Lightest Higgs Mass Research Articles

Higgs bosons in the Next-to-Minimal Supersymmetric Standard Model at the LHC

We review possible properties of Higgs bosons in the NMSSM, which allow to discriminate this model from the MSSM: masses of mostly Standard-Model-like Higgs bosons at or above 140 GeV, or enhanced branching fractions into two photons, or Higgs-to-Higgs decays. In the case of a Standard-Model-like Higgs boson above 140 GeV, it is necessarily accompagnied by a lighter state with a large gauge singlet component. Examples for such scenarios are presented. Available studies on Higgs-to-Higgs decays are discussed according to the various Higgs production modes, light Higgs masses and decay channels.

AnomalousB-meson mixing and baryogenesis

There exist experimental hints from the B sector for CP violation beyond the Standard Model (SM) CKM paradigm. An anomalous dimuon asymmetry was reported by the D0 collaboration, while tension exists between $B \to \tau \nu$ and $S_{\psi K}$. These measurements, disfavoring the SM at the ~3$\sigma$ level, can be explained by new physics in both $B_d$-$\bar{B}_d$ and $B_s$- $\bar{B}_s$ mixing, arising from (1) new bosonic degrees of freedom at or near the electroweak scale, and (2) new, large CP-violating phases. These two new physics ingredients are precisely what is required for electroweak baryogenesis to work in an extension of the SM. We show that a simple two Higgs doublet model with top-charm flavor violation can explain the B anomalies and the baryon asymmetry of the Universe. Moreover, the presence of a large relative phase in the top-charm Yukawa coupling, favored by $B_{d,s}$-$\bar{B}_{d,s}$ mixing, weakens constraints from $\epsilon_K$ and $b \to s \gamma$, allowing for a light charged Higgs mass of O(100 GeV).

Light neutralino dark matter with a very light Higgs boson for CoGeNT and DAMA/LIBRA data

Recently, the CoGeNT collaboration reported weakly interacting massive particle candidate-signal events exceeding the known backgrounds where the light WIMP with large cross section is supported. Motivated by this issue, we analyze a light neutralino dark matter scenario with a very light $CP$-even Higgs mediation in the elastic scattering process, which provides the mass and direct detection cross section to explain the CoGeNT result. To be compatible with the result of LEP experiments, the light $CP$-even Higgs is favored to be at around 9--10 GeV. Such a scenario can be realized in the ``beyond the minimal supersymmetric standard model'' context. The relic abundance consistent with the WMAP result can be obtained when twice neutralino mass is close to the light Higgs mass via the resonance enhancement of the annihilation cross section. As a result, the neutralino mass is predicted to be at around 5--6 GeV.

Light Higgs boson scenario in the supersymmetric seesaw model

It is demonstrated that the light Higgs boson scenario, in which the lightest Higgs mass is less than the LEP bound, ${m}_{h}>114.4\text{ }\text{ }\mathrm{GeV}$, is consistent with the supersymmetric seesaw model. With the assumptions of the universal right-handed neutrino mass and the hierarchical mass spectrum of the ordinary neutrinos, the bounds for the right-handed neutrino mass are investigated in terms of lepton flavor violating charged lepton decays. We also discuss the effect of the modification of renormalization group equations by the right-handed neutrinos on the $b\ensuremath{\rightarrow}s\ensuremath{\gamma}$ process and the relic abundance of dark matter in the light Higgs boson scenario.

Higgs phenomenology of scalar sequestering

The light Higgs mass in the MSSM is highly constrained and is predicted to be close to M_Z which causes a tension between the LEP II Higgs mass bound 114 GeV and the natural electroweak symmetry breaking in the MSSM. The usual way to increase the light CP even Higgs mass was to increase the quartic coupling of the up type Higgs. We point out that the light Higgs mass can be increased by reducing the off-diagonal term in the mass matrix when tan beta is moderate, which is about 5 to 10. As a result no mixing and/or a Higgs mixing angle of the opposite sign arises and the branching ratio of Higgs decay is drastically changed. This is possible in scalar sequestering scenario in which mu parameter can be large independently of the electroweak symmetry breaking. We also discuss the same effect in the BMSSM.

Light Higgs mass bound in supersymmetric left-right models

We show that in supersymmetric left-right models (SUSYLR), the upper bound on the lightest neutral Higgs mass can be appreciably higher than that in the minimal supersymmetric standard model (MSSM). The exact magnitude of the bound depends on the scale of parity restoration and can be 10--20 GeV above the MSSM bound if the mass of the right-handed ${W}_{R}$ is in the TeV range. An important implication of our result is that since SUSYLR models provide a simple realization of the seesaw mechanism for neutrino masses, measurement of the Higgs boson mass could provide an independent probe of a low seesaw scale.

Two-Higgs models for large tan β and heavy second Higgs

We study two Higgs models for large $\tan\beta$ and relatively large second Higgs mass. In this limit the second heavy Higgs should have small vev and therefore couples only weakly to two gauge bosons. Furthermore, the couplings to down type quarks can be significantly modified (so long as the second Higgs is not overly heavy). Both these facts have significant implications for search strategies at the LHC and ILC. We show how an effective theory and explicit fundamental two Higgs model approach are related and consider the additional constraints in the presence of supersymmetry or $Z_2$ flavor symmetries. We argue that the best tests of the two Higgs doublet potential are likely to be measurements of the light Higgs branching fractions. We show how higher dimension operators that have recently been suggested to raise the light Higgs mass are probably best measured and distinguished in this way.

SO(10)SUSY GUT for fermion masses: Lepton flavor andCPviolation

We discuss the results of a global ${\ensuremath{\chi}}^{2}$ analysis of a simple $SO(10)$ supersymmetric grand unified theory (SUSY GUT) with ${D}_{3}$ family symmetry and low energy $R$ parity. The model describes fermion mass matrices with 14 parameters and gives excellent fits to 20 observable masses and mixing angles in both quark and lepton sectors, giving six predictions. Bi-large neutrino mixing is obtained with hierarchical quark and lepton Yukawa matrices, thus avoiding the possibility of large lepton flavor violation. The model naturally predicts small 1--3 neutrino mixing, with $\mathrm{sin}{\ensuremath{\theta}}_{13}\ensuremath{\simeq}0.05--0.06$. In this paper we evaluate the predictions for the lepton flavor violating processes, $\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}$, $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\gamma}$ and $\ensuremath{\tau}\ensuremath{\rightarrow}e\ensuremath{\gamma}$ and also the electric dipole moment of the electron (${d}_{e}$), the muon, and the tau, assuming universal squark and slepton masses (${m}_{16}$) and a universal soft SUSY breaking $A$ parameter (${A}_{0}$) at the GUT scale. We find $\mathrm{Br}(\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma})$ is naturally below present bounds, but may be observable by MEG. Similarly, ${d}_{e}$ is below present bounds, but it is within the range of future experiments. We also give predictions for the light Higgs mass (using FeynHiggs). We find an upper bound given by ${m}_{h}\ensuremath{\le}127\text{ }\text{ }\mathrm{GeV}$, with an estimated $\ifmmode\pm\else\textpm\fi{}3\text{ }\text{ }\mathrm{GeV}$ theoretical uncertainty. Finally we present predictions for SUSY particle masses in the favored region of parameter space.

A model of electroweak symmetry breaking from a fifth dimension

We reconsider the idea of identifying the Higgs field as the internal component of a gauge field in the flat space R4×S1/Z2, by relaxing the constraint of having unbroken SO(4,1) Lorentz symmetry in the bulk. In this way, we show that the main common problems of previous models of this sort, namely the prediction of a too light Higgs and top mass, as well as of a too low compactification scale, are all solved. We mainly focus our attention on a previously constructed model. We show how, with few minor modifications and by relaxing the requirement of SO(4,1) symmetry, a potentially realistic model can be obtained with a moderate tuning in the parameter space of the theory. In this model, the Higgs potential is stabilized and the hierarchy of fermion masses explained.

Dark matter andBs→μ+μ−with minimal SO10soft SUSY breaking II

We update and extend to larger masses our previous analysis of the MSSM with minimal $SO_{10}$ [MSO$_{10}$SM] soft SUSY breaking boundary conditions. We find a well--defined, narrow region of parameter space which provides the observed relic density of dark matter, in a domain selected to fit precision electroweak data, including top, bottom and tau masses. The model is highly constrained which allows us to make several predictions. We find the light Higgs mass $m_h \leq 121 \pm 3$ GeV and also upper bounds on the mass of the gluino $\mgluino\lsim3.1$ TeV and lightest neutralino $\mchi\lsim450$ GeV. As the CP odd Higgs mass $m_A$ increases, the region of parameter space consistent with WMAP data is forced to larger values of $M_{1/2}$ and smaller values of $m_h$. Hence, we find an upper bound $m_A \lsim 1.3$ TeV. This in turn leads to lower bounds on ${\rm BR}(B_s\to \mu^+ \mu^-) > 10^{-8}$ (assuming minimal flavor violation) and on the dark matter spin independent detection cross section $\sigsip > 10^{-9}$ pb. Finally, we extend our previous analysis to include WIMP signals in indirect detection and find prospects for WIMP detection generally much less promising than in direct WIMP searches.

The stau neutralino co-annihilation region at an International Linear Collider

We probe the stau neutralino co-annihilation domain of the parameter space allowed by the current experimental bounds on the light Higgs mass, the b→sγ decay, and the amount of neutralino cold dark matter within the framework of minimal SUGRA models at a 500 GeV e+e− linear collider. The most favorable signals of SUSY are stau pair production and neutralino pair production where the small mass difference between the lighter stau and the lightest neutralino in the co-annihilation region is ∼5–15 GeV and hence generates low-energy tau leptons in the final state. This small mass difference would be a striking signal of many SUGRA models. We find that a calorimeter covering down to 1° from the beams is crucial to reduce the two-photon background and the mass difference could be measured at a level of 10% with 500 fb−1 of data where an invariant mass of two-tau jets and missing energy is used as a discriminator.

Running into New Territory in SUSY Parameter Space

The LEP-II bound on the light Higgs mass rules out the vast majority of parameter space left to the Minimal Supersymmetric Standard Model (MSSM) with weak-scale soft-masses. This suggests the importance of exploring extensions of the MSSM with non-minimal Higgs physics. In this article, we explore a theory with an additional singlet superfield and an extended gauge sector. The theory has a number of novel features compared to both the MSSM and Next-to-MSSM, including easily realizing a light CP-even Higgs mass consistent with LEP-II limits, tan(beta) < 1, and a lightest Higgs which is charged. These features are achieved while remaining consistent with perturbative unification and without large stop-masses. Discovery modes at the Tevatron and LHC are discussed.

Full [formula omitted] electroweak and [formula omitted] corrections to [formula omitted

We present the full O(α) electroweak radiative corrections to associated Higgs top pair production in e+e− collisions. We combine these results with a new calculation of the full one-loop QCD corrections. The computation is performed with the help of GRACE-loop. We find that the O(α) correction can be larger than the O(αs) corrections around the peak of the cross section especially for a light Higgs mass. At threshold these corrections are swamped by the QCD corrections which are enhanced by the gluon Coulomb contribution. We have also subtracted the complete QED corrections and expressed the genuine weak correction both in the α-scheme and the Gμ-scheme. This reveals that the genuine weak corrections are not negligible and should be taken into account for a precision measurement of this cross section and the extraction of the Yukawa tt̄H coupling.

A simulation of gauge mediated supersymmetry breaking with a supersymmetric tau as the next-to-lightest supersymmetric particle in the ATLAS detector at the large hadron collide

The feasibility for mass measurements of supersymmetric particles from minimal gauge mediated models in the ATLAS detector at the large hadron collider is studied using parameterized simulations. The covered models are characterized by having the supersymmetric tau as the only next-to-lightest supersymmetric particle (NLSP). Given independent measurements of the lightest Higgs mass and the NLSP lifetime, a sufficient number of supersymmetric particle mass measurements are performed such that all underlying model parameters are constrained.

The Minimal Supersymmetric Model without a μ term

We propose a supersymmetric extension of the standard model which is a realistic alternative to the MSSM, and which has several advantages. No ``mu'' supersymmetric Higgs/Higgsino mass parameter is needed for sufficiently heavy charginos. An approximate U(1) R symmetry naturally guarantees that tan beta is large, explaining the top/bottom quark mass hierarchy. This symmetry also suppresses supersymmetric contributions to anomalous magnetic moments, b to s gamma, and proton decay, and these processes place no lower bounds on superpartner masses, even at large tan beta. The soft supersymmetry breaking mass parameters can easily be obtained from either gauge or Planck scale mediation, without the usual mu problem. Unlike in the MSSM, there are significant upper bounds on the masses of superpartners, including an upper bound of 114 GeV on the mass of the lightest chargino. However the MSSM bound on the lightest Higgs mass does not apply.

Effects of largeCP-violating soft phases on supersymmetric electroweak baryogenesis

We revisit the results of recent electroweak baryogenesis calculations and include all allowed large CP-violating supersymmetric phases. If the phases are large, the resulting baryon asymmetry can be considerably larger than the observed value $n_B/s \sim 4 \times 10^{-11}$. Much of the asymmetry must therefore be washed out, and we argue that the upper bound on the light Higgs mass is larger than the value reported in previous work.

The lightest Higgs mass in supersymmetric models with extra dimensions

In the four-dimensional supersymmetric standard model extended with gauge singlets the lightest Higgs boson mass, M H , has an important contribution proportional to the squared of the superpotential coupling λ of singlets to Higgs fields, λ SH 1·H 2 . The requirement of perturbativity up to the unification scale yields an upper bound on M H ∼140 GeV. In extensions to theories with (longitudinal) extra dimensions at the TeV where such coupling exists and massive Kaluza-Klein states fall into N=2 representations, if either of the Higgs or singlet fields live in the bulk of the extra dimensions, the β-function of λ is suppressed due to the absence of anomalous dimension of hypermultiplets to leading order. This implies a slower running of λ and an enhancement of its low energy value. The M H upper bound increases to values M H ≲165 GeV.

Longitudinal polarization in KL→ μ+μ− in MSSM with large tan β

A complete experiment on decay K L → l + l − will not only consist of measurement of the decay rates but also lepton polarization etc. These additional observations will yield tests of CP invariance in these decays. In K L and K S decays, the e mode is slower than the μ mode by roughly ( m e / m μ ) 2 [4]. As well discussed in literature [5]the Standard Model contribution to the lepton polarization is of order 2×∼10 −3. We show that in MSSM with large tan β and light higgs masses (∼2 M W ), the longitudinal lepton polarization in K L → μ + μ − can be enhanced to a higher value, of about 10 −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%.

Sphalerons withCP-violating Higgs potentials

We investigate the effect on the sphaleron in the two Higgs doublet electroweak theory of including CP violation in the Higgs potential. To have better control over the relation between the sphaleron energy and the physical quantities in the theory, we show how to parametrize the Higgs potential in terms of physical masses and mixing angles, one of which causes CP violation. By altering this CP violating angle (and keeping the other physical quantities fixed) the sphaleron energy increases by up to 10%. We also calculate the static minimum energy path between adjacent vacua as a function of Chern-Simons number, using the method of gradient flow. The only effect CP violation has on the barrier is the change in height. As a by-product of our work on parametrization of the potential, we demonstrate that CP violation in the Higgs sector favours nearly degenerate light Higgs masses.