Higgs bosons in the Next-to-Minimal Supersymmetric Standard Model at the LHC

We review possible properties of Higgs bosons in the NMSSM, which allow to discriminate this model from the MSSM: masses of mostly Standard-Model-like Higgs bosons at or above 140 GeV, or enhanced branching fractions into two photons, or Higgs-to-Higgs decays. In the case of a Standard-Model-like Higgs boson above 140 GeV, it is necessarily accompanied by a lighter state with a large gauge singlet component. Examples for such scenarios are presented. Available studies on Higgs-to-Higgs decays are discussed according to the various Higgs production modes, light Higgs masses and decay channels.     

First-order electroweak phase transition powered by additional F-term loop effects in an extended supersymmetric Higgs sector

We investigate the one-loop effect of new charged scalar bosons on the Higgs potential at finite temperatures in the supersymmetric standard model with four Higgs doublet chiral superfields as well as a pair of charged singlet chiral superfields. In this model, the mass of the lightest Higgs boson h is determined only by the D-term in the Higgs potential at the tree-level, while the triple Higgs boson coupling for hhh can receive a significant radiative correction due to nondecoupling one-loop contributions of the additional charged scalar bosons. We find that the same nondecoupling mechanism can also contribute to realize stronger first order electroweak phase transition than that in the minimal supersymmetric standard model, which is definitely required for a successful scenario of electroweak baryogenesis. Therefore, this model can be a new candidate for a model in which the baryon asymmetry of the Universe is explained at the electroweak scale.     

Six-quark decays of the Higgs boson in supersymmetry with R-parity violation

Both electroweak precision measurements and simple supersymmetric extensions of the standard model prefer a mass of the Higgs boson less than the experimental lower limit (on a standard-model-like Higgs boson) of 114 GeV. We show that supersymmetric models with R parity violation and baryon-number violation have a significant range of parameter space in which the Higgs boson dominantly decays to six jets. These decays are much more weakly constrained by current CERN LEP analyses and would allow for a Higgs boson mass near that of the Z. In general, lighter scalar quark and other superpartner masses are allowed. The Higgs boson would potentially be discovered at hadron colliders via the appearance of new displaced vertices.     

Radiative corrections to the scalar Higgs masses in a non-minimal supersymmetric Standard Model

We calculate the dominant one-loop radiative corrections arising from quark-squark loops to the mass squared matrix of theCP-even Higgs bosons in a non-minimal supersymmetric Standard Model containing two Higgs doublets and a Higgs singlet chiral superfield using one-loop effective potential approximation. We use this result to evaluate upper and lower bounds on the radiatively corrected masses of all the scalar Higgs bosons as a function of the parameters of the model. We find that the one-loop radiative corrections are substantial only for the lightest Higgs boson of the model and can push its mass beyond the reach of LEP. We also calculate an absolute upper bound on the mass of the radiatively corrected lightest Higgs boson and compare it with the corresponding bound in the minimal supersymmetric Standard Model.     

Distinguishing the higgs boson from the dilaton at the large hadron collider

It is likely that the LHC will observe a color- and charge-neutral scalar whose decays are consistent with those of the standard model (SM) Higgs boson. The Higgs interpretation of such a discovery is not the only possibility. For example, electroweak symmetry breaking could be triggered by a spontaneously broken, nearly conformal sector. The spectrum of states at the electroweak scale would then contain a narrow scalar resonance, the pseudo-Goldstone boson of conformal symmetry breaking, with Higgs-boson-like properties. If the conformal sector is strongly coupled, this pseudodilaton may be the only new state accessible at high energy colliders. We discuss the prospects for distinguishing this mode from a minimal Higgs boson at the LHC and ILC. The main discriminants between the two scenarios are (i) cubic self-interactions and (ii) a potential enhancement of couplings to massless SM gauge bosons.     

Implications of the precision data for very light Higgs Boson scenarios in 2HDM(II)

We present an up-to-date analysis of the constraints the precision data impose on the (CP-conserving) Two Higgs Doublet Model of type II with emphasis on the possible existence of very light neutral (pseudo)scalar Higgs boson with mass below 20–30 GeV. We show that even in the presence of such light particles, the 2HDM(II) can describe the electroweak data with the precision comparable to that given by the SM. Particularly interesting lower limits on the mass of the lighter neutral CP-even scalar are obtained in the scenario with light CP-odd Higgs boson and large . Received: 8 June 1999 / Published online: 14 October 1999     

Search for Higgs bosons in {\rm e^+e^-} collisions at 183 GeV

The data collected by the OPAL experiment at GeV were used to search for Higgs bosons which are predicted by the Standard Model and various extensions, such as general models with two Higgs field doublets and the Minimal Supersymmetric Standard Model (MSSM). The data correspond to an integrated luminosity of approximately 54 pb. None of the searches for neutral and charged Higgs bosons have revealed an excess of events beyond the expected background. This negative outcome, in combination with similar results from searches at lower energies, leads to new limits for the Higgs boson masses and other model parameters. In particular, the 95% confidence level lower limit for the mass of the Standard Model Higgs boson is 88.3 GeV. Charged Higgs bosons can be excluded for masses up to 59.5 GeV. In the MSSM, GeV and GeV are obtained for , no and maximal scalar top mixing and soft SUSY-breaking masses of 1 TeV. The range is excluded for minimal scalar top mixing and GeV. More general scans of the MSSM parameter space are also considered. Received: 27 October 1998 / Published online: 19 February 1999     

The masses of the neutral {\cal CP}-even Higgs bosons in the MSSM: Accurate analysis at the two-loop level

We present detailed results of a diagrammatic calculation of the leading two-loop QCD corrections to the masses of the neutral -even Higgs bosons in the Minimal Supersymmetric Standard Model (MSSM). The two-loop corrections are incorporated into the full diagrammatic one-loop result and supplemented with refinement terms that take into account leading electroweak two-loop and higher-order QCD contributions. The dependence of the results for the Higgs-boson masses on the various MSSM parameters is analyzed in detail, with a particular focus on the part of the parameter space accessible at LEP2 and the upgraded Tevatron. For the mass of the lightest Higgs boson, , a parameter scan has been performed, yielding an upper limit on which depends only on . The results for the Higgs-boson masses are compared with results obtained by renormalization group methods. Good agreement is found in the case of vanishing mixing in the scalar quark sector, while sizable deviations occur if squark mixing is taken into account. Received: 11 January 1999 / Published online: 28 May 1999     

Search for neutral minimal supersymmetric standard model Higgs bosons decaying to tau pairs produced in association with b quarks in pp collisions at √s = 1.96 TeV

We report results from a search for neutral Higgs bosons produced in association with b quarks using data recorded by the D0 experiment at the Fermilab Tevatron Collider and corresponding to an integrated luminosity of 7.3 fb(-1). This production mode can be enhanced in several extensions of the standard model (SM) such as in its minimal supersymmetric extension (MSSM) at high tanβ. We search for Higgs bosons decaying to tau pairs with one tau decaying to a muon and neutrinos and the other to hadrons. The data are found to be consistent with SM expectations, and we set upper limits on the cross section times branching ratio in the Higgs boson mass range from 90 to 320 GeV/c(2). We interpret our result in the MSSM parameter space, excluding tanβ values down to 25 for Higgs boson masses below 170 GeV/c(2).     

Heavy charged Higgs boson production at next generation e^\pm\gamma colliders

We assess the potential of future electron-positron linear colliders operating in the mode in detecting charged Higgs bosons with mass around and larger than the top quark mass, using Compton back-scattered photons from laser light. We compare the pair production mode, , to a variety of channels involving only one charged Higgs scalar in the final state, such as the tree-level processes ( and ) and ( and ) as well as the loop-induced channel . We show that, when the charged Higgs boson mass is smaller than or comparable to half the collider energy, , single production cross sections are of the same size as the pair production rate, whereas, for charged Higgs boson masses larger than , all processes are heavily suppressed. In general, production cross sections of charged Higgs bosons via scatterings are smaller than those induced at an collider and the latter represents a better option to produce and analyse such particles. Received: 29 August 2001 / Published online: 23 November 2001     

Masses and couplings of the lightest Higgs bosons in (M + 1)SSM

We study the upper limits on the mass of the lightest and second lightest CP even Higgs bosons in the (M + 1)SSM, the MSSM extended by a gauge singlet. The dominant two loop contributions to the effective potential are included, which reduce the Higgs masses by GeV. Since the coupling R of the lightest Higgs scalar to gauge bosons can be small, we study in detail the relations between the masses and couplings of both lightest scalars. We present upper bounds on the mass of a ”strongly” coupled Higgs (R < 1/2) as a function of lower experimental limits on the mass of a ”weakly” coupled Higgs (R < 1/2). With the help of these results, the whole parameter space of the model can be covered by Higgs boson searches. Received: 7 September 1999 / Published online: 12 July 2002     

Single scale factor for the universe from the creation of radiation and matter till the present

For a long time, global fits of the electroweak sector of the standard model (SM) have been used to exploit measurements of electroweak precision observables at lepton colliders (LEP, SLC), together with measurements at hadron colliders (Tevatron, LHC) and accurate theoretical predictions at multi-loop level, to constrain free parameters of the SM, such as the Higgs and top masses. Today, all fundamental SM parameters entering these fits are experimentally determined, including information on the Higgs couplings, and the global fits are used as powerful tools to assess the validity of the theory and to constrain scenarios for new physics. Future measurements at the Large Hadron Collider (LHC) and the International Linear Collider (ILC) promise to improve the experimental precision of key observables used in the fits. This paper presents updated electroweak fit results using the latest NNLO theoretical predictions and prospects for the LHC and ILC. The impact of experimental and theoretical uncertainties is analysed in detail. We compare constraints from the electroweak fit on the Higgs couplings with direct LHC measurements, and we examine present and future prospects of these constraints using a model with modified couplings of the Higgs boson to fermions and bosons.     

Higgs boson properties in the Standard Model and its supersymmetric extensions

We review the realization of the Brout–Englert–Higgs mechanism in the electroweak theory and describe the experimental and theoretical constraints on the mass of the single Higgs boson expected in the minimal Standard Model. We also discuss the couplings of this Higgs boson and its possible decay modes as functions of its unknown mass. We then review the structure of the Higgs sector in the minimal supersymmetric extension of the Standard Model (MSSM), noting the importance of loop corrections to the masses of its five physical Higgs bosons. Finally, we discuss some non-minimal models. To cite this article: J. Ellis et al., C. R. Physique 8 (2007).     

Search for a Higgs boson in the diphoton final state in pp collisions at sqrt[s]=1.96 TeV

A search for a narrow Higgs boson resonance in the diphoton mass spectrum is presented based on data corresponding to 7.0 fb{-1} of integrated luminosity from pp collisions at sqrt[s]=1.96 TeV collected by the CDF experiment. No evidence of such a resonance is observed, and upper limits are set on the cross section times branching ratio of the resonant state as a function of Higgs boson mass. The limits are interpreted in the context of the standard model and one fermiophobic benchmark model where the data exclude fermiophobic Higgs bosons with masses below 114 GeV/c{2} at a 95% Bayesian credibility level.     

Do electroweak precision data and Higgs-mass constraints rule out a scalar bottom quark with mass of order 5 GeV?

We study the implications of a scalar bottom quark, with a mass of O (5 GeV), within the minimal supersymmetric standard model. Light sbottoms may naturally appear for large tan(beta) and, depending on the decay modes, may have escaped experimental detection. We show that a light sbottom cannot be ruled out by electroweak precision data and the bound on the lightest CP-even Higgs-boson mass. We infer that a light b scenario requires a relatively light scalar top quark whose mass is typically about the top-quark mass. In this scenario the lightest Higgs boson decays predominantly into b pairs and obeys the mass bound m(h) less, similar 123 GeV.     

Search for Higgs Bosons at LEP2 and Hadron Colliders

The search for the Higgs boson was one of the most relevant issues of the final years of LEP running at high energies. An excess of 3σ beyond the background expectation has been found, consistent with the production of the Higgs boson with a mass near 115 GeV/c². At the upgraded TeVatron and at LHC the search for the Higgs boson will continue. At TeVatron Higgs bosons can be detected with masses up to 180 GeV with an assumed total integrated luminosity of 20 fb^—1. LHC has the potential to discover the Higgs boson in many different decay channels for Higgs masses up to 1 TeV. It will be possible to measure Higgs boson parameters, such as mass, width, and couplings to fermions and bosons. The results from Higgs searches at LEP2 and the possibilities for searches at hadron colliders will be reviewed.     

Three-body decays of Higgs bosons at LEP2 and application to a hidden fermiophobic Higgs

We study the decays of Higgs bosons to a lighter Higgs boson and a virtual gauge boson in the context of the non-supersymmetric two-Higgs doublet model (2HDM). We consider the phenomenological impact at LEP2 and find that such decays, when open, may be dominant in regions of parameter space and thus affect current Higgs boson search techniques. Three-body decays would be a way of producing light neutral Higgs bosons which have so far escaped detection at LEP due to suppressed couplings to the Z, and are of particular importance in the 2HDM (Model I) which allows both a light fermiophobic Higgs and a light charged scalar.     

Search for the Higgs boson in events with missing transverse energy and b quark jets produced in pp collisions at square root(s)=1.96 TeV

We search for the standard model Higgs boson produced in association with an electroweak vector boson in events with no identified charged leptons, large imbalance in transverse momentum, and two jets where at least one contains a secondary vertex consistent with the decay of b hadrons. We use approximately 1 fb(-1) integrated luminosity of pp collisions at square root(s)=1.96 TeV recorded by the Collider Detector at Fermilab II experiment at the Tevatron. We find 268 (16) single (double) b-tagged candidate events, where 248+/-43 (14.4+/-2.7) are expected from standard model background processes. We observe no significant excess over the expected background and thus set 95% confidence level upper limits on the Higgs boson production cross section for several Higgs boson masses ranging from 110 to 140 GeV/c(2). For a mass of 115 GeV/c(2), the observed (expected) limit is 20.4 (14.2) times the standard model prediction.     

Superconformal technicolor

In supersymmetric theories with a strong conformal sector, soft supersymmetry breaking at the TeV scale naturally gives rise to confinement and chiral symmetry breaking at the same scale. We consider two such scenarios, one where the strong dynamics induces vacuum expectation values for elementary Higgs fields, and another where the strong dynamics is solely responsible for electroweak symmetry breaking. In both cases, the mass of the Higgs boson can exceed the LEP bound without tuning, solving the supersymmetry naturalness problem. A good precision electroweak fit can be obtained, and quark and lepton masses are generated without flavor-changing neutral currents. In addition to standard supersymmetry signals, these models predict production of multiple heavy standard model particles (t, W, Z, and b) from decays of resonances in the strong sector.     

High transverse momentum physics at the large hadron collider

This note summarizes many detailed physics studies done by the ATLAS and CMS Collaborations for the LHC, concentrating on processes involving the production of high mass states. These studies show that the LHC should be able to elucidate the mechanism of electroweak symmetry breaking and to study a variety of other topics related to physics at the TeV scale. In particular, a Higgs boson with couplings given by the Standard Model is observable in several channels over the full range of allowed masses. Its mass and some of its couplings will be determined. If supersymmetry is relevant to electroweak interactions, it will be discovered and the properties of many supersymmetric particles elucidated. Other new physics, such as the existence of massive gauge bosons and extra dimensions can be searched for extending existing limits by an order of magnitude or more.