Higgs Couplings Research Articles

Phenomenology of a supersymmetric model inspired by inflation

The current challenges in high energy physics and cosmology are to build coherent particle physics models to describe the phenomenology at colliders in the laboratory and the observations in the universe. From these observations, the existence of an inflationary phase in the early universe gives guidance for particle physics models. We study a supersymmetric model which incorporates successfully inflation by a non-minimal coupling to supergravity and shows a unique collider phenomenology. Motivated by experimental data, we set a special emphasis on a new singlet-like state at 97,text {GeV} and single out possible observables for a future linear collider that permit a distinction of the model from a similar scenario without inflation. We define a benchmark scenario that is in agreement with current collider and Dark Matter constraints, and study the influence of the non-minimal coupling on the phenomenology. Measuring the singlet-like state with high precision on the percent level seems to be promising for resolving the models, even though the Standard Model-like Higgs couplings deviate only marginally. However, a hypothetical singlet-like state with couplings of about 20,% compared to a Standard Model Higgs at 97,text {GeV} encourages further studies of such footprint scenarios of inflation.

New scenario for aligned Higgs couplings originated from the twisted custodial symmetry at high energies

We investigate a new scenario of the two Higgs doublet model, where the current experimental data for the electroweak rho parameter and those for the Higgs boson couplings can be simultaneously explained. In this scenario, the two Higgs doublet model is supposed to be a low energy effective theory up to a high energy scale Λ, above which a fundamental theory should appear. It is assumed that the Higgs potential respects a global symmetry at Λ (the twisted custodial symmetry), which is to be given as a consequence of the global symmetry structure of the fundamental theory above Λ. By the analysis using one-loop renormalization group equations, the above experimental data can be explained in a natural way even when the masses of the extra Higgs bosons are near the electroweak scale. We also discuss the predictions on the mass spectrum of the additional Higgs bosons and also those on the coupling constants of the standard-model-like Higgs boson, which make it possible to test this scenario at the current and future collider experiments.

Impact of LHC Higgs couplings measurements on bosonic decays of the neutral Higgs sector in the scNMSSM

We analyze the Next-to-minimal supersymmetric Standard Model with Grand unification boundary conditions under current theoretical and experimental constraints. We compute the mass spectrum of the model and focus on the three lightest particles in the Higgs sector (two CP-even scalars, [Formula: see text], [Formula: see text] and one CP-odd, [Formula: see text]). The reduced couplings of such particles, singlet-doublet components, their branching ratios to bosons and reduced cross-section to photons and massive gauge bosons via gluon fusion are thoroughly and systematically scrutinized. Our analysis is focused on the parameter space where the singlet-doublet coupling [Formula: see text] is as large as possible (keeping the perturbativity bound intact) and the ratio between the vacuum expectation values of the up-type and down-type Higgses [Formula: see text] is as small as possible, which is the region representing the most natural case of the NMSSM. We show the impact of recent constraints from the LHC on the SM-Higgs couplings to bosons and fermions on the parameter space of the model and the consequent implications on the Higgs sector. The results show that while the model is still able to account for current data, and provide an opportunity for discovery of extended Higgs sectors, recent LHC Higgs couplings constraints rule-out parts of the parameter space where [Formula: see text] (non-SM-like) and [Formula: see text] are non-singlet with masses below 400 GeV.

Effective field theory perspective on next-to-minimal composite Higgs models

We study both the CP-even and CP-odd effective chiral Lagrangians of next minimal composite Higgs model {with symmetry breaking pattern depicted by the coset $SO(6)/SO(5)$} through the sigma/omega decomposition, in which the Goldstone matrix of the coset is decomposed in terms of the standard model Higgs doublet and an additional scalar singlet $s$ at the electroweak scale. The effective Lagrangian is described by the electroweak chiral Lagrangian up to $p^4$ order, with a function dependence on the Higgs boson and new scalar $s$, named Higgs function. This function in the effective Lagrangian incorporates the Higgs non-linearity or vacuum misalignment effects in the next minimal composite Higgs model, due to the Riemann curvature on the Nambu-Goldstone bosons scalar manifold, leads to various Higgs couplings deviated from the standard model ones, and also indicates the relations among different Higgs couplings in the low energy. Matching to the Higgs effective field theory below the electroweak scale, we obtain various low energy observables such as the electroweak oblique parameters, anomalous triple and quartic gauge couplings, anomalous couplings of Higgs to gauge bosons, in which the Higgs non-linearity effects are encoded in the ratio $\xi\equiv v^2/f^2$ of the electroweak scale and the new physics scale.

Measuring Higgs CP and Couplings with Hadronic Event Shapes

Measuring Higgs CP and Couplings with Hadronic Event Shapes

Discrimination between the final state of tH and tb using neural network

After the discovery of the Higgs boson in 2012 at the Large Hadron Collider (LHC), the effort to understand the detailed properties of the Higgs bosons started. Of particular importance is study of the Higgs coupling to the top quark. This coupling can be studied through the associated production of Higgs boson with top-antitop quark pair, tH. This process however suffers from the indistinguishable background tH , since the Higgs boson decays predominately into bottom anti-bottom quark pair, b . This study presents systematic approach of using machine learning (ML), specifically neural network method to distinguish between the process tH and tb . Using input variables of kinematic variables (momentum), we found a signal efficiency of 46.7 % for signal events that have passed the preselection criteria. We conclude that the currently used input variables are not sufficient to discriminate between signal and background events, and we suggest that inclusion of input variables calculated from the fully reconstructed event could provide stronger discrimination between signal and background.

A warped scalar portal to fermionic dark matter

We argue that extensions of the SM with a warped extra dimension, together with a new {mathbb {Z}}_2-odd scalar singlet, provide a natural explanation not only for the hierarchy problem but also for the nature of fermion bulk masses and the observed dark matter relic abundance. In particular, the Kaluza-Klein excitations of the new scalar particle, which is required to naturally obtain fermion bulk masses through Yukawa-like interactions, can be the leading portal to any fermion propagating into the bulk of the extra dimension and playing the role of dark matter. Moreover, such scalar excitations will necessarily mix with the Higgs boson, leading to modifications of the Higgs couplings and branching ratios, and allowing the Higgs to mediate the coannihilation of the fermionic dark matter. We study these effects and explore the viability of fermionic dark matter in the presence of these new heavy scalar mediators both in the usual freeze-out scenario and in the case where the freeze-out happens during an early period of matter domination.

Probing the Higgs boson through Yukawa force

The ATLAS and CMS collaborations of the LHC have observed that the Higgs boson decays into the bottom quark-antiquark pair, and have also established that the Higgs coupling with the top quark-antiquark pair is instrumental in one of the modes for Higgs production. This underlines the discovery of the Yukawa force at the LHC. We demonstrate the impact of this discovery on the Higgs properties that are related to the dynamics of electroweak symmetry breaking. We show that these measurements have considerably squeezed the allowed window for new physics contributing to the Higgs couplings with the weak gauge bosons and the third generation quarks. The expected constraints at the HL-LHC and future Higgs factories are also shown. We project these constraints on the parameter space of a few motivated scenarios beyond the Standard Model. We pick them under two broad categories, namely, the composite Higgs and its RS dual, as well as various types of multi-Higgs models. The latter category includes models with singlet scalars, Type I, II and BGL-type two-Higgs doublet models, and models with scalar triplets à la Georgi and Machacek.

Electric dipole moment of the neutron in two-Higgs-doublet models with flavor changing couplings

I consider contributions to the neutron electric dipole moment within two-Higgs-doublet models which allow for small flavor changing neutral Higgs couplings. In a previous paper, I considered flavor changing interactions for the Standard Model Higgs boson to first order in the flavor changing coupling. In that paper I found that the obtained value of the neutron electric dipole moment was below the present experimental limit, given previous restrictions on such couplings. Because this was an effective theory, the result depended on an ultraviolet cut off $\mathrm{\ensuremath{\Lambda}}$, parametrized as $\mathrm{ln}({\mathrm{\ensuremath{\Lambda}}}^{2})$. In the present paper I demonstrate that, when going to two-Higgs-doublet models, the result stays the same as in the previous paper, up to ${M}_{\mathrm{SM}}^{2}/{M}_{H}^{2}$ corrections, where ${M}_{\mathrm{SM}}$ is the mass of the top quark or the $W$ boson. ${M}_{H}$ is the mass of the heavy neutral scalar Higgs boson $H$ which is much heavier than the light neutral Higgs boson $h$ with mass ${M}_{h}$. In the limit ${M}_{H}^{2}\ensuremath{\gg}{M}_{h}^{2}$, the $\mathrm{ln}({\mathrm{\ensuremath{\Lambda}}}^{2})$ behavior in the previous paper is replaced by $\mathrm{ln}({\stackrel{\texttildelow{}}{{M}_{H}}}^{2})$, where $\stackrel{\texttildelow{}}{{M}_{H}}$ is of order ${M}_{H}$. I also explain how some divergences due to exchange of the pseudoscalar Higgs $A$ are canceled by similar contributions from the scalar heavy Higgs $H$, and that these contributions, and finite contributions from $A$ exchange, are suppressed.

Collinear electroweak radiation in antenna parton showers

We present a first implementation of collinear electroweak radiation in the Vincia parton shower. Due to the chiral nature of the electroweak theory, explicit spin dependence in the shower algorithm is required. We thus use the spinor-helicity formalism to compute helicity-dependent branching kernels, taking special care to deal with the gauge relics that may appear in computation that involve longitudinal polarizations of the massive electroweak vector bosons. These kernels are used to construct a shower algorithm that includes all possible collinear final-state electroweak branchings, including those induced by the Yang–Mills triple vector boson coupling and all Higgs couplings, as well as vector boson emissions from the initial state. We incorporate a treatment of features particular to the electroweak theory, such as the effects of bosonic interference and recoiler effects, as well as a preliminary description of the overlap between electroweak branchings and resonance decays. Some qualifying results on electroweak branching spectra at high energies, as well as effects on LHC physics are presented. Possible future improvements are discussed, including treatment of soft and spin effects, as well as issues unique to the electroweak sector.

A more natural composite Higgs model

Composite Higgs models provide an attractive solution to the hierarchy problem. However, many realistic models suffer from tuning problems in the Higgs potential. There are often large contributions from the UV dynamics of the composite resonances to the Higgs potential, and tuning between the quadratic term and the quartic term is required to separate the electroweak breaking scale and the compositeness scale. We consider a composite Higgs model based on the SU(6)/Sp(6) coset, where an enhanced symmetry on the fermion resonances can minimize the Higgs quadratic term. Moreover, a Higgs quartic term from the collective symmetry breaking of the little Higgs mechanism can be realized by the partial compositeness couplings between elementary Standard Model fermions and the composite operators, without introducing new elementary fields beyond the Standard Model and the composite sector. The model contains two Higgs doublets, as well as several additional pseudo-Nambu-Goldstone bosons. To avoid tuning, the extra Higgs bosons are expected to be relatively light and may be probed in the future LHC runs. The deviations of the Higgs couplings and the weak gauge boson couplings also provide important tests as they are expected to be close to the current limits in this model.

Heavy dark matter through the dilaton portal

We re-examine current and future constraints on a heavy dilaton coupled to a simple dark sector consisting of a Majorana fermion or a Stückelberg vector field. We include three different treatments of dilaton-Higgs mixing, paying particular attention to a gauge-invariant formulation of the model. Moreover, we also invite readers to re-examine effective field theories of vector dark matter, which we show are missing important terms. Along with the latest Higgs coupling data, heavy scalar search results, and dark matter density/direct detection constraints, we study the LHC bounds on the model and estimate the prospects of dark matter production at the future HL-LHC and 100 TeV FCC colliders. We additionally compute novel perturbative unitarity constraints involving vector dark matter, dilaton and gluon scattering.

Hidden signals of new physics within the Yukawa couplings of the Higgs boson

The Large Hadron Collider (LHC) has measured the Higgs boson couplings with the heavier particles of the Standard Model (SM), and they seem to lay on a single line as function of the particle mass, as predicted in the SM. However a complete test of this property must involve the lighter generations, and the coming measurements at LHC, or future colliders, may reveal hidden patterns associated with physics beyond the SM. In renormalizable multi-Higgs models, the Higgs-fermion couplings could still be linear, but they could lay on multiple lines. Then, the angle subtended by these lines, with respect to the SM line, can be used to characterize different models, as it is shown here for the Two-Higgs doublet Model (2HDM). Models where fermion masses arise from higher-dimensional operators, may also result in large deviations from the SM values for the Higgs couplings, which would show an irregular pattern as a function of the fermion masses. In the case of neutrino masses, when they arise from the see-saw mechanism, one finds that the Higgs Yukawa couplings will show a non-linear mass relation.

Constraining the t→u flavor changing neutral Higgs coupling at the LHC

We study the constraints on $t\ensuremath{\rightarrow}u$ flavor changing neutral Higgs coupling and how it may be explored further at the LHC. In the general two Higgs doublet model, such transitions can be induced by a nonzero ${\ensuremath{\rho}}_{tu}$ Yukawa coupling. We show that such couplings can be constrained by existing searches at the LHC for ${m}_{H}$, ${m}_{A}$, and ${m}_{{H}^{+}}$ in the sub-TeV range, where $H$, $A$, and ${H}^{+}$ are the exotic $CP$-even, $CP$-odd, and charged scalars. We find that a dedicated $ug\ensuremath{\rightarrow}tH/tA\ensuremath{\rightarrow}tt\overline{u}$ search can probe the available parameter space of ${\ensuremath{\rho}}_{tu}$ down to a few percent level for $200\text{ }\text{ }\mathrm{GeV}\ensuremath{\lesssim}{m}_{H}$, ${m}_{A}\ensuremath{\lesssim}600\text{ }\text{ }\mathrm{GeV}$, with discovery possible at high luminosity. Effects of how other extra top Yukawa couplings, such as ${\ensuremath{\rho}}_{tc}$ and ${\ensuremath{\rho}}_{tt}$, dilute the sensitivity of the ${\ensuremath{\rho}}_{tu}$ probe are discussed.

Vector boson fusion at multi-TeV muon colliders

High-energy lepton colliders with a centre-of-mass energy in the multi-TeV range are currently considered among the most challenging and far-reaching future accelerator projects. Studies performed so far have mostly focused on the reach for new phenomena in lepton-antilepton annihilation channels. In this work we observe that starting from collider energies of a few TeV, electroweak (EW) vector boson fusion/scattering (VBF) at lepton colliders becomes the dominant production mode for all Standard Model processes relevant to studying the EW sector. In many cases we find that this also holds for new physics. We quantify the size and the growth of VBF cross sections with collider energy for a number of SM and new physics processes. By considering luminosity scenarios achievable at a muon collider, we conclude that such a machine would effectively be a “high-luminosity weak boson collider,” and subsequently offer a wide range of opportunities to precisely measure EW and Higgs couplings as well as discover new particles.

Towards the ultimate differential SMEFT analysis

We obtain SMEFT bounds using an approach that utilises the complete multi-dimensional differential information of a process. This approach is based on the fact that at a given EFT order, the full angular distribution in the most important electroweak processes can be expressed as a sum of a fixed number of basis functions. The coefficients of these basis functions — the so-called angular moments — and their energy dependance, thus form an ideal set of experimental observables that encapsulates the complete multi-dimensional differential information of the process. This approach is generic and the observables constructed allow to avoid blind directions in the SMEFT parameter space. While this method is applicable to many of the important electroweak processes, as a first example we study the pp → V(ℓℓ)h(bb) process (V ≡ Z/W±, ℓℓ ≡ ℓ+ℓ−/ℓ±ν), including QCD NLO effects, differentially. We show that using the full differential data in this way plays a crucial role in simultaneously and maximally constraining the different vertex structures of the Higgs coupling to gauge bosons. In particular, our method yields bounds on the {hV}_{mu nu}{V}^{mu nu},{hV}_{mu nu}{tilde{V}}^{mu nu} and hVffleft( ffequiv foverline{f}/foverline{f}^{prime}right) couplings, stronger than projected bounds reported in any other process. This matrix-element-based method can provide a transparent alternative to complement machine learning techniques that also aim to disentangle correlations in the SMEFT parameter space.

Exploring sizable triple Higgs couplings in the 2HDM

An important task at future colliders is the measurement of the triple Higgs coupling. Depending on its size relative to the Standard Model (SM) value, certain collider options result in a higher experimental accuracy. Within the framework of Two Higgs Doublet Models (2HDM) types I and II we investigate the allowed ranges for all triple Higgs couplings involving at least one light, SM-like Higgs boson. We take into account theoretical constraints (unitarity, stability), experimental constraints from direct Higgs-boson searches, measurements of the SM-like Higgs-boson properties, flavor observables and electroweak precision data. We find that the SM-type triple Higgs coupling w.r.t. its SM value, lambda _{hhh}/lambda _{mathrm {SM}}, can range between sim -0.5 and sim 1.5. Depending on which value is realized, the HL-LHC can compete with, or is clearly inferior to the ILC. We find the coupling lambda _{hhH} between sim -1.5 and sim 1.5. Triple Higgs couplings involving two heavy Higgs bosons, lambda _{hHH}, lambda _{hAA} and lambda _{hH^+H^-} can reach values up to {{mathcal {O}}}(10), roughly independent of the 2HDM type. This can lead to potentially strongly enhanced production of two Higgs-bosons at the HL-LHC or high-energy e^+e^- colliders.

Tree-level interference in vector boson fusion production of Vh

Vector boson scattering is a well known probe of electroweak symmetry breaking. Here we study a related process of two electroweak vector bosons scattering into a vector boson and a Higgs boson ($VV \rightarrow Vh, V=W,Z$). This process exhibits tree level interference and grows with energy if the Higgs couplings to electroweak bosons deviate from their Standard Model values. Therefore, this process is particularly sensitive to the relative sign of the ratio of the coupling between the Higgs and the $W$ and $Z$, $\lambda_{WZ}$. In this work we show that a high energy lepton collider is well suited to study this process through vector boson fusion, estimate the potential sensitivity to this ratio, and show that a relatively modest amount of data can exclude $\lambda_{WZ} \simeq -1$.

Di-Higgs production in SUSY models at the LHC

We study the modification to di-Higgs production via gluon fusion within the context of the minimal supersymmetric standard model and the next-to-minimal supersymmetric standard model in the parameter space allowed by current experimental and theoretical constraints, and also relevant to the Large Hadron Collider (LHC) experiments in the near future. The calculation is based on the analytical expression of the leading-order Feynman amplitudes (which includes both quark and squark loops). We separate the di-Higgs production cross section into resonant, non-resonant, and interference parts, in order to better understand the mechanisms that are responsible for the modification to di-Higgs production rate in different regions of the allowed parameter space. We also investigate the sensitivity of high-luminosity LHC (HL-LHC) to the di-Higgs production in these low-energy supersymmetry models. Furthermore, we examine the complementarity between di-Higgs searches and direct searches for BSM particles and precision Higgs couplings measurements at the HL-LHC. We found that the di-Higgs production cross section can be enhanced significantly through resonant production. In the region where the resonant production cross section is small, di-Higgs production receives a moderate enhancement due to the modifications in the Higgs couplings. In addition, there is a strong correlation between di-Higgs production and single Higgs production, and di-Higgs production is not as sensitive as single Higgs production at the HL-LHC.

Improved MSSM Higgs mass calculation using the 3-loop FlexibleEFTHiggs approach including xt-resummation

We present an improved calculation of the light CP-even Higgs boson pole mass in the MSSM based on the FlexibleEFTHiggs hybrid method. The calculation resums large logarithms to all orders and includes power-suppressed terms at fixed order. It uses state-of-the-art 2- and 3-loop matching of the quartic Higgs coupling and renormalization group running up to 4-loop, resulting in a resummation of large logarithmic corrections up to N3LL level. A conceptually novel ingredient is the expansion of the matching conditions in terms of high-scale MSSM parameters instead of SM parameters. In this way leading QCD-enhanced terms in the stop-mixing parameter are effectively resummed, leading to an improved numerical convergence of the perturbative expansion. Furthermore, the avoidance of double counting of loop corrections is more transparent than in other approaches and more independent of the high-scale model. We present numerical results and a detailed discussion of theoretical uncertainties for standard benchmark scenarios.