The Higgs Boson Mass as a Probe of the Minimal Supersymmetric Standard Model

Recently, the LEP collaborations have reported a lower bound on a Standard Model-like Higgs boson of order 89 GeV. We discuss the implications of this bound for the minimal supersymmetric extension of the Standard Model (MSSM). In particular, we show that the lower bound on $\tan\beta$, which can be obtained from the presently allowed Higgs boson mass value, becomes stronger than the one set by the requirement of perturbative consistency of the theory up to scales of order $M_{GUT}$ (associated with the infrared fixed-point solution of the top quark Yukawa coupling) in a large fraction of the allowed parameter space. The potentiality of future LEP2 searches to further probe the MSSM parameter space is also discussed.Comment: 15 pages, 5 figures, LateX, psfi

A 125 GeV SM-like Higgs in the MSSM and the γγ\gamma \gamma rate

We consider the possibility of a Standard Model (SM)-like Higgs in the context of the Minimal Supersymmetric Standard Model (MSSM), with a mass of about 125 GeV and with a production times decay rate into two photons which is similar or somewhat larger than the SM one. The relatively large value of the SM-like Higgs mass demands stops in the several hundred GeV mass range with somewhat large mixing, or a large hierarchy between the two stop masses in the case that one of the two stops is light. We find that, in general, if the heaviest stop mass is smaller than a few TeV, the rate of gluon fusion production of Higgs bosons decaying into two photons tends to be somewhat suppressed with respect to the SM one in this region of parameters. However, we show that an enhancement of the photon decay rate may be obtained for light third generation sleptons with large mixing, which can be naturally obtained for large values of $\tan\beta$ and sizable values of the Higgsino mass parameter.Comment: 14 pages, 4 figures. Corrected small typos and added reference

CPsuperH2.3: an Updated Tool for Phenomenology in the MSSM with Explicit CP Violation

We describe the Fortran code CPsuperH2.3, which incorporates the following updates compared with its predecessor CPsuperH2.0. It implements improved calculations of the Higgs-boson masses and mixing including stau contributions and finite threshold effects on the tau-lepton Yukawa coupling. It incorporates the LEP limits on the processes e^+ e^- to H_i Z, H_i H_j and the CMS limits on H_i to tau^+ tau^- obtained from 4.6/fb of data at a centre-of-mass energy of 7 TeV. It also includes the decay mode H_i to Z gamma and the Schiff-moment contributions to the electric dipole moments of Mercury and Radium225, with several calculational options for the case of Mercury. These additions make CPsuperH2.3 a suitable tool for analyzing possible CP-violating effects in the MSSM in the era of the LHC and a new generation of EDM experimentsComment: 31 pages, 10 eps figures, 7 tables; H to Z gamma and SM BRs included; To appear in CPC; Typos in Eq.(A.2) corrected;The program may be obtained from http://www.hep.man.ac.uk/u/jslee/CPsuperH.html, or by contacting the first author at [email protected]; A comment added after Eq.(15) and a typo in Eq.(A.4) correcte

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

We investigate the phenomenological implications of a light scalar bottom quark, with a mass of about the bottom quark mass, within the minimal supersymmetric standard model. The study of such a scenario is of theoretical interest, since, depending on their production and decay modes, light sbottoms may have escaped experimental detection up to now and, in addition, may naturally appear for large values of \tan\beta. In this article we show that such a light sbottom cannot be ruled out by the constraints from the electroweak precision data and the present bound on the lightest CP-even Higgs boson mass at LEP. It is inferred that a light sbottom scenario requires in general a relatively light scalar top quark whose mass is typically about the top-quark mass. It is also shown that under these conditions the lightest CP-even Higgs boson decays predominantly into scalar bottom quarks in most of the parameter space and that its mass is restricted to m_h ~< 123 GeV.Comment: 7 pages, 2 figures, LateX. Discussion about fine tuning and low-energy experiments enlarged. Version to appear in Phys. Rev. Let

The complementarity of LEP, the Tevatron and the LHC in the search for a light MSSM Higgs boson

We study the properties of the Higgs boson sector in the MSSM, putting special emphasis on radiative effects which can affect the discovery potential of the LHC, Tevatron and/or LEP colliders. We concentrate on the V b b-bar channel, with V=Z or W, and on the channels with diphoton final states, which are the dominant ones for the search for a light Standard Model Higgs boson at LEP/Tevatron and LHC, respectively. By analyzing the regions of parameter space for which the searches in at least one of these colliders can be particularly difficult, we demonstrate the complementarity of these three colliders in the search for a light Higgs boson which couples in a relevant way to the W and Z gauge bosons (and hence plays a relevant role in the mechanism of electroweak symmetry breaking).Comment: 35 pages, including 11 Postscript figures, using JHEP.cl

Light Stop Searches at the LHC in Events with One Hard Photon or Jet and Missing Energy

Low energy supersymmetric models provide a solution to the hierarchy problem and also have the necessary ingredients to solve two of the most outstanding issues in cosmology: the origin of the baryon asymmetry and the source of dark matter. In the MSSM, weak scale generation of the baryon asymmetry may be achieved in the presence of light stops, with masses lower than about 130 GeV. Moreover, the proper dark matter density may be obtained in the stop-neutralino co-annihilation region, where the stop-neutralino mass difference is smaller than a few tens of GeV. Searches for scalar top quarks (stops) in pair production processes at the Tevatron and at the Large Hadron Collider (LHC) become very challenging in this region of parameters. At the LHC, however, light stops proceeding from the decay of gluino pairs may be identified, provided the gluino mass is smaller than about 900 GeV. In this article we propose an alternative method for stop searches in the co-annihilation region, based on the search for these particles in events with missing energy plus one hard photon or jet. We show that this method is quite efficient and, when complemented with ongoing Tevatron searches, allows to probe stop masses up to about 160 GeV, fully probing the region of parameters consistent with electroweak baryogenesis in the MSSM.Comment: 17 pages, 6 figure

Constraints on split-UED from Electroweak Precision Tests

We present strongly improved electroweak precision constraints on the split-UED model. We find that the dominating effect arises from contributions to the muon decay rate by the exchange of even-numbered W-boson Kaluza-Klein modes at tree-level, which so far have not been discussed in the context of UED models. The constraints on the split-UED parameter space are translated into bounds on the mass difference of the first Kaluza-Klein mode of fermions and the lightest Kaluza-Klein mode, which will be tested is the LHC.Comment: 4 pages, 2 figure

Isolated leptons from heavy flavor decays: Theory and data

Events with isolated leptons play a prominent role in signatures of new physics phenomena at high energy collider physics facilities. In earlier publications, we examine the standard model contribution to isolated lepton production from bottom and charm mesons and baryons through their semileptonic decays (b, c -> l + X), showing that this source can overwhelm the effects of other standard model processes in some kinematic domains. In this paper, we show that we obtain good agreement with recent Tevatron collider data, both validating our simulations and showing that we underestimate the magnitude of the heavy-flavor contribution to the isolated lepton yields. We also show that the isolation requirement acts as a narrow bandpass filter on the momentum of the isolated lepton, and we illustrate the effect of this filter on the background to Higgs boson observation in the dilepton mode. We introduce and justify a new rule of thumb: isolated electrons and muons from heavy flavor decay are produced with roughly the same distributions as b and c quarks, but with 1/200 times the rates of b and c production, respectively.Comment: 12 pg, revtex, 5 fig, corrected typo

Photon Signatures for Low Energy Supersymmetry Breaking and Broken R-parity

The possible phenomenological consequences of R-parity violating interactions in the framework of low energy supersymmetry breaking are studied. It is pointed out that even very weak R-parity violation would completely overshadow one of the basic signatures of low energy supersymmetry breaking models, that is, the decay of the next to lightest supersymmetric particle into a photon (lepton) and missing energy. Thus, the observation of these decays would put very strong limits on R-parity violating couplings. Vice-versa, if R-parity violation is established experimentally, before a detailed knowledge of the spectrum is obtained, it will be very difficult to distinguish gravity mediated from low energy gauge mediated supersymmetry breaking. Those conclusions are very model independent. We also comment on the possibility of mixing between charged and neutral leptons with charginos and neutralinos, respectively, and its phenomenological consequences for the photon (lepton) signatures, in scenarios where this mixing is generated by the presence of bilinear or trilinear R-parity violating terms in the superpotential.Comment: 12 pages, Late