arXiv subjects

Gouranga C Nayak

Publications and source records attributed to Gouranga C Nayak.

45 records · Page 3Linked to original sources

arXiv2009

Proof of Factorization Using Background Field Method of QCD

Factorization theorem plays the central role at high energy colliders to study standard model and beyond standard model physics. The proof of factorization theorem is given by Collins, Soper and Sterman to all orders in perturbation theory by using diagrammatic approach. One might wonder if one can obtain the proof of factorization theorem through symmetry considerations at the lagrangian level. In this paper we provide such a proof.

hep-ph↗

arXiv2009

Schwinger Mechanism for Gluon Pair Production in the Presence of Arbitrary Time Dependent Chromo-Electric Field in Arbitrary Gauge

We study non-perturbative gluon pair production from arbitrary time dependent chromo-electric field E^a(t) with arbitrary color index a =1,2,...8 via Schwinger mechanism in arbitrary covariant background gauge α. We show that the probability of non-perturbative gluon pair production per unit time per unit volume per unit transverse momentum \frac{dW}{d^4xd^2p_T} is independent of gauge fixing parameter α. Hence the result obtained in the Fynman-'t Hooft gauge, α=1, is the correct gauge invariant and gauge parameter αindependent result.

hep-ph↗

arXiv2009

Factorization of Soft and Collinear Divergences in Non-Equilibrium Quantum Field Theory

Proof of factorization of soft and collinear divergences in non-equilibrium QCD may be necessary to study hadronic signatures of quark-gluon plasma at RHIC and LHC. In this paper we prove factorization of soft and collinear divergences in non-equilibrium QED by using Schwinger-Keldysh closed-time path integral formalism in the background field method in pure gauge.

hep-ph↗

arXiv2009

Renormalization Group Equation and QCD Coupling Constant in the Presence of SU(3) Chromo-Electric Field

We solve renormalization group equation in QCD in the presence of SU(3) constant chromo-electric field E^a with arbitrary color index a=1,2,...8 and find that the QCD coupling constant α_s depends on two independent casimir/gauge invariants C_1=[E^aE^a] and C_2=[d_{abc}E^aE^bE^c]^2 instead of one gauge invariant C_1=[E^aE^a]. The βfunction is derived from the one-loop effective action. This coupling constant may be useful to study hadron formation from color flux tubes/strings at high energy colliders and to study quark-gluon plasma formation at RHIC and LHC.

hep-ph↗

arXiv2009

String Theory at LHC Using Top Quarks From String Balls

According to string theory, string ball is a highly excited long string which decays to standard model particles at the Hagedorn temperature with thermal spectrum. If there are extra dimensions, the string scale can be $\sim$ TeV, and we should produce string balls at CERN LHC. In this paper we study top quark production from string balls at LHC and compare with the parton fusion results at NNLO using pQCD. We find significant top quark production from string balls at LHC which is comparable to standard model pQCD results. We also find that $\frac{dσ}{dp_T}$ of top quarks from string balls does not decrease significantly with increase in $p_T$, whereas it deceases sharply in case of standard model pQCD scenario. Hence, in the absence of black hole production at LHC, an enhancement in top quark cross section and its abnormal $p_T$ distribution can be a signature of TeV scale string physics at LHC. String theory is also studied at LHC via string Regge excitations in the weak coupling limit in model independent framework. Since massive quark production amplitude is not available in string Regge excitations scenario, we compute massless quark production in string Regge excitations scenario and make a clear comparison with that produced from string balls at LHC for a given luminosity.

hep-ph↗

arXiv2009

Fragmentation Function in Non-Equilibrium QCD Using Closed-Time Path Integral Formalism

In this paper we implement Schwinger-Keldysh closed-time path integral formalism in non-equilibrium QCD to the definition of Collins-Soper fragmentation function. We consider a high p_T parton in QCD medium at initial time t_0 with arbitrary non-equilibrium (non-isotropic) distribution function f(\vec{p}) fragmenting to hadron. We formulate parton to hadron fragmentation function in non-equilibrium QCD in the light-cone quantization formalism. It may be possible to include final state interactions with the medium via modification of the Wilson lines in this definition of the non-equilibrium fragmentation function. This may be relevant to study hadron production from quark-gluon plasma at RHIC and LHC.

hep-ph↗

arXiv1998

Dilepton emission from an equlibrating non-abelian plasma

We study dilepton production from a thermally equilibrating quark-gluon plasma expected to be formed in ultra relativistic heavy-ion collisions. The pre-equilibrium dynamics of quark-gluon plasma is studied within the color flux-tube model by solving non-abelian relativistic transport equations. This dilepton rate crucially depends on the collision time of the plasma. The results are compared with the Drell-Yan productions. We suggest that a measurement of this rate at RHIC and LHC will determine the initial field energy density.

hep-ph↗

arXiv1998

J/Psi suppressions in a thermally equilibrating quark-gluon plasma at RHIC

We estimate the survival probability of $J/ψ$ in relativistic heavy-ion collisions, using both short-distance QCD and nuclear absorption mechanism. The suppression is found to be almost 100 percent for a thermally equilibrating quark-gluon plasma. The measurement of such a huge suppression of $J/ψ$ may suggest the existence of a deconfined partonic medium, possibly a thermalised quark-gluon plasma, at RHIC.

hep-ph↗

arXiv1998

Pre-equilibrium evolution of quark-gluon plasma

We study the production and the evolution of quark-gluon plasma expected to be formed in ultra relativistic heavy-ion collisions, within the color flux-tube model. We introduce the gluonic component in the Boltzmann equation, which we solve in the phase space which is extended to include the SU(3) color degree of freedom. The color degree of freedom is shown to play a decisive role in equilibration, and in fixing the temperature of the plasma. We further find that the soft partons that we study here contribute substantially to the bulk properties. Finally, the model is shown to provide a detailed picture of how the quark-gluon plasma evolves and is driven towards a hydrodynamic flow, which starts occuring around 1 $fm$.

hep-ph↗