Pair Of Gluons Research Articles

A comparative study of flavour-sensitive observables in hadronic Higgs decays

Jet production from hadronic Higgs decays at future lepton colliders will have significantly different phenomenological implications than jet production via off-shell photon and Z-boson decays, owing to the fact that Higgs bosons decay to both pairs of quarks and gluons. We compute observables involving flavoured jets in hadronic Higgs decays to three partons at Born level including next-to-leading order corrections in QCD (i.e., up to O(αs2))\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\mathcal {O}(\\alpha _\ extrm{s}^2))$$\\end{document}. The calculation is performed in the framework of an effective theory in which the Higgs boson couples directly to gluons and massless b-quarks retaining a non-vanishing Yukawa coupling. For the energy of the leading and subleading flavoured jet, the angular separation and the invariant mass of the leading b–b¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\bar{b}$$\\end{document} pair, we contrast the results obtained in both Higgs-decay categories and using either of the infrared-safe flavoured jet algorithms flavour-kT\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$k_{\ extrm{T}}$$\\end{document} and flavour-dressing.

Glauber phases in non-global LHC observables: resummation for gluon-initiated processes

The resummation of the “Glauber series” in non-global LHC observables is extended to processes with gluons in the initial state. This series simultaneously incorporates large double-logarithmic corrections, the so-called “super-leading logarithms”, together with higher-order exchanges of pairs of Glauber gluons associated with the large numerical factor (iπ)2. On a technical level, the main part of this work is devoted to the systematic reduction of the appearing color traces and construction of basis structures, which consist of thirteen elements for gg and eleven elements for qg scattering. Numerical estimates for wide-angle gap-between-jet cross sections at the parton level show that, in particular for gg scattering at relatively small vetoes Q0, the contribution involving four Glauber exchanges gives a sizeable correction and should not be neglected.

Invisible dark matter decays of a non-Standard Model like CP-even scalar boson

We investigate two extensions of the standard model that include particle dark matter candidates: the Next-to-Two Higgs Doublet Model and the Next-to-minimal Supersymmetric Standard Model. These models feature a non-Standard Model like CP-even scalar with a sub-TeV mass, denoted by H2, among other particles. At a 13 TeV proton–proton collider, the primary production channel for such scalars is via the fusion of a pair of gluons. Subsequently, these scalars can decay invisibly into a pair of dark matter candidates, which can be dominant. In the supersymmetric model, it is possible for the Lightest Supersymmetric Particle (LSP) and Next-to Lightest Supersymmetric Particle (NLSP) to be mass degenerate, leading to quasi-invisible H2 decays to LSP+NLSP and NLSP+NLSP. We present the predictions of both models for this challenging scenario while ensuring compatibility with recent experimental constraints.

An observation on Feynman diagrams with axial anomalous subgraphs in dimensional regularization with an anticommuting γ5

Through the calculation of the matrix element of the singlet axial-current operator between the vacuum and a pair of gluons in dimensional regularization with an anti-commuting γ5 defined in a Kreimer-scheme variant, we find that additional renormalization counter-terms proportional to the Chern-Simons current operator are needed starting from O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O} $$\\end{document}(αs2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\alpha}_s^2 $$\\end{document}) in QCD. This is in contrast to the well-known purely multiplicative renormalization of the singlet axial-current operator defined with a non-anticommuting γ5. Consequently, without introducing compensation terms in the form of additional renormalization, the Adler-Bell-Jackiw anomaly equation does not hold automatically in the bare form in this kind of schemes. We determine the corresponding (gauge-dependent) coefficient to O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O} $$\\end{document}(αs3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\alpha}_s^3 $$\\end{document}) in QCD, using a variant of the original Kreimer prescription which is implemented in our computation in terms of the standard cyclic trace together with a constructively-defined γ5. Owing to the factorized form of these divergences, intimately related to the axial anomaly, we further performed a check, using concrete examples, that with γ5 treated in this way, the axial-current operator needs no more additional renormalization in dimensional regularization but only for non-anomalous amplitudes in a perturbatively renormalizable theory. To be complete, we provide a few additional ingredients needed for a proposed extension of the algorithmic procedure formulated in the above analysis to potential applications to a renormalizable anomaly-free chiral gauge theory, i.e. the electroweak theory.

The parton-level structure of Higgs decays to hadrons at N3LO

We present the quantum chromodynamics (QCD) corrections for Higgs boson decays to hadronic final states at next-to-next-to-next-to-leading order (N3LO) in the strong coupling constant αs. In particular, we consider the Higgs boson decay to massless bottom quarks and the Higgs boson decay to a pair of gluons in the limit of a heavy top quark. The tree-level five-parton, the one-loop four-parton, the two-loop three-parton, and the three-loop two-parton matrix elements are integrated separately over the inclusive phase space and classified by partons appearing in the final state and by colour structure. As a check, we reproduce known results for the inclusive hadronic decay rates at N3LO. We study patterns of infrared singularity cancellation within the colour layers of the integrated expressions and we comment on the similarities between H → boverline{b} and γ∗→ qoverline{q} . We anticipate that our result will be an essential ingredient for the formulation of N3LO subtraction schemes.

Machine learning-enhanced search for a vectorlike singlet B quark decaying to a singlet scalar or pseudoscalar

The presence of a new decay mode relaxes the current mass exclusion limits on vectorlike quarks considerably. We consider the case of a weak-singlet vectorlike $B$ quark that can decay to a singlet scalar or pseudoscalar $\Phi$. In an earlier paper [A. Bhardwaj et al., Roadmap to explore vectorlike quarks decaying to a new scalar or pseudoscalar, Phys. Rev. D, 106 (2022) 095014; arXiv:2203.13753], we mapped the possibilities to explore such setups at the LHC. We showed that it is possible for a $B$ quark to decay into $\Phi$ and the $\Phi$ to dominantly decay to a pair of gluons or $b$ quark(s) without fine-tuning the parameters. In this paper, we present a collider search strategy to look for the pair production of singlet $B$ quarks. If both $B$ quarks decay into $b\Phi$ pairs, the final state is fully hadronic: $B{B}\to(b\Phi)({b}\Phi)\to (bgg)({b}gg)/(bb{b})({b}b{b})$, which is very challenging to probe. Therefore, we consider a simpler mixed decay specific to the singlet $B$ case, $BB\to(b\Phi)(tW)$ with a lepton in the final state, to achieve the best sensitivity at the high-luminosity LHC. We use a deep neural network with a weighted cross-entropy loss to separate the signal from the huge SM background. Our analysis shows that large areas of the $M_{B}-M_{\Phi}$ parameter space are discoverable through this signature. We show how the discovery and exclusion regions scale with the branching ratio in the new decay mode. We also estimate the reach in the inclusive monolepton channel with the same network model.

Construction of non-Abelian electric strings

We detail the construction of electric string solutions in $SU(2)$ Yang-Mills-Higgs theory with a scalar in the fundamental representation and discuss the properties of the solution. We show that Schwinger gluon pair production in the electric string background is absent. A similar construction in other models, such as with an adjoint scalar field and the electroweak model, does not yield solutions.

Probing Gluon Bose Correlations in Deep Inelastic Scattering.

We study correlations originating from the quantum nature of gluons in a hadronic wave function. Bose-Einstein correlation between identical particles lead to the enhancement in the number of pairs of gluons with the same quantum numbers and small relative momentum. We show that these preexisting correlations can be probed in deep inelastic scattering experiments at high energy. Specifically, we consider diffractive dijet plus a third jet production. The azimuthal dependence displays a peak at the zero relative angle between the transverse momentum imbalance of the photon-going dijet and the transverse momentum of the hadron-going jet. Our calculations explicitly show that the peak originates from Bose enhancement. Comparing electron-proton to electron-nucleus collisions, we demonstrate that the nuclear target enhances the relative strength of the peak. With the future high luminosity electron-ion collider the proposed measurements of gluon Bose enhancement become experimentally feasible.

Hadron collider probes of the quartic couplings of gluons to the photon and Z boson

We explore the experimental sensitivities of measuring the gg → Zγ process at the LHC to the dimension-8 quartic couplings of gluon pairs to the Z boson and photon, in addition to comparing them with the analogous sensitivities in the gg → γγ process. These processes can both receive contributions from 4 different CP-conserving dimension-8 operators with distinct Lorentz structures that contain a pair of gluon field strengths, {hat{G}}_{mu v}^a , and a pair of electroweak SU(2) gauge field strengths, {W}_{mu v}^i , as well as 4 similar operators containing a pair of {hat{G}}_{mu v}^a and a pair of U(1) gauge field strengths, Bμν. We calculate the scattering angular distributions for gg → Zγ and the Z → overline{f}f decay angular distributions for these 4 Lorentz structures, as well as the Standard Model background. We analyze the sensitivity of ATLAS measurements of the Z(→ ℓ+ℓ−, overline{nu}nu , overline{q}q )γ final states with integrated luminosities up to 139 fb−1 at sqrt{s} = 13 TeV, showing that they exclude values ≲ 2 TeV for the dimension-8 operator scales, and compare the Zγ sensitivity with that of an ATLAS measurement of the γγ final state. We present combined Zγ and γγ constraints on the scales of dimension-8 SMEFT operators and γγ constraints on the nonlinearity scale of the Born-Infeld extension of the Standard Model. We also estimate the sensitivities to dimension-8 operators of experiments at possible future proton-proton colliders with centre-of-mass energies of 25, 50 and 100 TeV, and discuss possible measurements of the Z spin and angular correlations.

Jets and photons spectroscopy of Higgs-ALP interactions

Axion-like particles (ALPs) and Higgs bosons can interact in scalar sectors beyond the Standard Model, leading the Higgs boson to decay into pairs of gluons and photons through the ALP interaction and giving rise to resonances in the decay products of the process h → aa → gg + γγ, resembling a spectral-line analysis. We explore this signature to constrain an ALP effective field theory formulation. Our analyses show that the forthcoming runs of the LHC will be capable of probing the ALP-Higgs interaction in the ALP mass range from 0.5 to 60 GeV using an automatized search strategy that adapts to different ALP masses in inclusive jets plus photons final states. Such interaction can also be tested in mass regions where the two and four-photon search channels are currently ineffective.

Curvature perturbations and anomaly explain dark energy

Abstract We investigate the history of dark energy to explain the present magnitude. We assume the dark energy is the residual cosmological constant. The most important channel in the reheating process is gluon pair production by the quantumchromodynamic trace anomaly. We argue that dark energy decays rapidly by gluon pair emissions during the reheating and after the big bang. The reheating temperature is determined by the decay width of dark energy, $\Gamma$, and the Planck mass, $M_\mathrm{p}$, as $\sqrt{M_\mathrm{P}\Gamma} \sim 10^6 \, GeV$. This is a consequence of Friedmann’s equation and the equilibrium condition $\Gamma\sim H$. As the Universe cools below the hadronic scale, the dark energy density is almost frozen. Nevertheless, the dark energy further decreases by emitting two photons. We have estimated the current decay rate of dark energy from the quantum electrodynamic trace anomaly. The consistent solution of the Friedmann equation is in excellent agreement with the observations. The suppression factor of the dark energy scale is the product of the fine structure constant, $\alpha$, and the curvature perturbation, $P$: $10^{-30}=(\alpha^2P/4\pi)^2$. We argue that the conformal symmetry breaking in both ultraviolet and infrared are necessary unless dark energy is subtracted. We also investigate leptogenesis by adding massive right-handed neutrinos: realistic leptogenesis takes place during the reheating process.

LHC signals for KK graviton from an extended warped extra dimension

We analyze signals at the Large Hadron Collider (LHC) from production and decay of Kaluza-Klein (KK) gravitons in the context of “extended” warped extra-dimensional models, where the standard model (SM) Higgs and fermion fields are restricted to be in-between the usual ultraviolet/Planck brane and a ∼ O(10) TeV (new, “intermediate”) brane, whereas the SM gauge fields (and gravity) propagate further down to the ∼ O(TeV) infrared brane. Such a framework suppresses flavor violation stemming from KK particle effects, while keeping the KK gauge bosons and gravitons accessible to the LHC. We find that the signals from KK graviton are significantly different than in the standard warped model. This is because the usually dominant decay modes of KK gravitons into top quark, Higgs and longitudinal W/Z particles are suppressed by the above spatial separation between these two sets of particles, thus other decay channels are allowed to shine themselves. In particular, we focus on two novel decay channels of the KK graviton. The first one is the decay into a pair of radions, each of which decays (dominantly) into a pair of SM gluons, resulting in a resonant 4-jet final state consisting of two pairs of dijet resonance. On the other hand, if the radion is heavier and/or KK gluon is lighter, then the KK graviton mostly decays into a KK gluon and a SM gluon. The resulting KK gluon has a significant decay branching fraction into radion and SM gluon, thereby generating (again) a 4-jet signature, but with a different underlying event topology, i.e., featuring now three different resonances. We demonstrate that the High-Luminosity LHC (HL-LHC) has sensitivity to KK graviton of (up to) ∼ 4 TeV in both channels, in the specific model with only gluon field (and gravity) propagating in the extended bulk, whereas it is unlikely to have sensitivity in the standard dijet resonance search channel from KK graviton decay into two gluons.

On Sugawara construction on celestial sphere

Conformally soft gluons are conserved currents of the Celestial Conformal Field Theory (CCFT) and generate a Kac-Moody algebra. We study celestial amplitudes of Yang-Mills theory, which are Mellin transforms of gluon amplitudes and take the double soft limit of a pair of gluons. In this manner we construct the Sugawara energy-momentum tensor of the CCFT. We verify that conformally soft gauge bosons are Virasoro primaries of the CCFT under the Sugawara energy-momentum tensor. The Sugawara tensor though does not generate the correct conformal transformations for hard states. In Einstein-Yang- Mills theory, we consider an alternative construction of the energy-momentum tensor, similar to the double copy construction which relates gauge theory amplitudes with gravity ones. This energy momentum tensor has the correct properties to generate conformal transformations for both soft and hard states. We extend this construction to supertranslations.

Improving the measurement of the Higgs boson-gluon coupling using convolutional neural networks at e+e− colliders

In this paper we propose to use convolutional neural networks (CNNs) to improve the precision measurement of the Higgs boson-gluon effective coupling at lepton colliders. The CNN is employed to recognize the Higgs boson and a $Z$ boson associated production process, with the Higgs boson decaying to a gluon pair and the $Z$ boson decaying to a lepton pair at the center-of-mass energy 250 GeV and integrated luminosity 5 ab$^{-1}$. By using CNNs, the uncertainty of the effective coupling measurement can be decreased from $1.94\%$ to about $1.28\%$ using the PYTHIA data and from $1.82\%$ to about $1.22\%$ using the HERWIG data in the Monte Carlo simulation. Moreover, the performance of CNNs using different final state constituents shows that the energy distributions of the leading and subleading jets constituents play a major role in the identification and the optimal uncertainty of effective coupling using CNNs is reduced by about $35\%$ compared to that using conventional method.

Impact of the pre-equilibrium stage of ultra-relativistic heavy ion collisions: isotropization and photon production

We present a model in which gluon and quark pairs are produced by means of the Schwinger mechanism from the decay of color-electric flux tubes, which are expected to be produced in the early stage of ultra-relativistic heavy ion collisions. The evolution equations of the initial field are coupled to the relativistic transport equation which describes the dynamics of the many particle system and is formulated in terms of a fixed viscosity over entropy density ratio $ \eta$ /s. This self-consistent solution of the problem allows to take into account the backreaction of the color currents on the classical field. We study isotropization and thermalization of the plasma produced by the field decay for a expanding geometry in $ 1+1{\rm D}$ and in $ 3+1{\rm D}$ . We find that the initial color-electric field decays within 1fm/c ; in the case of large $ \eta$ /s oscillations of the field appear along the whole temporal evolution of the system, affecting also the ratio between longitudinal and transverse pressure. In the case of small viscosities ( $ \eta/s\lesssim3/4\pi$ ) we find an equilibration time less than 1 fm/c, in agreement with the common lore of hydrodynamics. Including the pertinent scattering processes into the collision integral of the Boltzmann equation we investigate photon production within our model for the pre-equilibrium dynamics and with simulations starting with equilibrium initial conditions. Thus, we are able to identify the contribution of the early-stage to the photon spectrum in Au-Au collisions at RHIC $\sqrt{s_{NN}}=200$ GeV and in Pb-Pb collisions at LHC $ \sqrt{s_{NN}}=2.76$ TeV. We find that there is no dark age in relativistic heavy ion collisions: early-stage photons enhance the direct photon spectrum in the intermediate transverse momentum region ( $ p_{T}\gtrsim 1.5$ -2 GeV depending on the collision energy) and their abundance is comparable with that produced by a thermalized quark-gluon plasma.

Forward trijet production in proton–nucleus collisions

Using the formalism of the light-cone wave function in perturbative QCD together with the hybrid factorization, we compute the cross-section for three particle production at forward rapidities in proton–nucleus collisions. We focus on the quark channel, in which the three produced partons — a quark accompanied by a gluon pair, or two quarks plus one antiquark — are all generated via two successive splittings starting with a quark that was originally collinear with the proton. The three partons are put on-shell by their scattering off the nuclear target, described as a Lorentz-contracted “shockwave”. The three-parton component of the quark light-cone wave function that we compute on this occasion is also an ingredient for other interesting calculations, like the next-to-leading order correction to the cross-section for the production of a pair of jets.

ANÁLISIS DE LOS DECAIMIENTOS DE UN BOSÓN ESCALAR EN EL MODELO BESTEST LITTLE HIGGS

The Bestest Little Higgs (BLH) model provides an interesting way to address the problem of hierarchy but also manages to overcome certain difficulties that arise in Little Higgs type models, for example, the mechanism to generate a Higgs quantum coupling frequently leads to great violations in custodial symmetry. The proposal in this work is to study the decays of a massive scalar Iƒ predicted in the BLH scenario to a pair of gluons and a pair of photons. It is of our interest, the decays that are induced at the one loop-level involving heavy quarks, since in this type of models the quadratic divergences due to the corrections of the Higgs boson mass can be canceled by the contribution of new heavy particles, with masses of the order of tera-electron volts (TeV). In this work, we determine the decay fractions corresponding to the processes Iƒ --> gg and Iƒ --> I³I³ at the one-loop level. We also present a study of the effective production section of the scalar Iƒ via fusion of gluons, these parameters are a function of the energy scale of the breakdown of the global symmetry of the model, denoted as f.

Confronting the fourth generation two-Higgs-doublet model with the phenomenology of heavy Higgs bosons

A sequential fourth generation is known to be excluded because the non-decoupling contribution to $\kappa_g$, the Higgs coupling modifier with a gluon pair, is unacceptably large. Recently a new way to save the model was suggested in the Type-II two Higgs doublet model: if the Yukawa couplings of down-type fermions have wrong-sign, the contributions from $t'$ and $b'$ to $\kappa_g$ are cancelled. We study the theoretical and experimental constraints on this model, focusing on the heavy Higgs bosons. Two constraining features are pointed out. First the exact wrong-sign limit does not allow the alignment, which makes the perturbative unitarity for the scalar-scalar scattering put the upper bounds on the heavy Higgs boson masses like $M_H, M_A \lesssim 920$ GeV and $M_{H^\pm} \lesssim 620$ GeV. Secondly, the Yukawa couplings of the fourth generation fermions to the heavy Higgs bosons are generically large as being proportional to the heavy fermion mass and, for the down-type fermions, to $\tan\beta$ as well. The gluon fusion productions of $H$ and $A$ through the fourth generation quark loops become significant. We found that the current LHC data on $pp \to Z Z$ for $H$ along with the theoretical and indirect constraints exclude the model at leading order.

Probing the Higgs boson-gluon coupling via the jet energy profile at e+e− colliders

The effective coupling of the Higgs boson to a gluon pair is one of the most important parameters to test the Standard Model and search for the new physics beyond. In this paper, we propose several new observables based on the jet energy profile to extract the effective coupling. The statistical uncertainties of the effective coupling extracted by using new observables are derived and estimated based on the simulation at the future $e^+e^-$ collider for $250$ GeV center-of-mass energy and 5 ab$^{-1}$ integrated luminosity. We found that the statistical uncertainties of effective coupling via the optimized observable can reach about $1.6\%$ in the channels of a $Z$ boson decaying to lepton pairs and is reduced by $52\%$ compared to the relevant uncertainties in the conventional approach. These new observables potentially can be helpful for the measurement of effective coupling at future $e^+e^-$ colliders.

Toward initial conditions of conserved charges. Part I. Spatial correlations of quarks and antiquarks

In this paper, we study the spatial correlations among quarks and antiquarks produced at mid-rapidity by gluon pair production in the color glass condensate framework. This paper is the first part of a series in which we calculate a complete set of quark/quark, quark/antiquark, and antiquark/antiquark spatial correlation functions in heavy-light ion collisions, with the goal of incorporating their conserved charges into the initial conditions of hydrodynamics. The physical mechanisms captured in this calculation include geometric, entanglement, and interaction-mediated correlations. In this first paper, we construct the building blocks for the correlations arising from single- and double-pair production, studying in detail the single-pair case and the general features of the double-pair case. We find a rich correlation structure in transverse coordinate space, with different mechanisms dominating over different length scales, and we present explicit results for the quark-antiquark correlations in the single-pair production regime. We reserve a detailed discussion of the double-pair production regime for the next paper in this sequence.