We report that the saturation/CGC model of gluon distribution is unstable under action of the chaotic solution in a nonlinear QCD evolution equation, and it evolves to the distribution with a sharp peak at the critical momentum. We find that this gluon condensation is caused by a new kind of shadowing-antishadowing effects, and it leads to a series of unexpected effects in high energy hadron collisions including astrophysical events. For example, the extremely intense fluctuations in the transverse-momentum and rapidity distributions of the gluon jets present the gluon-jet bursts; a sudden increase of the proton-proton cross sections may fill the GZK suppression; the blocking QCD evolution will restrict the maximum available energy of the hadron-hadron colliders.
A new type of gamma ray spectrum is predicted in a general hadronic framework if considering the gluon condensation effects in proton. The result presents the power-law with a sharp break in the gamma ray spectra at the TeV-band. We suggest to probe this GC-signature in the Earth limb gamma-ray spectra using the DArk Matter Particle Explorer and the CALorimetric Electron Telescope on orbit.
Gluons dominate the proton behavior at high energy collisions, they can be condensed at ultra high energy. The collisions of the accelerated high energy protons with interplanetary matter in cosmic rays will produce a huge number of secondary particles at the gluon condensate energy region, which break the primary power-law of cosmic rays. The above predictions seem to be consistent with the recent DAMPE data concerning the electron plus positron spectra. We find that the smoothly broken power-law at $\sim 0.9 TeV$ and $3\sim 4 TeV$ in the DAMPE data can be understood as the gluon condensation…
The gluon condensation (GC)-effects in high energy cosmic rays are investigated. After a brief review of the GC, several examples including gamma-, electron-, and positron-spectra in a broad GeV$\sim $TeV region can be explained by the GC-effects. We find that the GC may break the power-law of the cosmic ray spectra if the energy of accelerated protons exceeds the GC-threshold. The GC is a new phenomenon that is not yet known, it provides a new window to understand the high energy cosmic ray spectra.
The accumulation of gluons inside nucleons, i.e., the gluon condensation, may lead to a characteristic broken power-law gamma-ray spectrum in high-energy nucleon collisions. Here we show that the observed spectra of at least 25 sources in the second Fermi Large Area Telescope Catalog of Gamma-ray Pulsars can be well fitted by such a broken power-law function that has only four free parameters. It strongly indicates that the gamma-ray emission from these pulsars is of hadronic origin, but with gluon condensation inside hadrons. It is well known that the quark-gluon distribution in a free nucleo…
The very high energy gamma-ray emissions from pulsars are usually considered to be dominated by leptonic scenario since the hadronic flux is weak. We point out that the gluon condensation predicted by a nonlinear QCD evolution equation may greatly enhance the cross sections of proton-target interactions and give rise to a characteristic broken power law in the gamma-ray spectra. The result is used to explore the gluon condensation signature in the observed gamma-ray spectra from pulsars.
The gluon condensation effect in cosmic proton-proton collisions at high energy is used to explain an excess in the positron spectrum observed by AMS. We find that this excess may originate from the GC-effect in Tycho's supernova remnant.
Gluons may converge to a stable state at a critical momentum in hadrons. This gluon condensation is predicted by a nonlinear QCD evolution equation. We review the understanding of the gluon condensation and present a clear physical picture that produces the gluon condensation from the colour glass condensate. We summarize the applications of the GC effect in the $p-p(A)$ collisions and predict that the $p-Pb$ and $Pb-Pb$ collisions at the LHC are close to the energy region of the gluon condensation. We warn that for the next generation of hadron colliders with the increasing of the collision e…
Hardening of cosmic proton- and nuclei-spectra is explained by using the gluon condensation (GC) model, which states that a large amount of gluons in proton may condense near the high energy threshold. The results present the GC-effect as common origin of a series of anomalous astrophysical phenomena including the broken power-law in gamma-ray spectra, the excess in positron- and electron-spectra and hardening of proton- and nuclei-spectra.
We study the thermalization of gluons far from thermal equilibrium in relativistic kinetic theory. The initial distribution of gluons is assumed to resemble that in the early stage of ultrarelativistic heavy ion collisions. Only elastic scatterings in static, nonexpanding gluonic matter are considered. At first we show that the occurrence of condensation in the limit of vanishing particle mass requires a general constraint for the scattering matrix element. Then the thermalization of gluons with Bose-Einstein condensation is demonstrated in a transport calculation. We see a continuously increa…
We consider a black hole solution with a non-trivial dilaton from IIB super gravity which is expected to describe a strongly coupled hot gauge plasma with non-vanishing gluon condensation present. We construct a rotating and moving baryon to probe the screening and phases of the plasma. Melting of the baryons in hot plasma in this background had been studied previously, however, we show that baryons melt much lower temperature than has been suggested previously.
We consider gluon condensation (GC) at finite temperature using AdS/CFT. We first show that in the presence of regular horizon, the GC is forbidden in high temperature. Then we consider gravity back-reaction to dilaton coupling and show that the back-reaction develops an singularity, and non-vanishing value of gluon condensation is allowed. We also study thermodynamic quantities and the trace anomaly in the presence of the GC. We discuss how to define a temperature in the presence of the singularity which forbids Hawking temperature. Finally we describe the thermodynamics of the gluon condensa…
We study the transport equation describing a dense system of gluons, in the small scattering angle approximation, taking into account medium-generated effective masses of the gluons. We focus on the case of overpopulated systems that are driven to Bose-Einstein condensation on their way to thermalization. The presence of a mass modifies the dispersion relation of the gluon, as compared to the massless case, but it is shown that this does not change qualitatively the scaling behavior in the vicinity of the onset.
Using a simple kinetic model we study whether a pion condensate can be formed during the hadronization of the quark-gluon plasma in ultrarelativistic heavy-ion collisions. If hadronization proceeds fast and the pion effective mass is close to zero, some pions condense into the zero momentum state. On the other hand, for the pion effective mass equal to the vacuum one or larger no onset of the Bose-Einstein condensation is observed. The constraints on the condensation process coming from the requirement of the entropy increase are discussed in detail.
Gluons may converge to a stable state at a critical momentum in nucleon. This gluon condensation will greatly increase the proton-proton cross section provided that the collision energies exceed the gluon condensation threshold. Based on the analyses of cosmic gamma-ray spectra, we find that the $p-Pb$ and $Pb-Pb$ collisions at the LHC are close to the energy region of the gluon condensation effect. We warn that for the next generation of hadron colliders increasing the collision energies, the extremely strong gamma-rays will be emitted in a narrow space of the accelerator due to the gluon con…
The large density of gluons, which is present shortly after a nuclear collision at very high energies, can lead to the formation of a condensate. We identify a gauge-invariant order parameter for condensation based on elementary non-perturbative excitations of the plasma, which are described by spatial Wilson loops. Using real-time lattice simulations, we demonstrate that a self-similar transport process towards low momenta builds up a macroscopic zero mode. Our findings reveal intriguing similarities to recent discoveries of condensation phenomena out of equilibrium in table-top experiments w…
The problem of the gluonic quasiparticle excitations in QCD is considered under the aspect of the condensation of gluon pairs in the ''squeezed'' vacuum. The present approach is a field theoretical generalization of the Bogoliubov model which successfully reproduced the Landau spectrum in the microscopic theory of superfluidity. We construct a gauge invariant QCD Hamiltonian by formally solving the Gauss equation such that the physical variables are separated by a non-Abelian projection operator, instead of fixing a gauge. By using Dirac quantization we show that the Bogoliubov condensation of…
Hypothesis of quark binding through condensation of gluons inside hadrons is formulated in the context of a renormalization group procedure for effective particles (RGPEP) in the light-front (LF) Hamiltonian approach to QCD. At the momentum scales of relative motion of hadronic constituents that are comparable with Lambda_QCD, the hypothetical boost-invariant constituent dynamics is identified using gauge symmetry. The resulting picture of mesons and baryons closely resembles constituent quark models with harmonic oscillator potentials, shares some features of AdS/QCD, and can be systematicall…
An upper limit to the critical density for the transition to the deconfined phase, at zero temperature, has been evaluated by analyzing the behavior of the gluon condensate in nuclear matter. Due to the non linear baryon density effects, the upper limit to the critical density, ρ_c turns out about nine times the saturation density, rho_0 for the value of the gluon condensate in vacuum <(α_s/π) G^2>=0.012 GeV^4. For neutron matter ρ_c \simeq 8.5 ρ_0. The dependence of the critical density on the value of the gluon condensate in vacuum is studied.
The collinear color electric and magnetic fields have been discussed to be produced immediately after high energy heavy ion collisions. We discuss anomalous gluon production under the background gauge fields. The gluons are Nielsen-Olesen unstable modes. The production rate of the modes by Schwinger mechanism has recently been found to be anomalously larger than the rate of quarks or other stable gluons. Analyzing classical evolutions of the modes with initial conditions given by vacuum fluctuations, we find that their production makes the color electric field decay very rapidly. The life time…
In the present paper, we return to the problem on a spontaneous generation of the $A_0$-background field in QCD at finite temperature and include in addition a quark chemical potential, $μ$. We reproduce the known expressions in terms of Bernoulli's polynomials for the gluons and quarks using the same formalism. Then we calculate the $μ$-dependence, both for small $μ$ as expansion, and numerically for finite $μ$. One result is that the chemical potential only weakly changes the values of the condensed field, but quite strongly deepens the minima of the effective potential. The gauge dependence…
In this paper, we study the evolution of a dense system of gluons, such as those produced in the early stages of ultra-relativistic heavy ion collisions. We describe the approach to thermal equilibrium using the small angle approximation for gluon scattering in a Boltzmann equation that includes the effects of Bose statistics. In the present study we ignore the effect of the longitudinal expansion, i.e., we restrict ourselves to spatially uniform systems, with spherically symmetric momentum distributions. Furthermore we take into account only elastic scattering, i.e., we neglect inelastic, num…
The discriminators of quark-gluon jets developed for $pp$ collisions at the LHC can be used to measure the gluon jet fraction in a jet sample. It allows to measure various characteristics of the quark and gluon jets. The methodology of such measurements for modern hadron colliders is discussed.
I reexamine the phenomena of the chromomagnetic gluon condensation in Yang-Mills theory. The extension of the Heisenberg-Euler Lagrangian to the Yang-Mills theory allows to calculate the effective action, the energy-momentum tensor and demonstrate that the energy density curve crosses the zero energy level of the perturbative vacuum state at nonzero angle and continuously enters to the negative energy density region. At the crossing point and further down the effective coupling constant is small and demonstrate that the true vacuum state of the Yang-Mills theory is below the perturbative vacuu…
We study the production and decay of neutral scalars and pseudo-scalars at hadron colliders, in theories where the top-quark mass is the result of a $t\bar t$ condensate. We show that the dominant decay channel for masses below the $t\bar t$ threshold is the flavor changing mode $tc$. This is a consequence of the non-universal nature of the underlying interactions in all top-condensation models and provides a model-independent signature of these scenarios. We show that an upgraded Tevatron is sensitive to a sizeable region of the interesting parameter space and that the LHC will highly constra…
Signatures of dominant and central production of glueballs (binary gluonic mesons) in heavy ion and hadromic collisions are discussed. Search strategies are proposed.
In this work, the role of inelastic processes in the formation of a transient Bose-Einstein condensation (BEC) is investigated based on kinetic theory. We calculate the condensation rate for an overpopulated gluon system which is assumed to be in thermal equilibrium and with the presence of a BEC. The matrix elements of the inelastic processes are chosen as the isotropic one and the gluons are considered to have a finite mass. Our calculations indicate that the inelastic processes can hinder the formation of a BEC since the negatively infinite net condensation rate can destroy any BEC instantl…
We examine the effects of color screening on the transition of a parton plasma into a hadron gas at RHIC energies. It is found that as expected, color screening posed itself as a significant barrier for hadronization. Parton-hadron conversion would therefore be delayed and prolonged when compared to that occuring in a vacuum. Due to the on-going expansion, the resulting hadron densities are lowered. Parton equilibration is also shown to be seriously disrupted in the process.
We study the deep inelastic scattering (DIS) of a proton-targeted lepton in the presence of gluon condensation using gauge/gravity duality. We use a modified $AdS_5$ background where the modification parameter $c$ corresponds to the gluon condensation in the boundary theory. Firstly, when examining the electromagnetic field, we find that non-zero $c$ can increase the magnitude of the field. Our goal is to find the acceptable value of $c$ for this scattering and our method is based on setting the mass of the proton as an eigenvalue of the baryonic state equations of the DIS to find the acceptab…
An interaction term is added to the QCD Lagrangian involving hadron and gluon fields. An effective vertex is calculated for such interactions through exchanges of reggeized gluons. This gives rise to an effective coupling for hadron-gluon elastic scattering in the t-channel, which is used in an inclusive hadron-hadron interaction from which the Pomeron intercept alpha(0) is calculated.
We investigate the infrared (strong-coupling) regime of SU(N)-Yang-Mills theory on a self-dual background. We present an evaluation of the full effective potential for the field strength invariant F_{μν}F^{μν} from non-perturbative gauge correlation functions and find a non-trivial minimum corresponding to the existence of a dimension four gluon condensate in the vacuum. We also relate the infrared asymptotic form of the beta function of the running background-gauge coupling to the asymptotic behavior of Landau-gauge gluon and ghost propagators. Consistency between both gauges in the infrared …
The Equation of State and the properties of matter in the high temperature deconfined phase are analyzed by a quasiparticle approach for $T> 1.2~T_c$. In order to fix the parameters of our model we employ the lattice QCD data of energy density and pressure. First we consider the pure SU(3) gluon plasma and it turns out that such a system can be described in terms of a gluon condensate and of gluonic quasiparticles whose effective number of degrees of freedom and mass decrease with increasing temperature. Then we analyze QCD with finite quark masses. In this case the numerical lattice data for …
The deconfinement transition and the hadronization mechanism at high energy are related to the quark-antiquark string breaking and the corresponding temperature depends on the string tension $σ$. In the Unruh scheme of hadron production it turns out $T = \sqrt{σ/2π}$, with $σ\simeq \E$, the vacuum energy density. In heavy ion collisions at lower energy, i.e. large baryonchemical potential, $μ_B$, the dynamics is dominated by Fermi statistics and baryon repulsion. However one can still consider $\E$ as the relevant physical scale and its evaluation as a function of the baryon density, in a nucl…
We study the associated production of an electroweak vector boson and the Higgs boson with a jet via gluon-gluon fusion. At the leading order, these processes occur at one-loop level. The amplitudes of these one-loop processes are gauge invariant and finite. Therefore, their contributions towards the corresponding hadronic cross sections and kinematic distributions can be calculated separately. We present results for the Large Hadron Collider and its discussed upgrades. We find that the gluon-gluon one-loop process gives dominant contribution to the $γH j$ production. We observe a destructive …
Following our recent paper on the calculations of diffractive quark jet production at hadron colliders, we present here the calculations of gluon jet production at hadron colliders in the two-gluon exchange parameterization of the Pomeron model. We use the helicity amplitude method to calculate the cross section formula. We find that for the gluon jet production the diffractive process is related to the differential off-diagonal gluon distribution function in the proton. We estimate the production rate for this process at the Fermilab Tevatron by approximating the off-diagonal gluon distributi…
In ultra-relativistic heavy ion collisions, the matter formed shortly after the collision is a dense, out of equilibrium, system of gluons characterized by a semi-hard momentum scale $Q_{\rm s}$. Simple power counting arguments indicate that this system is over-occupied: the gluon occupation number is parametrically large when compared to a system in thermal equilibrium with the same energy density. On short time scales, soft elastic scatterings tend to drive the system towards the formation of a Bose--Einstein condensate that contains a large fraction of the gluons while contributing little t…
We analyse in detail the possibility of Bose-Einstein condensation of pions produced in heavy-ion collisions at the beam energy $\sqrt{s_{\rm NN}}$ = 2.76 TeV. Our approach is based on the chemical non-equilibrium thermal model of hadron production which has been generalised to include separately the contribution from the local zero-momentum state. In order to study both the hadronic multiplicities and the transverse-momentum spectra, we use the Cracow freeze-out model which parameterises the flow and space-time geometry of the system at freeze-out in a very economic way. Our analysis indicate…
It is shown that due to contribution of the hadrons, emitted directly from the inner hot region of central heavy ion collision, radial flow of the final state hadrons is rather sensitive to the creation of quark-gluon plasma with mixed phase.
The possibility of formation of Bose-Einstein Condensation (BEC) is studied in $pp$ collisions at $\sqrt s$ = 7 TeV at the Large Hadron Collider. A thermodynamically consistent non-extensive formulation of the identified hadron transverse momentum distributions is used to estimate the critical temperature required to form BEC of charged pions, which are the most abundant species in a multi-particle production process in hadronic and nuclear collisions. The obtained results have been contrasted with the systems produced in Pb-Pb collisions to have a better understanding. We observe an explicit …
We report recent progress on understanding the thermalization of the quark-gluon plasma during the early stage in a heavy ion collision. The initially high overpopulation in the far-from-equilibrium gluonic matter ("Glasma") is shown to play a crucial role. The strongly interacting nature (and thus fast evolution) naturally arises as an {\em emergent property} of this pre-equilibrium matter where the intrinsic coupling is weak but the highly occupied gluon states coherently amplify the scattering. A possible transient Bose-Einstein Condensate is argued to form dynamically on a rather general g…
We discuss new physical phenomena expected in particle production in hadron-hadron collisions at high energy, as a consequence of Pomeron loop effects in the evolution equations for the Color Glass Condensate. We focus on gluon production in asymmetric, `dilute-dense', collisions : a dilute projectile scatters off a dense hadronic target, whose gluon distribution is highly evolved. This situation is representative for particle production in proton-proton collisions at forward rapidities (say, at LHC) and admits a dipole factorization similar to that of deep inelastic scattering (DIS). We show …
We present the gluon-gluon and photon-gluon helicity amplitudes for color singlet and octet charmonium production in polarized and unpolarized hadron-hadron and photon-hadron collisions.
The small surface tension of the interface between hadronic and quark-gluon-plasma domains, along with a negative curvature tension, implies that the uniform plasma is unstable against spontaneous formation of hadronic bubbles. We furthermore show that spherical bubbles are not stable against small perturbations.
We discuss a collective effect, which can be possible in hadron--hadron collisions at superhigh energies, that is, a quasi-diffraction production of several white clusters of quarks and gluons. Being transformed into hadrons, such clusters are sources of the fastest particles, which move forward nearly parallel to each other.
A new approach to the analysis of soft and semihard hadron processes is suggested. In the frame of the Quark-Gluon String Model the interaction of valence quarks and diquarks and sea quarks (antiquarks) of colliding hadrons is taken into account. This one is calculated as the exchange by one nonpertubative gluon, i.e., the cut-off parameter in the gluonic propagator is included. This one allows us to analise the inclusive hadron spectra in hadron collisions at transverse momenta up to 3-4 Gev/c.
The gauge-links connecting the parton field operators in the hadronic matrix elements appearing in the transverse momentum dependent distribution functions give rise to T-odd effects. Due to the process-dependence of the gauge-links the T-odd distribution functions appear with different pre-factors. A consequence is that in the description of single spin asymmetries the parton distribution and fragmentation functions are convoluted with gluonic pole cross sections rather than the basic partonic cross sections. In this paper we calculate the gluonic pole cross sections encountered in single spi…
A hard $γ$-ray spectrum of supernova remnant G106.3+2.7 can be explained by using the hadronic model with the gluon condensation effect. This implies that not only PeVatrons but also EeVatrons generally exist in the universe including our galaxy, and they can accelerate protons to beyond "ankle" ($10^{19}~eV$). Although these proton beams are very weak in the galaxy and cannot be observed individually on the earth, the gluon condensation effect may greatly enhance the proton-proton cross section, which can compensate for the weak proton flux and produce the observed $γ$-rays. We also show that…
Recently we have reported the correct formulation of the lattice QCD method at the zero temperature to study the hadron formation from the quarks and gluons by incorporating the non-zero boundary surface term in QCD which arises due to the confinement of quarks and gluons inside the finite size hadron. In this paper we extend this to the finite temperature QCD and present the correct formulation of the lattice QCD method at the finite temperature to study the hadron formation from the quark-gluon plasma.
We compute the contributions to continuum photon pair production at hadron colliders from processes initiated by gluon-gluon and gluon-quark scattering into two photons through a four-leg virtual quark loop. Complete two-loop cross sections in perturbative quantum chromodynamics are combined with contributions from soft parton radiation resummed to all orders in the strong coupling strength. The structure of the resummed cross section is examined in detail, including a new type of unintegrated parton distribution function affecting azimuthal angle distributions of photons in the pair's rest fr…
We report on the calculation of the next-to-next-to-leading order (NNLO) QCD corrections to the production of two gluonic jets at hadron colliders. In previous work, we discussed gluonic dijet production in the gluon-gluon channel. Here, for the first time, we update our numerical results to include the leading colour contribution to the production of two gluonic jets via quark-antiquark scattering.
We numerically study the effects of high gluon density at small x on the evolution of gluon distribution function in both hadrons and nuclei. Using a newly derived, Wilson renormalization group-based evolution equation which includes n to 1 gluon ladder fusion, we find significant reduction in nuclear gluon distribution function for large nuclei at zero impact parameter at energies relevant for RHIC and LHC experiments.
We propose to access the gluon polarization $ΔG$ by measuring the cross section spin-asymmetry in semi-inclusive polarized lepton -- nucleon scattering. The photon-gluon fusion sub-process will be tagged by detecting high-$p_T$ correlated hadron pairs in the forward hemisphere. Selecting oppositely charged kaon pairs will allow to suppress the background coming from gluon radiation.
The exclusive production of axionlike particles (ALPs) by gluon -- induced interactions is investigated in this exploratory study considering $pp$ and $PbPb$ collisions for the energies of the next run of the Large Hadron Collider (LHC). Assuming the Duhram model, we estimate the associated cross sections for the rapidity ranges probed by central and forward detectors. A comparison with the predictions for the exclusive ALP production by photon -- induced interactions is presented. Our results indicate that the contribution of gluon -- induced interactions is nonnegligible and can become domin…
We investigate the discovery potential of Kaluza-Klein gluons as a dijet resonance at hadron colliders with different center-of-mass energies, from 14 TeV to 33 TeV to 100 TeV. We also present the current bounds from dijet searches at UA2, Tevatron, and LHC.
$Q\bar{Q}$ potential is studied in the SU(2) gauge theory. Based on the nonlinear gauge of the Curci-Ferrari type, the possibility of a gluon condensation $\langle A_μ^+A_μ^-\rangle$ in low-energy region has been considered at the one-loop level. Instead of the magnetic monopole condensation, this condensation makes classical gluons massive, and can yield a linear potential. We show this potential consists of the Coulomb plus linear part and an additional part. Comparing with the Cornell potential, we study this confining potential in detail, and find that the potential has two implicit scales…
