LHC Higgs Searches Research Articles

HiggsBounds-5: testing Higgs sectors in the LHC 13 TeV Era

We describe recent developments of the public computer code HiggsBounds. In particular, these include the incorporation of LHC Higgs search results from Run 2 at a center-of-mass energy of 13 TeV, and an updated and extended framework for the theoretical input that accounts for improved Higgs cross section and branching ratio predictions and new search channels. We furthermore discuss an improved method used in HiggsBounds to approximately reconstruct the exclusion likelihood for LHC searches for non-standard Higgs bosons decaying to tau tau final states. We describe in detail the new and updated functionalities of the new version HiggsBounds-5.

Is well-tempered neutralino in MSSM still alive after 2016 LUX results?

It is pointed out that a bino-dominated well-tempered bino-higgsino in the Minimal Supersymmetric Standard Model (MSSM) with heavy non-SM- like scalars can satisfy the 2016 LUX constraints on the scattering cross-section of dark matter on nuclei only if $\tan\beta$ is smaller than about 3. This, together with the Higgs mass constraint, sets a lower bound on the stops masses of about 25 TeV. The LUX constraints can be satisfied for larger $\tan\beta$ if the non-SM-like Higgs bosons are light enough. However, this region of parameter space is strongly constrained by recent LHC results of the Higgs boson searches. Satisfying both the LUX and LHC constraints requires the non-SM-like Higgs bosons to be lighter than about 400 GeV and $\tan\beta$ below about 8. This implies a lower bound on the stop masses of about 1.5 TeV. This small corner of the parameter space will be probed in the near future by the direct detection experiments, the LHC Higgs searches and precision Higgs coupling measurements. The recent LUX constraints improved also the lower mass limit on higgsino-dominated well-tempered neutralino to about 950 (900) GeV with heavy (light) MSSM-like Higgs doublet, assuming the stop masses below 10 TeV.

LHC benchmark scenarios for the real Higgs singlet extension of the standard model

We present benchmark scenarios for searches for an additional Higgs state in the real Higgs singlet extension of the Standard Model in Run 2 of the LHC. The scenarios are selected such that they fulfill all relevant current theoretical and experimental constraints, but can potentially be discovered at the current LHC run. We take into account the results presented in earlier work and update the experimental constraints from relevant LHC Higgs searches and signal rate measurements. The benchmark scenarios are given separately for the low mass and high mass region, i.e. the mass range where the additional Higgs state is lighter or heavier than the discovered Higgs state at around 125 GeV. They have also been presented in the framework of the LHC Higgs Cross Section Working Group.

Three loop neutrino model with isolatedk±±

We propose a three loop radiative neutrino mass scenario with an isolated doubly charged singlet scalar $k^{\pm\pm}$ without couplings to the charged leptons, while two other singly charged scalars $h_1^\pm$ and $h_2^\pm$ attach to them. In this setup, the lepton flavor violation originating from $k^{\pm\pm}$ exchanges is suppressed and the model is less constrained, where some couplings can take sizable values. As reported in our previous work, the loop suppression factor at the three loop level would be too strong and realized neutrino masses in a three loop scenario could be smaller than the observed minuscule values. The sizable couplings can help us to enhance neutrino masses without drastically large scalar trilinear couplings appearing in a neutrino mass matrix, which tends to drive the vacuum stability to become jeopardized at the one loop level. Now the doubly charged scalar $k^{\pm\pm}$ has less constraint via lepton flavor violation and the vacuum can be quite stable, and thus a few hundred GeV mass in $k^{\pm\pm}$ is possible, which is within the LHC reach and this model can be tested in the near future. Note that the other $h_1^\pm$ and $h_2^\pm$ should be heavy at least around a few TeV. We suitably arrange the charges of an additional global $U(1)$ symmetry, where the decay constant of the associated Nambu-Goldstone boson can be around a TeV scale consistently. Also, this model is indirectly limited through a global analysis on results of the LHC Higgs search and issues on a dark matter candidate, the lightest Majorana neutrino. After $h_1^\pm$ and $h_2^\pm$ are decoupled, this particle couples to the standard model particles only through two charge parity even scalars in theory and thus information on this scalar sector is important. Consistent solutions are found, but a part of them is now on the edge.

Class of Higgs-portal dark matter models in the light of gamma-ray excess from galactic center

Recently the study of anomalous gamma-ray emission in the regions surrounding the galactic center has drawn a lot of attention as it points out that the excess of $\sim 1-3$ GeV gamma-ray in the low latitude is consistent with the emission expected from annihilating dark matter. The best-fit to the gamma-ray spectrum corresponds to dark matter (DM) candidate having mass in the range $\sim 31-40$ GeV annihilating into $b\bar{b}$-pair with cross-section $\langle \sigma v \rangle = (1.4-2.0)\times 10^{-26}\;\textrm{cm}^3 \textrm{sec}^{-1}$. We have shown that the Higgs-portal dark matter models in presence of scalar resonance (in the annihilation channel) are well-suited for explaining these phenomena. In addition, the parameter space of these models also satisfy constraints from the LHC Higgs searches, relic abundance and direct detection experiments. We also comment on real singlet scalar Higgs-portal DM model which is found to be incompatible with the recent analysis.

Constraining type II 2HDM in light of LHC Higgs searches

We study the implication of the LHC Higgs search results on the Type II Two Higgs-Doublet Model. In particular, we explore the scenarios in which the observed 126 GeV Higgs signal is interpreted as either the light CP-even Higgs $h^0$ or the heavy CP-even Higgs $H^0$. Imposing both theoretical and experimental constraints, we analyze the surviving parameter regions in $m_H$ ($m_h$), $m_A$, $m_{H^\pm}$, $\tan\beta$ and $\sin(\beta - \alpha)$. We further identify the regions that could accommodate a 126 GeV Higgs with cross sections consistent with the observed Higgs signal. We find that in the $h^0$-126 case, we are restricted to narrow regions of $\sin(\beta-\alpha) \approx \pm 1$ with $\tan\beta$ up to 4, or an extended region with $0.55 < \sin(\beta-\alpha) < 0.9$ and $1.5 < \tan\beta < 4$. The values of $m_H$, $m_A$ and $m_{H^\pm}$, however, are relatively unconstrained. In the $H^0$-126 case, we are restricted to a narrow region of $\sin(\beta-\alpha) \sim 0$ with $\tan\beta$ up to about 8, or an extended region of $\sin(\beta-\alpha) $ between $-0.8$ to $-0.05$, with $\tan\beta$ extended to 30 or higher. $m_A$ and $m_{H^\pm}$ are nearly degenerate due to $\Delta\rho$ constraints. Imposing flavor constraints shrinks the surviving parameter space significantly for the $H^0$-126 case, limiting $\tan\beta \lesssim 10$, but has little effect in the $h^0$-126 case. We also investigate the correlation between $\gamma\gamma$, $VV$ and $bb/\tau\tau$ channels. $\gamma\gamma$ and $VV$ channels are most likely to be highly correlated with $\gamma\gamma:VV \sim 1$ for the normalized cross sections.

Dark matter in the little Higgs model under current experimental constraints from the LHC, Planck, and Xenon data

We examine the status of dark matter (heavy photon) in the littlest Higgs model with T-parity (LHT) in light of the new results from the LHC Higgs search, the Planck dark matter relic density and the XENON100 limit on the dark matter scattering off the nucleon. We obtain the following observations: (i) For the LHC Higgs data, the LHT can well be consistent with the CMS results but disfavored by the ATLAS observation of diphoton enhancement; (ii) For the dark matter relic density, the heavy photon in the LHT can account for the Planck data for the small mass splitting of mirror lepton and heavy photon; (iii) For the dark matter scattering off the nucleon, the heavy photon can give a spin-independent cross section below the XENON100 upper limit for $m_{A_H}>95$ GeV ($f> 665$ GeV); (iv) A fit using the CMS Higgs data gives the lowest chi-square of 2.63 (the SM value is 4.75) at $f\simeq$ 1120 GeV and $m_{A_H}\simeq$ 170 GeV (at this point the dark matter constraints from Planck and XENON100 can also be satisfied). Such a best point and its nearby favored region (even for a $f$ value up to 3.8 TeV) can be covered by the future XENON1T (2017) experiment.

Natural electroweak symmetry breaking from scale invariant Higgs mechanism

We construct a minimal viable extension of the standard model (SM) with classical scale symmetry. Its scalar sector contains a complex singlet in addition to the SM Higgs doublet. The scale-invariant and CP-symmetric Higgs potential generates radiative electroweak symmetry breaking à la Coleman–Weinberg, and gives a natural solution to the hierarchy problem, free from fine-tuning. Besides the 125 GeV SM-like Higgs particle, it predicts a new CP-even Higgs (serving as the pseudo-Nambu–Goldstone boson of scale symmetry breaking) and a CP-odd scalar singlet (providing the dark matter candidate) at weak scale. We systematically analyze experimental constraints from direct LHC Higgs searches and electroweak precision tests, as well as theoretical bounds from unitarity, triviality and vacuum stability. We demonstrate the viable parameter space, and discuss implications for new Higgs searches at the upcoming LHC runs and the on-going direct detections of dark matter.

Should we still believe in constrained supersymmetry?

We calculate Bayes factors to quantify how the feasibility of the constrained minimal supersymmetric standard model (CMSSM) has changed in the light of a series of observations. This is done in the Bayesian spirit where probability reflects a degree of belief in a proposition and Bayes' theorem tells us how to update it after acquiring new information. Our experimental baseline is the approximate knowledge that was available before LEP, and our comparison model is the Standard Model with a simple dark matter candidate. To quantify the amount by which experiments have altered our relative belief in the CMSSM since the baseline data we compute the Bayes factors that arise from learning in sequence the LEP Higgs constraints, the XENON100 dark matter constraints, the 2011 LHC supersymmetry search results, and the early 2012 LHC Higgs search results. We find that LEP and the LHC strongly shatter our trust in the CMSSM (with $M_0$ and $M_{1/2}$ below 2 TeV), reducing its posterior odds by a factor of approximately two orders of magnitude. This reduction is largely due to substantial Occam factors induced by the LEP and LHC Higgs searches.

Peccei-Quinn symmetry as the origin of Dirac neutrino masses

We propose a model of Dirac neutrino masses generated at one-loop level. The origin of this mass is induced from Peccei-Quinn symmetry breaking which was proposed to solve the so-called strong CP problem in QCD, therefore, the neutrino mass is connected with the QCD scale, $\Lambda_{\rm QCD}$. We also study the parameter space of this model confronting with neutrino oscillation data and leptonic rare decays. The phenomenological implications to leptonic flavor physics such as the electromagnetic moment of charged leptons and neutrinos are studied. Axion as the dark matter candidate is one of the byproduct in our scenario. Di-photon and Z-photon decay channels in the LHC Higgs search are investigated, we show that the effects of singly charged singlet scalar can be distinguished from the general two Higgs doublet model.

One-loop effects on MSSM parameter determination via chargino production at the LC

At a future linear collider very precise measurements, typically with errors of <1 %, are expected to be achievable. Such an accuracy gives sensitivity to the quantum corrections, which therefore must be incorporated in theoretical calculations in order to determine the underlying new physics parameters from prospective linear collider measurements. In the context of the chargino–neutralino sector of the minimal supersymmetric standard model, this involves fitting one-loop predictions to prospective measurements of the cross sections, forward–backward asymmetries and of the accessible chargino and neutralino masses. Taking recent results from LHC SUSY and Higgs searches into account we consider three phenomenological scenarios, each with characteristic features. Our analysis shows how an accurate determination of the desired parameters is possible, providing in addition access to the stop masses and mixing angle.

Gravitino decays and the cosmological lithium problem in light of the LHC Higgs and supersymmetry searches

We studied previously the impact on light-elementabundances of gravitinos decaying during or after Big-Bang nucleosynthesis (BBN). We foundregions of the gravitino mass m3/2 and abundance ζ3/2 plane where its decays couldreconcile the calculated abundance of 7Li with observation without perturbingthe other light-element abundances unacceptably. Here we revisit this issuein light of LHC measurements of the Higgs mass and constraints on supersymmetric model parameters,as well as updates in the astrophysical measurements of light-element abundances. In addition to the constrained minimal supersymmetric extension of the Standard Model with universal soft supersymmetry-breaking massesat the GUT scale (the CMSSM) studied previously, we also study models with universality imposed below the GUTscale and models with non-universal Higgs masses (NUHM1). We calculate the total likelihood function for the light-element abundances, taking into account the observational uncertainties.We find that gravitino decays provide a robust solution to the cosmological 7Liproblem along strips in the (m3/2,ζ3/2) plane along which theabundances of deuterium, 4He and 7Li may be fit with χ2min≲3,compared with χ2 ∼ 34 if the effects of gravitino decays are unimportant.The minimum of the likelihood function is reduced to χ2 < 2 when the uncertainty on D/H is relaxedand < 1 when the lithium abundance is taken from globular cluster data.

Little Higgs theory confronted with the LHC Higgs data

We confront the little Higgs theory with the LHC Higgs search data (up to 17 fb$^{-1}$ of the combined 7 and 8 TeV run). Considering some typical models, namely the littlest Higgs model (LH), the littlest Higgs model with T-parity (LHT-A and LHT-B) and the simplest little Higgs model (SLH), we scan over the parameter space in the region allowed by current experiments. We find that in these models the inclusive and exclusive (via gluon-gluon fusion) diphoton and $ZZ^*$ signal rates of the Higgs boson are always suppressed and approach to the SM predictions for a large scale $f$. Thus, the $ZZ^*$ signal rate is within the $1\sigma$ range of the experimental data while the inclusive diphoton signal rate is always outside the $2\sigma$ range. Especially, in the LHT-A the diphoton signal rate is outside the $3\sigma$ range of the experimental data for $f < 800$ GeV. We also perform a global $\chi^2$ fit to the available LHC and Tevatron Higgs data, and find that these models provide no better global fit to the whole data set (only for some special channels a better fit can be obtained, specially in the LHT-B).

First Glimpses at Higgs’ face

Abstract The 8 TeV LHC Higgs search data just released indicates the existence of a scalar resonance with mass ~ 125 GeV. We examine the implications of the data reported by ATLAS, CMS and the Tevatron collaborations on understanding the properties of this scalar by performing joint fits on its couplings to other Standard Model (SM) particles. We discuss and characterize to what degree this resonance has the properties of the SM Higgs, and consider what implications can be extracted for New Physics in a (mostly) model-independent fashion. We find that, if the Higgs couplings to fermions and weak vector bosons are allowed to differ from their standard values, the SM is ~ 2σ from the best fit point to the current data. Fitting to a possible invisible decay branching ratio, we find BRinv ≃ 0.05 ± 0.32 (95% C.L.). We also discuss and develop some ways of using the data in order to bound or rule out models which modify significantly the properties of this scalar resonance, and apply these techniques to the current global dataset.

Constraints on new scalars from the LHC 125 GeV Higgs signal

We study the implications the recent results from the LHC Higgs searches have on scalar new physics. We study the impact on both the Higgs production and decay from scalars with and without colour, and in cases where decoupling do and do not happen. We investigate possible constraints on scalar parameters from the production rate in the diphoton channel, and also the two vector boson channels. Measurements from both channels can help disentangle new physics due to colour from that due to charge, and thus reveal the nature of the new scalar states.

Beyond the MSSM Higgs bosons at 125 GeV

Beyond the MSSM framework is an effective theory approach that encapsulates a variety of extensions beyond the MSSM with which it shares the same field content. The lightest Higgs mass can be much heavier than in the MSSM without creating a tension with naturalness or requiring superheavy stops. The phenomenology of the Higgs sector is at the same time much richer. We critically review the properties of a Higgs with mass around 125 GeV in this model. In particular, we investigate how the rates in the important inclusive $2\ensuremath{\gamma}$ channel, the $2\ensuremath{\gamma}+2$ jets and the $ZZ\ensuremath{\rightarrow}4l$ (and/or $WW$) can be enhanced or reduced compared to the standard model and what kind of correlations between these rates are possible. We consider both a vanilla model where stops have moderate masses with no trilinear stop mixing term and a model having a large stop mixing with a light stop. We show that in both cases there are scenarios that lead to enhancements in these rates at a mass of 125 GeV corresponding to either the lightest Higgs or the heaviest $CP$-even Higgs of the model. In all of these scenarios we study the prospects of finding other signatures of either the 125 GeV Higgs or those of the heavier Higgses. In most cases the $\overline{\ensuremath{\tau}}\ensuremath{\tau}$ channels are the most promising. Exclusion limits from the recent LHC Higgs searches are folded in our analyses while the tantalizing hints for a Higgs signal at 125 GeV are used as an example of how to constrain beyond the MSSM and/or direct future searches.

Erratum: Technipion limits from LHC Higgs searches [Phys. Rev. D84, 115025 (2011)

Erratum: Technipion limits from LHC Higgs searches [Phys. Rev. D<b>84</b>, 115025 (2011)

Electroweakinos hiding in Higgs searches

Direct production of electroweakly charged states may not produce the high energy jets or the significant missing energy required in many new physics searches at the LHC. However, because these states produce leptons, they are still potentially detectable over the sizeable Standard Model backgrounds. We show that current LHC Higgs searches, particularly in the WW* and ZZ* channels, are sensitive to new electroweak states, such as supersymmetric charginos or neutralinos. Indeed, the 1.7 fb^{-1} Higgs searches can provide the strongest limits in certain regions of parameter space, extending the LEP bound up to ~200 GeV in some cases. Additionally, electroweakino production can form an interesting physics background for Higgs searches, especially at low luminosity and statistics. We show that dilepton searches with low missing energy requirements are complementary to existing searches in exploring regions of parameter space where new electroweak states are light or have compressed spectra.

Exploring the Higgs portal with 10 fb−1 at the LHC

We consider the impact of new exotic colored and/or charged matter interacting through the Higgs portal on Standard Model Higgs boson searches at the LHC. Such Higgs portal couplings can induce shifts in the effective Higgs-gluon-gluon and Higgs-photon-photon couplings, thus modifying the Higgs production and decay patterns. We consider two possible interpretations of the current LHC Higgs searches based on ~ 5/fb of data at each detector: 1) a Higgs boson in the mass range (124-126) GeV and 2) a `hidden' heavy Higgs boson which is underproduced due to the suppression of its gluon fusion production cross section. We first perform a model independent analysis of the allowed sizes of such shifts in light of the current LHC data. As a class of possible candidates for new physics which gives rise to such shifts, we investigate the effects of new scalar multiplets charged under the Standard Model gauge symmetries. We determine the scalar parameter space that is allowed by current LHC Higgs searches, and compare with complementary LHC searches that are sensitive to the direct production of colored scalar states.

Updated global fits of the cMSSM including the latest LHC SUSY and Higgs searches and XENON100 data

We present new global fits of the constrained Minimal Supersymmetric Standard Model (cMSSM), including LHC 1/fb integrated luminosity SUSY exclusion limits, recent LHC 5/fb constraints on the mass of the Higgs boson and XENON100 direct detection data. Our analysis fully takes into account astrophysical and hadronic uncertainties that enter the analysis when translating direct detection limits into constraints on the cMSSM parameter space. We provide results for both a Bayesian and a Frequentist statistical analysis. We find that LHC 2011 constraints in combination with XENON100 data can rule out a significant portion of the cMSSM parameter space. Our results further emphasise the complementarity of collider experiments and direct detection searches in constraining extensions of Standard Model physics. The LHC 2011 exclusion limit strongly impacts on low-mass regions of cMSSM parameter space, such as the stau co-annihilation region, while direct detection data can rule out regions of high SUSY masses, such as the Focus-Point region, which is unreachable for the LHC in the near future. We show that, in addition to XENON100 data, the experimental constraint on the anomalous magnetic moment of the muon plays a dominant role in disfavouring large scalar and gaugino masses. We find that, should the LHC 2011 excess hinting towards a Higgs boson at 126 GeV be confirmed, currently favoured regions of the cMSSM parameter space will be robustly ruled out from both a Bayesian and a profile likelihood statistical perspective.