gauge-Higgs Coupling Research Articles

Influence of new states in searches for negative gauge-Higgs couplings

In this work, we explore how constraints based on interference effects for the negative gauge-Higgs coupling scenario are affected by new physics. Models that achieve this wrong-sign gauge-Higgs coupling inevitably have new charged Higgs states. These states affect the interpretation of interference effects. We recast the ATLAS analysis for VBF Wh, showing that the previously excluded negative gauge-Higgs coupling scenario is still experimentally viable for charged Higgs masses below 370 GeV. We show that it is possible to weaken this bound further with mild tuning in the parameter space. We discuss how to further constrain the wrong-sign gauge-Higgs coupling hypothesis and point out the potential of VBF Zh to exclude this scenario in a model-independent way.

Higgs boson precision analysis of the full LHC run 1 and run 2 data

We perform global fits of the Higgs boson couplings to the full Higgs datasets collected at the LHC with the integrated luminosities per experiment of approximately 5/fb at 7 TeV, 20/fb at 8 TeV, and up to 139/fb at 13 TeV. Our combined analysis based on the experimental signal strengths used in this work and the theoretical ones elaborated for our analysis reliably reproduce the results in the literature. We reveal that the LHC Higgs precision data are no longer best described by the Standard Model (SM) Higgs boson taking account of extensive and comprehensive CP-conserving and CP-violating scenarios found in several well-motivated models beyond the SM. Especially, in most of the fits considered in this work, we observe that the best-fitted values of the normalized Yukawa couplings are about 2σ below the corresponding SM ones with the 1σ errors of 3%–5%. On the other hand, the gauge-Higgs couplings are consistent with the SM with the 1σ errors of 2%–3%. Incidentally, the reduced Yukawa couplings help to explain the excess of the H→Zγ signal strength of 2.2±0.7 recently reported by the ATLAS and CMS collaborations. Published by the American Physical Society 2024

Quartic Gauge-Higgs couplings: constraints and future directions

Constraints on quartic interactions of the Higgs boson with gauge bosons have been obtained by the experimental LHC collaborations focussing on the so-called κ framework of flat rescalings of SM-like interactions in weak boson fusion (WBF) Higgs pair production. While such approaches are admissible to obtain a qualitative picture of consistency with the SM when the statistical yield is low, once more statistics become available a more theoretically consistent framework of limit setting is desirable. Reviewing the constraints provided at the Large Hadron Collider, we first show that these limits are robust when considered in a leading order context. Turning to radiative corrections, we demonstrate the limitations of this approach in the SM, and by adopting Higgs effective field theory techniques, we clarify the sensitivity from single Higgs measurements to rescalings of quartic Higgs-gauge couplings. We then discuss avenues for sensitivity improvements of WBF analyses employing Graph Neural Networks to combat the large contributing backgrounds.

A fully differential SMEFT analysis of the golden channel using the method of moments

The Method of Moments is a powerful framework to disentangle the relative contributions of amplitudes of a specific process to its various phase space regions. We apply this method to carry out a fully differential analysis of the Higgs decay channel h → 4ℓ and constrain gauge-Higgs coupling modifications parametrised by dimension-six effective operators. We find that this analysis approach provides very good constraints and minimises degeneracies in the parameter space of the effective theory. By combining the decay h → 4ℓ with Higgs-associated production processes, Wh and Zh, we obtain the strongest reported bounds on anomalous gauge-Higgs couplings.

Entangling Higgs production associated with a single top and a top-quark pair in the presence of anomalous top-Yukawa coupling

The ATLAS and CMS collaborations observed a mild excess in the associated Higgs production with a top-quark pair left(toverline{t}hright) and reported the signal strengths of μtthATLAS = 1.81 ± 0.80 and μtthCMS = 2.75 ± 0.99 based on the data collected at sqrt{s}=7 and 8 TeV. Although, at the current stage, there is no obvious indication whether the excess is real or due to statistical fluctuations, here we perform a case study of this mild excess by exploiting the strong entanglement between the associated Higgs production with a single top quark (thX) and toverline{t}h production in the presence of anomalous top-Yukawa coupling. As well known, toverline{t}h production only depends on the absolute value of the top-Yukawa coupling. Meanwhile, in thX production, this degeneracy is lifted through the strong interference between the two main contributions which are proportional to the top-Yukawa and the gauge-Higgs couplings, respectively. Especially, when the relative sign of the top-Yukawa coupling with respect to the gauge-Higgs coupling is reversed, the thX cross section can be enhanced by more than one order of magnitude. We perform a detailed study of the influence of thX production on toverline{t}h production in the presence of the anomalous top-Yukawa coupling and point out that it is crucial to include thX production in the analysis of the toverline{t}h data to pin down the sign and the size of the top-Yukawa coupling in future. While assuming the Standard Model (SM) value for the gauge-Higgs coupling, we vary the top-Yukawa coupling within the range allowed by the current LHC Higgs data. We consider the Higgs decay modes into multileptons, boverline{b} and γγ putting a particular emphasis on the same sign dilepton events. We also discuss the prospects for the LHC Run-2 on how to disentangle thX production from toverline{t}h one and how to probe the anomalous top-Yukawa coupling.

Comparison of complex Langevin and mean field methods applied to effective Polyakov line models

Effective Polyakov line models, derived from SU(3) gauge-matter systems at finite chemical potential, have a sign problem. In this article I solve two such models, derived from SU(3) gauge-Higgs and heavy quark theories by the relative weights method, over a range of chemical potentials where the sign problem is severe. Two values of the gauge-Higgs coupling are considered, corresponding to a heavier and a lighter scalar particle. Each model is solved via the complex Langevin method, following the approach of Aarts and James, and also by a mean field technique. It is shown that where the results of mean field and complex Langevin agree, they agree almost perfectly. Where the results of the two methods diverge, it is found that the complex Langevin evolution has a branch cut crossing problem, associated with a logarithm in the action, that was pointed out by Mollgaard and Splittorff.

Disentangling a dynamical Higgs

The pattern of deviations from Standard Model predictions and couplings is different for theories of new physics based on a non-linear realization of the $SU(2)_L\times U(1)_Y$ gauge symmetry breaking and those assuming a linear realization. We clarify this issue in a model-independent way via its effective Lagrangian formulation in the presence of a light Higgs particle, up to first order in the expansions: dimension-six operators for the linear expansion and four derivatives for the non-linear one. Complete sets of pure gauge and gauge-Higgs operators are considered, implementing the renormalization procedure and deriving the Feynman rules for the non-linear expansion. We establish the theoretical relation and the differences in physics impact between the two expansions. Promising discriminating signals include the decorrelation in the non-linear case of signals correlated in the linear one: some pure gauge versus gauge-Higgs couplings and also between couplings with the same number of Higgs legs. Furthermore, anomalous signals expected at first order in the non-linear realization may appear only at higher orders of the linear one, and vice versa. We analyze in detail the impact of both type of discriminating signals on LHC physics.

Charged Higgs production in association withW±at large hadron colliders

Many new physics models beyond the standard model, such as the littlest higgs models and the left right twin higgs models, predict the existence of the large charged higgs couplings H^-q\bar b and H^+b\bar q, where q=t or the new vector-like heavy quark T; On the other hand, some new physics models like the littlest higgs also predict the gauge-higgs couplings. Such couplings may have rich collider phenomenology. We focus our attention on these couplings induced by the littlest higgs models and the left right twin higgs models models and consider their contributions to the production cross section for W^\pm H^\mp production at the large hadron colliders. We find that the cross sections, in the littlest higgs models, on the parton level gg \to W^\pm H^\mp and q\bar q \to W^\pm H^\mp (q=u,d,s,c,b) may reach tens of several dozen femtobarns in reasonable parameters space at the collision energy of 14 TeV and that the total cross section can even reach a few hundred femtobarns in certain favored space. While in the left right twin higgs models, the production rates are basically one order lower than these in littlest higgs. Therefore, due to the large cross sections of that in the littlest higgs, it may be possible to probe the charged higgs via this process in a large parameter space.

The effective chiral Lagrangian for a light dynamical “Higgs particle”

We generalize the basis of CP-even chiral effective operators describing a dynamical Higgs sector, to the case in which the Higgs-like particle is light. Gauge and gauge-Higgs operators are considered up to mass dimension five. This analysis completes the tool needed to explore at leading order the connection between linear realizations of the electroweak symmetry breaking mechanism — whose extreme case is the Standard Model — and non-linear realizations with a light Higgs-like particle present. It may also provide a model-independent guideline to explore which exotic gauge-Higgs couplings may be expected, and their relative strength to Higgsless observable amplitudes. With respect to fermions, the analysis is reduced by nature to the consideration of those flavor-conserving operators that can be written in terms of pure-gauge or gauge-Higgs ones via the equations of motion, but for the standard Yukawa-type couplings.

Distinguishing various models of the 125 GeV boson in Vector Boson Fusion

The hint of a new particle around 125 GeV at the LHC through the decay modes of diphoton and a number of others may point to quite a number of possibilities. While at the LHC the dominant production mechanism for the Higgs boson of the standard model and some other extensions is via the gluon fusion process, the alternative vector boson fusion is more sensitive to electroweak symmetry breaking through the gauge-Higgs couplings and therefore can be used to probe for models beyond the standard model. In this work, using the well known dijet-tagging technique to single out the vector boson fusion mechanism, we investigate its capability to discriminate a number of models that have been suggested to give an enhanced inclusive diphoton production rate, including the standard model Higgs boson, fermiophobic Higgs boson, Randall-Sundrum radion, inert-Higgs-doublet model, two-Higgs-doublet model, and the MSSM. The rates in vector-boson fusion can give more information of the underlying models to help distinguishing among the models.

Electroweak constraints on warped geometry in five dimensions and beyond

Here we consider the tree level corrections to electroweak (EW) observables from standard model (SM) particles propagating in generic warped extra dimensions. The scale of these corrections is found to be dominated by three parameters, the Kaluza-Klein (KK) mass scale, the relative coupling of the KK gauge fields to the Higgs and the relative coupling of the KK gauge fields to fermion zero modes. It is found that 5D spaces that resolve the hierarchy problem through warping typically have large gauge-Higgs coupling. It is also found in $D>5$ where the additional dimensions are warped the relative gauge-Higgs coupling scales as a function of the warp factor. If the warp factor of the additional spaces is contracting towards the IR brane, both the relative gauge-Higgs coupling and resulting EW corrections will be large. Conversely EW constraints could be reduced by finding a space where the additional dimension's warp factor is increasing towards the IR brane. We demonstrate that the Klebanov Strassler solution belongs to the former of these possibilities.

Anomalous Couplings in [formula omitted] at LHC and ILC

We consider sensitivities on anomalous gauge and gauge-Higgs couplings in the process γ γ → W + W − at the LHC and the ILC. Within an effective Lagrangian approach we find that six anomalous couplings can be studied in this process using the normalised event distributions. We employ optimal observables to disentangle the contributions from these six anomalous couplings. Preliminary results indicate that sensitivities in γ γ → W + W − at the LHC may be competitive with available results for certain gauge couplings and give direct access to two anomalous gauge-Higgs couplings. Measuring γ γ → W + W − with the photon mode of the ILC could improve the corresponding sensitivities by two orders of magnitude. Polarisation of the initial photons is a valuable tool to achieve very high precisions.

On the SU(2)-Higgs phase transition

We investigate the properties of the Confinement-Higgs phase transition in the SU(2)-Higgs model. The system is shown to exhibit a transient behavior up to L = 24 along which, the order of the phase transition cannot be discerned. In order to get a global vision on the problem, we have introduced a second (next-to-nearest neighbors) gauge-Higgs coupling ( κ 2). On this extended parameter space we find a line of phase transitions becoming increasely weak as the standard case is approached ( κ 2 = 0). From the global behavior on this parameter space we conclude that the transition is also first order in the standard case.

On the SU (2) -Higgs phase transition

The properties of the confinement-Higgs phase transition in the SU(2)-Higgs model with fixed modulus are investigated. We show that the system exhibits a transient behavior up to L = 24 along which the order of the phase transition cannot be discerned. To get stronger conclusions about this point, without going to prohibitively large lattice sizes, we have introduced a second (next-to-nearest neighbors) gauge-Higgs coupling ( κ 2). On this extended parameter space we find a line of phase transitions which become increasingly weaker as κ 2 → 0. The results point to a first-order character for the transition with the standard action ( κ 2 = 0).

Chiral symmetry properties of U(1) lattice gauge theory with scalar and fermion fields

We report new results in three areas concerning the chiral transition in U(1) lattice gauge-Higgs theory with fermions. First, the case of a theory with two differently charged fermions simultaneously present is studied, and it is shown analytically that there are two associated continuous chiral phase transitions. Second, a general theorem is proved classifying the strong gauge-coupling behavior of any U(1) theory with a fermion and Higgs fields of arbitrary nonzero charges q f and q h: such a theory has a chiral transitions along the β g = 0 line if and only if q f is a nonzero multiple of q h. Third, new data is presented on the chiral transition with quenched fermions in the interiof of the phase diagram at small or zero gauge-Higgs coupling, completing our earlier mapping of the chiral phase boundary.

Analytic and numerical results on the chiral transition in SU(2) lattice gauge-Higgs theory with fermions

We present an analytic study of the (zero-temperature) chiral symmetry-breaking phase transition in SU(2) lattice gauge-Higgs theory with fermions, relevant to the SU(2) sector of the standard electroweak theory. The transition is found to be second-order and the critical gauge-Higgs coupling is calculated in the limit of strong gauge coupling. New Monte Carlo measurements for quenched I = 1 2 fermions are presented and found to be in excellent agreement with the analytic results, which are not limited to the quenched approximation.

The phase structure of the non-compact abelian Higgs model

We study the non-compact abelian Higgs model on the lattice in a version with fixed-length Higgs and a Villain form of the gauge-Higgs coupling. This version permits a simplified proof of the earlier results that the model is in its Coulomb phase at sufficiently strong gauge coupling or at sufficiently small values for the Higgs length. Also, it enables us to establish the Coulomb phase simultaneously in these two regions. Similar methods demonstrate the occurence of a phase transition to a new phase - shown previously to be the Higgs phase - valid at Large Higgs lenght when the gauge coupling is not too strong. We use the correlation length of the Higgs field as an order parameter, and also study the behavior of the gauge propagator.