Electroweak Sector Research Articles

A Symmetric Two Higgs Doublet Model

In the light of ongoing experimental search efforts for the dark matter and the post-Higgs Beyond the Standard Model (BSM) null results at the Large Hadron Collider (LHC), the Electroweak sector demands to be investigated for possible new scalar states discoverable at the LHC fulfilling the role of the dark matter. In this work we present a symmetric two Higgs doublet model with a discrete interchange symmetry among the two Higgs doublets (Φ1 ↔ Φ2). Apart from the Standard Model (SM)-like scalar state (h) with mh = 125 GeV, the model has several distinguishing features including the pseudoscalar (A), the charged scalars(H±) and the neutral scalar H, not having any direct coupling to the fermions. The neutral scalar H is assumed to have mass lighter than the 125 GeV SM-like Higgs state h. Due to the presence of a residual Z2 symmetry after the spontaneous symmetry breaking (SSB), the neutral scalar H can emerge as a viable dark matter candidate. We discuss the constraints on such scalar dark matter from the current direct and indirect detection experiments. As a by-product of this construction, the SM-like scalar h ends up having an extra invisible decay mode of h → HH in this model which can also influence the dark matter parameter space. We discuss these model features in detail along with a guideline of relevant phenomenological searches at the LHC for this scenario.

The new \u201cMUON G-2\u201d result and supersymmetry

The electroweak (EW) sector of the Minimal Supersymmetric Standard Model (MSSM), with the lightest neutralino as Dark Matter (DM) candidate, can account for a variety of experimental data. This includes the DM content of the universe, DM direct detection limits, EW SUSY searches at the LHC and in particular the so far persistent 3-4,sigma discrepancy between the experimental result for the anomalous magnetic moment of the muon, (g-2)_mu , and its Standard Model (SM) prediction. The recently published “MUON G-2” result is within {0.8},sigma in agreement with the older BNL result on (g-2)_mu . The combination of the two results was given as a_mu ^{mathrm{exp}} = (11 659 {206.1}pm {4.1}) times 10^{-10}, yielding a new deviation from the SM prediction of Delta a_mu = ({25.1}pm {5.9}) times 10^{-10}, corresponding to {4.2},sigma . Using this improved bound we update the results presented in Chakraborti et al. (Eur Phys J C 80(10):984, 2020) and set new upper limits on the allowed parameters space of the EW sector of the MSSM. We find that with the new (g-2)_mu result the upper limits on the (next-to-) lightest SUSY particle are in the same ballpark as previously, yielding updated upper limits on these masses of sim 750 ,, mathrm {GeV}. In this way, a clear target is confirmed for future (HL-)LHC EW searches, as well as for future high-energy e^+e^- colliders, such as the ILC or CLIC.

Improved {(g-2)_mu } measurements and wino/higgsino dark matter

The electroweak (EW) sector of the Minimal Supersymmetric Standard Model (MSSM) can account for a variety of experimental data. In particular it can explain the persistent 3-4,sigma discrepancy between the experimental result for the anomalous magnetic moment of the muon, (g-2)_mu , and its Standard Model (SM) prediction. The lightest supersymmetric particle (LSP), which we take as the lightest neutralino, {tilde{chi }}_{1}^0, can furthermore account for the observed Dark Matter (DM) content of the universe via coannihilation with the next-to-LSP (NLSP), while being in agreement with negative results from Direct Detection (DD) experiments. Concerning the unsuccessful searches for EW particles at the LHC, owing to relatively small production cross-sections a comparably light EW sector of the MSSM is in full agreement with the experimental data. The DM relic density can fully be explained by a mixed bino/wino LSP. Here we take the relic density as an upper bound, which opens up the possibility of wino and higgsino DM. We first analyze which mass ranges of neutralinos, charginos and scalar leptons are in agreement with all experimental data, including relevant LHC searches. We find roughly an upper limit of sim 600 ,, mathrm {GeV} for the LSP and NLSP masses. In a second step we assume that the new result of the Run 1 of the “MUON G-2” collaboration at Fermilab yields a precision comparable to the existing experimental result with the same central value. We analyze the potential impact of the combination of the Run 1 data with the existing (g-2)_mu data on the allowed MSSM parameter space. We find that in this case the upper limits on the LSP and NLSP masses are substantially reduced by roughly 100 ,, mathrm {GeV}. We interpret these upper bounds in view of future HL-LHC EW searches as well as future high-energy e^+e^- colliders, such as the ILC or CLIC.

Lorentz-symmetry violation in the electroweak sector: Scattering processes in future e+ e− colliders

We study CPT-odd non-minimal Lorentz-symmetry violating couplings in the electroweak sector modifying the interactions between leptons, gauge mediators and the Higgs boson. The tree-level (differential) cross sections for three important electroweak processes are discussed: e+e−→ZH, e+e−→ZZ and γγ→W+W−. By considering next-generation e+e− colliders reaching center-of-mass energies at the TeV scale and the estimated improved precision for the measurements of the respective cross sections, we are able to project upper bounds on the purely time-like background 4-vector as strict as ≲10−5GeV−1, in agreement with previous work on similar Lorentz-violating couplings.

New physics through Drell-Yan standard model EFT measurements at NLO

Drell Yan production is a sensitive probe of new physics and as such has been calculated to high order in both the electroweak and QCD sectors of the standard model, allowing for precision comparisons between theory and data. Here we extend these calculations to the standard model effective field theory and present the next-to-leading order QCD and electroweak contributions to the neutral Drell-Yan process.

Full NLO predictions for vector-boson scattering into Z bosons and its irreducible background at the LHC

Vector-boson scattering into two Z bosons at the LHC is a key channel for the exploration of the electroweak sector of the Standard Model. It allows for the full reconstruction of the scattering process but at the price of a huge irreducible background. For the first time, we present full next-to-leading-order predictions for pp → e+e−μ+μ−jj + X including all electroweak and QCD contributions for vector-boson scattering signal and irreducible background. The results are presented in the form of cross sections and differential distributions. A particular emphasis is put on the newly computed ( {alpha}_{mathrm{s}}^2 α5) corrections.

The new (g-2)_mu result and the mu nu SSM

The mu nu mathrm {SSM} is a highly predictive alternative model to the MSSM. In particular, the electroweak sector of the model can explain the longstanding discrepancy between the experimental result for the anomalous magnetic moment of the muon, (g-2)_mu , and its Standard Model prediction, while being in agreement with all other theoretical and experimental constraints. The recently published MUON G-2 result is within {0.8},sigma in agreement with the older BNL result on (g-2)_mu . The combined result was announced as a_mu ^{mathrm{exp}} = (11 659 {206.1}pm {4.1}) times 10^{-10}, yielding a new deviation from the Standard Model prediction of Delta a_mu = ({25.1}pm {5.9}) times 10^{-10}, corresponding to {4.2},sigma . Using this improved bound we update the analysis in the mu nu mathrm {SSM} as presented in Kpatcha et al. (Eur Phys J C 81(2):154. arXiv:1912.04163 [hep-ph], 2021) and set new limits on the allowed parameters space of the electroweak sector of the model. We conclude that significant regions of the model can explain the new (g-2)_mu data.

Operators and Field Equations in the Electroweak Sector of Particle Physics

Operators and Field Equations in the Electroweak Sector of Particle Physics

Systematizing and addressing theory uncertainties of unitarization with the Inverse Amplitude Method

Effective Field Theories (EFTs) constructed as derivative expansions in powers of momentum, in the spirit of Chiral Perturbation Theory (ChPT), are a controllable approximation to strong dynamics as long as the energy of the interacting particles remains small, as they do not respect exact elastic unitarity. This limits their predictive power towards new physics at a higher scale if small separations from the Standard Model are found at the LHC or elsewhere. Unitarized chiral perturbation theory techniques have been devised to extend the reach of the EFT to regimes where partial waves are saturating unitarity, but their uncertainties have hitherto not been addressed thoroughly. Here we take one of the best known of them, the Inverse Amplitude Method (IAM), and carefully following its derivation, we quantify the uncertainty introduced at each step. We compare its hadron ChPT and its electroweak sector Higgs EFT applications. We find that the relative theoretical uncertainty of the IAM at the mass of the first resonance encountered in a partial-wave is of the same order in the counting as the starting uncertainty of the EFT at near-threshold energies, so that its unitarized extension should a priori be expected to be reasonably successful. This is so provided a check for zeroes of the partial wave amplitude is carried out and, if they appear near the resonance region, we show how to modify adequately the IAM to take them into account.

Minimal twist for the Standard Model in noncommutative geometry: The field content

Noncommutative geometry provides both a unified description of the Standard Model of particle physics together with Einstein-Hilbert action (in euclidean signature) and some tools to go beyond the Standard Model. In this paper, we extend to the full noncommutative geometry of the Standard Model the twist (in the sense of Connes-Moscovici) initially worked out for the electroweak sector and the free Dirac operator only. Namely, we apply the twist also to the strong interaction sector and the finite part of the Dirac operator. To do so, we are forced to take into account a violation of the twisted first-order condition. As a result, we still obtain the extra scalar field required to stabilise the electroweak vacuum and fit the Higgs mass, but it now has two chiral components. We also get the additive field of 1-forms already pointed out in the electroweak model, but with a richer structure. Finally, we obtain a pair of Higgs doublets, which are expected to combine into a single Higgs doublet in the action formula, as will be investigated in the second part of this work.

The anomalous case of axion EFTs and massive chiral gauge fields

We study axion effective field theories (EFTs), with a focus on axion couplings to massive chiral gauge fields. We investigate the EFT interactions that participate in processes with an axion and two gauge bosons, and we show that, when massive chiral gauge fields are present, such interactions do not entirely originate from the usual anomalous EFT terms. We illustrate this both at the EFT level and by matching to UV-complete theories. In order to assess the consistency of the Peccei-Quinn (PQ) anomaly matching, it is useful to introduce an auxiliary, non-dynamical gauge field associated to the PQ symmetry. When applied to the case of the Standard Model (SM) electroweak sector, our results imply that anomaly-based sum rules between EFT interactions are violated when chiral matter is integrated out, which constitutes a smoking gun of the latter. As an illustration, we study a UV-complete chiral extension of the SM, containing an axion arising from an extended Higgs sector and heavy fermionic matter that obtains most of its mass by coupling to the Higgs doublets. We assess the viability of such a SM extension through electroweak precision tests, bounds on Higgs rates and direct searches for heavy charged matter. At energies below the mass of the new chiral fermions, the model matches onto an EFT where the electroweak gauge symmetry is non-linearly realised.

Explaining (g \u2212 2)\u03bc with multi-TeV sleptons

We present a supersymmetric extension of the Standard Model in which the new physics contributions to the anomalous magnetic moment of the muon can be more than an order of magnitude larger than in the minimal supersymmetric Standard Model. The extended electroweak symmetry breaking sector of the model can consistently accommodate Higgs bosons and Higgsinos with O(1) couplings to muons. We find that sleptons with masses in the multi-TeV range can comfortably explain the recently confirmed discrepancy in the anomalous magnetic moment of the muon. We discuss additional phenomenological aspects of the model, including its effects on tau flavor changing decays.

W+W−H production through bottom quarks fusion at hadron colliders

With the standard model working well in describing the collider data, the focus is now on determining the standard model parameters as well as for any hint of deviation. In particular, the determination of the couplings of the Higgs boson with itself and with other particles of the model is important to better understand the electroweak symmetry breaking sector of the model. In this letter, we look at the process pp→WWH, in particular through the fusion of bottom quarks. Due to the non-negligible coupling of the Higgs boson with the bottom quarks, there is a dependence on the WWHH coupling in this process. This sub-process receives the largest contribution when the W bosons are longitudinally polarized. We compute one-loop QCD corrections to various final states with polarized W bosons. We find that the corrections to the final state with the longitudinally polarized W bosons are large. It is shown that the measurement of the polarization of the W bosons can be used as a tool to probe the WWHH coupling in this process. We also examine the effect of varying WWHH coupling in the κ-framework.

Test of the fourth quark generation from the Cabibbo–Kobayashi–Maskawa matrix

The structure of the mixing matrix in the electroweak quark sector with four generations of quarks is investigated. We conclude that the area of the unitarity quadrangle is not a good choice as a possible measure of the CP violation. In search of new physics, we analyze how the existence of the fourth quark family may influence on the values of the Cabibbo–Kobayashi–Maskawa matrix and we show that one can test for the existence of the fourth generation using the Jarlskog invariants of the known quarks only. The analysis based on the measured unitary triangle exhibits some tension with the assumption of three quark generations. The measurement of the unitarity triangle obtained from the scalar product of the second row/column of the CKM matrix by the complex conjugate of third row/column can provide information about the existence of the fourth generation of quarks.

SMEFT analysis of vector boson scattering and diboson data from the LHC Run II

We present a systematic interpretation of vector boson scattering (VBS) and diboson measurements from the LHC in the framework of the dimension-six standard model effective field theory (SMEFT). We consider all available measurements of VBS fiducial cross-sections and differential distributions from ATLAS and CMS, in most cases based on the full Run II luminosity, and use them to constrain 16 independent directions in the dimension-six EFT parameter space. Compared to the diboson measurements, we find that VBS provides complementary information on several of the operators relevant for the description of the electroweak sector. We also quantify the ultimate EFT reach of VBS measurements via dedicated projections for the high luminosity LHC. Our results motivate the integration of VBS processes in future global SMEFT interpretations of particle physics data.

Probing non-standard [formula omitted] interaction at the LHC at [formula omitted] TeV

In the detailed probe of Higgs boson properties at the Large Hadron Collider (LHC), and in looking for new physics signatures in the electroweak symmetry breaking sector, the bottom quark Yukawa coupling has a crucial role. We investigate possible departure from the standard model value of bb¯h coupling, phenomenologically expressed in terms of a modification factor αb, in bb¯-associated production of the 125-GeV scalar at the high-luminosity LHC. In a next-to-leading order estimate, we make use of a gradient boosting algorithm to improve the statistical significance upon a cut-based analysis. It is found possible to probe down to αb=3 with more than 5σ significance, with L=3000 fb−1 and s = 13 TeV, while the achievable limit at 95% C.L. is ±1.95. Scale dependence of this limit is also reported.

Universal gravitational-wave signatures from heavy new physics in the electroweak sector

We calculate the gravitational-wave spectra produced by the electroweak phase transition with TeV-scale Beyond-Standard-Model physics in the early universe. Our study captures the effect of quantum and thermal fluctuations within a non-perturbative framework. We discover a universal relation between the mean bubble separation and the strength parameter of the phase transition, which holds for a wide range of new-physics contributions.The ramifications of this result are three-fold: first, they constrain the gravitational-wave spectra resulting from heavy (TeV-scale) new physics. Second, they contribute to distinguishing heavy from light new physics directly from the gravitational-wave signature. Third, they suggest that a concerted effort of gravitational-wave observations together with collider experiments could be required to distinguish between different models of heavy new physics.

Electric charge quantization in SU(3)c ⊗ SU(n)L ⊗ U(1)Y gauge models

We prove that the Cotăescu general method of solving SU(3)c ⊗ SU(n)L ⊗ U(1)Y gauge models exactly predicts the observed electric charge quantization, as the theory remains renormalizable, both in its strong and electroweak sectors, while all the fermions get their masses—by means of Yukawa terms—the spontaneous symmetry breakdown (SSB) successively. The latter is achieved by a scalar sector consisting of n Higgs multiplets, each acquiring its own vacuum expectation value (VEV).

SMEFTsim 3.0 \u2014 a practical guide

The SMEFTsim package [1] is designed to enable automated computations in the Standard Model Effective Field Theory (SMEFT), where the SM Lagrangian is extended with a complete basis of dimension six operators. It contains a set of models written in FeynRules and pre-exported to the UFO format, for usage within Monte Carlo event generators. The models differ in the flavor assumptions and in the input parameters chosen for the electroweak sector. The present document provides a self-contained, pedagogical reference that collects all the theoretical and technical aspects relevant to the use of SMEFTsim and it documents the release of version 3.0. Compared to the previous release, the description of Higgs production via gluon-fusion in the SM has been significantly improved, two flavor assumptions for studies in the top quark sector have been added, and a new feature has been implemented, that enables the treatment of linearized SMEFT corrections to the propagators of unstable particles.SMEFTsim 3.0 is available on the Github website https://SMEFTsim.github.io and on the FeynRules database http://feynrules.irmp.ucl.ac.be/wiki/SMEFT.

Remarks on an Anomalous Triple Gauge Boson Couplings

We address the effect of an anomalous triple gauge boson couplings on a physical observable for the electroweak sector of the Standard Model, when the S U 2 L ⊗ U 1 Y symmetry is spontaneously broken by the Higgs mechanism to U 1 e m . Our calculation is done within the framework of the gauge-invariant, but path-dependent variable formalism is an alternative to the Wilson loop approach. Our result shows that the interaction energy is the sum of a Yukawa and a linear potential, leading to the confinement of static probe charges. The point we wish to emphasize, however, is that the anomalous triple gauge boson couplings ( Z γ γ ) contributes to the confinement for distances on the intranuclear scale.