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.     

Inverse seesaw in NMSSM and 126 GeV Higgs boson

We consider extensions of the next-to-minimal supersymmetric model (NMSSM) in which the observed neutrino masses are generated through a TeV scale inverse seesaw mechanism. The new particles associated with this mechanism can have sizable couplings to the Higgs field which can yield a large contribution to the mass of the lightest CP-even Higgs boson. With this new contribution, a 126 GeV Higgs is possible along with order of 200 GeV masses for the stop quarks for a broad range of tan β. The Higgs production and decay in the diphoton channel can be enhanced due to this new contribution. It is also possible to solve the little hierarchy problem in this model without invoking a maximal value for the NMSSM trilinear coupling and without severe restrictions on the value of tan β.     

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.     

Infrared quasifixed solutions in a nonminimal supersymmetric standard model

The constraints from LEPII on the mass of the lightest Higgs boson are such that, in the parameter space of the minimal supersymmetric standard model (MSSM), a considerable part of the region that corresponds to the scenario of an infrared fixed point is virtually ruled out by available experimental data. In a nonminimal supersymmetric standard model (NMSSM), the mass of the lightest Higgs boson takes its maximum value in the regime of strong Yukawa coupling, in which case the Yukawa coupling constants are much greater than the gauge coupling constants at the Grand Unification scale $(Y_i (0) \gg \tilde \alpha _i (0))$ . In this limiting case, solutions to the renormalization-group equations are attracted to Hill and infrared fixed lines or surfaces in the space of Yukawa coupling constants; for Y _i (0) → ∞, they are concentrated in the vicinities of quasifixed points. However, this attraction is quite weak. For this reason, solutions to the renormalization-group equations are grouped near some line on the Hill surface when all Y _i (0) are close to unity. Approximate solutions for the Yukawa coupling constants within the NMSSM are presented. In addition, the possibility of unifying the Yukawa coupling constants for the b quark and the τ lepton at the scale M _X is discussed.     

Non-anomalous discrete R-symmetry, extra matters, and enhancement of the lightest SUSY Higgs mass

We consider low-energy supersymmetric model with non-anomalous discrete R-symmetry. To make the R-symmetry non-anomalous, we add new particles to the particle content of the minimal supersymmetric standard model (MSSM). Those new particles may couple to the Higgs boson, resulting in a significant enhancement of the lightest Higgs mass. We show that, in such a model, the lightest Higgs mass can be much larger than the MSSM upper bound; the lightest Higgs mass as large as 140 GeV (or larger) becomes possible.     

Triviality bound on lightest Higgs mass in next to minimal supersymmetric model

We study the implication of triviality on Higgs sector in next to minimal supersymmetric model (NMSSM) using variational field theory. It is shown that the mass of the lightest Higgs boson in NMSSM has an upper bound ∼10M _W which is of the same order as that in the standard model.     

Particle mass limits in minimal and nonminimal supersymmetric models

A review of the Higgs and neutralino sector of supersymmetric models is presented. This includes the upper limit on the mass of the lightest Higgs boson in the minimal supersymmetric standard model, as well as models based on the standard model gauge groupSU(2) _L xU(l) _Y with extended Higgs sectors. We then discuss the Higgs sector of left-right supersymmetric models, which conserveR-parity as a consequence of gauge invariance, and present a calculable upper bound on the mass of the lightest Higgs boson in these models. We also discuss the neutralino sector of general supersymmetric models based on the SM gauge group. We show that, as a consequence of gauge coupling unification, an upper bound on the mass of the lightest neutralino as a function of the gluino mass can be obtained.     

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.     

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.     

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.     

Solving the little hierarchy problem with a light singlet and supersymmetric mass terms

A generalization of the Next-to-Minimal Supersymmetric Model (NMSSM) is studied in which an explicit μ-term as well as a small supersymmetric mass term for the singlet superfield are incorporated. We study the possibility of raising the Standard Model-like Higgs mass at tree level through its mixing with a light, mostly-singlet, CP-even scalar. We are able to generate Higgs boson masses up to 145 GeV with top squarks below 1.1 TeV and without the need to fine tune parameters in the scalar potential. This model yields light singlet-like scalars and pseudoscalars passing all collider constraints.     

Di-photon Higgs signals at the LHC in the next-to-minimal supersymmetric standard model

The NMSSM contains a Higgs singlet in addition to the two Higgs doublets typical of the MSSM, thus resulting in a total of seven physical Higgs mass states. Therefore, the phenomenology of the NMSSM Higgs sector can differ considerably from that of the MSSM, and there are good prospects of finding in regions of the NMSSM parameter space Higgs signals that cannot be reproduced in the MSSM. We examined here the two-photon decay mode of a Higgs boson and found that up to three neutral Higgs states, heavy and/or light, could be simultaneously observable at the LHC, a possibility precluded to the MSSM. There are also some possibilities that only the lightest NMSSM Higgs boson be detectable via this mode, with a mass beyond the upper limit of the corresponding MSSM state, thus also allowing one to distinguish between the two scenarios. However, in most of the NMSSM parameter space the configurations of the non-minimal model are not very different from those arising in the minimal case.     

Confronting the MSSM and the NMSSM with the discovery of a signal in the two photon channel at the LHC

We confront the discovery of a boson decaying into two photons, as reported recently by ATLAS and CMS, with the corresponding predictions in the Minimal Supersymmetric Standard Model (MSSM) and the Next-to-Minimal Supersymmetric Standard Model (NMSSM). We perform a scan over the relevant regions of parameter space in both models and evaluate the MSSM and NMSSM predictions for the dominant Higgs production channel and the photon–photon decay channel. Taking into account the experimental constraints from previous direct searches, flavor physics, electroweak measurements as well as theoretical considerations, we find that a Higgs signal in the two photon channel with a rate equal to, or above, the SM prediction is viable over the full mass range 123?M _H ?127 GeV, both in the MSSM and the NMSSM. We find that besides the interpretation of a possible signal at about 125 GeV in terms of the lightest $\mathcal {CP}$ -even Higgs boson, both the MSSM and the NMSSM permit also a viable interpretation where an observed state at about 125 GeV would correspond to the second-lightest $\mathcal {CP}$ -even Higgs boson in the spectrum, which would be accompanied by another light Higgs with suppressed couplings to W and Z bosons. We find that a significant enhancement of the γγ rate, compatible with the signal strengths observed by ATLAS and CMS, is possible in both the MSSM and the NMSSM, and we analyse in detail different mechanisms in the two models that can give rise to such an enhancement. We briefly discuss also our predictions in the two models for the production and subsequent decay into two photons of a $\mathcal {CP}$ -odd Higgs boson.     

Effective two Higgs doublets in nonminimal supersymmetric models

The Higgs sectors of supersymmetric extensions of the Standard Model have two doublets in the minimal version (MSSM), and two doublets plus a singlet in two others: with (UMSSM) and without (NMSSM) an extra U(1)′. A very concise comparison of these three models is possible if we assume that the singlet has a somewhat larger breaking scale compared to the electroweak scale. In that case, the UMSSM and the NMSSM become effectively two-Higgs-doublet models (THDM), like the MSSM. In this approach the well-known upper mass bounds on the lightest CP-even neutral Higgs boson can be derived in a very simple and transparent way.     

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.     

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).     

The Higgs boson: shall we see it soon or is it still far away?

The status of the Higgs boson mass in the Standard Model and its supersymmetric extensions is reviewed and the perspectives of Higgs searches are discussed. The parameter space of the Minimal Supersymmetric Standard Model (MSSM) is analysed with the emphasis on the lightest Higgs mass. The infrared behaviour of renormalization group equations for the parameters of MSSM is examined and infrared quasi-fixed points are used for the Higgs mass predictions. They strongly suggest the Higgs mass to be lighter than 100 or 130 GeV for low and high tan β scenarios, respectively. Extended models, however, allow one to increase these limits for low tan β up to 50%.     

Ba（d）^o-Ba（d）^o Mixing and New Physics Effects in a Top Quark Two-Higgs Doublet Model

We calculate the new physics contributions to the neutral Bd^o and Ba^o meson mass splitting △Md and △Ma induced by the box diagrams involving the charged-Higgs bosons in the top quark two-Higgs doublet model （T2HDM）. Using the precision data, we obtain the bounds on the parameter space of the T2HDM： （a） For fixed MH = 400 GeV and 5= [0°, 60°], the upper bound on tan β is tan β≤ 30 after the inclusion of major theoretical uncertainties; （b） For the case of tan β≤ 20, a light charged Higgs boson with a mass around 300 GeV is allowed; and （c） The bounds on tan β and MH are strongly correlated： a smaller （larger） tan β means a lighter （heavier） charged Higgs boson.     

Production and decay of neutralinos in the Next-to-Minimal Supersymmetric Standard Model

Within the framework of the Next-to-Minimal Supersymmetric Standard Model (NMSSM) we study neutralino production (i,j=1, …, 5) at center-of-mass energies between 100 and 600 GeV and the decays of the heavier neutralinos into the LSP plus a fermion pair, a photon or a Higgs boson. For representative gaugino/higgsino mixing scenarios, where the light neutralinos have significant singlet components, we find some striking differences between the NMSSM and the minimal supersymmetric model. Since in the NMSSM neutralino and Higgs sector are strongly correlated, the decay of the second lightest neutralino into a Higgs boson and the LSP often is kinematically possible and even dominant in a large parameter region of typical NMSSM scenarios. Also, the decay rates into final states with a photon may be enhanced.     

Rare decays B_(s,d)~O→e~+e~- in a top quark two-Higgs-doublet model

In the framework of T2HDM, we calculated the new physics contributions involving neutral Higgs bosons to the branching ratios of B_(s,d)~0→e~+e~-(e=e,μ) decays. Comparing the theoretical predictions with the experimental upper-limits, we found that (a) The data of Br(B_d~0→e~+e~-)give the upper bound on tanβ: tanβ≤ 22, while Br(B_s~0→e~+e~-)give tanβ≤12 for fixed δ = 0°, m_H+=350 GeV, m_Ho = 160 GeV, m_Ho= 115 GeV and m_Ao=120 GeV; (b) A light neutral Higgs boson mass m_Ho (m_Ao) less than 50 GeV (120 GeV) is excluded by the data of branching ratios for B_(s,d)~0→e~+e~-(e=μ) decays with tanβ=10; (c) The bounds on m_(h~0) and tanβ, or m_(A~0) and tanβ are strongly correlated: a smaller (larger) tanβ means a lighter (heavier) neutral Higgs boson.