Higgs Boson Couplings Research Articles

Higgs boson couplings in multi-doublet models with natural flavour conservation

We investigate the deviation in the couplings of the standard model (SM) like Higgs boson ($h$) with a mass of 125 GeV from the prediction of the SM in multi-doublet models within the framework where flavour changing neutral currents at the tree level are naturally forbidden. After we present the general expressions for the modified gauge and Yukawa couplings for $h$, we show the correlation between the deviation in the Yukawa coupling for the tau lepton $h\tau^+\tau^-$ and that for the bottom quark $hb\bar{b}$ under the assumption of a non-zero deviation in the $hVV$ $(V=W,Z)$ couplings in two Higgs doublet models (2HDMs) and three Higgs doublet models (3HDMs) as simple examples. We clarify the possible allowed prediction of the deviations in the 3HDMs which cannot be explained in the 2HDMs even taking into account the one-loop electroweak corrections to the Yukawa coupling.

Doubling up on supersymmetry in the Higgs sector

We explore the possibility that physics at the TeV scale possesses approximate $N = 2$ supersymmetry, which is reduced to the $N=1$ minimal supersymmetric extension of the Standard Model (MSSM) at the electroweak scale. This doubling of supersymmetry modifies the Higgs sector of the theory, with consequences for the masses, mixings and couplings of the MSSM Higgs bosons, whose phenomenological consequences we explore in this paper. The mass of the lightest neutral Higgs boson $h$ is independent of $\tan \beta$ at the tree level, and the decoupling limit is realized whatever the values of the heavy Higgs boson masses. Radiative corrections to the top quark and stop squarks dominate over those due to particles in $N=2$ gauge multiplets. We assume that these radiative corrections fix $m_h \simeq 125$ GeV, whatever the masses of the other neutral Higgs bosons $H, A$, a scenario that we term the $h$2MSSM. Since the $H, A$ bosons decouple from the $W$ and $Z$ bosons in the $h$2MSSM at tree level, only the LHC constraints on $H, A$ and $H^\pm$ couplings to fermions are applicable. These and the indirect constraints from LHC measurements of $h$ couplings are consistent with $m_A \gtrsim 200$ GeV for $\tan \beta \in (2, 8)$ in the $h$2MSSM.

Search for two Higgs bosons in final states containing two photons and two bottom quarks in proton-proton collisions at 8 TeV

A search is presented for the production of two Higgs bosons in final states containing two photons and two bottom quarks. Both resonant and nonresonant hypotheses are investigated. The analyzed data correspond to an integrated luminosity of 19.7 inverse femtobarns of proton-proton collisions at sqrt(s) = 8 TeV collected with the CMS detector. Good agreement is observed between data and predictions of the standard model (SM). Upper limits are set at 95% confidence level on the production cross section of new particles and compared to the prediction for the existence of a warped extra dimension. When the decay to two Higgs bosons is kinematically allowed, assuming a mass scale Lambda[R] = 1 TeV for the model, the data exclude a radion scalar at masses below 980 GeV. The first Kaluza-Klein excitation mode of the graviton in the RS1 Randall-Sundrum model is excluded for masses between 325 and 450 GeV. An upper limit of 0.71 pb is set on the nonresonant two-Higgs-boson cross section in the SM-like hypothesis. Limits are also derived on nonresonant production assuming anomalous Higgs boson couplings.

Probing charged Higgs boson couplings at a future circular hadron collider

Many of the new physics models predicts a light Higgs boson similar to the Higgs boson of the Standard Model (SM) and also extra scalar bosons. Beyond the search channels for a SM Higgs boson, the future collider experiments will explore additional channels that are specific to extended Higgs sectors. We study the charged Higgs boson production within the framework of two Higgs doublet models (THDM) in the proton-proton collisions at the FCC-hh collider. With an integrated luminosity of 500 fb$^{-1}$ at very high energy frontier, we obtain a significant coverage of the parameter space and distinguish the charged Higgs-top-bottom interaction within the THDM or other new physics models with charged Higgs boson mass up to 1 TeV.

Synergy between measurements of gravitational waves and the triple-Higgs coupling in probing the first-order electroweak phase transition

Probing the Higgs potential and new physics behind the electroweak symmetry breaking is one of the most important issues of particle physics. In particular, nature of electroweak phase transition is essential for understanding physics at the early Universe, such that the strongly first order phase transition is required for a successful scenario of electroweak baryogenesis. The strongly first order phase transition is expected to be tested by precisely measuring the triple Higgs boson coupling at future colliders like the International Linear Collider. It can also be explored via the spectrum of stochastic gravitational waves to be measured at future space-based interferometers such as eLISA and DECIGO. We discuss complementarity of both the methods in testing the strongly first order phase transition of the electroweak symmetry in models with additional isospin singlet scalar fields with and without classical scale invariance. We find that they are synergetic in identifying specific models of electroweak symmetry breaking in more details.

The complete HEFT Lagrangian after the LHC Run I

The complete effective chiral Lagrangian for a dynamical Higgs is presented and constrained by means of a global analysis including electroweak precision data together with Higgs and triple gauge boson coupling data from the LHC Run~I. The operators' basis up to next-to-leading order in the expansion consists of 148 (188 considering right-handed neutrinos) flavour universal terms and it is presented here making explicit the custodial nature of the operators. This effective Lagrangian provides the most general description of the physical Higgs couplings once the electroweak symmetry is assumed, and it allows for deviations from the $SU(2)_L$ doublet nature of the Standard Model Higgs. The comparison with the effective linear Lagrangian constructed with an exact $SU(2)_L$ doublet Higgs and considering operators with at most canonical dimension six is presented. A promising strategy to disentangle the two descriptions consists in analysing i) anomalous signals present only in the chiral Lagrangian and not expected in the linear one, that are potentially relevant for LHC searches, and ii) decorrelation effects between observables that are predicted to be correlated in the linear case and not in the chiral one. The global analysis presented here, that includes several kinematic distributions, is crucial for reducing the allowed parameter space and for controlling the correlations between parameters. This improves previous studies aimed at investigating the Higgs Nature and the origin of the electroweak symmetry breaking.

Measuring the trilinear neutral Higgs boson couplings in the minimal supersymmetric standard model at e+e− colliders in the light of the discovery of a Higgs boson

We consider the measurement of the trilinear couplings of the neutral Higgs bosons in the minimal supersymmetric standard model (MSSM) at a high energy [Formula: see text] linear collider in the light of the discovery of a Higgs boson at the CERN Large Hadron Collider (LHC). We identify the state observed at the LHC with the lightest Higgs boson [Formula: see text] of the MSSM, and impose the constraints following from this identification, as well as other experimental constraints on the MSSM parameter space. In order to measure trilinear neutral Higgs couplings, we consider different processes where the heavier Higgs boson [Formula: see text] of the MSSM is produced in electron–positron collisions, which subsequently decays into a pair of lighter Higgs boson. We identify the regions of the MSSM parameter space where it may be possible to measure the trilinear couplings of the Higgs boson at a future electron–positron collider. A measurement of the trilinear Higgs couplings is a crucial step in the construction of the Higgs potential, and hence in establishing the phenomena of spontaneous symmetry breaking in gauge theories.

Symmetries behind the 750 GeV diphoton excess

A 750 GeV resonance has been observed at the Run 2 LHC in the diphoton channel. In this paper, we explain this resonance as a CP-even scalar, S, that triggers the spontaneous breaking of local $U(1)_B$ or $U(1)_{B+L}$ gauge symmetries. S couples to gluon and photon pairs at the one-loop level, where particles running in the loop are originally introduced to cancel anomalies. The gluon fusion is the dominate production channel of S at the LHC. The model automatically contains a scalar dark matter candidate, stabilized by the new gauge symmetry. Our study shows that both the observed production cross section at the LHC and the best fit decay width of S can be explained in this concrete model, without conflicting with any experimental data. Constraints on couplings of S are studied, which shows a negligible mixing with the standard model Higgs boson but sizable coupling with the dark matter.

The sensitivity of the Higgs boson branching ratios to the W boson width

The Higgs boson branching ratio into vector bosons is sensitive to the decay widths of those vector bosons because they are produced with at least one boson significantly off-shell. Gamma(H to V V ) is approximately proportional to the product of the Higgs boson coupling and the vector boson width. Gamma Z is well known, but Gamma W gives an uncertainty on Gamma(H to W W ) which is not negligible. The ratio of branching ratios, BR(H to W W )/BR(H to ZZ) measured by a combination of ATLAS and CMS at LHC is used herein to extract a width for the W boson of Gamma W = 1.8+0.4-0.3 GeV by assuming Standard Model couplings of the Higgs bosons. This dependence of the branching ratio on Gamma W is not discussed in most Higgs boson coupling analyses.

Probing the Higgs sector of the minimal Left-Right symmetric model at future hadron colliders

If neutrino masses arise from a TeV-scale minimal Left-Right seesaw model, the ensuing extended Higgs sector with neutral, singly and doubly-charged scalars has a plethora of implications for new Higgs boson searches beyond the Standard Model at future hadron colliders, such as the $\sqrt s=14$ TeV High-Luminosity Large Hadron Collider (HL-LHC) and the proposed $\sqrt s=100$ TeV collider (FCC-hh or SPPC). In this article, we provide a glimpse of this new physics in the Higgs sector. Our discussion focuses on the minimal non-supersymmetric version of the Left-Right model with high-scale parity breaking but TeV-scale $SU(2)_R$-breaking, a property desirable to suppress the type-II seesaw contribution to neutrino masses. We analyze the masses and couplings of the physical Higgs bosons in this model, and discuss their dominant production and decay modes at hadron colliders. We identify the best discovery channels for each of the non-SM Higgs bosons and estimate the expected SM backgrounds in these channels to derive the sensitivity reaches for the new Higgs sector at future hadron colliders under discussion. Following a rather conservative approach, we estimate that the heavy Higgs sector can be effectively probed up to 15 TeV at the $\sqrt s=100$ TeV machine. We also discuss how the LR Higgs sector can be distinguished from other extended Higgs sectors.

Radiative corrections to the Higgs boson couplings in the model with an additional real singlet scalar field

We calculate renormalized Higgs boson couplings with gauge bosons and fermions at the one-loop level in the model with an additional isospin singlet real scalar field. These coupling constants can deviate from the predictions in the standard model due to tree-level mixing effects and one-loop contributions of the extra neutral scalar boson. We investigate how they can be significant under the theoretical constraints from perturbative unitarity and vacuum stability and also the condition of avoiding the wrong vacuum. Furthermore, comparing with the predictions in the Type I two Higgs doublet model, we numerically demonstrate how the singlet extension model can be distinguished and identified by using precision measurements of the Higgs boson couplings at future collider experiments.

Higgs Boson Studies at the Tevatron

We present the combination of searches for the Standard Model Higgs boson at a center-of-mass energy of s=1.96 TeV, using the full Run 2 dataset collected with the CDF and D0 detectors at the Fermilab Tevatron collider. We also present combined measurements of Higgs Boson production cross sections, branching ratios, and couplings to fermions and bosons. Finally, we present tests of different spin and parity hypotheses for a particle H of mass 125 GeV produced in association with a vector boson and decaying into a pair of b quarks, and place constraints on such hypotheses using the D0 data.

Radiative corrections to Higgs coupling constants in two Higgs doublet models

A pattern of deviations in the Standard Model (SM) like Higgs boson (h) couplings from their SM predictions depends on the structure of the Higgs sector and the Yukawa interaction. In particular, in Two Higgs Doublet Models (THDMs) with a softly-broken Z2 symmetry, different characteristic patterns of deviation in Yukawa coupling constants (hff‾) can be allowed depending on four types of Yukawa interactions. We calculate hff‾ coupling constants at the one-loop level in all the types of THDMs. Even if there is no deviation in the hff‾ couplings at the tree level, they can deviate from the SM predictions by a few percent due to extra Higgs boson loop contributions. We find that if the deviations in the gauge couplings hVV(V=Z,W) are found with an enough large to be measured at the International Linear Collider (ILC), the scale factors for the hff‾ couplings do not overlap among the THDMs with four types of Yukawa interactions even taking into account the radiative corrections. Therefore, in such a case, we can indirectly determine the type of the THDMs at the ILC even without information from direct searches of the additional Higgs bosons.

Higgs-strahlung production process e+e− → hZ at the future Higgs factory in the SM extension with color-octet scalars

We investigate the Higgs-strahlung production process e+e− → hZ at the future Higgs factory in the Manohar-Wise model, which extends the SM by a family of color-octet and isospin-doublet scalars. We scan over the parameter space of the Manohar-Wise model considering the theoretical and experimental constraints from unitarity, electroweak data and LHC searches for the color-octet scalars and perform fits with the Higgs data from ATLAS and CMS. Then we calculate the cross section σ(e+e− → hZ) at s=240GeV by including the radiative corrections from loops mediated by color-octet scalars. We find that the deviation of the cross section in the Manohar-Wise model from its SM prediction can maximally reach 11%, and the large deviations are mainly due to the potentially large coupling of Higgs boson with CP-odd color-octet scalars SIA (i.e., the coupling hSIA∗SIB).

Higgs Phenomenology of the Supersymmetric Grand Unification with the Hosotani Mechanism

The supersymmetric S U(5) grand unified theory with the gauge symmetry broken by the Hosotani mechanism naturally solves the mass hierarchy problem between the colored Higgs triplet and the electroweak Higgs doublet, and predicts the existence of adjoint chiral superfields with masses of the order of the supersymmetry breaking scale as a byproduct. In addition to the two SU(2)L Higgs doublets of the minimal supersymmetric standard model, the Higgs sector is extended by an SU(2)L triplet chiral supermultiplet with hypercharge zero and a neutral singlet one. Such new triplet and singlet chiral supermultiplets deviate the standard model-like Higgs boson couplings and the additional Higgs boson masses from their Standard Model predictions. We show that this model can be distinguished from other new physics models using by precisely measuring such Higgs couplings and masses, and that our model is a good example of grand unification testable at the luminosity up-graded Large Hadron Collider and future electron-positron colliders.

Measurement of Higgs boson couplings at the International Linear Collider

Precision measurement of Higgs boson couplings will be the central task of high energy physics in the next decades, as the key to the unknown. This article gives an overview of how various Higgs couplings will be measured at the International Linear Collider (ILC). Emphases are placed on the ILC's capability of performing fully model independent determination of absolute HZZ and HWW couplings, the Higgs total width, and hence various other Higgs couplings, such as Hbb and Hcc, which cover essentially all the crucial ones including the top-Yukawa coupling Htt and the self-coupling λHHH. The strategy to get the best precision measurements at the ILC is through staged running. A method of global fitting is applied to utilize all of the available information from each stage and to derive combined precisions.

Measurement of the Higgs Boson Coupling to the Top Quark and the Higgs Boson Self-coupling at the ILC

The International Linear Collider is a proposed 50 km electron-positron collider in the Kitakami hills in northern Japan. Precision measurements of Higgs properties and direct searches for new physics will complement the LHC experiments and their upgrades in our drive to answer open questions about the universe and the origin of matter. Two detector concepts have been validated as being feasible to deliver the necessary precision. In its baseline configuration the machine has a collision energy of about 500 GeV, upgradeable to 1 TeV. The electron beam is 80% polarized. The polarization of the positron beam is 30% at 500 GeV and 20% at 1 TeV. The integrated luminosity in a high-luminosity scenario is 1.6 ab-1 at 500 GeV and 2.5 ab-1 at 1 TeV. The measurements of the Higgs boson self-coupling and the coupling to the top quark are important pieces of the ILC physics program.

Search for H to [formula omitted] in association with single top quarks as a test of Higgs boson couplings

The production of a Higgs boson in association with a single top quark is one of a few channels which are sensitive for not yet excluded anomalous couplings of the Higgs boson to fermions. Multivariate analysis tools are used for the reconstruction and classification of signal events, where the Higgs boson decays into bottom quarks and the single top quark decays leptonically. In this conference report the most recent results at time of the conference using the full dataset recorded by the CMS detector at 8 TeV are presented.

Higgs Measurement at e+e- Circular Colliders

Now that the mass of the Higgs boson is known, circular electron positron colliders, able to measure the properties of these particles with high accuracy, are receiving considerable attention. Design studies have been launched (i) at CERN with the Future Circular Colliders (FCC), of which an e+e- collider is a potential first step (FCC-ee, formerly caller TLEP) and (ii) in China with the Circular Electron Positron Collider (CEPC). Hosted in a tunnel of at least 50 km (CEPC) or 80-100 km (FCC), both projects can deliver very high luminosity from the Z peak to HZ threshold (CEPC) and even to the top pair threshold and above (FCC-ee).At the ZH production optimum, around 240 GeV, the FCC-ee (CEPC) will be able to deliver 10 (5) ab-1 integrated luminosity in 5 (10) years with 4 (2) interaction points: hence to produce millions of Higgs bosons through the Higgsstrahlung process and vector boson fusion processes. This sample opens the possibility of sub-per-cent precision absolute measurements of the Higgs boson couplings to fermions and to gauge-bosons, and of the Higgs boson width. These precision measurements are potentially sensitive to multi-TeV range new physics interacting with the scalar sector. The ZH production mechanism also gives access to the invisible or exotic branching ratios down to the per mil level, and with a more limited precision to the triple Higgs coupling. For the FCC-ee, the luminosity expected at the top pair production threshold (s∼340–350 GeV) further improves some of these accuracies significantly, and is sensitive to the Higgs boson coupling to the top quark.

Update of the electroweak precision fit, interplay with Higgs-boson signal strengths and model-independent constraints on new physics

We present updated global fits of the Standard Model and beyond to electroweak precision data, taking into account recent progress in theoretical calculations and experimental measurements. From the fits, we derive model-independent constraints on new physics by introducing oblique and epsilon parameters, and modified Zbb‾ and HVV couplings. Furthermore, we also perform fits of the scale factors of the Higgs-boson couplings to observed signal strengths of the Higgs boson.