arXiv subjects
Publications and source records attributed to Howard E. Haber.
We consider the leading one-loop Yukawa-coupling corrections to the h^0 b b-bar coupling at O(m_t^2)in the MSSM in the decoupling limit. The decoupling behavior of the corrections from the various MSSM sectors is analyzed in the case of having some or all of the supersymmetric mass parameters and/or the CP-odd Higgs mass large as compared to the electroweak scale.
In the most general two-Higgs-doublet model (2HDM), unitary transformations between the two Higgs fields do not change the functional form of the Lagrangian. All physical observables of the model must therefore be independent of such transformations (i.e., independent of the Lagrangian basis choice for the Higgs fields). We exhibit a set of basis-independent quantities that determine all tree-level Higgs couplings and masses. Some examples of the basis-independent treatment of 2HDM discrete symmetries are presented. We also note that the ratio of the neutral Higgs field vacuum expectation values, tan(beta), is not a meaningful parameter in general, as it is basis-dependent. Implications for the more specialized 2HDMs (e.g., the Higgs sector of the MSSM and the so-called Type-I and Type-II 2HDMs) are explored.
The most general Higgs potential of the two-Higgs-doublet model (2HDM) contains three squared-mass parameters and seven quartic self-coupling parameters. Among these, one squared-mass parameter and three quartic coupling parameters are potentially complex. The Higgs potential explicitly violates CP symmetry if and only if no choice of basis exists in the two-dimensional Higgs ``flavor'' space in which all the Higgs potential parameters are real. We exhibit four independent potentially complex invariant (basis-independent) combinations of mass and coupling parameters and show that the reality of all four invariants provides the necessary and sufficient conditions for an explicitly CP-conserving 2HDM scalar potential. Additional potentially complex invariants can be constructed that depend on the Higgs field vacuum expectation values (vevs). We demonstrate how these can be used together with the vev-independent invariants to distinguish between explicit and spontaneous CP-violation in the Higgs sector.
A brief overview is given of the theory of Higgs bosons and electroweak symmetry breaking that is relevant for the Higgs physics program at the Linear Collider.
We review the theory of Higgs bosons, with emphasis on the Higgs scalars of the Standard Model and its non-supersymmetric and supersymmetric extensions. After surveying the expected knowledge of Higgs boson physics after the Tevatron and LHC experimental programs, we examine in detail expectations for precision Higgs measurements at a future e+e- linear collider (LC). A comprehensive phenomenological profile can be assembled from LC Higgs studies (both in e+e- and gamma-gamma collisions). The Giga-Z option can provide important constraints and consistency checks for the theory of electroweak symmetry breaking.
A CP-even neutral Higgs boson with Standard-Model-like couplings may be the lightest scalar of a two-Higgs-doublet model. We study the decoupling limit of the most general CP-conserving two-Higgs-doublet model, where the mass of the lightest Higgs scalar is significantly smaller than the masses of the other Higgs bosons of the model. In this case, the properties of the lightest Higgs boson are nearly indistinguishable from those of the Standard Model Higgs boson. The first non-trivial corrections to Higgs couplings in the approach to the decoupling limit are also evaluated. The importance of detecting such deviations in precision Higgs measurements at future colliders is emphasized. We also clarify the case in which a neutral Higgs boson can possess Standard-Model-like couplings in a regime where the decoupling limit does not apply. The two-Higgs-doublet sector of the minimal supersymmetric model illustrates many of the above features.
A short review of the theory and phenomenology of Higgs bosons is given, with focus on the Standard Model (SM) and the minimal supersymmetric extension of the Standard Model (MSSM). The potential for Higgs boson discovery at the Tevatron and LHC, and precision Higgs studies at the LHC and a future e+e- linear collider are briefly surveyed. The phenomenological challenge of the approach to the decoupling limit, where the properties of the lightest CP-even Higgs boson of the MSSM are nearly indistinguishable from those of the SM Higgs boson is emphasized.
Precision electroweak data presently favors a weakly-coupled Higgs sector as the mechanism responsible for electroweak symmetry breaking. Low-energy supersymmetry provides a natural framework for weakly-coupled elementary scalars. In this review, we summarize the theoretical properties of the Standard Model (SM) Higgs boson and the Higgs sector of the minimal supersymmetric extension of the Standard Model (MSSM). We then survey the phenomenology of the SM and MSSM Higgs bosons at the Tevatron, LHC and a future e+e- linear collider. We focus on the Higgs discovery potential of present and future colliders and stress the importance of precision measurements of Higgs boson properties.
In lepton-number-violating supersymmetric models, there is no natural choice of basis to distinguish the down-type Higgs and lepton superfields. We employ basis-independent techniques to identify the massless majoron and associated light scalar in the case of spontaneously-broken lepton number (L). When explicit L-violation is added, these two scalars can acquire masses of order the electroweak scale and can be identified as massive sneutrinos.
In the decoupling limit of a non-minimal Higgs sector, the lightest CP-even Higgs boson (h) is indistinguishable from the Standard Model (SM) Higgs boson. In the two-Higgs-doublet sector of the MSSM, the approach to the decoupling limit (for m_A>>m_Z) persists, even in the presence of potentially large (tan(beta)-enhanced) radiative corrections to the hbb coupling. Radiative corrections can also generate an accidental cancellation between tree-level and one-loop terms, resulting in a SM-like Higgs boson for moderate m_A outside the decoupling regime.
In this summary report of the 2001 Snowmass Electroweak Symmetry Breaking Working Group, the main candidates for theories of electroweak symmetry breaking are surveyed, and the criteria for distinguishing among the different approaches are discussed. The potential for observing electroweak symmetry breaking phenomena at the upgraded Tevatron and the LHC is described. We emphasize the importance of a high-luminosity $e^+e^-$ linear collider for precision measurements to clarify the underlying electroweak symmetry breaking dynamics. Finally, we note the possible roles of the $μ^+μ^-$ collider and VLHC for further elucidating the physics of electroweak symmetry breaking.
The decoupling properties of the Higgs sector in the Minimal Supersymmetric Standard Model (MSSM) imply that a light CP-even Higgs boson discovered at the Tevatron or LHC may closely resemble the Standard Model (SM) Higgs boson. In this paper, we investigate how precision measurements of Higgs properties at a Linear Collider (LC) can distinguish between a CP-even Higgs boson of the MSSM and the SM Higgs boson. We review the expected theoretical behavior of the partial widths and branching ratios for decays of the neutral MSSM Higgs bosons with significant couplings to the W and Z bosons, including the leading radiative corrections to the mixing angle alpha and tan beta-enhanced vertex corrections. The general expectation is that the Higgs couplings to W+W-, ZZ, c cbar and t tbar should quickly approach their SM values for increasing CP-odd Higgs mass mA, while the couplings to b bbar and tau+ tau- do so more slowly. Using the expected experimental and theoretical accuracy in determining SM branching ratios and partial widths, we demonstrate the sensitivity of measurements at the LC to variations in the MSSM parameters, with particular attention to the decoupling limit. For a wide range of MSSM parameters, the LC is sensitive to mA ~ 600 GeV almost independently of tan beta. For large values of tan beta and some specific choices of MSSM parameters [e.g., A_t mu < 0 and |A_t| ~ |mu| ~ O(M_S)], one of the CP-even Higgs bosons can be SM-like independent of the value of mA. In the case of large deviations from the SM, we present a procedure using Higgs coupling measurements to extract the supersymmetric correction to the relation between the b quark mass and Yukawa coupling.
The structure of low-energy supersymmetric models of fundamental particles and interactions is reviewed, with an emphasis on the minimal supersymmetric extension of the Standard Model (MSSM) and some of its variants. Various approaches to the supersymmetry-breaking mechanism are considered. The implications for the phenomenology of Higgs bosons and supersymmetric particles at future colliders are discussed.
A light CP-even Higgs boson (h) with a mass of about 10 GeV could explain the recent BNL measurement of the muon anomalous magnetic moment, in the framework of a general CP-conserving two-Higgs-doublet extension of the Standard Model with no tree-level flavor-changing neutral Higgs couplings. However, the allowed Higgs mass window is quite small and the corresponding model parameters are very constrained. The Higgs sector can contribute significantly to the observed BNL result for g-2 without violating known experimental constraints only if the hZZ coupling (approximately) vanishes and m_h lies between the Upsilon mass and 2m_B.
In R-parity-violating supersymmetric models (with a conserved baryon number), there are no quantum numbers that distinguish the lepton-doublet and down-type Higgs supermultiplets. As a result, the R-parity-violating parameters depend on the basis choice for these superfields, although physical observables are independent of the choice of basis. This paper presents a basis-independent computation of the sneutrino/antisneutrino squared-mass splitting in terms of basis-independent quantities. Techniques are developed for an arbitrary number of sneutrino generations; specific results are provided for the one, two and three generation cases.
We analyze the supersymmetric (SUSY) QCD contribution to the $h^0 b \bar{b}$ coupling at one loop in the Minimal Supersymmetric Model (MSSM) in the decoupling limit. Analytic expressions in the large SUSY mass region are derived and the decoupling behavior of the corrections is examined in various limiting cases, where some or all of the SUSY mass parameters become large. We show that in the decoupling limit of large SUSY mass parameters and large CP-odd Higgs mass, the $h^0 b \bar b$ coupling approaches its Standard Model value at one loop. However, the onset of decoupling is delayed when $\tanβ$ is large. In addition, the one-loop SUSY-QCD corrections decouple if the masses of either the bottom squarks or the gluino are separately taken large; although the approach to decoupling is significantly slower in the latter case.
We explore the radiative corrections to the process $Z \to b \bar b$ in models with extended Higgs sectors. The observables $R_b = Γ(Z \to b \bar b)/Γ(Z \to \rm{hadrons})$ and the $Z b \bar b$ coupling asymmetry, $A_b = (g_L^2 - g_R^2)/(g_L^2 + g_R^2)$, are sensitive to these corrections. We present general formulae for the one-loop corrections to $R_b$ and $A_b$ in an arbitrary extended Higgs sector, and derive explicit results for a number of specific models. We find that in models containing only doublets, singlets, or larger multiplets constrained by a custodial $SU(2)_{c}$ symmetry so that $M_W = M_Z \cosθ_W$ at tree level, the one-loop corrections due to virtual charged Higgs bosons always worsen agreement with experiment. The $R_{b}$ measurement can be used to set lower bounds on the charged Higgs masses. Constraints on models due to the one-loop contributions of neutral Higgs bosons are also examined.
R-parity-violating supersymmetry with a conserved baryon number B provides a framework for particle physics with lepton number (L) violating interactions. Two important probes of the L-violating physics are neutrino masses and sneutrino-antisneutrino mass-splittings. We evaluate these quantities in the context of the most general CP-conserving, R-parity-violating B-conserving extension of the minimal supersymmetric standard model. In generic three-generation models, three sneutrino-antisneutrino mass splittings are generated at tree-level. In contrast, only one neutrino mass is generated at tree-level; the other two neutrinos acquire masses at one-loop. In many models, the dominant contribution to the radiative neutrino masses is induced by the non-zero sneutrino-antisneutrino mass splitting.