Quarks and gluons in color fields

Production and collective motion ofq \(\bar q\) and gluon pairs in strong color fields is studied using boost-invariant version of collisionless Boltzmann-Vlasov transport equations. It is shown that, for realistic fields, the effective formation time for pair production according to Schwinger mechanism is a small fraction of 1 fermi. Collective oscillations of quarkgluon gas, although damped by pair production and expansion of the system, remain an important feature of the process. The considered mechanism produces quark and gluons in a state which is rather far from equilibrium and thus strong collision effects (collision time ?1 fm) are needed to achieve equilibrated distributions at formation time. Finally, it is observed that, if such equilibrated distribution is produced at later times, the expansion of the system modifies dramatically its properties, as is explicitly shown for small oscillations of quark-gluon plasma in a weak external field.     

Does color confinement imply massive gluons?

Color confinement is one of the central issues in QCD, and there are various interpretations of this feature. In this paper we have adopted the interpretation that colored particles cannot be observed just because colored states are unphysical in the sense of Q_B|quark〉≠0, Q_B|gluon〉≠0. It is shown that there are two phases in QCD distinguished by different choices of the gauge parameter. In one phase, called the “confinement phase,” color confinement is realized and gluons are no longer massless. In the other phase, called the “deconfinement phase,” color confinement is not realized, but the gluons remain massless.     

Cooling rates of anisotropic color superconductors

We compute neutrino emissivities, specific heat, and the resulting cooling rates in spin-one color-superconducting phases. In particular, the role of anisotropies and point nodes of the gap function are investigated.     

Electromagnetic Meissner effect in spin-one color superconductors

It is shown that color-superconducting quark matter, where quarks of the same flavor form Cooper pairs with spin one, exhibits an electromagnetic Meissner effect. This is in contrast to spin-zero color superconductors where Cooper pairs consist of quarks with different flavors.     

Spin-one color superconductors: Collective modes and effective Lagrangian

We investigate the collective excitations in spin-one color superconductors. We classify the Nambu–Goldstone modes by the pattern of spontaneous symmetry breaking, and then use the Ginzburg–Landau theory to derive their dispersion relations. These soft modes play an important role for the low-energy dynamics of the system such as the transport phenomena and hence are relevant for late-stage evolution of neutron stars. In the case of the color-spin-locking phase, we use a functional technique to obtain the low-energy effective action for the physical Nambu–Goldstone bosons that survive after gauging the color symmetry.     

Collective excitations of gluons

Three gauge invariant antisymmetric tensor fields are introduced in the nonabelian gauge theories. They are certain non-linear combinations of the conjugate field tensor and they obey O(3) algebra. An effective chiral lagrangian for these fields is derived. It describes 3 vector and 3 axial mesons with vacuum quantum numbers. The masses are generated by spontaneous restoration of Lorentz invariance.     

Soft gluons in logarithmic summations

We demonstrate that all the known single- and double-logarithm summations for a parton distribution function can be unified in the Collins–Soper resummation technique by applying soft approximations appropriate in different kinematic regions to real gluon emissions. Neglecting the gluon longitudinal momentum, we obtain the (double-logarithm) resummation for two-scale QCD processes, and the Balitsky–Fadin–Kuraev–Lipatov (single-logarithm) equation for one-scale processes. Neglecting the transverse momentum, we obtain the threshold (double-logarithm) resummation for two-scale processes, and the Dokshitzer–Gribov–Lipatov–Altarelli–Parisi (single-logarithm) equation for one-scale processes. If we keep the longitudinal and transverse momenta simultaneously, we derive a unified resummation for a large Bjorken variable x, and a unified evolution equation appropriate for both intermediate and small x. Received: 9 March 1999 / Revised version: 12 April 1999 / Published online: 3 August 1999     

Dynamics of confined gluons

Propagation of gluons in the confining vacuum is studied in the framework of background perturbation theory, where nonperturbative background contains confining correlators. Two settings of the problem are considered. In the first, the confined gluon evolves in time together with the static quark and antiquark forming the one-gluon static hybrid. The hybrid spectrum is calculated in terms of string tension and is in agreement with earlier analytic and lattice calculations. In the second setting, the confined gluon is exchanged between quarks and the gluon Green’s function is calculated, giving rise to the Coulomb potential modified at large distances. The resulting screening radius of 0.5 fm presents a problem when confronted with lattice and experimental data. A possible solution of this discrepancy is discussed.     

Properties of anisotropic superconductors containing impurities in SR model

The Josephson current for an anisotropic superconductor, described by Shiba-Rusinov model, containing paramagnetic impurities is calculated by an extension of the theory of Nagi and Upadhyayya. The slope $\text{S}{}^1$ of $\text{J}{}_{\mathrm{s}}\text{(}\text{C}\text{?}\text{, T,}\text{Ω}\text{?}\text{)}$ against temperature T near T_c is also computed and compared with the limiting isotropic case. Thermodynamic critical field $\text{H}{}_{\mathrm{c}}\text{(}\text{C}\text{?}\text{, T,}\text{Ω}\text{?}\text{)}$ for an anisotropic superconductor is also investigated.     

Confinement models for gluons

Confinement model for gluons using a ‘colour super current’ is formulated. An attempt has been made to derive a suitable dielectric function corresponding to the current confinement. A simple inhomogeneous dielectric confinement model for gluons is studied for comparison. The model Hamiltonians are second quantized and the glueball states are constructed. The spurious motion of the centre of confinement is accounted for. The results of the current confinement scheme is found in good agreement with experimental candidates.     

Soft gluons and factorization

We clarify the role of soft gluons in hard inclusive hadron-hadron cross sections, emphasizing the mechanisms by which they decouple from the incoming hadrons and cancel.     

CMS ridge effect at LHC as a manifestation of bremsstrahlung of gluons off quarks accelerated in a strong color field

The recently reported effect of long-range near-side angular correlations at LHC occurs for large multiplicities of particles with 1 GeV<p _T <3 GeV. To understand the effect several possibilities have been discussed. In the letter we propose a simple qualitative mechanism which corresponds to gluon bremsstrahlung of quarks moving with acceleration defined by the string tension. The smallness of azimuthal angle difference Δφ along with large Δη at large multiplicities in this interval of p _T are natural in this mechanism. The mechanism predicts also bremsstrahlung photons with mean values of p _T ≈2.9 and 0.72 GeV.     

Topological “vector gluons”

It is shown that the axion can be made invisible in the family-unifyingSU(9) model and that all the light fermions become massive due to the radiative correction.     

Medium-induced emissions of hard gluons

We present a derivation of the medium-induced gluon radiation spectrum beyond the current limitation of soft gluon emission. Making use of the path integral approach to describe the propagation of high-energy particles inside a medium, we study the limiting case of a hard gluon emission. Analytical and numerical results are presented and discussed within the multiple soft scattering approximation. An ansatz interpolating between soft and hard gluon emissions is provided. The Landau–Pomeranchuk–Migdal effect is observed in the expected kinematic region.     

Elastic forward scattering of gluons

The colour octet and singlet parts of the elasticgggg-scattering amplitude are evaluated in the Regge kinematical regions–t in the LLA, withi-terms taken into account, by constructing and solving a set of the infrared evolution equations.This work was supported, in part, by a Soros Foundation Grant awarded by the American Physical Society     

Integrating out gluons in flow equations

We present an exact nonperturbative flow equation for the average action for quarks which incorporates the effects of gluon fluctuations. With suitable truncations this allows one to compute effective multi-quark interactions in dependence on an infrared scalek. Our method amounts to integrating out the gluons with momenta larger thank.