Standard Model Higgs Boson Mass Research Articles

CP-violation, asymmetries and interferences in toverline{t}phi

In this paper, we use the associated production of top-quark pairs ( toverline{t} ) with a generic scalar boson (ϕ) at the LHC (pp → toverline{t}phi ) to explore the sensitivity of a large set of observables to the sign of the CP mixing angle (α), present in the coupling between the scalar boson and the top quarks. The mass of the scalar boson is set to mϕ = 125 GeV (the Standard Model Higgs boson mass) and its coupling to top-quarks is varied such that α = 0°, 22.5°, 45.0°, 67.5°, 90.0°, 135.0° and 180.0°. Dileptonic final states of the toverline{t}phi system are used (pp → bℓ+νℓ overline{b} ℓ− overline{nu} ℓb overline{b} ), where the scalar boson is expected to decay according to ϕ → boverline{b} . A new method to reconstruct the scalar mass, originally designed for the low mass regime is used, improving the resolution of the Higgs mass by roughly a factor of two. A full phenomenological analysis is performed using Standard Model (SM) background and signal events generated with MadGraph5_aMC@NLO, in turn reconstructed using a kinematical fit. The most sensitive CP-observables are selected to compute Confidence Level (CL) limits as a function of the sign of the top quark Yukawa couplings to the ϕ boson. We also explore the sensitivity to interference terms using differential distributions and angular asymmetries. Given the significant difference between the pure scalar (σ0+) and pure pseudo-scalar (σ0−) production cross section values, it is unlikely the toverline{t}phi channel alone will be sensitive to the sign of the CP-mixing angle or interference terms, even at the end of the LHC. Using the {b}_2^{toverline{t}phi } and {b}_4^{toverline{t}phi } variables, exclusion limits at 95% CL for the CP-even and CP-odd components of the top quark Yukawa couplings are expected to be set to overset{sim }{kappa } ∈ [-0.698,+0.698] and |κ| ∈ [0.878,1.04], respectively, at the end of the High Luminosity phase of the LHC (HL-LHC) by using the dileptonic decay channel alone.

Consistency of the dual formulation of axion solutions to the strong CP problem

An exact duality between axion with arbitrary potential and antisymmetric form-field has been derived some time ago. Using this duality, the axion solution to strong-CP problem has been formulated as a gauge invariant theory of forms. In this description, the QCD axion is represented by a Kalb-Ramond field which is eaten-up by the Chern-Simons $3$-form of QCD, thereby making it massive. This ensures the CP-invariance of the vacuum. Although viewed as an effective low energy theory, this formulation accomplishes the same goal as ordinary Peccei-Quinn mechanism, due to its gauge invariance, it is protected against unwanted UV-corrections. In the previous work it has been shown that dual formulation is insensitive to UV-physics in the sense that the corrections to CP-conserving vacuum from arbitrary massive sources are strictly zero. By going carefully through duality transformations and source-resolution, we reproduce this curious result and give some further consistency checks. We apply similar analysis to other approaches to naturalness problems based on form fields and axions, such as cosmological relaxation of the standard model Higgs boson mass via the attractor mechanism.

Messenger inflation in gauge mediation and super-WIMP dark matter

We discuss phenomenological viability of a novel inflationary model in the minimal gauge mediated supersymmetry breaking scenario. In this model, cosmic inflation is realized in the flat direction along the messenger supermultiplets and a natural dark matter candidate is the gravitino from the out-of-equilibrium decay of the binolike neutralino at late times, which is called the super-WIMP scenario. The produced gravitino is warmish and can have a large free-streaming length; thus the cusp anomaly in the small scale structure formation may be mitigated. We show that the requirement of the Standard Model Higgs boson mass to be ${m}_{{h}^{0}}=125.1\text{ }\text{ }\mathrm{GeV}$ gives a relation between the spectrum of the cosmic microwave background and the messenger mass $M$. We find, for the $e$-folding number ${N}_{e}=60$, the Planck 2018 constraints (TT, TE, $\mathrm{EE}+\mathrm{lowE}+\mathrm{lensing}+\mathrm{BK}15+\mathrm{BAO}$, 68% confidence level) give $M>3.64\ifmmode\times\else\texttimes\fi{}{10}^{7}\text{ }\text{ }\mathrm{GeV}$. The gravitino dark matter mass is ${m}_{3/2}<5.8\text{ }\text{ }\mathrm{GeV}$ and the supersymmetry breaking scale $\mathrm{\ensuremath{\Lambda}}$ is found to be in the range $(1.28--1.33)\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }\mathrm{GeV}$. Future cosmic microwave background observation is expected to give tighter constraints on these parameters.

Light sterile neutrinos, dark matter, and new resonances in a U(1) extension of the MSSM

We present $\psi'$MSSM, a model based on a $U(1)_{\psi'}$ extension of the minimal supersymmetric standard model. The gauge symmetry $U(1)_{\psi'}$, also known as $U(1)_N$, is a linear combination of the $U(1)_\chi$ and $U(1)_\psi$ subgroups of $E_6$. The model predicts the existence of three sterile neutrinos with masses $\lesssim 0.1~{\rm eV}$, if the $U(1)_{\psi'}$ breaking scale is of order 10 TeV. Their contribution to the effective number of neutrinos at nucleosynthesis is $\Delta N_{\nu}\simeq 0.29$. The model can provide a variety of possible cold dark matter candidates including the lightest sterile sneutrino. If the $U(1)_{\psi'}$ breaking scale is increased to $10^3~{\rm TeV}$, the sterile neutrinos, which are stable on account of a $Z_2$ symmetry, become viable warm dark matter candidates. The observed value of the standard model Higgs boson mass can be obtained with relatively light stop quarks thanks to the D-term contribution from $U(1)_{\psi'}$. The model predicts diquark and diphoton resonances which may be found at an updated LHC. The well-known $\mu$ problem is resolved and the observed baryon asymmetry of the universe can be generated via leptogenesis. The breaking of $U(1)_{\psi'}$ produces superconducting strings that may be present in our galaxy. A $U(1)$ R symmetry plays a key role in keeping the proton stable and providing the light sterile neutrinos.

Fermion dark matter in gauge-Higgs unification

We propose a Majorana fermion dark matter in the context of a simple gauge-Higgs Unification (GHU) scenario based on the gauge group SU(3)×U(1)′ in 5-dimensional Minkowski space with a compactification of the 5th dimension on S1/Z2 orbifold. The dark matter particle is identified with the lightest mode in SU(3) triplet fermions additionally introduced in the 5-dimensional bulk. We find an allowed parameter region for the dark matter mass around a half of the Standard Model Higgs boson mass, which is consistent with the observed dark matter density and the constraint from the LUX 2016 result for the direct dark matter search. The entire allowed region will be covered by, for example, the LUX-ZEPLIN dark matter experiment in the near future. We also show that in the presence of the bulk SU(3) triplet fermions the 125 GeV Higgs boson mass is reproduced through the renormalization group evolution of Higgs quartic coupling with the compactification scale of around 108 GeV.

Search for the Higgs Boson decaying into tau pairs

A search for the Standard Model Higgs Boson decaying into τ pairs is performed using events recorded by the CMS experiment at the LHC in 2011 and 2012. An excess of events is observed over a broad range of Higgs mass hypotheses, with a maximum local significance of 2.93 standard deviations at mH = 120 GeV. The excess is compatible with the presence of a standard-model Higgs boson of mass 125 GeV/c2.

Search for a Higgs boson decaying into a Z and a photon in pp collisions at [formula omitted

A search for a Higgs boson decaying into a Z boson and a photon is described. The analysis is performed using proton–proton collision datasets recorded by the CMS detector at the LHC. Events were collected at center-of-mass energies of 7 TeV and 8 TeV, corresponding to integrated luminosities of 5.0 fb−1 and 19.6 fb−1, respectively. The selected events are required to have opposite-sign electron or muon pairs. No excess above standard model predictions has been found in the 120–160 GeV mass range and the first limits on the Higgs boson production cross section times the H→Zγ branching fraction at the LHC have been derived. The observed at 95% confidence level limits are between about 4 and 25 times the standard model cross section times the branching fraction. For a standard model Higgs boson mass of 125 GeV the expected limit at the 95% confidence level is 10 and the observed limit is 9.5. Models predicting the Higgs boson production cross section times the H→Zγ branching fraction to be larger than one order of magnitude of the standard model prediction are excluded for most of the 125–157 GeV mass range.

Uncovering the charming Higgs at the LHC

We study the observability of the Higgs boson in the "charming Higgs" model. In this model the Higgs boson primarily undergoes a cascade decay to four charm quarks via light intermediate pseudoscalars. Such a decay allows the Higgs boson to escape the most stringent LEP bounds on the Standard Model Higgs boson mass. If the light pseudoscalars are sufficiently light they become highly boosted and their decay products collimated into jets. We show that by using jet substructure techniques, this model is potentially observable at the LHC. For a Higgs boson mass of 100 GeV and light pseudoscalar mass of 12 GeV, we find a signal significance of 3.8 sigma with a luminosity of 30 fb^-1 and that a 5 sigma significance can be obtained with 50 fb^-1 of luminosity at the 14 TeV LHC.

Searches for Low Mass Higgs Boson at the Tevatron

We present the result of the searches for a low mass Standard Model Higgs boson performed at the Tevatron ppbar collider (sqrt(s) =1.96 TeV) by the CDF and D0 experiments with an integrated luminosity of up to 8.5 fb^-1. Individual searches are discussed and classified according to their sensitivity. Primary channels rely on the associate production with a vector boson (WH or ZH) and the H->bbbar decay channel (favored for M_H<135 GeV/c^2). Event selection is based on the leptonic decay of the vector boson and the identification of b-hadron enriched jets. Each individual channel is sensitive, for M_H=115 GeV/c^2, to less than 5 times the SM expected cross section and the most sensitive channels can exclude a production cross section of 2.3 x sigma_H SM. Secondary channels rely on a variety of final states. Although they are from 2 to 5 times less sensitive than any primary channel, they contribute to the Tevatron combination and, in some cases, they pose strong constrains on exotic Higgs boson models.

Higgs mass and inflation

We show that the standard-model Higgs boson mass mh is correlated with the spectral index of density perturbation ns in the inflation scenario with the inflaton being identified with the B–L Higgs boson. The Higgs boson mass ranges from mh≃120 GeV to 140 GeV for ns≃0.95–0.96. In particular, as ns approaches to 0.96, the Higgs mass is predicted to be in the range of 125 GeV to 140 GeV in the case of relatively light gauginos, and 120 GeV to 135 GeV in the case where all SUSY particle masses are of the same order. This will be tested soon by the LHC experiment and the Planck satellite. The relation is due to the PeV-scale supersymmetry required by the inflationary dynamics. We also comment on the cosmological implications of our scenario such as non-thermal leptogenesis and dark matter.

The Tevatron Higgs exclusion limits and theoretical uncertainties: A critical appraisal

We examine the exclusion limits set by the CDF and D0 experiments on the Standard Model Higgs boson mass from their searches at the Tevatron in the light of large theoretical uncertainties on the signal and background cross sections. We show that when these uncertainties are consistently taken into account, the sensitivity of the experiments becomes significantly lower and the currently excluded mass range MH=158–175 GeV could be entirely reopened. The necessary luminosity required to recover the current sensitivity is found to be a factor of two higher than the present one.

Higgs boson mass bounds in seesaw extended standard model with non-minimal gravitational coupling

In the presence of non-minimal gravitational coupling ξH†HR between the standard model (SM) Higgs doublet H and the curvature scalar R, the effective ultraviolet cutoff scale is given by Λ≈mP/ξ, where mP is the reduced Planck mass, and ξ≳1 is a dimensionless coupling constant. In type I and type III seesaw extended SM, which can naturally explain the observed solar and atmospheric neutrino oscillations, we investigate the implications of this non-minimal gravitational coupling for the SM Higgs boson mass bounds based on vacuum stability and perturbativity arguments. A lower bound on the Higgs boson mass close to 120 GeV is realized with type III seesaw and ξ∼10–103.

Prospects for observing the standard model Higgs boson decaying intobb¯final states produced in weak boson fusion with an associated photon at the LHC

One of the primary goals of the Large Hadron Collider is to understand the electroweak symmetry breaking mechanism. In the standard model, electroweak symmetry breaking is described by the Higgs mechanism which includes a scalar Higgs boson. Electroweak measurements constrain the standard model Higgs boson mass to be in the 114.4 to $157\text{ }\text{ }\mathrm{GeV}/{c}^{2}$ range. For ${m}_{h}&lt;135\text{ }\text{ }\mathrm{GeV}/{c}^{2}$, the Higgs predominantly decays into two $b$-quarks. As such, we investigate the prospect of observing the standard model Higgs decaying to $b\overline{b}$ produced in weak-boson-fusion with an associated central photon. An isolated, high ${p}_{\mathrm{T}}$, central photon trigger is expected to be available at the ATLAS and CMS experiments. In this study, we investigated the effects originating from showering, hadronization, the underlying event model, and jet performance including $b$-jet calibration on the sensitivity of this channel. We found that the choice of Monte Carlo simulation and its tune has a large effect on the efficacy of the central jet veto and consequently the signal significance. A signal significance of ${1.6}_{\ensuremath{-}0.3}^{+0.5}$ can be achieved for ${m}_{h}=115\text{ }\text{ }\mathrm{GeV}/{c}^{2}$ with $100\text{ }\text{ }{\mathrm{fb}}^{\ensuremath{-}1}$ of integrated luminosity which correspond to 1 yr at design luminosity at 14 TeV $pp$ collisions.

Standard model Higgs boson mass from inflation: two loop analysis

We extend the analysis of \cite{Bezrukov:2008ej} of the Standard Model Higgs inflation accounting for two-loop radiative corrections to the effective potential. As was expected, higher loop effects result in some modification of the interval for allowed Higgs masses m_min<m_H<m_max, which somewhat exceeds the region in which the Standard Model can be considered as a viable effective field theory all the way up to the Planck scale. The dependence of the index n_s of scalar perturbations on the Higgs mass is computed in two different renormalization procedures, associated with the Einstein (I) and Jordan (II) frames. In the procedure I the predictions of the spectral index of scalar fluctuations and of the tensor-to-scalar ratio practically do not depend on the Higgs mass within the admitted region and are equal to n_s=0.97 and r=0.0034 respectively. In the procedure II the index n_s acquires the visible dependence on the Higgs mass and and goes out of the admitted interval at m_H below m_min. We compare our findings with the results of \cite{DeSimone:2008ei}.

Standard Model Higgs boson mass from inflation

We analyse one-loop radiative corrections to the inflationary potential in the theory, where inflation is driven by the Standard Model Higgs field. We show that inflation is possible provided the Higgs mass m H lies in the interval m min < m H < m max , where m min = [ 136.7 + ( m t − 171.2 ) × 1.95 ] GeV , m max = [ 184.5 + ( m t − 171.2 ) × 0.5 ] GeV and m t is the mass of the top quark. In the renormalization scheme associated with the Einstein frame the predictions of the spectral index of scalar fluctuations and of the tensor-to-scalar ratio practically do not depend on the Higgs mass within the admitted region and are equal to n s = 0.97 and r = 0.0034 correspondingly.

Higgs boson mass bounds in the Standard Model with type III and type I seesaw

In type III seesaw utilized to explain the observed solar and atmospheric neutrino oscillations the Standard Model (SM) particle spectrum is extended by introducing three SU(2)L triplet fermion fields. This can have important implications for the SM Higgs boson mass (MH) bounds based on vacuum stability and perturbativity arguments. We compute the appropriate renormalization group equations for type III seesaw, and then proceed to identify regions of the parameter space such that the SM Higgs boson mass window is enlarged to 125 GeV≲MH≲174 GeV, with the type III seesaw scale close to TeV. We also display regions of the parameter space for which the vacuum stability and perturbativity bounds merge together for large neutrino Yukawa couplings. Comparison with type I seesaw is also presented.

The muong−2and the bounds on the Higgs boson mass

After a brief review of the muon $g\ensuremath{-}2$ status, we analyze the possibility that the present discrepancy between experiment and the standard model (SM) prediction may be due to hypothetical errors in the determination of the hadronic leading-order contribution to the latter. In particular, we show how an increase of the hadroproduction cross section in low-energy ${e}^{+}{e}^{\ensuremath{-}}$ collisions could bridge the muon $g\ensuremath{-}2$ discrepancy, leading however to a decrease on the electroweak upper bound on ${M}_{H}$, the SM Higgs boson mass. That bound is currently ${M}_{H}\ensuremath{\lesssim}150\text{ }\text{ }\mathrm{GeV}$ (95% C.L.) based on the preliminary top quark mass ${M}_{t}=172.6(1.4)\text{ }\text{ }\mathrm{GeV}$ and the recent determination $\ensuremath{\Delta}{\ensuremath{\alpha}}_{\mathrm{had}}^{(5)}({M}_{Z})=0.027\text{ }68(22)$, while the direct-search lower bound is ${M}_{H}&gt;114.4\text{ }\text{ }\mathrm{GeV}$ (95% C.L.). By means of a detailed analysis we conclude that this solution of the muon $g\ensuremath{-}2$ discrepancy is unlikely in view of current experimental error estimates. However, if this turns out to be the solution, the 95% C.L. upper bound on ${M}_{H}$ is reduced to about 130 GeV which, in conjunction with the experimental lower bound, leaves a narrow window for the mass of this fundamental particle.

Unparticle effects on unitarity constraints from Higgs boson scattering

We study the effects of two-body Higgs boson scattering by exchanging unparticles. The unparticle contribution can change the standard model prediction for two-body Higgs boson scattering partial wave amplitude significantly leading to modification of the unitarity constraint on the standard model Higgs boson mass. For unparticle dimension ${d}_{\mathcal{U}}$ between 1 and 2, the unitarity constraint on the Higgs boson mass can be larger than that in the standard model. Information on unparticle interaction can also be obtained.

CMS detector sensitivity to the Standard Model Higgs boson in H → ZZ (∗) → 4leptons decay channel

The search for the Higgs boson is one of the most important tasks of the CMS experiment at pp LHC collider. The most recent results on the Standard Model Higgs boson discovery potential are presented, obtained using the most recent full simulation and reconstruction software as well as with detailed treatment of systematic uncertainties. Results show that the whole Standard Model Higgs boson mass range will be covered with about ∼ 10 f b −1 .

Window for Higgs boson mass from gauge-Higgs unification

We consider six-dimensional gauge models compactified on the orbifold T2/ZN (N=2,3,4,6) such that the Standard Model (SM) Higgs doublet arises from the extra-dimensional components of the gauge field. For Λ⩽1019GeV, where Λ denotes the compactification scale, we obtain 114.4GeV⩽mH⩽164GeV for the SM Higgs boson mass. We also consider gauge-Higgs-top and gauge-Higgs-bottom Yukawa unification which respectively yield mH=131−5+4GeV and mH=150−2+2GeV for a top quark pole mass Mt=170.9−1.8+1.8GeV. As a special case we recover the result mH⩽132GeV previously obtained for five-dimensional models.