Gauge Boson Pair Research Articles

Enhancement of the Higgs decay into a Z′ pair in models with U(1)X gauge symmetry

We discuss the Higgs phenomenology in models with a new U(1)X gauge symmetry including the U(1)B−L scenario, where three right-handed neutrinos are inevitably introduced due to the gauge anomaly cancellations. We find that the decay branching ratio of the discovered Higgs boson into a pair of new massive gauge bosons (Z′) can significantly be enhanced in the Dirac neutrino case as compared with the Majorana case for a fixed value of the new gauge coupling and the mass of Z′ under constraints from current experimental data. Because of such an enhancement, the Dirac case can indirectly be discriminated from the Majorana case via the Higgs decay.

A model of pseudo-Nambu-Goldstone dark matter with two complex scalars

Pseudo-Nambu-Goldstone (pNG) dark matter (DM) is a promising DM candidate and able to explain the measured DM abundance by the thermal freeze-out mechanism evading the stringent bound from DM direct detection experiments. We propose a new model providing a pNG DM by introducing two Standard-Model-singlet complex scalars with the same charges of a dark U(1) gauge symmetry. They are also charged under a U(1) global symmetry corresponding to their relative phase rotations, which is explicitly broken by a soft-breaking term in the scalar potential. The both U(1) symmetries are spontaneously broken by their vacuum expectation values, giving rise to one real pNG boson. We also introduce a discrete ℤ2 symmetry exchanging the two scalars to stabilize the pNG boson as DM. It is shown that this model reproduces the DM abundance consistently with the current bound from the direct detection experiments. The model has a gauge kinetic mixing between the dark and U(1)Y gauge fields, which allows the dark gauge boson to decay even with a relatively light mass and prevents it from being an additional DM component. The Landau pole is avoided thanks to the small gauge coupling constant. In addition, a DM pair dominantly annihilates into a pair of the dark gauge bosons if the gauge boson mass is lighter than the DM mass, and thus its cross section has significantly different parameter dependence from other pNG DM models. We also calculate the DM-nucleon scattering cross section at the loop level. It turns out that it is necessary to probe region covered by the neutrino fog in order to test this model.

Bounds on quartic gauge couplings in HEFT from electroweak gauge boson pair production at the LHC

Precision measurements of anomalous quartic couplings of electroweak gauge bosons allow us to search for deviations of the Standard Model predictions and signals of new physics. Here, we obtain the constraints on anomalous quartic gauge couplings using the presently available data on the production of gauge-boson pairs via vector boson fusion. We work in the Higgs effective theory framework and obtain the present bounds on the operator’s Wilson coefficients. We show that the combination of different datasets breaks the degeneracies in analysis with more than one nonvanishing Wilson coefficient. Anomalous quartic gauge boson couplings lead to rapidly growing cross sections and we discuss the impact of a unitarization procedure on the attainable limits. Published by the American Physical Society 2024

Pair Production of Heavy Charged Gauge Bosons in pp Collisions at LHC

Abstract Two oppositely charged new heavy gauge boson pair production at the Large Hadron Collider (LHC), is presented in this paper. These bosons are known as W ′ boson due to the reason that it is the heavy version of Standard Model’s weak force carrier, the W boson. The production cross section and decay width in proton-proton (pp) collision at s = 8 TeV are calculated for different masses and coupling strengths of W ′ . Efficiencies for different signal regions and branching ratios for different decay channels are computed. In this study, the pair production ( W ′ + W ′ − ) is considered in emerging new physics as a result of pp collision at s = 8 TeV at the LHC with final state containing two tau (τ) leptons and two neutrinos (each W ′ decay to τ and its neutrino). The event selection efficiency similar to the CMS experiment is used for the mass of W ′ to set lower limits for different coupling strengths of W ′ and, the obtained results are presented in this work. For heavy gauge bosons, when coupling strength is similar to that of Standard Model’s W boson, the mass of W ′ below 445 GeV are excluded at a confidence level of 95%.

LEX-EFT: the Light Exotics Effective Field Theory

We propose the creation of a Light Exotics Effective Field Theory (LEX-EFT) catalog. LEX-EFT is a generic framework to capture all interactions between the Standard Model (SM) and all (or at least a large class of) theoretically allowed exotic states beyond the Standard Model (bSM), indexed by their SM and bSM charges. These states are light enough to be on or nearly on shell in some collider processes. This framework, which subsumes beyond the Standard Model paradigms as generally as possible, is meant to extend recent successful implementations of bSM EFTs and complement e.g. the Standard Model Effective Field Theory (SMEFT), which can capture the off-shell effects of exotic fields. In this work, we review a general method for the construction of a complete list of gauge-invariant operators involving SM interactions with light exotics via iterative tensor product decomposition, up to the desired order in mass dimension. Each operator is characterized by specific Clebsch-Gordan coefficients determined by the charge flow; we show how this charge flow affects the range of EFT validity and cross sections associated with an effective operator. We create an example catalog of exotic scalars coupling to SM gauge boson pairs, and we highlight some operators with exotic weak SU(2)L charges that can produce spectacular LHC phenomenology. We further demonstrate the utility of the LEX-EFT approach with several examples of effects on kinematic distributions and cross sections that would not be captured by EFTs agnostic to the exotic degrees of freedom and may evade the main inclusive collider searches tailored to the existing preferred set of standard bSM theories.

Impact of dimension-eight SMEFT operators in the electroweak precision observables and triple gauge couplings analysis in universal SMEFT

We perform a complete study of the electroweak precision observables and electroweak gauge boson pair production in terms of the SMEFT up to ${\cal O}(1/\Lambda^4)$ under the assumption of universal, C and P conserving new physics. We show that the analysis of data from those two sectors allows us to obtain closed constraints in the relevant parameter space in this scenario. In particular we find that the Large Hadron Collider data can independently constrain the Wilson coefficients of the dimension-six and -eight operators directly contributing to the triple gauge boson vertices. Our results show that the impact of dimension-eight operators in the study of triple gauge couplings is small.

Exploring extended Higgs sectors via pair production at the LHC

Higgs sectors extended by electroweakly charged scalars can be explored by scalar pair production at the LHC. We consider a fermiophobic scenario, with decays into a pair of gauge bosons, and a fermiophilic one, with decays into top and bottom quarks. After establishing the current bounds on simplified models, we focus on an SU(5)/SO(5) composite Higgs model. This first exploration demonstrates the need for dedicated searches at current and future colliders.

Improved Constraints on the Heavy Gauge Bosons Decaying to Pairs of Electroweak Bosons by Using the Expected Run 3 Data and HL-LHC Options

The expected ATLAS Run 3 data set with time-integrated luminosity of 300 fb−1 and HL–LHC options at the LHC in the diboson channels are used to probe a simple benchmark model with an extended gauge sector, proposed by Altarelli et al. This model accommodates new charged W' and neutral Z' vector bosons with modified trilinear Standard Model gauge couplings, decaying into electroweak gauge boson pairs W Z or W W, where W / Z decay semileptonically. Also presented, from a similar analysis of W' and Z' bosons arising in the EGM, which can decay through W' → lν and Z' → ll , are limits on the W–W' and Z–Z' mixing parameters and the W' and Z' vector boson masses. We present upper limits on the mixing parameters, Z–Z' and W–W', by using the expected Run 3 data and HL–LHC options.

Exploring HVV amplitudes with CP violation using decomposition and the on-shell scattering amplitude method* *Supported by the National Natural Science Foundation of China ( 11847168), the Fundamental Research Funds for the Central Universities of China (GK202003018) and the Natural Science Foundation of Shannxi Province, China (2019JM-431, 2019JQ-739)

violation may play an important role in baryogenesis in the early universe and should be examined comprehensively at colliders. We study the properties of vertexes between Higgs and gauge boson pairs by defining a violation phase angle ξ, which indicates the mixture of -even and -odd Higgs states in in new physics. A series of amplitudes, , and , with a phase angle are studied systematically to explicitly explain why violation can only be probed independently in the process. We obtain a novel amplitude decomposition relation that illustrates that if two preconditions (multilinear momentum dependent vertexes, and the current of is formally proportional to a photon's polarization vector) are satisfied, a higher-point amplitude can be decomposed into a summation of a series of lower-point amplitudes. As a practical example, the amplitude of the and processes can be decomposed into a summation of many amplitudes. We calculate these amplitudes in the framework of the on-shell scattering amplitude method, considering both massless and massive vector gauge bosons with the violation phase angle. The above two approaches provide consistent results and clearly reveal the violation ξ dependence in the amplitudes.

Searching for exotic Higgs bosons at the LHC

We analyse in a model independent way the possibilities of digging out neutral exotic Higgs states, should they exist endowed with unconventional couplings with ordinary matter and gauge fields, at the 14 TeV run of the Large Hadron Collider (LHC), adding some comparative studies for 13.6 and 13 TeV runs. Flavor models, based on some discrete symmetry groups, with extended scalar sectors are known to yield exotic spin-0 states, both CP-even and CP-odd, with purely flavor off-diagonal Yukawa couplings. The gauge interaction of one such CP-even state is also unusual that, unlike the Standard Model Higgs boson, it does not couple to gauge boson pairs. Such unconventional properties immune these exotic states from receiving traditional collider and electroweak constraints, and hence those states could be light. Without committing to any specific model, exploiting their peculiar Yukawa and gauge properties, we explore the discovery potential of those exotic Higgs states through some interesting topologies by figuring out some specific kinematic variables that suppress the backgrounds.

Parameter dependence and analysis of the 2HDM neutral Higgs boson pair production and decay at future lepton colliders

In this work, we present a study of the neutral Higgs bosons in the two Higgs doublet model (2HDM) in terms of their production processes and decay channels as a function of the model parameters. The analysis is performed for all four types of the 2HDM and the most promising processes and decay channels are identified for each type of the model. Several Higgs boson mass scenarios below and above the threshold of decay to gauge boson pair are introduced and the corresponding categories of final states are analyzed. The event analysis including collider beam spectrum and detector simulation shows that future lepton colliders have the potential to explore regions in the 2HDM parameter space, which have not yet been excluded by LHC, in a few weeks of operation. Final results are presented in terms of the signal distributions on top of the background and 95% CL exclusion and 5σ contours based on center of mass energy of s=500 GeV at the Compact Linear Collider (CLIC) or International Linear Collider (ILC).

New physics in triboson event topologies

We present a study of the sensitivity to models of new physics of proton collisions resulting in three electroweak bosons. As a benchmark, we analyze models in which an exotic scalar field $\ensuremath{\phi}$ is produced in association with a gauge boson ($V=\ensuremath{\gamma}$ or $Z$). The scalar then decays to a pair of bosons, giving the process $pp\ensuremath{\rightarrow}\ensuremath{\phi}V\ensuremath{\rightarrow}{V}^{\ensuremath{'}}{V}^{\ensuremath{'}\ensuremath{'}}V$. We interpret our results in a set of effective field theories where the exotic scalar fields couple to the Standard Model through pairs of electroweak gauge bosons. We estimate the sensitivity of the LHC and HL-LHC datasets and find sensitivity to cross sections in the 10 fb--0.5 fb range, corresponding to scalar masses of 500 GeV to 2 TeV and effective operator coefficients up to 35 TeV.

UPDATED CONSTRAINTS ON HEAVY RESONANCES USING THE RUN 2 DATA AT LHC

The full ATLAS and CMS Run 2 data set at the Large Hadron Collider (LHC) with time- integrated luminosity of 139 fb −1 and 137 fb −1 , re- spectively, in the diboson channel is used to probe benchmark models with extended gauge sectors: theE 6 -motivated Grand Unification models, the left-right symmetric LR and the sequential standard model. These all predict neutral Z' and charged W' vector bosons, decaying into lepton or electroweak gauge boson pairs. We present constraints on the parameter space of the Z' and W' and compare them to those obtained from the previous analyses performed withLHC data collected at 7 and 8 TeV in Run 1 as well as at 13 TeV in Run 2 at time-integrated luminosity of 36.1 fb −1 . We show that proton-proton collision data at √ s = 13 TeV collected by the ATLAS and the CMS experiments allow to set the most stringent bounds to date on Z-Z' and W-W' mixing.

CepGen – A generic central exclusive processes event generator for hadron-hadron collisions

We present an event generator for the simulation of central exclusive processes in hadron-hadron reactions. Among others, it implements the two-photon production of lepton pairs previously introduced in LPAIR. As a proof of principle, we show that the two approaches are numerically consistent. The kT-factorized description of this process is also handled, along with the two-photon production of a quark, or a W± gauge boson pair. This toolbox may be used as a common framework for the definition of many other processes following this approach. Additionally, photoproduction and other photon induced processes are also considered, or being implemented. Program summaryProgram title: CepGenCPC Library link to program files:https://doi.org/10.17632/24jg665g65.1Developer's repository link:https://github.com/cepgen/cepgenLicensing provisions: GNU General Public License 3Programming language: C++/PythonExternal routines/libraries: GSL [1] for MC integration and histogramming, optional wrappers for LHAPDF [2] for the partonic proton structure functions evaluation, or ROOT [3], Delphes [4] for the output treatment.Nature of problem: The simulation of central exclusive, and in particular two-photon induced processes is becoming increasingly topical given its potential source of contamination for electroweak studies and resonance searches at LHC and future colliders. However, most of simulation tools available are only accounting for the production of photons collinear to the incoming proton beams. Legacy codes such as LPAIR, have however shown their effectiveness in predicting such processes at LHC energies. Unfortunately, they are barely maintained nor maintainable with modern computing infrastructures.Solution method: CepGen provides a modern implementation of legacy photon-induced matrix elements (γγ→ℓ+ℓ−, and W+W−, with more to be added), including standard e+e−, or pp beams (both elastic and dissociative final beam states for the latter). For the modern implementation of LPAIR, it inherits from the former fine treatment of the low-|t| region accounting for a large fraction of the cross section. It also introduces a general wrapping framework to define new photon-induced and diffractive processes, either in C++ or in Fortran. This wrapper provides the kT factorization procedure for 2→4 process computation, and a highly flexible 2→N process placeholder. A user-defined taming of the matrix element is also included to study the effect of kinematic variables-dependent survival factors observed experimentally.Additional comments including restrictions and unusual features: Depending on the complexity of the central process, memory and CPU time. Currently event generation runs only in single-threaded mode, development ongoing to support multi-threading.

New heavy gauge bosons decaying to pair of electroweak bosons: prospect studies at Run 3 and HL-LHC with ATLAS

The expected ATLAS Run 3 data set with time-integrated luminosity of 300 fb-1 and HL-LHC option of the LHC with L = 3000 fb-1 in the diboson channels in semileptonic final states are used to probe a simple benchmark model with an extended gauge sector, proposed by Altarelli et al. This model accommodates new charged W' and neutral Z' vector bosons with modified trilinear Standard Model gauge couplings, decaying into electroweak gauge boson pairs WZ or WW , where W / Z decay semileptonically. We present upper limits on the mixing parameters, W - W' and Z- Z ' , by using the expected Run 3 data and HL-LHC options of the LHC.

UV completed composite Higgs model with heavy composite partners

We study electroweak symmetry breaking in minimal composite Higgs models $SU(4)/Sp(4)$ with purely fermionic UV completions based on a confining Hypercolor gauge group and find that the extra Higgs potential from the underlying preon mass can destruct the correlation between the mass of Higgs and composite partners. Thus the composite partners can be very heavy for successful electroweak symmetry breaking without enhancing the separation between the new physical scale and Higgs VEV. So this kind of model can be easily realized by ordinary strong dynamics theories without artificial assumptions and more likely consistent with lattice simulations. The UV completion of partial compositeness predicts a light singlet Goldstone boson which interacts with QCD and electroweak gauge bosons through Wess-Zumino-Witten terms. It can be produced through gluon fusion at LHC and decay into gauge boson pairs. We briefly discuss its phenomenology and derive its bounds from LHC searches.

Four-lepton production in gluon fusion at NLO matched to parton showers

We present a calculation of the next-to-leading order (NLO) QCD corrections to gluon-induced electroweak gauge boson pair production, gg rightarrow ZZ and gg rightarrow W^+W^-, matched to the PYTHIA 8 parton shower in the POWHEG approach. The calculation consistently incorporates the continuum background, the Higgs-mediated ggrightarrow H^* rightarrow VV process, and their interference. We consider leptonic decay modes of the vector bosons and retain offshell and non-resonant contributions. The processes considered are loop-induced at leading order and thus contain two-loop virtual contributions as well as loop-squared real contributions. Parton-shower effects are found to be marginal in inclusive observables and quite sizeable in observables that are exclusive in additional jet radiation. The Monte Carlo generator presented here allows for realistic experimental effects to be incorporated in state-of-the-art precision analyses of diboson production and of the Higgs boson in the offshell regime.

The electro-weak phase transition at colliders: confronting theoretical uncertainties and complementary channels

We explore and contrast the capabilities of future colliders to probe the nature of the electro-weak phase transition. We focus on the real singlet scalar field extension of the Standard Model, representing the most minimal, yet most elusive, framework that can enable a strong first-order electro-weak phase transition. By taking into account the theoretical uncertainties and employing the powerful complementarity between gauge and Higgs boson pair channels in the searches for new scalar particles, we find that a 100 TeV proton collider has the potential to confirm or falsify a strong first-order transition. Our results hint towards this occurring relatively early in its lifetime. Furthermore, by extrapolating down to 27 TeV, we find that a lower-energy collider may also probe a large fraction of the parameter space, if not all. Such early discoveries would allow for precise measurements of the new phenomena to be obtained at future colliders and would pave the way to definitively verify whether this is indeed the physical remnant of a scalar field that catalyses a strong first-order transition.

Updated constraints on Z′ and W′ bosons decaying into bosonic and leptonic final states using the run 2 ATLAS data

The full ATLAS Run 2 data set with time-integrated luminosity of 139 fb$^{-1}$ in the diboson and dilepton channels is used to probe benchmark models with extended gauge sectors: the $E_6$-motivated Grand Unification models, the left-right symmetric $LR$ and the sequential standard model (EGM). These all predict neutral $Z'$ vector bosons, decaying into lepton pairs, $\ell\ell$, or into electroweak gauge boson pairs $WW$, where one $W$ in turn decays semileptonically. 95% C.L. exclusion limits on the $Z'$ resonance production cross section times branching ratio to electroweak gauge boson pairs and to lepton pairs in the mass range of $\sim$ 1 - 6 TeV are converted to constraints on the $Z$-$Z'$ mixing parameter and the heavy resonance mass. We present exclusion regions on the parameter space of the $Z'$ which are significantly extended compared to those obtained from the previous analyses performed with LHC data collected at 7 and 8 TeV in Run 1 as well as at 13 TeV in Run 2 at time-integrated luminosity of 36.1 fb$^{-1}$ and are the most stringent bounds to date. Also presented, from a similar analysis of electrically charged $W'$ bosons arising in the EGM, which can decay through $W'\to WZ$ and $W'\to \ell\nu$, are limits on the $W$-$W'$ mixing parameter and the charged $W'$ vector boson mass.

Search for SU(2) V singlet Higgs boson in the Georgi–Machacek model at the LHC

In this paper, we study in detail the phenomenology of the non-SM SU(2) V singlet Higgs boson at the 14 TeV Large Hadron Collider (LHC) in the Georgi–Machacek (GM) model. We present a systematic comparison of the production mechanisms and decay modes of , especially the vector-boson fusion (VBF) and gluon–gluon fusion (ggF) production mechanisms and the decays to W + W −, ZZ, H 5 H 5, H 3 H 3, and . After performing a comprehensive scan over the seven-dimensional parameter space of the GM model, we find that the , and decay channels are almost excluded by the theoretical and experimental constraints, while can decay into H 5 H 5 in an appreciable region of the GM parameter space. Based on the scanning results, we discuss detailedly the production via ggF and VBF with subsequent decays of , and at the 14 TeV LHC. The integrated cross sections and some kinematic distributions of final products for both the signals at some benchmark points of the GM parameter space and the corresponding SM backgrounds are provided. If the decay to H 5 H 5 is kinematically allowed, can be detected in the decay channel at high-luminosity LHC unless is too small or is too high. In the mass range of , the vector-boson fusion is the most promising production channel in search of due to the two hard tagging jets in the final state, and we may expect to discover in both and decay channels with of data if the decay branching ratio of to a pair of weak gauge bosons is sufficiently large.