Gauge Boson Pair Research Articles

Superheavy dark matter in R+R^2 cosmology with conformal anomaly

Cosmological evolution and particle creation in R^2-modified gravity are considered for the case of the dominant decay of the scalaron into a pair of gauge bosons due to conformal anomaly. It is shown that in the process of thermalization superheavy dark matter with the coupling strength typical for the GUT SUSY can be created. Such dark matter would have the proper cosmological density if the particle mass is close to 10^{12} GeV.

High-precision limits on W\u2013W' and Z\u2013Z' mixing from diboson production using the full LHC Run 2 ATLAS data set

The full ATLAS Run 2 data set with time-integrated luminosity of 139 , {text {fb}}^{-1} in the diboson channels in hadronic final states is used to probe a simple model with an extended gauge sector (EGM), proposed by Altarelli et al., and often taken as a convenient benchmark by experimentalists. 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 hadronically. Exclusion limits at the 95% CL on the Z' and W' resonance production cross section times branching ratio to electroweak gauge boson pairs in the mass range of sim 1–5 TeV are here converted to constraints on W–W' and Z–Z' mixing parameters and masses for the EGM. We present exclusion regions on the parameter space of the W' and Z' by using the full Run 2 data set comprised of pp collisions at sqrt{s}=13 , hbox {TeV} and recorded by the ATLAS detector at the CERN LHC. The obtained exclusion regions are significantly extended compared to those obtained from the previous analysis performed with Tevatron data as well as with LHC data collected at 7 and 8 TeV in Run 1 and are the most stringent bounds to date.

Improved bounds on W−W′ mixing with ATLAS resonant WZ production data at the LHC at s=13 TeV

New charged vector bosons $W'$ decaying into gauge boson pairs $WZ$ are predicted in many scenarios of new physics, including models with an extended gauge sector (EGM). Due to the large variety of models (other unification groups, models with Supersymmetry, Little Higgs Models, Extra Dimensions) the more general EGM approach is here considered. For what concerns $W'$-production, these models are parametrised by two parameters, the $W^\prime$ mass $M_{W^\prime}$ and the $W$-$W^\prime$ mixing parameter $\xi$. The diboson $WZ$ production allows to place stringent constraints on this mixing angle and the $W'$ mass, which we determine and present for the first time by using data from $pp$ collisions at $\sqrt{s}=13$ TeV recorded by the ATLAS detector at the CERN LHC, with integrated luminosity of 36.1 fb$^{-1}$. By comparing the experimental limits to the theoretical predictions for the total cross section of $W'$ resonant production and its subsequent decay into $WZ$ pairs, we show that the derived constraints on the mixing angle for the benchmark model are rather small, between $10^{-4}$ and $10^{-3}$, i.e., greatly improved with respect to those derived from the global analysis of electroweak data which yield $\xi\sim 10^{-2}$. We combine the limits derived from $WZ$ production data with those obtained from the $W'\to e\nu$ process in order to significantly extend the exclusion region in the $M_{W'}$-$\xi$ parameter plane and obtain the most stringent exclusion limits to date. We present the combined allowed parameter space for the EGM $W'$ boson after incorporating indirect constraints from low energy electroweak data, direct search constraints from Tevatron and from the LHC Run I with 7 and 8 TeV as well as at Run II with 13 TeV data.

Signs of heavy Higgs bosons at CLIC: an e^+ e^- road to the electroweak phase transition

We analyse the sensitivity of the proposed compact linear collider (CLIC) to the existence of beyond the standard model (SM) Higgs bosons through their decays into pairs of massive gauge bosons H rightarrow VV and SM-like Higgses H rightarrow hh, considering CLIC centre of mass energies sqrt{s} = 1.4 TeV and 3 TeV. We find that resonant di-Higgs searches at CLIC would allow for up to two orders of magnitude improvement w.r.t. the sensitivity achievable by HL-LHC in the mass range m_H in [250,mathrm {GeV},, 1 ,mathrm {TeV}]. Focusing then on a real singlet extension of the SM, we explore the prospects of heavy Higgs searches at CLIC for probing the regions of parameter space yielding a strongly first order electroweak phase transition that could generate the observed matter-antimatter asymmetry of the Universe. Our study illustrates the complementarity between CLIC and other possible future colliders like FCC-ee in probing singlet extensions of the SM, and shows that high-energy e^+ e^- colliders provide a powerful means to unravel the nature of electroweak symmetry breaking in the early Universe.

Improved constraints on the mixing and mass of Z′ bosons from resonant diboson searches at the LHC at s=13 TeV and predictions for Run II

New neutral vector bosons $Z'$ decaying to charged gauge boson pairs $W^+W^-$ are predicted in many scenarios of new physics, including models with an extended gauge sector such as $E_6$, left-right symmetric $Z^\prime_{\rm LRS}$ and the sequential standard model $Z'_{\rm SSM}$. For these benchmark models we calculate and present theoretical expectations for different values of the $Z^\prime$ mass $M_2$ and mixing parameter $\xi$. Our results are based on the narrow width approximation which allows to make a convenient comparison of experiment to theoretical benchmark models. The diboson production allows to place stringent constraints on the $Z$-$Z'$ mixing angle and the $Z'$ mass, which we determine by using data from $pp$ collisions at $\sqrt{s}=13$ TeV recorded by the ATLAS detector at the CERN LHC, with integrated luminosity of $\sim$ 36 fb$^{-1}$. By comparing the experimental limits to the theoretical predictions for the total cross section of $Z'$ resonant production and its subsequent decay into $W^+W^-$ pairs, we show that the derived constraints on the mixing angle for the benchmark models are of the order of a few $\times 10^{-4}$, i.e., greatly improved with respect to those derived from the global analysis of electroweak data. We combine the limits derived from diboson production data with those obtained from the Drell--Yan process in order to significantly extend the exclusion region in the $M_{2}$-$\xi$ parameter plane. Also, we demonstrate that further improvement on the constraining of this mixing can be achieved through analysis of the full set of Run~II data.

Electroweak corrections to Higgs boson decays to γγ and W+W− in standard model EFT

Higgs decays to gauge boson pairs are a crucial ingredient in the study of Higgs properties, with the decay $H\rightarrow\gamma\gamma$ being particularly sensitive to new physics effects. Assuming all potential new physics occurs at energies much above the weak scale, deviations from Standard Model predictions can be parameterized in terms of the coefficients of an effective field theory (SMEFT). When experimental limits on the SMEFT coefficients reach an accuracy of a few percent, predictions must be done beyond the lowest order in the SMEFT in order to match theory and experimental accuracy. This paper completes a program of computing the one-loop electroweak SMEFT corrections to $H\rightarrow VV^\prime$, $V=W^\pm,Z,\gamma$. The calculation of the real contribution to $H\rightarrow W^+W^-\gamma$ is performed by mapping two-loop amplitudes to the $3-$ body phase space.

Loop effects on the Higgs decay widths in extended Higgs models

In order to identify the Higgs sector using future precision data, we calculate the partial decay widths of the discovered Higgs boson with the mass of 125 GeV into fermion pairs and gauge-boson pairs with one-loop electroweak and one-loop QCD corrections in various extended Higgs models, such as the Higgs singlet model and four types of two Higgs doublet models. In the tree-level analysis, the patterns of deviations from the standard model predictions in the partial decay widths for various decay modes are distinctive for each model, due to the mixing of the Higgs boson with other neutral scalars. Our present analysis shows that even with a full set of radiative corrections we can discriminate these extended Higgs models via the partial decay widths as long as any of the deviations is detected at future precision measurements. Furthermore, we quantitatively show that in each model the magnitude of the deviations can provide important information on the mass scale of extra Higgs bosons under the theoretical constraints from perturbative unitary and vacuum stability, which can be obtained without discovery of the additional Higgs bosons.

Universality of next-to-leading power threshold effects for colourless final states in hadronic collisions

We consider the production of an arbitrary number of colour-singlet particles near partonic threshold, and show that next-to-leading order cross sections for this class of processes have a simple universal form at next-to-leading power (NLP) in the energy of the emitted gluon radiation. Our analysis relies on a recently derived factorisation formula for NLP threshold effects at amplitude level, and therefore applies both if the leading-order process is tree-level and if it is loop-induced. It holds for differential distributions as well. The results can furthermore be seen as applications of recently derived next-to-soft theorems for gauge theory amplitudes. We use our universal expression to re-derive known results for the production of up to three Higgs bosons at NLO in the large top mass limit, and for the hadro-production of a pair of electroweak gauge bosons. Finally, we present new analytic results for Higgs boson pair production at NLO and NLP, with exact top-mass dependence.

The inert doublet model in the light of Fermi-LAT gamma-ray data: a global fit analysis

We perform a global fit within the inert doublet model taking into account experimental observables from colliders, direct and indirect dark matter searches and theoretical constraints. In particular, we consider recent results from searches for dark matter annihilation-induced gamma-rays in dwarf spheroidal galaxies and relax the assumption that the inert doublet model should account for the entire dark matter in the Universe. We, moreover, study in how far the model is compatible with a possible dark matter explanation of the so-called Galactic center excess. We find two distinct parameter space regions that are consistent with existing constraints and can simultaneously explain the excess: One with dark matter masses near the Higgs resonance and one around 72 GeV where dark matter annihilates predominantly into pairs of virtual electroweak gauge bosons via the four-vertex arising from the inert doublet’s kinetic term. We briefly discuss future prospects to probe these scenarios.

Electroweak diboson production at ATLAS

This paper is giving an overview of recent ATLAS results on the production cross sections of gauge boson pairs decaying leptonically using data from pp collisions at √s = 13 TeV for ZZ and at √s = 8 TeV for W ± Z and W ± W ± at the LHC at CERN. The cross sections are found to be in agreement with the expectations from the Standard Model within the estimated uncertainties. The production cross section measurements also allow for studies of anomalous triple and quartic gauge couplings for which 95% confidence level limits are set.

LHC signals from cascade decays of warped vector resonances

Recently (arXiv:1608.00526), a new framework for warped higher-dimensional compactifications with “bulk” standard model (SM) was proposed: in addition to the UV (Planck scale) and IR (a couple of TeV) branes, there is an intermediate brane, taken to be around 10TeV. The SM matter and Higgs fields propagate from the UV brane down to this intermediate brane only, while gauge and gravity fields propagate in the entire bulk. Such a configuration renders the lightest gauge Kaluza-Klein (KK) states within LHC reach, simultaneously satisfying flavor and CP constraints. In addition, the usual leading decay modes of the lightest KK gauge bosons into top and Higgs bosons are suppressed. This effect permits erstwhile subdominant channels to become significant. These include flavor-universal decays to SM fermions and Higgs bosons, and a novel channel — decay to a radion and a SM gauge boson, followed by radion decay to a pair of SM gauge bosons. In this work, we first delineate the parameter space where the above mentioned cascade decay of gauge KK particles dominates, and thereby can be the discovery mode at the LHC. We then perform a detailed analysis of the LHC signals from this model, finding that 300/fb suffices for evidence of KK-gluon in tri-jet, jet + di-photon and jet + di-boson channels. However, KK photon in photon + di-jet, and KK-W in leptonic W + di-jet require 3000/fb. The crucial feature of this decay chain is a “double” resonance, i.e. 3-particle and 2-particle invariant mass peaks, corresponding to the KK gauge boson and the radion respectively.

UV complete partially composite pseudo-Nambu Goldstone boson Higgs

We explore an electroweak symmetry breaking (EWSB) scenario based on the mixture of a fundamental Higgs doublet and an SU(4)/Sp(4) composite pseudo-Nambu-Goldstone doublet---a particular manifestation of bosonic technicolor/induced EWSB. Taking the fundamental Higgs mass parameter to be positive, EWSB is triggered by the mixing of the doublets. This setup has several attractive features and phenomenological consequences, which we highlight: (i) Unlike traditional bosonic technicolor models, the hierarchy between ${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{TC}}$ and the electroweak scale depends on vacuum (mis)alignment and can be sizable, yielding an attractive framework for natural EWSB; (ii) As the strong sector is based on SU(4)/Sp(4), a fundamental (UV-complete) description of the strong sector is possible, that is informed by the lattice; (iii) The lightest vector resonances occur in the 10-plet, 5-plet and singlet of Sp(4). Misalignment leads to a 10-plet ``parity-doubling'' cancellation in the $S$ parameter, and a suppressed 5-plet contribution; (iv) Higgs coupling deviations are typically of $\mathcal{O}(1%)$; (v) The 10-plet isotriplet resonances decay dominantly to a massive technipion and a gauge boson, or to technipion pairs, rather than to gauge boson or fermion pairs; moreover, their couplings to fermions are small. Thus, the bounds on this setup from conventional heavy-vector-triplet searches are weak. A supersymmetric $U(1{)}_{R}$ symmetric realization is briefly described.

LHC Probes of TeV-Scale Scalars in SO(10) Grand Unification

We investigate the possibility of TeV-scale scalars as low energy remnants arising in the nonsupersymmetric SO(10) grand unification framework where the field content is minimal. We consider a scenario where the SO(10) gauge symmetry is broken into the gauge symmetry of the Standard Model (SM) through multiple stages of symmetry breaking, and a colored and hypercharged scalar χ picks a TeV-scale mass in the process. The last stage of the symmetry breaking occurs at the TeV-scale where the left-right symmetry, that is, SU(2)L⊗SU(2)R⊗U(1)B-L⊗SU(3)C, is broken into that of the SM by a singlet scalar field S of mass MS~1 TeV, which is a component of an SU(2)R-triplet scalar field, acquiring a TeV-scale vacuum expectation value. For the LHC phenomenology, we consider a scenario where S is produced via gluon-gluon fusion through loop interactions with χ and also decays to a pair of SM gauge bosons through χ in the loop. We find that the parameter space is heavily constrained from the latest LHC data. We use a multivariate analysis to estimate the LHC discovery reach of S into the diphoton channel.

Erratum: Massive gauge boson pair production at the LHC: A next-to-leading order story [Phys. Rev. D 88 , 113005 (2013)

Electroweak gauge boson pair production is one of the most important Standard Model processes at the LHC, not only because it is a benchmark process but also by its ability to probe the electroweak interaction directly. We present full next-to-leading order predictions for the production cross sections and distributions of on-shell massive gauge boson pair production in the Standard Model. This includes the QCD and electroweak (EW) corrections. We study the hierarchy between the different channels when looking at the size of the QCD gluon-induced processes and the EW photon-induced processes and provide the first comprehensive explanation of this hierarchy thanks to analytical leading-logarithmic results. We also provide a detailed study of the theoretical uncertainties affecting the total cross section predictions that stem from scale variation, parton distribution function and $\alpha_s$ errors. We then compare with the present LHC data.

Three types of gravitons in emergent modified gravity

Since it has been proposed that gravity is emergent and gravitons are composed of pairs of gauge bosons, from the fact that the mass (self-energy) of a particle corresponds to the sum of the contributions of the three fundamental interactions, we suggest that there may exist three types of gravitons, each corresponding to the gauge-boson pairings of the three fundamental interactions. Comparisons with observations at galactic and cosmic scales are attempted, and tests at very small distances are envisaged.

Supersoft SUSY models and the 750 GeV diphoton excess, beyond effective operators

We propose that the sbino, the scalar partner of a Dirac bino can explain the 750 GeV diphoton excess observed by ATLAS and CMS . We analyze a model in which the sbino couples to pairs of Standard Model (SM) gauge bosons. We analyze an effective operator model, as well as a completion in which the sbino couples to pairs of gauge bosons through loops of heavy sfermions. We find that the sbino may be given an appreciable decay width through tree level coupling in the Higgs or Higgsino sector and additionally fit the 750 GeV excess by considering gluon fusion processes with decay to diphotons.

Resummation prediction on gauge boson pair production with a jet veto

We investigate the resummation effects with a jet veto, for WZ and ZZ productions at the LHC in soft-collinear effective theory. We present the invariant mass distributions and the total cross section with different jet veto and jet radius for these process at Next-to-Next-to-Leading-Logarithmic level. Our results show that the jet-veto resummation can increase the jet-veto cross section and decrease the scale uncertainties, especially in the large center-of-mass energy. We find that for pt_veto>30 GeV and R=0.4, the resummation results can increase POWHEG+PYTHIA predictions by about 19% for WZ production and 18% for ZZ production, respectively. Our results agree with the CMS data for WZ productions within 2$\sigma$ C.L. at 8 TeV, which can explain the 2$\sigma$ discrepancy between the CMS experimental results and theoretical predictions based on NLO calculation with parton showers.

A model for the LHC diboson excess

The first run of the LHC showed hints of a new resonance with mass near 1.9 TeV decaying into electroweak gauge boson pairs as well as into dijets. While Run 2 has neither confirmed nor ruled out such a resonance, it has yielded new constraints on models attempting to explain these decays. Additionally in W′ models where this new resonance is a charged vector boson that is a weak isospin singlet there is the potential for conflict with the electroweak precision T parameter. We construct variants of a W′ resonance model that provide an excellent fit to both Run 1 and Run 2 data, as well as electroweak precision measurements. The model also predicts a neutral vector boson, a Z′, with mass close to 3 TeV. This Z′ is compatible with the intriguing Run 2 observation of a dielectron pair with invariant mass of 2.9 TeV at CMS.

Footprints of New Strong Dynamics via Anomaly and the 750GeV Diphoton.

The chiral anomaly provides smoking-gun evidence of a new confining gauge theory. Motivated by a reported event excess in a diphoton invariant mass distribution at the LHC, we discuss a scenario that a pseudo-Nambu-Goldstone (PNG) boson of a new QCD-like theory is produced by gluon fusion and decays into a pair of the standard model gauge bosons. Despite the strong dynamics, the production cross section and the decay widths are determined by an anomaly matching condition. The excess can be explained by the PNG boson with mass of around 750GeV. The model also predicts exotic hadrons such as a color-octet scalar and baryons. Some of them are within the reach of the LHC experiment.

Cancellation of Glauber Gluon Exchange in the Double Drell–Yan Process

For any factorisation proof, a crucial step is a demonstration of the cancellation of so-called Glauber gluons. We summarise a recent paper in which we demonstrated this cancellation for double Drell–Yan production (the double parton scattering process in which a pair of electroweak gauge bosons is produced), both for the integrated cross section and for the cross section differential in the boson transverse momenta.