Particle spectrum in the modified nonminimal supersymmetric standard model in the strong Yukawa coupling regime

A theoretical analysis of solutions of renormalization group equations in the minimal supersymmetric standard model, which lead to a quasi-fixed point has shown that the mass of the lightest Higgs boson in these models does not exceed 94 ± 5 GeV. This implies that a considerable part of the parameter space in the minimal supersymmetric model is in fact eliminated by existing LEPII experimental data. In the nonminimal supersymmetric standard model the upper bound on the mass of the lightest Higgs boson reaches its maximum in the strong Yukawa coupling regime when the Yukawa constants are substantially greater than the gauge constants on the grand unification scale. In the present paper the particle spectrum is studied using the simplest modification of the nonminimal supersymmetric standard model which gives a self-consistent solution in this region of parameter space. This model can give m _h ～ 125 GeV even for comparatively low values of β ≥ 1.9. The spectrum of Higgs bosons and neutralinos is analyzed using the method of diagonalizing mass matrices proposed earlier. In this model the mass of the lightest Higgs boson does not exceed 130.5 ± 3.5 GeV.     

The b \to X_s \gamma rate and Higgs boson limits in the constrained minimal supersymmetric model

New NLO calculations have become available using resummed radiative corrections. Using these calculations we perform a global fit of the supergravity inspired constrained minimal supersymmetric model. We find that the resummed calculations show similar constraints as the LO calculations, namely that only with a relatively heavy supersymmetric mass spectrum of (1 TeV) the b– Yukawa unification and the rate can coexist in the large scenario. The resummed calculations are found to reduce the renormalization scale uncertainty considerably. The low scenario is excluded by the present Higgs limits from LEP II. The constraint from the Higgs limit in the plane is severe, if the trilinear coupling at the GUT scale is fixed to zero, but is considerably reduced for . The relatively heavy SUSY spectrum required by corresponds to a Higgs mass of GeV in the CMSSM. Received: 14 February 2001 / Revised version: 22 March 2001 / Published online: 29 June 2001     

Quantum weakdynamics as an SU(3)_I gauge theory: Grand unification of strong and electroweak interactions

Quantum weakdynamics (QWD) as an gauge theory with the vacuum term is considered to be the unification of the electroweak interaction as an gauge theory. The grand unification of beyond the standard model is established by the group . The grand unified interactions break down to weak and strong interactions at a new grand unification scale, GeV, through dynamical spontaneous symmetry breaking (DSSB); the weak and strong coupling constants are the same, , at this scale. DSSB is realized by the condensation of scalar fields, postulated to be spatially longitudinal components of gauge bosons, instead of Higgs particles. Quark and lepton family generation, the Weinberg angle , and the Cabbibo angle are predicted. The electroweak coupling constants are , , , and ; there are symmetric isospin interactions. Received: 21 January 2001 / Published online: 21 November 2001     

Associate Production of w± and H± with a Single Top Quark at LEP Ⅱ

Searching for a single top-quark production at LEP where the backgrohnd is relatively clean is interesting. We study e⁺e^- tb (t
b)+X cross sections at √s =200 GeV and √s =250 GeV energies in the framework of the minimal standard model and the extended standard model with two Higgs doublets. The resultant evaluation of the cross sections is not very encouraging, but can be optimistic and worth further serious studies in experiments and theories, if there exists charged Higgs with a large coupling parameter cotβ or the design luminosity is enhanced by several orders.     

An estimate of the Higgs boson mass in two loop approximation in a noncommutative differential geometry

An estimation of the Higgs boson mass is performed by numerically solving the renormalization group equations in the two loop approximation based on the condition for SU(2), U(1) gauge and the Higgs quartic coupling constants, respectively. This condition is introduced in the new scheme of our noncommutative differential geometry (NCG) for the reconstruction of the standard model. However, contrary to GUT without supersymmetry, the grand unification of coupling constants is not realized in this scheme. The physical mass of the Higgs boson depends strongly on the top quark mass through the Yukawa coupling of the top quark in the functions. The two loop effect lowers the numerical value calculated within the one loop approximation by several GeV. The Higgs boson mass varies from 150.93 GeV to 167.96 GeV corresponding to . We find GeV for GeV and GeV for GeV. Received: 16 July 1997 / Published online: 23 February 1998     

Seesaw induced Higgs mechanism

We discuss a two scalar doublets model which induces the Higgs mechanism by means of a seesaw mechanism. This model naturally predicts a light Higgs scalar whose mass is suppressed by the grand unification scale. The model requires an intermediate scale between the electroweak symmetry breaking scale and the grand unification scale at 10⁹ GeV. Below this intermediate energy scale the usual standard model appears as an effective theory. An implementation of this mechanism in models where the Planck scale is in the TeV region is discussed. Received: 20 September 2002 / Revised version: 6 March 2003 / Publishes online: 13 May 2003 RID="a" ID="a" e-mail: calmet@theory.caltech.edu     

Third generation Yukawa couplings unification in supersymmetric SO(10) model

In the minimal supersymmetric standard model (MSSM) contained in SUSY SO(10), top-- Yukawa unification is achieved at the intermediate mass scale GeV using the recent world average experimental value of the top-quark mass, GeV, which has been directly established by CDF and D0 experiments at the Tevatron Collider. It is also observed that the Yukawa couplings unification scale can be further decreased by taking lower input values of the top-quark mass. This trend indicates the possible existence of an intermediate symmetry breaking scale in SUSY SO(10). The present finding does not agree with the earlier notion that the third generation Yukawa couplings unification should occur at the GUT scale . Received: 22 September 1997 / Revised version: 22 January 1998 / Published online: 24 March 1998     

NMSSM Higgs benchmarks near 125 GeV

The recent LHC indications of a SM-like Higgs boson near 125 GeV are consistent not only with the Standard Model (SM) but also with Supersymmetry (SUSY). However naturalness arguments disfavour the Minimal Supersymmetric Standard Model (MSSM). We consider the Next-to-Minimal Supersymmetric Standard Model (NMSSM) with a SM-like Higgs boson near 125 GeV involving relatively light stops and gluinos below 1 TeV in order to satisfy naturalness requirements. We are careful to ensure that the chosen values of couplings do not become non-perturbative below the grand unification (GUT) scale, although we also examine how these limits may be extended by the addition of extra matter to the NMSSM at the two-loop level. We then propose four sets of benchmark points corresponding to the SM-like Higgs boson being the lightest or the second lightest Higgs state in the NMSSM or the NMSSM-with-extra-matter. With the aid of these benchmark points we discuss how the NMSSM Higgs boson near 125 GeV may be distinguished from the SM Higgs boson in future LHC searches.     

Improved predictions for intermediate and heavy supersymmetry in the MSSM and beyond

For a long time, the minimal supersymmetric standard model (MSSM) with light masses for the supersymmetric states was considered as the most natural extension of the Standard Model of particle physics. Consequently, a valid approximation was to match the MSSM to the precision measurement directly at the electroweak scale. This approach was also utilized by all dedicated spectrum generators for the MSSM. However, the higher the supersymmetric (SUSY) scale is, the bigger the uncertainties which are introduced by this matching. We point out important consequences of a two-scale matching, where the running parameters within the SM are calculated at \(M_Z\) and evaluated up to the SUSY scale, where they are matched to the full model. We show the impact on gauge coupling unification as well as the SUSY mass spectrum. Also the Higgs mass prediction for large supersymmetric masses has been improved by performing the calculation within an effective SM. The approach presented here is now also available in the spectrum generator SPheno. Moreover, also SARAH was extended accordingly and gives the possibility to study these effects now in many different supersymmetric models.     

Grand unification and B&L conservation

A brief summary of some of the recent developments in grand unification and B&;L conservation is given. Proton stability in supergravity unified models is discussed. Also discussed are the effects of supersymmetric dark matter constraints and the constraints of proton lifetime on the SUSY spectrum. Other topics reviewed include Planck scale effects and p decay, effects of textures, and extension to nonminimal models including models with many Higgs triplets. Recent developments in GUTs and strings are also discussed.     

Search for gauge mediated SUSY breaking topologies in ee collisions at centre-of-mass energies up to 209 GeV

A total of 628 bp^-1 of data collected with the ALEPH detector at centre-of-mass energies from 189 to 209 GeV is analysed in the search for gauge mediated SUSY breaking (GMSB) topologies. These topologies include two acoplanar photons, non-pointing single photons, acoplanar leptons, large impact parameter leptons, detached slepton decay vertices, heavy stable charged sleptons and multi-leptons plus missing energy final states. No evidence is found for new phenomena, and lower limits on masses of supersymmetric particles are derived. A scan of a minimal GMSB parameter space is performed and lower limits are set for the next-to-lightest supersymmetric particle (NLSP) mass at 54 GeV/c² and for the mass scale parameter at 10 TeV/c², independently of the NLSP lifetime. Including the results from the neutral Higgs boson searches, a NLSP mass limit of 77 GeV/c² is obtained and values of up to 16 TeV/c² are excluded. Received: 14 March 2002 / Published online: 20 September 2002     

Quasifixed-point scenario in a modified nonminimal supersymmetric standard model

The modified next-to-minimal supersymmetric standard model is the simplest model that is obtained as an extension of the minimal supersymmetric standard model and which is compatible with the LEP II experimental constraint on the mass of the lightest Higgs boson at tan β～1. The renormalization of Yukawa coupling constants and of the parameters of a soft breakdown of supersymmetry is investigated within this model. The possibility of unifying the Yukawa coupling constants for the b quark and the τ lepton at the Grand Unification scale M _X is studied. The spectrum of particles is analyzed in the vicinity of a quasifixed point where solutions to the renormalization-group equations are concentrated at the electroweak scale.     

The coupling of the lightest SUSY Higgs boson to two photons in the decoupling regime

We analyze the contribution of the SUSY particles to the coupling of the lightest Higgs boson to two photons in supersymmetric theories. We discuss to what extent these contributions can be large enough to allow for a discrimination between the lightest SUSY and the standard Higgs particles in the decoupling limit where all other Higgs bosons are very heavy and no supersymmetric particle has been discovered at future colliders. We find that only chargino and top squark loops can generate a sizeable difference between the standard and the SUSY Higgs-photon couplings. For masses above 250 GeV, the effect of chargino loops on the two-photon width is however smaller than ≈ 10% in the entire SUSY parameter space. Top squarks heavier than 250 GeV can induce deviations larger than 10% only if their couplings to the Higgs boson are large. Since top squark contributions can be sizeable, we derive the two-loop QCD correction to squark loops and show that they are well under control.     

Top compositeness and precision unification

The evolution of standard model gauge couplings is studied in a nonsupersymmetric scenario in which the hierarchy problem is resolved by Higgs compositeness above the weak scale. It is argued that massiveness of the top quark combined with precision tests of the bottom quark imply that the right-handed top must also be composite. If, further, the standard model gauge symmetry is embedded into a simple subgroup of the unbroken composite-sector flavor symmetry, then precision coupling unification is shown to occur at approximately 10(15) GeV, to a degree comparable to supersymmetric unification.     

Higgs mass implications on the stability of the electroweak vacuum

We update instability and metastability bounds of the Standard Model electroweak vacuum in view of the recent ATLAS and CMS Higgs results. For a Higgs mass in the range 124–126 GeV, and for the current central values of the top mass and strong coupling constant, the Higgs potential develops an instability around 10¹¹ GeV, with a lifetime much longer than the age of the Universe. However, taking into account theoretical and experimental errors, stability up to the Planck scale cannot be excluded. Stability at finite temperature implies an upper bound on the reheat temperature after inflation, which depends critically on the precise values of the Higgs and top masses. A Higgs mass in the range 124–126 GeV is compatible with very high values of the reheating temperature, without conflict with mechanisms of baryogenesis such as leptogenesis. We derive an upper bound on the mass of heavy right-handed neutrinos by requiring that their Yukawa couplings do not destabilize the Higgs potential.     

Search for gauge mediated SUSY breaking topologies at \sqrt{{\mathrm s}} \sim 189 GeV

Searches for topologies characteristic of Gauge Mediated SUSY Breaking models (GMSB) are performed by analysing 173.6 of data collected at = 188.6 GeV with the ALEPH detector. These topologies include acoplanar photons, non-pointing single photon, acoplanar leptons, large impact parameter leptons, detached slepton decay vertices, heavy stable charged sleptons and four leptons plus missing energy final states. No evidence for these new phenomena is observed and limits on production cross sections and sparticle masses are derived. A scan of a minimal GMSB parameter space is performed and model dependent lower limits of about 45 GeV/ on the next-to-lightest supersymmetric particle (NLSP) mass and of about 9 TeV on the mass scale parameter are derived, independently of the NLSP lifetime. Received: 30 November 1999 / Published online: 14 April 2000     

Where to look for solving the gauge hierarchy problem?

A mass of the Higgs boson close to 126 GeV may give a hint that the standard model of particle physics is valid up to the Planck scale. We discuss perspectives for the solution of the gauge hierarchy problem at high scales. Scenarios with an ultraviolet fixed point have predicted a Higgs boson mass very close to 126 GeV if the fixed point value of the quartic scalar coupling is small. In this case the top quark pole mass should be close to 172 GeV.     

Grand unification on noncommutative spacetime

We compute the beta-functions of the standard model formulated on a noncommutative spacetime. If we assume that the scale for spacetime noncommutativity is of the order of 2.2×10¹⁵ GeV, we find that the three gauge couplings of the standard model merge at a scale of 2.3×10¹⁷ GeV. The proton lifetime is thus much longer than in conventional unification models.     

General formulation for proton decay rate in minimal supersymmetric SO(10) GUT

We give an explicit formula for the proton decay rate in the minimal renormalizable supersymmetric (SUSY) SO(10) model. In this model, the Higgs fields consist of the 10 and SO(10) representations in the Yukawa interactions with matter and of the 10, , 126, and 210 representations in the Higgs potential. We present all the mass matrices for the Higgs fields contained in this minimal SUSY SO(10) model. Finally, we discuss the threshold effects of these Higgs fields on the gauge coupling unification.Received: 8 March 2005, Published online: 8 June 2005PACS: 12.10.-g, 12.10.Dm, 12.10.Kt     

Upper bounds on superpartner masses from upper bounds on the Higgs boson mass

The LHC is putting bounds on the Higgs boson mass. In this Letter we use those bounds to constrain the minimal supersymmetric standard model (MSSM) parameter space using the fact that, in supersymmetry, the Higgs mass is a function of the masses of sparticles, and therefore an upper bound on the Higgs mass translates into an upper bound for the masses for superpartners. We show that, although current bounds do not constrain the MSSM parameter space from above, once the Higgs mass bound improves big regions of this parameter space will be excluded, putting upper bounds on supersymmetry (SUSY) masses. On the other hand, for the case of split-SUSY we show that, for moderate or large tanβ, the present bounds on the Higgs mass imply that the common mass for scalars cannot be greater than 10(11) GeV. We show how these bounds will evolve as LHC continues to improve the limits on the Higgs mass.