Lightest Higgs Boson Mass Research Articles

Implications of initial LHC searches for supersymmetry

The CMS and ATLAS Collaborations have recently published the results of initial direct LHC searches for supersymmetry analyzing ∼35/pb of data taken at 7 TeV in the centre of mass. We incorporate these results into a frequentist analysis of the probable ranges of parameters of simple versions of the minimal supersymmetric extension of the Standard Model (MSSM), namely the constrained MSSM (CMSSM), a model with common non-universal Higgs masses (NUHM1), the very constrained MSSM (VCMSSM) and minimal supergravity (mSUGRA). We present updated predictions for the gluino mass, \(m_{\tilde{g}}\), the light-Higgs boson mass, M h , BR(B s →μ + μ −) and the spin-independent dark matter scattering cross section, \(\sigma^{\mathrm{SI}}_{p}\). The CMS and ATLAS data make inroads into the CMSSM, NUHM1 and VCMSSM (but not mSUGRA) parameter spaces, thereby strengthening previous lower limits on sparticle masses and upper limits on \(\sigma^{\mathrm{SI}}_{p}\) in the CMSSM and VCMSSM. The favoured ranges of BR(B s →μ + μ −) in the CMSSM, VCMSSM and mSUGRA are close to the Standard Model, but considerably larger values of BR(B s →μ + μ −) are possible in the NUHM1. Applying the CMS and ATLAS constraints improves the consistency of the model predictions for M h with the LEP exclusion limits.

Frequentist analysis of the parameter space of minimal supergravity

We make a frequentist analysis of the parameter space of minimal supergravity (mSUGRA), in which, as well as the gaugino and scalar soft supersymmetry-breaking parameters being universal, there is a specific relation between the trilinear, bilinear and scalar supersymmetry-breaking parameters, A_0 = B_0 + m_0, and the gravitino mass is fixed by m_{3/2} = m_0. We also consider a more general model, in which the gravitino mass constraint is relaxed (the VCMSSM). We combine in the global likelihood function the experimental constraints from low-energy electroweak precision data, the anomalous magnetic moment of the muon, the lightest Higgs boson mass M_h, B physics and the astrophysical cold dark matter density, assuming that the lightest supersymmetric particle (LSP) is a neutralino. In the VCMSSM, we find a preference for values of m_{1/2} and m_0 similar to those found previously in frequentist analyses of the constrained MSSM (CMSSM) and a model with common non-universal Higgs masses (NUHM1). On the other hand, in mSUGRA we find two preferred regions: one with larger values of both m_{1/2} and m_0 than in the VCMSSM, and one with large m_0 but small m_{1/2}. We compare the probabilities of the frequentist fits in mSUGRA, the VCMSSM, the CMSSM and the NUHM1: the probability that mSUGRA is consistent with the present data is significantly less than in the other models. We also discuss the mSUGRA and VCMSSM predictions for sparticle masses and other observables, identifying potential signatures at the LHC and elsewhere.

CDMS II result and light Higgs boson scenario of the MSSM

The CDMS Collaboration has reported two candidate events for dark matter. If the events are due to the elastic scattering of dark matter, the dark matter would be a WIMP dark matter with its mass of the order of 10-100GeV and its scattering cross section with a nucleon is about 10−44-10−43 cm2. We show that such a dark matter is properly realized as a neutralino dark matter in the light higgs boson scenario of the MSSM. The lightest higgs boson mass can be lighter than 114.4GeV in the scenario because of a suppressed interaction between higgs boson and Z bosons. As a result, a large scattering cross section between the dark matter and ordinary matter is obtained.

Radiative electroweak symmetry breaking in a Little Higgs model

We present a new Little Higgs model, motivated by the deconstruction of a five-dimensional gauge-Higgs model. The approximate global symmetry is SO(5)0 × SO(5)1, breaking to SO(5), with a gauged subgroup of [SU(2)0L × U(1)0R ] × O(4)1, breaking to SU(2) L ×U(1) Y . Radiative corrections produce an additional small vacuum misalignment, breaking the electroweak symmetry down to U(1)EM. Novel features of this model are: the only un-eaten pseudo-Goldstone boson in the effective theory is the Higgs boson; the model contains a custodial symmetry, which ensures that \( \widehat{T} = 0 \) at tree-level; and the potential for the Higgs boson is generated entirely through one-loop radiative corrections. A small negative mass-squared in the Higgs potential is obtained by a cancellation between the contribution of two heavy partners of the top quark, which is readily achieved over much of the parameter space. We can then obtain both a vacuum expectation value of v = 246 GeV and a light Higgs boson mass, which is strongly correlated with the masses of the two heavy top quark partners. For a scale of the global symmetry breaking of f = 1 TeV and using a single cutoff for the fermion loops, the Higgs boson mass satisfies 120 GeV ≲ M H ≲ 150 GeV over much of the range of parameter space. For f raised to 10 TeV, these values increase by about 40 GeV. Effects at the ultraviolet cutoff scale may also raise the predicted values of the Higgs boson mass, but the model still favors M H ≲ 200GeV.

Next generation Higgs bosons: Theory, constraints, and discovery prospects at the Large Hadron Collider

Particle physics model building within the context of string theory suggests that further copies of the Higgs boson sector may be expected. Concerns regarding tree-level flavor-changing neutral currents are easiest to allay if little or no couplings of next generation Higgs bosons to standard model fermions are allowed. We detail the resulting general Higgs potential and mass spectroscopy in both a standard model extension and a supersymmetric extension. We present the important experimental constraints from meson-meson mixing, loop-induced $b\ensuremath{\rightarrow}s\ensuremath{\gamma}$ decays, and LEP2 direct production limits. We investigate the energy range of the valid perturbation theory of these ideas. In the supersymmetric context we present a class of examples that marginally aids the fine-tuning problem for parameter space where the lightest Higgs boson mass is greater than the standard model limit of 114 GeV. Finally, we study collider physics signatures generic to next generation Higgs bosons, with special emphasis on $Ah\ensuremath{\rightarrow}hhZ\ensuremath{\rightarrow}4b+2l$ signal events, and describe the capability of discovery at the Large Hadron Collider.

ON THE ORIGIN OF APPROXIMATE CUSTODIAL SYMMETRY IN THE TWO-HIGGS DOUBLET MODEL

We argue that the consistent implementation of the multiple point principle (MPP) in the general nonsupersymmetric two-Higgs doublet model (2HDM) can lead to a set of approximate global custodial symmetries that ensure CP conservation in the Higgs sector and the absence of flavor changing neutral currents (FCNC) in the considered model. In particular, the existence of a large set of degenerate vacua at some high energy scale Λ caused by the MPP can result in approximate U(1) and Z2 symmetries that suppress FCNC and CP-violating interactions in the 2HDM. We explore the renormalization group (RG) flow of the Yukawa and Higgs couplings within the MPP inspired 2HDM with approximate custodial symmetries and show that the solutions to the RG equations are focused near quasifixed points at low energies if the MPP scale Λ is relatively high. We study the Higgs spectrum and couplings near the quasifixed point at moderate values of tan β and compute a theoretical upper bound on the lightest Higgs boson mass. If Λ ≳ 1010 GeV the lightest CP-even Higgs boson is always lighter than 125 GeV. When the MPP scale is low, the mass of the lightest Higgs particle can reach 180–220 GeV while its coupling to the top quark can be significantly larger than in the SM, resulting in the enhanced production of Higgs bosons at the LHC. Other possible scenarios that appear as a result of the implementation of the MPP in the 2HDM are also discussed.

The lightest Higgs boson mass in effective field theory with bulk and brane supersymmetry breaking

We study the mass of the lightest Higgs boson in an effective Kaluza–Klein theory with two sources of supersymmetry breaking. When stop mass matrices are non-diagonal with respect to Kaluza–Klein modes and each element is not small in unit of the inverse compactification radius, a very small eigenvalue can be accommodated in the diagonalized basis. We show that in the model with the two sources, the Higgs boson mass can receive suitable corrections for various compactification radii.

High precision calculations within the MSSM

In this talk we report on two recent high precision calculations within the minimal supersymmetric extension of the Standard Model. In the first part of the talk we present the computation of the light CP-even Higgs boson mass with three-loop accuracy, taking into account the next-to-next-to-leading order effects from supersymmetric Quantum Chromodynamics. Furthermore, we discuss a consistent evolution of the strong coupling constant α s from M Z to the GUT scale, involving three-loop running and two-loop decoupling. For both observables the numerical results amount to corrections of the same order as the current experimental accuracy or that expected at the CERN Large Hadron Collider (LHC).

Confronting finite unified theories with low-energy phenomenology

Finite Unified Theories (FUTs) are N=1 supersymmetric Grand Unified Theories that can be made all-loop finite. The requirement of all-loop finiteness leads to a severe reduction of the free parameters of the theory and, in turn, to a large number of predictions. FUTs are investigated in the context of low-energy phenomenology observables. We present a detailed scanning of the all-loop finite SU(5) FUTs, where we include the theoretical uncertainties at the unification scale and we apply several phenomenological constraints. Taking into account the restrictions from the top and bottom quark masses, we can discriminate between different models. Including further low-energy constraints such as B physics observables, the bound on the lightest Higgs boson mass and the cold dark matter density, we determine the predictions of the allowed parameter space for the Higgs boson sector and the supersymmetric particle spectrum of the selected model.

Trilinear Higgs couplings in the two Higgs doublet model withCPviolation

We carry out a detailed analysis of the general two Higgs doublet model with CP violation. We describe two different parametrizations of this model, and then study the Higgs boson masses and the trilinear Higgs couplings for these two parametrizations. Within a rather general model, we find that the trilinear Higgs couplings have a significant dependence on the details of the model, even when the lightest Higgs boson mass is taken to be a fixed parameter. We include radiative corrections in the one-loop effective potential approximation in our analysis of the Higgs boson masses and the Higgs trilinear couplings. The one-loop corrections to the trilinear couplings of the two Higgs doublet model also depend significantly on the details of the model, and can be rather large. We study quantitatively the trilinear Higgs couplings, and show that these couplings are typically several times larger than the corresponding standard model trilinear Higgs coupling in some regions of the parameter space. We also briefly discuss the decoupling limit of the two Higgs doublet model.

Neutralino dark matter in light Higgs boson scenario

Phenomenology of neutralino dark matter in the minimal supersymmetric model is discussed for a scenario where the lightest Higgs boson mass is lighter than 114.4 GeV. We show that the scenario is consistent not only with many collider experiments but also with the observed relic abundance of dark matter. The allowed region may be probed by experiments of Bs→μ+μ− in near future. The scenario predicts a large scattering cross section between the dark matter and ordinary matter and thus it may be tested in present direct detection experiments of dark matter.

Fixed point scenario in the two Higgs doublet model inspired by degenerate vacua

We consider the renormalisation group flow of Higgs and Yukawa couplings within the simplest non-supersymmetric two Higgs doublet extension of the Standard Model (SM). In this model the couplings are adjusted so that the multiple point principle (MPP) assumption, which implies the existence of a large set of degenerate vacua at some high energy scale Λ, is realised. When the top quark Yukawa coupling at the scale Λ is large, the solutions of RG equations in this MPP inspired 2 Higgs Doublet Model (2HDM) converge to quasi-fixed points. We analyse the Higgs spectrum and couplings in the quasi-fixed point scenario and compute a theoretical upper bound on the lightest Higgs boson mass. When the scale Λ is low, the coupling of the SM-like Higgs scalar to the top quark can be significantly larger in the considered model than in the SM, resulting in the enhanced production of Higgs bosons at the LHC.

Supersymmetric unparticle effects on Higgs boson mass and dark matter

We propose a model that introduces a supersymmetric unparticle operator in the minimal supersymmetric Standard Model. We analyze the lowest dimension operator involving an unparticle. This operator behaves as a Standard Model gauge singlet and it introduces a new parameter into the Higgs potential which can provide an alternative way to relax the upper limit on the lightest Higgs boson mass. This operator also introduces several unparticle interactions which can induce a neutral Higgsino to decay into a spinor unparticle. It also induces violation of scale invariance around the electroweak scale. It is necessary for the scale of this violation to be larger than the lightest supersymmetric particle mass to maintain the latter as the usual weakly interacting massive particle dark matter candidate. An alternative is to have unparticle state as dark matter candidate. We also comment on some collider implications.

A solution to the supersymmetric fine-tuning problem within the MSSM

Weak scale supersymmetry has a generic problem of fine-tuning in reproducing the correct scale for electroweak symmetry breaking. The problem is particularly severe in the minimal supersymmetric extension of the Standard Model (MSSM). We present a solution to this problem that does not require an extension of the MSSM at the weak scale. Superparticle masses are generated by a comparable mixture of moduli and anomaly mediated contributions, and the messenger scale of supersymmetry breaking is effectively lowered to the TeV region. Crucial elements for the solution are a large A term for the top squarks and a small B term for the Higgs doublets. Requiring no fine-tuning worse than 20%, we obtain rather sharp predictions on the spectrum. The gaugino masses are almost universal at the weak scale with the mass between 450 and 900 GeV. The squark and slepton masses are also nearly universal at the weak scale with the mass a factor of 2 smaller than that of the gauginos. The only exception is the top squarks whose masses split from the other squark masses by about m t / 2 . The lightest Higgs boson mass is smaller than 120 GeV, while the ratio of the vacuum expectation values for the two Higgs doublets, tan β , is larger than about 5. The lightest superparticle is the neutral Higgsino of the mass below 190 GeV, which can be dark matter of the universe. The mass of the lighter top squark can be smaller than 300 GeV, which may be relevant for Run II at the Tevatron.

Probing the light neutral Higgs boson scenario of the CP-violating MSSM Higgs sector at the LHC

In the CP-violating Minimal Supersymmetric Standard Model (MSSM), for certain values of the CP-violating phases associated to the universal trilinear couplings $(A_t, A_b)$ and the gluino mass $(M_{\tilde g})$, e.g., $\Phi_{\rm{CP}} = 60^\circ$ or $90^\circ$, for $M_{H^+} \lsim 140 $ GeV and $\tan \beta \sim 2-5 $, the lightest Higgs boson mass ($M_{H_1}$) is $\lsim 50 $ GeV. This mass interval is still allowed from standard LEP Higgs searches because of a strongly suppressed $H_1ZZ$ coupling. However, in the same region of parameter space in which these two conditions occur, the $H_1 H^\mp W^\pm $ coupling is enhanced because the two mentioned sets of couplings satisfy a sum rule. In this paper we probe such a light Higgs scenario at the Large Hadron Collider (LHC) by studying $H^\pm H_1$ associate production, leading to a $4b + \ell^\pm + \mET $ signal. We show that the latter is readily accessible at the CERN hadron collider, upon the application of suitable selection cuts against the Standard Model (SM) backgrounds. Our parton level Monte Carlo (MC) analysis yields $\sim 15-45 $ signal events, completely free of SM background, for ${\cal L} = 10-30 {\rm fb}^{-1}$ of accumulated luminosity, after taking into account the overall efficiency for tagging four $b$-jets.

Relaxing the upper bound on the mass of the lightest supersymmetric Higgs boson

We present a class of supersymmetric models in which the lightest Higgs boson mass can be as large as a few hundred GeV ($200\ensuremath{\sim}300\text{ }\text{ }\mathrm{G}\mathrm{e}\mathrm{V}$) while the successful minimal supersymmetric standard model prediction for gauge coupling unification is preserved. The theories are formulated on a 5D warped space truncated by two branes, and a part of the Higgs sector is localized on the infrared brane. The structure of the Higgs sector in the four-dimensional effective theory below the Kaluza-Klein mass scale is essentially that of the next-to-minimal supersymmetric standard model, or related theories. However, large values of the next-to-minimal supersymmetric standard model couplings at the weak scale are now possible as these couplings are required to be perturbative only up to the infrared cutoff scale, which in general can be much lower than the unification scale. This allows the possibility of generating a large quartic coupling in the Higgs potential thereby significantly raising the Higgs boson mass bound. We present two particularly simple models. In the first model, the quark and lepton fields are localized on the ultraviolet brane, where the grand unified symmetry is broken. In the second model, the quark and lepton fields are localized on the infrared brane, and the unified symmetry is broken both on the ultraviolet and infrared branes. Our theories potentially allow the possibility of a significant reduction in the fine-tuning needed for correct electroweak symmetry breaking, although this is somewhat model dependent.

Dark matter, light top squarks, and electroweak baryogenesis

We examine the neutralino relic density in the presence of a light top squark, such as the one required for the realization of the electroweak baryogenesis mechanism, within the minimal supersymmetric standard model. We show that there are three clearly distinguishable regions of parameter space, where the relic density is consistent with WMAP and other cosmological data. These regions are characterized by annihilation cross sections mediated by either light Higgs bosons, Z bosons, or by the co-annihilation with the lightest top squark. Tevatron collider experiments can test the presence of the light top squark in most of the parameter space. In the co-annihilation region, however, the mass difference between the light top squark and the lightest neutralino varies between 15 and 30 GeV, presenting an interesting challenge for top squark searches at hadron colliders. We present the prospects for direct detection of dark matter, which provides a complementary way of testing this scenario. We also derive the required structure of the high energy soft supersymmetry breaking mass parameters where the neutralino is a dark matter candidate and the top squark spectrum is consistent with electroweak baryogenesis and the present bounds on the lightest Higgs boson mass.

Minimal supersymmetric fat Higgs model

We present a calculable supersymmetric theory of a composite ``fat'' Higgs boson. Electroweak symmetry is broken dynamically through a new gauge interaction that becomes strong at an intermediate scale. The Higgs boson mass can easily be 200--450 GeV along with the superpartner masses, solving the supersymmetric little hierarchy problem. We explicitly verify that the model is consistent with precision electroweak data without fine-tuning. Gauge coupling unification can be maintained despite the inherently strong dynamics involved in electroweak symmetry breaking. Supersymmetrizing the standard model therefore does not imply a light Higgs boson mass, contrary to the lore in the literature. The Higgs sector of the minimal fat Higgs model has a mass spectrum that is distinctly different from that of the minimal supersymmetric standard model.

On the two-loop Yukawa corrections to the MSSM Higgs boson masses at large tan β

We complete the effective potential calculation of the two-loop, top/bottom Yukawa corrections to the Higgs boson masses in the minimal supersymmetric standard model, by computing the O(α t 2+α tα b+α b 2) contributions for arbitrary values of the bottom Yukawa coupling. We also compute the corrections to the minimization conditions of the effective potential at the same perturbative order. Our results extend the existing O(α t 2) calculation, and are relevant in regions of the parameter space corresponding to tan β⪢1. We extend to the Yukawa corrections a convenient renormalization scheme, previously proposed for the O(α bα s) corrections, that avoids unphysically large threshold effects associated with the bottom mass and absorbs the bulk of the corrections into the one-loop expression. For large values of tan β, the new contributions can account for a variation of several GeV in the lightest Higgs boson mass.

Supersymmetric grand unification with a fourth generation?

The possibility of incorporating a chiral fourth generation into a SUSY-GUT is investigated. Precision fits to electroweak observables require us to introduce light supersymmetric particles, with masses less than MZ. These particles might also provide decay channels for the fourth generation quarks of mass ∼ 100 GeV. We also require tanβ to lie in the range 1.50 ≲tanβ≲ 1.75 and obtain an upper limit on the lightest Higgs boson mass in the MSSM4 of 152 GeV.