Higgs Resonance Research Articles

Multipleb-jets reveal top superpartners and the 125 GeV Higgs

We demonstrate that in supersymmetry (SUSY) with relatively light top superpartners, h -> bb can be a very promising channel to discover the SM-like Higgs resonance at the Large Hadron Collider (LHC), although in general contexts it is thought to be challenging because of its huge QCD background. In this scenario, the SM-like Higgs boson is mainly produced via cascade decays initiated by pair-produced stop or sbottom squarks. The good sensitivity to h -> bb owes a great deal to the application of multiple (>= 4) b-jet tagging in removing the QCD background, and color-flow variables for reconstructing the Higgs resonance. We show in two benchmark points that a SM-like Higgs resonance can be discovered at the 14 TeV LHC (with a signal-to-background ratio as high as 0.35), with ~< 40/fb of data. Potentially, this strategy can be also applied to non-SUSY theories with cascade decays of top partners for the SM-like Higgs search, such as little Higgs, composite Higgs, and Randall-Sundrum models.

How to test for mass degenerate Higgs resonances

The Higgs-like signal observed at the LHC could be due to several mass degenerate resonances. We show that the number of resonances is related to the rank of a "production and decay" matrix, $R_{if}$. Each entry in this matrix contains the observed rate in a particular production mode $i$ and final state $f$. In the case of $N$ non-interfering resonances, the rank of $R$ is, at most, $N$. If interference plays a role, the maximum rank is $N^2$ or in the CP limit $N(N+1)/2$. As an illustration we use the present experimental data to constrain the rank of the corresponding matrix. We estimate the LHC reach of probing two and three resonances under various speculations on future measurements and uncertainties.

Curvaton decay by resonant production of the Standard Model higgs

We investigate in detail a model where the curvaton is coupled to the Standard Model higgs. Parametric resonance might be expected to cause a fast decay of the curvaton, so that it would not have time to build up the curvature perturbation. However, we show that this is not the case, and that the resonant decay of the curvaton may be delayed even down to electroweak symmetry breaking. This delay is due to the coupling of the higgs to the thermal background, which is formed by the Standard Model degrees of freedom created from the inflaton decay. We establish the occurrence of the delay by considering the curvaton evolution and the structure of the higgs resonances. We then provide analytical expressions for the delay time, and for the subsequent resonant production of the higgs, which ultimately leads to the curvaton effective decay width. Contrary to expectations, it is possible to obtain the observed curvature perturbation for values of the curvaton-higgs coupling as large as 10−1. Our calculations also apply in the general case of curvaton decay into any non Standard Model species coupled to the thermal background.

Composite scalar dark matter

Abstract We show that the dark matter (DM) could be a light composite scalar η, emerging from a TeV-scale strongly-coupled sector as a pseudo Nambu-Goldstone boson (pNGB). Such state arises naturally in scenarios where the Higgs is also a composite pNGB, as in O(6)/O(5) models, which are particularly predictive, since the low-energy interactions of η are determined by symmetry considerations. We identify the region of parameters where η has the required DM relic density, satisfying at the same time the constraints from Higgs searches at the LHC, as well as DM direct searches. Compositeness, in addition to justify the lightness of the scalars, can enhance the DM scattering rates and lead to an excellent discovery prospect for the near future. For a Higgs mass m h ≃ 125 GeV and a pNGB characteristic scale f ≲ 1 TeV, we find that the DM mass is either m η ≃ 50–70 GeV, with DM annihilations driven by the Higgs resonance, or in the range 100–500 GeV, where the DM derivative interaction with the Higgs becomes dominant. In the former case the invisible Higgs decay to two DM particles could weaken the LHC Higgs signal.

Bayesian implications of current LHC and XENON100 search limits for the CMSSM

The CMS Collaboration has released the results of its search for supersymmetry, by applying an ${\ensuremath{\alpha}}_{T}$ method to $1.1/\mathrm{fb}$ of data at 7 TeV. The null result excludes (at 95% C.L.) a low-mass region of the Constrained MSSM's parameter space that was previously favored by other experiments. Additionally, the negative result of the XENON100 dark matter search has excluded (at 90% C.L.) values of the spin-independent scattering cross sections ${\ensuremath{\sigma}}_{p}^{\mathrm{SI}}$ as low as ${10}^{\ensuremath{-}8}\text{ }\text{ }\mathrm{pb}$. We incorporate these improved experimental constraints into a global Bayesian fit of the Constrained MSSM by constructing approximate likelihood functions. In the case of the ${\ensuremath{\alpha}}_{T}$ limit, we simulate detector efficiency for the CMS ${\ensuremath{\alpha}}_{T}1.1/\mathrm{fb}$ analysis and validate our method against the official 95% C.L. contour. We identify the 68% and 95% credible posterior regions of the CMSSM parameters, and also find the best-fit point. We find that the credible regions change considerably once a likelihood from ${\ensuremath{\alpha}}_{T}$ is included, in particular, the narrow light Higgs resonance region becomes excluded, but the focus point/horizontal branch region remains allowed at the $1\ensuremath{\sigma}$ level. Adding the limit from XENON100 has a weaker additional effect, in part due to large uncertainties in evaluating ${\ensuremath{\sigma}}_{p}^{\mathrm{SI}}$, which we include in a conservative way, although we find that it reduces the posterior probability of the focus point region to the $2\ensuremath{\sigma}$ level. The new regions of high posterior favor squarks lighter than the gluino and all but one Higgs bosons heavy. The dark matter neutralino mass is found in the range $250\text{ }\text{ }\mathrm{GeV}\ensuremath{\lesssim}{m}_{\ensuremath{\chi}}\ensuremath{\lesssim}343\text{ }\text{ }\mathrm{GeV}$ (at $1\ensuremath{\sigma}$) while, as the result of improved limits from the LHC, the favored range of ${\ensuremath{\sigma}}_{p}^{\mathrm{SI}}$ is pushed down to values below ${10}^{\ensuremath{-}9}\text{ }\text{ }\mathrm{pb}$. We highlight tension between $\ensuremath{\delta}(g\ensuremath{-}2{)}_{\ensuremath{\mu}}^{\mathrm{SUSY}}$ and $\mathcal{B}\mathcal{R}(\overline{B}\ensuremath{\rightarrow}{X}_{s}\ensuremath{\gamma})$, which is exacerbated by including the ${\ensuremath{\alpha}}_{T}$ limit; each constraint favors a different region of the CMSSM's mass parameters.

FINITE-WIDTH EFFECTS IN THE NEAR-THRESHOLD ZZZ AND ZWW PRODUCTION AT ILC

We calculate the cross-section of the near-threshold off-shell ZZZ and ZW+W-production at the International Linear Collider taking into account their instability and the principal part of next-to-leading order corrections. The calculations are performed in the framework of the model of unstable particles with smeared mass-shell. We show that the contribution of the finite Z/W and H widths (their instability) is large in the Higgs resonance range (about -24% and -18% for ZZZ and ZW+W-, respectively, at [Formula: see text]) and should be taken into account in the Higgs boson studies at the future International Linear Collider.

Higgs portal dark matter in the minimal gaugedU(1)B−Lmodel

We propose a scenario of the right-handed neutrino dark matter in the context of the minimal gauged $U(1)_{B-L}$ model by introducing an additional parity which ensures the stability of dark matter particle. The annihilation of this right-handed neutrino takes place dominantly through the s-channel Higgs boson exchange, so that this model can be called Higgs portal dark matter model. We show that the thermal relic abundance of the right-handed neutrino dark matter with help of Higgs resonance can match the observed dark matter abundance. In addition we estimate the cross section with nucleon and show that the next generation direct dark matter search experiments can explore this model.

Invisible Higgs decays from Higgs-graviscalar mixing

We recompute the invisible Higgs decay width arising from Higgs-graviscalar mixing in the Arkani-Hamed, Dimopoulos, Dvali model, comparing the original derivation in the nondiagonal mass basis to that in a diagonal mass basis. The results obtained are identical (and differ by a factor of 2 from the original calculation) but the diagonal-basis derivation is pedagogically useful for clarifying the physics of the invisible width from mixing. We emphasize that both derivations make it clear that a direct scan in energy for a process such as $WW\ensuremath{\rightarrow}WW$ mediated by Higgs plus graviscalar intermediate resonances would follow a single Breit-Wigner form with total width given by ${\ensuremath{\Gamma}}^{\mathrm{tot}}={\ensuremath{\Gamma}}_{h}^{\mathrm{SM}}+{\ensuremath{\Gamma}}_{\mathrm{invisible}}$. We also compute the additional contributions to the invisible width due to direct Higgs to graviscalar-pair decays. We find that the invisible width due to the latter is relatively small, unless the Higgs mass is comparable to or larger than the effective extra-dimensional Planck mass.

Neutralino dark matter in BMSSM effective theory

We study thermal neutralino dark matter in an effective fieldtheory extension of the MSSM, called ``Beyond the MSSM'' (BMSSM) in Dine, Seiberg and Thomas (2007). In this classof effective field theories, the field content of the MSSM is unchanged, but the little hierarchy problem is alleviated by allowing smallcorrections to the Higgs/higgsino part of the Lagrangian. We perform parameter scans and compute the dark matter relic density. The light higgsino LSP scenario is modifiedthe most; we find new regions of parameter space compared to the standard MSSM. This involvesinteresting interplay between the WMAP dark matter boundsand the LEP chargino bound. We also find some changes for gaugino LSPs,partly due to annihilation through a Higgs resonance, and partlydue to coannihilation with light top squarks in models that are ruled inby the new effective terms.

Dark matter in CP-violating Supersymmetry

Supersymmetry provides ideal candidates for explaining the dark matter mystery of our universe. Compelling cold dark matter (CDM) candidates are the neutralino, gravitino and the superpartner of the elusive axion, the axino. The LSP neutralino is perhaps the best motivated candidate for CDM and the popular SUSY models can be in agreement with accelerator and WMAP data. Supersymmetric CP-violating phases, although phenomenologically and theoretically interesting, especially for baryogenesis scenarios, are tightly constrained by electric dipole moment (EDM) data. Two-loop renormalization group equation (RGE) running from the unification to the electroweak scale renormalizes the gaugino mass phases with important consequences for EDMs. In minimal CP-violating extensions of mSUGRA, with non-universal boundary conditions at the unification scale, EDMs and WMAP data can be sumiltaneously satisfied for large values of the phases in regions where neutralinos annihilate through a rapid Higgs resonance. These regions of the parameter space are accessible to LHC.

Refining the predictions of supersymmetricCP-violating models: A top-down approach

We explore in detail the consequences of the CP-violating phases residing in the supersymmetric and soft SUSY breaking parameters in the approximation that family flavour mixings are ignored. We allow for non-universal boundary conditions and in such a consideration the model is described by twelve independent CP-violating phases and one angle which misaligns the vacuum expectation values (VEVs) of the Higgs scalars. We run two-loop renormalization group equations (RGEs), for all parameters involved, including phases, and we properly treat the minimization conditions using the one-loop effective potential with CP-violating phases included. We show that the two-loop running of phases may induce sizable effects for the electric dipole moments (EDMs) that are absent in the one-loop RGE analysis. Also important corrections to the EDMs are induced by the Higgs VEVs misalignment angle which are sizable in the large tan β region. Scanning the available parameter space we seek regions compatible with accelerator and cosmological data with emphasis on rapid neutralino annihilations through a Higgs resonance. It is shown that large CP-violating phases, as required in Baryogenesis scenarios, can be tuned to obtain agreement with WMAP3 cold dark matter constraints, EDMs and all available accelerator data, in extended regions of the parameter space which may be accessible to LHC.

Dark matter in a constrained next-to-minimal supersymmetric standard model

We explore the parameter space of a constrained next-to-minimal supersymmetric standardmodel with grand unified theory scale boundary conditions, and find regions where therelic density of the lightest neutralino is compatible with the WMAP (WilkinsonMicrowave Anisotropy Probe) measurement. We emphasize differences from theminimal supersymmetric standard model: cases where annihilation of the lightestsupersymmetric particle (LSP) occurs via a Higgs resonance at low values oftanβ and cases where the LSP has a large singlino component. The particle spectrum as well astheoretical and collider constraints are calculated with NMSSMTools. All neutralinoannihilation and coannihilation processes are then computed with micrOMEGAs, takinginto account higher order corrections to the Higgs sector.

Mass limits on neutralino dark matter

We set an upper limit on the mass of a supersymmetric neutralino dark matter particle using the MicrOMEGAS and DarkSUSY software packages and the most recent constraints on relic density from combined Wilkinson Microwave Anisotropy Probe and Sloan Digital Sky Survey data. We explore several different possible scenarios within the minimal supersymmetric standard model, including coannihilation with charginos and sfermions and annihilation through a massive Higgs resonance, using low-energy mass inputs. We find that no coannihilation scenario is consistent with dark matter in observed abundance with a mass greater than 2.5 TeV for a W-ino-type particle or 1.8 TeV for a Higgsino-type. Contrived scenarios involving Higgs resonances with finely tuned mass parameters can allow masses as high as 34 TeV. The resulting gamma-ray energy distribution is not in agreement with the recent multi-TeV gamma-ray spectrum observed by H. E. S. S. originating from the center of the Milky Way. Our results are relevant only for dark matter densities resulting from a thermal origin.

Heavy Higgs resonances for the neutralino relic density in the Higgs decoupling limit of the CP-noninvariant minimal supersymmetric standard model

The lightest neutralino is a compelling candidate to account for cold dark matter in the universe in supersymmetric theories with $R$--parity. In the CP-invariant theory, the neutralino relic density can be found in accord with recent WMAP data if neutralino annihilation in the early universe occurs via the s-channel $A$ funnel. In contrast, in the CP-noninvariant theory two heavy neutral Higgs bosons can contribute to the Higgs funnel mechanism significantly due to a CP-violating {\it complex} mixing between two heavy states, in particular, when they are almost degenerate. With a simple analytic and numerical analysis, we demonstrate that the CP-violating Higgs mixing can modify the profile of the neutralino relic density {\it considerably} in the heavy Higgs funnel with the neutralino mass close to half of the heavy Higgs masses.

Precision measurements of Higgs-chargino couplings in chargino pair production at a muon collider

We study chargino pair production on the heavy Higgs resonances at a muon collider in the MSSM. At $\sqrt{s} \approx 350$ GeV cross sections up to 2 pb are reached depending on the supersymmetric scenario and the beam energy spread. The resonances of the scalar and pseudoscalar Higgs bosons may be separated for $\tan\beta <8$. Our aim is to determine the ratio of the chargino couplings to the heavy scalar and pseudoscalar Higgs boson independently of the specific chargino decay characteristics. The precision of the measurement depends on the energy resolution of the muon collider and on the error in the measurement of the cross sections of the non-Higgs channels including an irreducible standard model background. With a high energy resolution the systematic error can be reduced to the order of a few percent.

Photonic and QCD radiative corrections to Higgs-boson production inμ+μ−→ff¯

The photonic and QCD radiative corrections at next-to-leading order are calculated for fermion-pair production at muon colliders, maintaining the full mass dependence and helicity information of the muons and the produced fermions. Higher-order effects of initial-state radiation are included at the leading logarithmic level. In the calculation particular attention is paid to the issue of gauge invariance in the vicinity of resonances. The most important corrections are presented in analytical form. The detailed numerical discussion concentrates on the corrections to the (s-channel) Higgs-boson resonances in the standard model and its minimal supersymmetric extension. The results show that photonic initial- and QCD final-state corrections are very important in a precision study of Higgs resonances, but that (photonic) initial--final interferences are widely suppressed and only modify the nonresonant background.

Neutralino relic density in minimal supergravity with co-annihilations

We evaluate the relic density of neutralinos in the minimal supergravity (mSUGRA) model. All 2-->2 neutralino annihilation diagrams, as well as all processes involving sleptons, charginos, neutralinos and third generation squarks are included. Relativistic thermal averaging of the velocity times cross sections is performed. We find that co-annihilation effects are only important on the edges of the model parameter space, where some amount of fine-tuning is necessary to obtain a reasonable relic density. Alternatively, at high tan(beta), annihilation through very broad Higgs resonances gives rise to an acceptable neutralino relic density over broad regions of parameter space where little or no fine-tuning is needed. Finally, we compare our results against the reach of various e+e- and hadron colliders for supersymmetric matter.

Associated production of Higgs bosons and heavy quarks at photon colliders

The idea of fermion mass generation through Yukawa couplings between Higgs bosons and fermions may be tested by their associated production at future linear colliders (LC). We study the production mechanism in the minimal supersymmeric standard model at photon colliders that can be realized by the laser back-scattering technique at the LC. We find that the cross sections for the production of the light Higgs-top pair, heavy Higgs-bottom pair and pseudoscalr Higgs-bottom pair can reach the level of \sim 1.0 fb or higher for phenomenologically favoured values of the parameters in the Higgs sector. Since this mechanism is not affected by the appearance of Higgs resonances as in electron collisions, it may provide a more sensitive way to determine the Yukawa couplings between Higgs bosons and heavy quarks.

Higgs boson decays to τ-pairs in the s-channel at a muon collider

We study the observability of the τ − τ + decay mode of a Higgs boson produced in the s-channel at a muon collider. We find that the spin correlations of the τ − τ + in τ→ πν τ , ρν τ decays are discriminative between the Higgs boson signal and the Standard Model background. Observation of the predicted distinctive distribution can confirm the spin-0 nature of the Higgs resonance. The relative coupling strength of the Higgs boson to b and τ can also be experimentally determined.

Scalar resonances in leptophilic multi-Higgs-boson models

We show that the Higgs resonance can be amplified in a 3-3-1 model with a multi-Higgs "leptophilic" scalar sector. This would allow the observation of the Higgs particle in muon colliders even for Higgs masses considerably higher than the ones expected to be seen in the electroweak standard model framework.