Higgs boson searches in CP-conserving and CP-violating MSSM scenarios with the DELPHI detector

This paper presents the final interpretation of the results from DELPHI on the searches for Higgs bosons in the minimal supersymmetric extension of the Standard Model (MSSM). A few representative scenarios are considered, that include CP conservation and explicit CP violation in the Higgs sector. The experimental results encompass the searches for neutral Higgs bosons at LEP1 and LEP2 in final states as expected in the MSSM, as well as LEP2 searches for charged Higgs bosons and for neutral Higgs bosons decaying into hadrons independent of the quark flavour. The data reveal no significant excess with respect to background expectations. The results are translated into excluded regions of the parameter space in the various scenarios. In the CP-conserving case, these lead to limits on the masses of the lightest scalar and pseudoscalar Higgs bosons, h and A, and on tanβ. The dependence of these limits on the top quark mass is discussed. Allowing for CP violation reduces the experimental sensitivity to Higgs bosons. It is shown that this effect depends strongly on the values of the parameters responsible for CP violation in the Higgs sector.     

Neutral Higgs bosons in the MNMSSM with explicit CP violation

Within the framework of the minimal non-minimal supersymmetric standard model (MNMSSM) with tadpole terms, CP violation effects in the Higgs sector are investigated at the one-loop level, where the radiative corrections from the loops of the quark and squarks of the third generation are taken into account. Assuming that the squark masses are not degenerate, the radiative corrections due to the stop and sbottom quarks give rise to CP phases which trigger the CP violation explicitly in the Higgs sector of the MNMSSM. The masses, the branching ratios for dominant decay channels, and the total decay widths of the five neutral Higgs bosons in the MNMSSM are calculated in the presence of explicit CP violation. The dependence of these quantities on the CP phases is quite recognizable, for given parameter values.     

Review of searches for Higgs bosons and beyond the Standard Model Physics at the Tevatron

The energy frontier is currently at the Fermilab Tevatron accelerator, which collides protons and antiprotons at a center-of-mass energy of 1.96 TeV. The luminosity delivered to the CDF and DØ experiments has now surpassed the 4 fb^?1. This paper reviews the most recent direct searches for Higgs bosons and beyond-the-standard-model (BSM) physics at the Tevatron. The results reported correspond to an integrated luminosity of up to 2.5 fb^?1 of Run II data collected by the two Collaborations. Searches covered include the standard model (SM) Higgs boson (including sensitivity projections), the neutral Higgs bosons in the minimal supersymmetric extension of the standard model (MSSM), charged Higgs bosons and extended Higgs models, supersymmetric decays that conserve or violate R-parity, gauge-mediated supersymmetric breaking models, long-lived particles, leptoquarks, compositeness, extra gauge bosons, extra dimensions, and finally signature-based searches. Given the excellent performance of the collider and the continued productivity of the experiments, the Tevatron physics potential looks promising for discovery with the coming larger data sets. In particular, evidence for the SM Higgs boson could be obtained if its mass is light or near 160 GeV. The observed (expected) upper limits are currently a factor of 3.7 (3.3) higher than the expected SM Higgs boson cross section at m _H =115 GeV and 1.1 (1.6) at m _H =160 GeV at 95% C.L.     

TheZ-width in the two Higgs doublet model

Effects from an extended Higgs sector on the partial widths \(\Gamma _{{\rm Z} \to b\bar b} \) and \(\Gamma _{{\rm Z} \to \tau ^ + \tau ^ - } \) are analysed with emphasis on enhanced Yukawa couplings to the fermions with the weak isospinT ₃=?1/2. Contributions from charged and neutral Higgs bosons are incorporated. Vertex corrections from a heavy top quark and from charged Higgs bosons are always negative. One can however find regions in the parameter space where neutral Higgs bosons lead to positive vertex corrections. The charged Higgs bosons decouple from the ratio \(\Gamma ^{_{{\rm Z} \to \tau ^ + \tau ^ - } } /\Gamma ^{_{{\rm Z} \to \mu ^ + \mu ^ - } } \) if their mass is beyond 80 GeV. This ratio is then sensitive to the neutral sector only.     

The Higgs sector of the minimal supersymmetric standard model including radiative corrections

We discuss the Higgs sector of the minimal supersymmetric standard model including effects of radiative corrections. The formalism is explained in detail for computing radiative corrections to the masses and the coupling constants of the Higgs bosons. The radiative corrections to the masses are studied in the on-shell renormalization scheme. The radiative corrections to the mixing angles between the two CP-even Higgs bosons and the Higgs self-coupling constants are investigated in a simple procedure. The explicit analytic expressions are given for the radiative corrections due to the loops containing the top and bottom quarks and their superpartners. Simple approximate formulae are derived from the analytic expressions obtained in the on-shell renormalization scheme. We numerically study the effects of radiative corrections on the mass of the lighter Higgs boson and the mixing angles between the two CP-even Higgs bosons.     

Strangephilic Higgs bosons in the MSSM

We suggest a new CPX-derived scenario for the search for strangephilic MSSM Higgs bosons at the Tevatron and the LHC, in which all neutral and charged Higgs bosons decay predominantly into pairs of strange quarks and into a strange and a charm quark, respectively. The proposed scenario is realized within a particular region of the MSSM parameter space and requires large values of tan?β, where threshold radiative corrections are significant to render the effective strange-quark Yukawa coupling dominant. Experimental searches for neutral Higgs bosons based on the identification of b-quark jets or τ leptons may miss a strangephilic Higgs boson and its existence could be inferred indirectly by searching for hadronically decaying charged Higgs bosons. Potential strategies and experimental challenges to search for strangephilic Higgs bosons at the Tevatron and the LHC are discussed.     

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.     

Electroweak chiral Lagrangian for left–right symmetric models: The matter sector

The matter sector of electroweak chiral Lagrangian up to dimension four operators for left–right symmetric models with a neutral light Higgs is provided. The connection of these operators to Yukawa couplings, anomalous gauge couplings and parameters in the matter sector of conventional electroweak chiral Lagrangian is made. It is shown that there exists proper parameter space to loosen constraint for the mass of right handed gauge boson from the mass difference of neutral K meson.     

MSSM Higgs sector CP violation at photon colliders: revisited

The CP violating phases in soft SUSY breaking terms may induce indirect CP violation in the neutral Higgs boson sector through SUSY particle loops as well as direct CP violation in the γγ→H_i (i=1,2,3) through CP violating vertices. We present a complete analysis of the MSSM Higgs sector CP violation at photon colliders including the chargino loop contributions in the regime , where the CP violating mixing in the neutral Higgs sector is very strongly influenced by the scalar top loop, more so than the chargino and neutralino ones. However, the CP violating phases of the higgsino and wino mass parameters may still generate direct CP violation in γγ→H_i. In this process, the CP violating phenomena become very rich, and thus we study the production rates and polarization asymmetries in the Higgs production in detail. Photon colliders with high luminosity and well controlled polarized initial photon beams are indispensable in determining the CP properties of neutral Higgs bosons. PACS 14.80.Cp; 12.60.Jv; 11.30.Er     

Higher-order corrections to Higgs boson decays in the MSSM with complex parameters

We discuss Higgs boson decays in the CP-violating MSSM, and examine their phenomenological impact using cross section limits from the LEP Higgs searches. This includes a discussion of the full 1-loop results for the partial decay widths of neutral Higgs bosons into lighter neutral Higgs bosons (h _a →h _b h _c ) and of neutral Higgs bosons into fermions (\(h_{a} \to f \bar{f}\)). In calculating the genuine vertex corrections, we take into account the full spectrum of supersymmetric particles and all complex phases of the supersymmetric parameters. These genuine vertex corrections are supplemented with Higgs propagator corrections incorporating the full 1-loop and the dominant 2-loop contributions, and we illustrate a method of consistently treating diagrams involving mixing with Goldstone and Z bosons. In particular, the genuine vertex corrections to the process h _a →h _b h _c are found to be very large and, where this process is kinematically allowed, can have a significant effect on the regions of the CPX benchmark scenario which can be excluded by the results of the Higgs searches at LEP. However, there remains an unexcluded region of CPX parameter space at a lightest neutral Higgs boson mass of ～45 GeV. In the analysis, we pay particular attention to the conversion between parameters defined in different renormalisation schemes and are therefore able to make a comparison to the results found using renormalisation group improved/effective potential calculations.     

Neutral Higgs bosons in the standard model and in the minimal supersymmetric model: Searches at LEP

During the twelve years of operation of thee ⁺ e ⁻ collider LEP, the associated collaborations, ALEPH, DELPHI, L3 and OPAL, have extensively searched for Higgs bosons over a broad range of masses. We present the final results from LEP for the standard model Higgs boson which are obtained from a statistical combination of the data from the four experiments. We also present preliminary combined results for neutral Higgs bosons in the minimal supersymmetric model (MSSM) where the Higgs sector is assumed to be CP invariant. Finally, we discuss an alternative MSSM scenario including CP violation in the Higgs sector.     

Spontaneous CP violating phase as the CKM matrix phase

We propose that the CP violating phase in the CKM mixing matrix is identical to the CP phases responsible for the spontaneous CP violation in the Higgs potential. A multi-Higgs model with Peccei–Quinn (PQ) symmetry is constructed to realize this idea. The CP violating phase does not vanish when all Higgs masses become large. In general, here are flavor changing neutral current (FCNC) interactions mediated by neutral Higgs bosons at the tree level. However, unlike general multi-Higgs models, the FCNC Yukawa couplings are fixed in terms of the quark masses and CKM mixing angles. Implications for meson–anti-meson mixing, including recent data on D–D̄ mixing, and the electric dipole moment (EDM) of the neutron are studied. We find that the neutral Higgs boson masses can be at the order of one hundred GeV. The neutron EDM can be close to the present experimental upper bound.     

Search for heavy neutral MSSM Higgs bosons with CMS: reach and Higgs mass precision

The search for MSSM Higgs bosons will be an important goal at the LHC. We analyze the search reach of the CMS experiment for the heavy neutral MSSM Higgs bosons with an integrated luminosity of 30 or 60 fb^-1. This is done by combining the latest results for the CMS experimental sensitivities based on full simulation studies with state-of-the-art theoretical predictions of the MSSM Higgs-boson properties. The results are interpreted in MSSM benchmark scenarios in terms of the parameters tan β and the Higgs-boson mass scale, M_A. We study the dependence of the 5σ discovery contours in the M_A–tan β plane on variations of the other supersymmetric parameters. The largest effects arise from a change in the higgsino mass parameter μ, which enters both via higher-order radiative corrections and via the kinematics of Higgs decays into supersymmetric particles. While the variation of μ can shift the prospective discovery reach (and correspondingly the ”LHC wedge” region) by about Δtan β=10, we find that the discovery reach is rather stable with respect to the impact of other supersymmetric parameters. Within the discovery region we analyze the accuracy with which the masses of the heavy neutral Higgs bosons can be determined. We find that an accuracy of 1–4% should be achievable, which could make it possible in favorable regions of the MSSM parameter space to experimentally resolve the signals of the two heavy MSSM Higgs bosons at the LHC.     

Chargino decays in the complex MSSM: a full one-loop analysis

We evaluate two-body decay modes of charginos in the Minimal Supersymmetric Standard Model with complex parameters (cMSSM). Assuming heavy scalar quarks we take into account all decay channels involving charginos, neutralinos, (scalar) leptons, Higgs bosons and Standard Model gauge bosons. The evaluation of the decay widths is based on a full one-loop calculation including hard and soft QED radiation. Special attention is paid to decays involving the Lightest Supersymmetric Particle (LSP), i.e. the lightest neutralino, or a neutral or charged Higgs boson. The higher-order corrections of the chargino decay widths involving the LSP can easily reach a level of about ±10%, while the corrections to the decays to Higgs bosons are slightly smaller, translating into corrections of similar size in the respective branching ratios. These corrections are important for the correct interpretation of LSP and Higgs production at the LHC and at a future linear e ⁺ e ⁻ collider. The results will be implemented into the Fortran code FeynHiggs.     

Explicit CP violation in the Dine–Seiberg–Thomas model

The possibility of explicit CP violation is studied in a supersymmetric model proposed by Dine, Seiberg, and Thomas, with two effective dimension-five operators. The explicit CP violation may be triggered by complex phases in the coefficients for the dimension-five operators in the Higgs potential, and by a complex phase in the scalar top quark masses. Although the scenario of explicit CP violation is found to be inconsistent with the experimental data at LEP2 at tree level, it may be possible at the one-loop level. For a reasonable parameter space, the masses of the neutral Higgs bosons and their couplings to a pair of Z bosons are consistent with the LEP2 data, at the one-loop level.     

Charged Higgs Pair Production in a General Two Higgs Doublet Model at e^＋e^- and μ^＋μ^- Linear Colliders

In this paper, charged Higgs pair production through l^＋l^- → H^＋ H^-, where l = e or μ, is studied within the framework of a general Two Higgs Doublet Model （2HDM）. The analysis is relevant to a future e^＋e^- or μ^＋ μ^- collider operating at center of mass energy of √s = 500 GeV. Two different scenarios of small and large a values are studied. Here a is the parameter, which diagonMizes the neutral CP-even Higgs boson mass matrix. Within the Minimal Supersymmetric Standard Model （MSSM）, cross section of this process is almost the same at e＋ e- and #＋#- colliders. It is shown that at e^＋e^- eolliders within a general 2HDM, cross section is not sensitive to the mass of neutral Higgs bosons, however, it can acquire large values up to several picobarn at μ^＋μ^- colliders with the presence of heavy neutral Higgs bosons. A scan over Higgs boson mass parameter space is performed to analyze the effect of large masses of neutral Higgs bosons involved in the s-channel propagator and thus in the total cross section of this process.     

Determining the CP parity of Higgs bosons via their tau decay channels at the Large Hadron Collider

If neutral Higgs bosons are discovered at the CERN Large Hadron Collider (LHC), then an important subsequent issue will be the investigation of their CP nature. Higgs boson decays into tau lepton pairs are particularly suited in this respect. By analyzing the three charged pion decay modes of the tau leptons and taking expected measurement uncertainties at the LHC into account, we show that the CP properties of a Higgs boson can be pinned down with appropriately chosen observables, provided that sufficiently large event numbers will eventually be available.     

Mini little Higgs and dark matter

We construct a little Higgs model with the most minimal extension of the standard model gauge group by an extra U(1)$U(1)$ gauge symmetry. For specific charge assignments of scalars, an approximate U(3)$U(3)$ global symmetry appears in the cutoff-squared scalar mass terms generated from gauge bosons at one-loop level. Hence, the Higgs boson, identified as a pseudo-Goldstone boson of the broken global symmetry, has its mass radiatively protected up to scales of 5–10 TeV. In this model, a Z₂$Z_2$ symmetry, ensuring the two U(1)$U(1)$ gauge groups to be identical, also makes the extra massive neutral gauge boson stable and a viable dark matter candidate with a promising prospect of direct detection.     

CP violation in t → W + b decays in two-Higgs doublet model

Due to the large mass of top quark, CP violation in the top-quark decay is sensitive to the interactions mediated by Higgs bosons. We consider CP violation in t → W ⁺ b decay by calculating consistently in unitary gauge the CP-violating up-down asymmetry of the leptons from W boson decays in t → W ⁺ b, defined by Grz?dkowski and Gunion, in the two-Higgs doublet model with CP-violating neutral sector. The asymmetry is shown to be at most of the order of (1–4) × 10^-4 for tan β = 1.0, where tan β is the ratio of vacuum expectation values for the two neutral Higgs bosons.     

Search strategies for non-standard Higgs bosons at future ee colliders

Already in the simplest two-Higgs-doublet model with CP violation in the Higgs sector, the 3×3 mixing matrix for the neutral Higgs bosons can substantially modify their couplings, thereby endangering the “classical” Higgs search strategies. However, there are sum rules relating Yukawa and Higgs–Z couplings which ensure that the ZZ, and couplings of a given neutral 2HDM Higgs boson cannot all be simultaneously suppressed. This result implies that any single Higgs boson will be detectable at an e⁺e⁻ collider if the Z+Higgs, Higgs and Higgs production channels are all kinematically accessible and if the integrated luminosity is sufficient. We explore, as a function of Higgs mass, the luminosity required to guarantee Higgs boson detection, and find that for moderate tanβ values the needed luminosity is unlikely to be available for all possible mixing scenarios. Implications of the sum rules for Higgs discovery at the Tevatron and LHC are briefly discussed.