and early 1990s, and it took two decades to turn the concepts to reality. Novel and innovative technologies needed to be developed and turned into superbly functioning engines for providing proton-proton collisions in the case of the LHC and physics results in the case of the experiments. The most significant discovery so far to emerge from the LHC project is that of a heavy scalar boson, announced on 4th July 2012. The data collected so far point strongly to its properties as those expected for the Higgs boson associated with the Brout-Englert-Higgs mechanism. [ABSTRACT FROM AUTHOR]

The discovery of the Higgs particle at 125 GeV is demanding a detailed knowledge of the properties of this fundamental component of the Standard Model. To that aim various proposals of electron and muon colliders have been put forward for precision studies of the partial widths of the various decay channels. It is shown that in the case of a Higgs factory through a muon collider, sizeable radiative effects - of order of 50% - must be carefully taken into account for a precise measurement of the leptonic and total widths of the Higgs particle. Similar effects do not apply in the case of Higgs production in electron-positron colliders. [ABSTRACT FROM AUTHOR]

Extending the Standard Model with sterile ('right-handed') neutrinos is one of the best motivated ways to account for the observed neutrino masses. We discuss the expected sensitivity of the Circular Electron Positron Collider (CEPC) for testing such extensions. An interesting scenario is given by symmetry protected seesaw models, which theoretically allow for sterile neutrino masses around the electroweak scale with up to order one mixings with the active (SM) neutrinos. When the masses of the sterile neutrinos are well above the electroweak scale, they affect precision data via effective non-unitarity of the leptonic mixing matrix in a model independent way. The expected improvement of the electroweak precision observables from the CEPC may allow to test mixings between active and sterile neutrinos down to (using currently discussed CEPC performance parameters). For sterile neutrinos with masses around the electroweak scale, direct searches are possible. Such tests are given by the search for sterile neutrino decays at the pole, by deviations from the SM cross section for four leptons at and beyond the threshold, and by Higgs boson production and decays. The expected sensitivities at the CEPC could reach down to mixings as small as . [ABSTRACT FROM AUTHOR]

We present the first realization of a "twin Higgs" model as a holographic composite Higgs model. Uniquely among composite Higgs models the Higgs potential is protected by a new standard model (SM) singlet elementary "mirror" sector at the sigma model scale/and not by the composite states at mKK, naturally allowing for wKK beyond the LHC reach. As a result naturalness in our model cannot be constrained by the LHC but may be probed by precision Higgs measurements at future lepton colliders and by direct searches for Kaluza-Klein excitations at a 100 TeV collider. [ABSTRACT FROM AUTHOR]

The discovery of the Higgs boson has been one the most important results in the whole story of particle physics. A review of the aspects of the long path, starting from the speculative introduction of the Brout-Englert-Higgs mechanism, continuing with the long search to detect the Higgs particle, and arriving to the discovery is given. The first measurements of the properties are described, their implications are discussed and the future prospects are given. [ABSTRACT FROM AUTHOR]

A warped extra dimension model predicts an extra scalar particle beyond the Standard Model (SM) which is called a radion. Although interactions of the radion are similar to those of the Higgs boson in the SM, a relatively light radion (< 100 GeV) is not severely constrained from the Higgs search experiments at the LHC. In this paper we study discovery potential of the radion at a photon collider as an option of ILC. Owing to the trace anomaly of the energy-momentum tensor, both a production of radion in 7 7 collision and its decay to gluon pair are enhanced sizably. We find that the photon collider has a sensitivity for discovering the radion in low-mass region up to Aw, ~ 3 TeV, where A, is a scale parameter which suppresses the interactions of radion to the SM particles. [ABSTRACT FROM AUTHOR]

We review the No-Scale ℱ-SU(5) model with extra TeV-scale vector-like flippon multiplets and its associated collider phenomenology in the search for supersymmetry at the LHC. The model framework possesses the rather unique capacity to provide a light CP-even Higgs boson mass in the favored 124-126 GeV window while simultaneously retaining a testably light SUSY spectrum that is consistent with emerging low-statistics excesses beyond the Standard Model expectation in the ATLAS and CMS multijet data. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the prospects for detecting a hidden sector at an collider. The hidden sector is assumed to be composed of invisible particles that carry no charges under the Standard Model gauge interactions, and whose primary interactions with ordinary matter are through the Higgs portal. We consider both the cases when the decays of an on-shell Higgs into a pair of hidden sector particles are kinematically allowed, and the case when such decays are kinematically forbidden. We find that at collider energies below a TeV, the most sensitive channel involves production of an on-shell or off-shell Higgs in association with a Z boson, and the subsequent decay of the Higgs into invisible hidden sector states. Focusing on this channel, we find that with order a thousand inverse fb of data at 250 GeV, the decay branching fraction of an on-shell Higgs to invisible hidden sector states can be constrained to lie below half a percent. The corresponding limits on Higgs portal dark matter will be stronger than the bounds from current and upcoming direct detection experiments in much of parameter space. With the same amount of data at 500 GeV, assuming order one couplings, decays of an off-shell Higgs to hidden sector states with a total mass up to about 200 GeV can also be probed. Both the on-shell and off-shell cases represent a significant improvement in sensitivity when compared to the Large Hadron Collider (LHC). [Copyright &y& Elsevier]

We re-investigate the scalar potential and the Higgs sector of the supersymmetric economical 3-3-1 model (SUSYE331) in the presence of the $$B/\mu $$ -type terms, which has many important consequences. First, the model contains no massless Higgs fields. Second, we prove that the soft mass parameters of the Higgses must be at the $$\hbox {SU}(3)_L$$ scale. As a result, the masses of the Higgses drift toward this scale except one light real neutral Higgs with the mass of $$m_Z|c_{2\gamma }|$$ at the tree level. We also show that there are some Higgses containing many properties of the Higgses in the minimal supersymmetric standard model (MSSM), especially in the neutral Higgs sector. One exact relation in the MSSM, $$m^2_{H^{\pm }}=m^2_{A}+m^2_W$$ , is still true in the SUSYE331. Based on this result we make some comments on the lepton flavor violating decays of these Higgses as one of signatures of new physics in the SUSYE331 model which may be detected by present colliders. [ABSTRACT FROM AUTHOR]

As one of the most important parameters in the Standard Model (SM), the mass of the W boson (mW) is currently the limiting factor in our ability to tighten the constraint on the mass of the Higgs boson (mH) within the SM framework. This review summarizes the world's most precise mW measurement to date using ~2.2 -1 data collected in collisions at with the CDF II detector at the Fermilab Tevatron Collider. This review will first describe the motivation for improving the precision of mW measurement, then present the details of this analysis, followed by the final measurement result and the future perspective. [ABSTRACT FROM AUTHOR]

Abstract: The quest for the Higgs boson of the Standard Model, which was a cornerstone in the physics programme at particle colliders operating at the energy frontier for several decades, is the subject of this review. After reviewing the formulation of electroweak symmetry breaking via the Higgs mechanism within the Standard Model, the phenomenology of the Higgs boson at colliders and the theoretical and phenomenological constraints on the Standard Model Higgs sector are discussed. General remarks on experimental searches and the methodology of statistical interpretation are followed by a description of the phenomenology of Higgs-boson production and the corresponding precise predictions. The strategies of the experimental searches and their findings are discussed for the Large Electron Positron Collider (LEP) at CERN, the proton–antiproton collider Tevatron at Fermilab, and the proton–proton Large Hadron Collider (LHC) at CERN. The article concludes with the description of the observation of a Higgs-like boson at the LHC. [Copyright &y& Elsevier]

The investigation of the properties of the Higgs boson, especially a test of the predicted linear dependence of the branching ratios on the mass of the final state is going to be an integral part of the physics program at colliders at the energy frontier for the foreseeable future. The large Higgs boson production cross section at a 3 TeV CLIC machine allows for a precision measurement of the Higgs branching ratios. The cross section times branching ratio of the decays $\mathrm {H}\to \mathrm {b}\overline {\mathrm {b}}$, $\mathrm {H}\to \mathrm {c}\overline {\mathrm {c}}$ and H→μμ of a Standard Model Higgs boson with a mass of 120 GeV can be measured with a statistical uncertainty of 0.23 %, 3.1 % and 15 %, respectively, assuming an integrated luminosity of 2 ab. [ABSTRACT FROM AUTHOR]

The new particle around 125 GeV observed at the Large Hadron Collider (LHC) is almost consistent with the standard model (SM) Higgs boson, except that the diphoton decay mode may be excessive. We summarize a number of possibilities. While at the LHC the dominant production mechanism for the Higgs boson of SM and some other extensions is via the gluon fusion process, the alternative vector-boson fusion (VBF) is more sensitive to electroweak symmetry breaking. Using the well-known dijet-tagging technique to single out the VBF mechanism, we investigate potential of VBF to discriminate a number of models suggested to give an enhanced inclusive diphoton production rate. [ABSTRACT FROM AUTHOR]

We review non-Standard Model Higgs signatures which are missed in standard analyses by both ATLAS and CMS and show how the strong bounds by recent measurements can be relaxed in strongly-interacting theories. We also review strategies how to measure or constrain exotic Higgs decay at the LHC and a future linear collider. [ABSTRACT FROM AUTHOR]

We present the results of the combination of searches for the standard model Higgs boson produced in association with a W or Z boson and decaying into bb using the data sample collected with the DO detector in p&pmacr; collisions at √s = 1.96 TeV at the Fermilab Tevatron Collider. We derive 95% C.L. upper limits on the Higgs boson cross section relative to the standard model prediction in the mass range 100 GeV ≤ MH 150 GeV, and we exclude Higgs bosons with masses smaller than 102 GeV at the 95% C.L. In the mass range 120 GeV ≤ MH ≤ 145 GeV, the data exhibit an excess above the background prediction with a global significance of 1.5 standard deviations, consistent with the expectation in the presence of a standard model Higgs boson. [ABSTRACT FROM AUTHOR]

We report on a search for the standard model Higgs boson produced in association with a vector boson in the full data set of proton-antiproton collisions at √s = 1.96 TeV recorded by the CDF II detector at the Tevatron, corresponding to an integrated luminosity of 9.45 fb-1. We consider events having no identified charged lepton, a transverse energy imbalance, and two or three jets, of which at least one is consistent with originating from the decay of ab quark. We place 95% credibility level upper limits on the production cross section times standard model branching fraction for several mass hypotheses between 90 and 150 GeV/c2. For a Higgs boson mass of 125 GeV/c2, the observed (expected) limit is 6.7 (3.6) times the standard model prediction. [ABSTRACT FROM AUTHOR]

We present a search for the standard model Higgs boson produced in association with a Z boson in data collected with the CDF II detector at the Tevatron, corresponding to an integrated luminosity of 9.45 fb-1. In events consistent with the decay of the Higgs boson to a bottom-quark pair and the Z boson to electron or muon pairs, we set 95% credibility level upper limits on the ZH production cross section times the H → b&bmacr; branching ratio as a function of Higgs boson mass. At a Higgs boson mass of 125 GeV/c2, we observe (expect) a limit of 7.1 (3.9) times the standard model value. [ABSTRACT FROM AUTHOR]

Abstract: We present a search for the standard model Higgs boson in final states with an electron or muon and a hadronically decaying tau lepton in association with zero, one, or two or more jets using data corresponding to an integrated luminosity of up to collected with the D0 detector at the Fermilab Tevatron collider. The analysis is sensitive to Higgs boson production via gluon–gluon fusion, associated vector boson production, and vector boson fusion, and to Higgs boson decays to ττ, WW, ZZ and pairs. Observed (expected) limits are set on the ratio of 95% C.L. upper limits on the cross section times branching ratio, relative to those predicted by the Standard Model, of 22 (14) at a Higgs boson mass of 115 GeV and 6.8 (7.7) at 165 GeV. [Copyright &y& Elsevier]

Abstract: We propose a novel left–right symmetric model where the standard model fermion and Higgs fields are doublets or singlets while their mirror partners are doublets or singlets. The scalar fields also include a real singlet for dark matter and two triplets for seesaw. The mixing between the standard model and mirror fermions is forbidden by a discrete symmetry. The mirror charged fermions can decay into their standard model partners with the dark-matter scalar while the mirror neutrinos can decay into the mirror charged fermions through the right-handed gauge interactions. Our model can have new implications on the strong CP problem, leptogenesis, collider phenomenology and dark matter detection. [Copyright &y& Elsevier]

Abstract: We examine the exclusion limits set by the CDF and D0 experiments on the Standard Model Higgs boson mass from their searches at the Tevatron in the light of large theoretical uncertainties on the signal and background cross sections. We show that when these uncertainties are consistently taken into account, the sensitivity of the experiments becomes significantly lower and the currently excluded mass range could be entirely reopened. The necessary luminosity required to recover the current sensitivity is found to be a factor of two higher than the present one. [Copyright &y& Elsevier]

I discuss LHC physics in the historical perspective of the progress in particle physics. After a recap of the Standard Model (SM) of particle physics, I discuss the high energy colliders leading up to LHC and their role in the discovery of these SM particles. Then I discuss the two main physics issues of LHC, i.e. Higgs mechanism and supersymmetry. I briefly touch upon Higgs and SUSY searches at LHC along with their cosmological implications. [ABSTRACT FROM AUTHOR]

Abstract: Recent fits of electroweak precision data to the Standard Model (SM) with a 4th sequential family (SM4) point to a possible “three-prong composite solution”: (1) the Higgs mass is at the TeV-scale, (2) the masses of the 4th family quarks are of and (3) the mixing angle between the 4th and 3rd generation quarks is of the order of the Cabibbo angle, . Such a manifestation of the SM4 is of particular interest as it may suggest that the Higgs is a composite state, predominantly of the 4th generation heavy quarks. Motivated by the above, we show that the three-prong composite solution to the SM4 can have interesting new implications for Higgs phenomenology. For example, the Higgs can decay to a single heavy 4th generation quark via the 3-body decays (through an off-shell or ) and . These flavor diagonal decays can be dramatically enhanced at the LHC (by several orders of magnitudes) due to the large width effects of the resonating heavy Higgs in the processes and , thus yielding a viable signal above the corresponding continuum QCD production rates. In addition, the Higgs can decay to a single and in the loop-generated flavor changing (FC) channels . These FC decays are essentially “GIM-free” and can, therefore, have branching ratios as large as . [Copyright &y& Elsevier]

Abstract: If the sparticles are relatively heavy (a few TeV) while the Higgs sector is not so heavy ( is not so large), the Higgs boson Yukawa couplings can harbor sizable quantum effects of sparticles and these large residual effects may play a special role in probing supersymmetry at foreseeable colliders. In this work, focusing on the supersymmetric QCD effects in the coupling (h is the lightest CP-even Higgs boson), we give a comparative study for the two popular supersymmetric models: the MSSM and NMSSM. While for both models the supersymmetric QCD can leave over large residual quantum effects in coupling, the NMSSM can allow for a much broader region of such effects. Since these residual effects can be over 20% for the coupling (and thus over 40% for the ratio ), future measurements may unravel the effects of heavy sparticles or even distinguish the two models. [Copyright &y& Elsevier]

Abstract: The production of a single neutral Higgs boson h through (loop-induced) γγ collisions is explored in the context of the linear colliders within the general Two-Higgs-Doublet Model (2HDM). Two different mechanisms are analyzed: on the one hand, the scattering of two real photons in a γγ collider; on the other, the more traditional mechanism of virtual photon fusion, . Owing to the peculiar properties of the Higgs boson self-interactions within the general 2HDM, we find that the overall production rates can be boosted up significantly, provided the charged Higgs mass is not too heavy. For example, if and, in addition, falls in the ballpark of the LEP bound on the SM Higgs mass up to a few hundred GeV, the cross-sections may typically render and – in both cases well above the SM prediction. Although for the rates become virtually insensitive to the Higgs boson self-couplings, a significant tail of non-SM effects produced by the combined contribution of the Yukawa couplings and gauge bosons could still reveal a smoking gun. [Copyright &y& Elsevier]

Abstract: In models with extended Higgs sectors, Higgs-boson-mediated Lepton Flavour Violation (LFV) can naturally appear. We study the physics potential of an electron–photon collider on searching LFV processes (; ) where H and A are extra CP even and odd Higgs bosons, respectively, in the minimal supersymmetric standard model and the effective two Higgs doublet model. The production cross section can be significantly large for the maximal allowed values of the LFV coupling constants under the current experimental data. Present experimental upper bounds on the effective LFV coupling constants would be considerably improved by searching these processes, which would be better than MEG and COMET experiments and also those at LHCb and SuperKEKB. Moreover, one can separately measure chirality of effective LFV coupling constants via these processes by selecting electron polarizations. [Copyright &y& Elsevier]

Abstract: We calculate the cross section of Higgs boson pair production at a photon collider in the two Higgs doublet model. We focus on the scenario in which the lightest CP even Higgs boson (h) has the Standard Model like couplings to the gauge bosons. We take into account the one-loop correction to the hhh coupling as well as additional one-loop diagrams due to charged Higgs bosons to the helicity amplitudes. It is found that the full cross section can be enhanced by both these effects to a considerable level. We discuss the impact of these corrections on the hhh coupling measurement at the photon collider. [Copyright &y& Elsevier]