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Search Results: 1 - 10 of 224018 matches for " R. Venugopalan "
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Decoherence and the Quantum Zeno Effect
Anu Venugopalan,R. Ghosh
Physics , 1995,
Abstract: The measurements in the optical test of quantum Zeno effect [Itano et al. Phys. Rev. A\underbar{41} (1990) 2295) are analyzed using the environment-induced decoherence theory, where the spontaneous emission lifetime of the relevant level emerges as the 'decoherence time'. The implication of this finite decoherence time in setting a fundamental limit on the realizability of the condition of continuous measurements is investigated in detail.
Decoherence and the Quantum Zeno Effect
Anu Venugopalan,R. Ghosh
Physics , 1995, DOI: 10.1016/0375-9601(95)00443-7
Abstract: The experiment of Etano et al which demonstrated the quantum Zeno effect (QZE) in an optical experiment was explained by Frerichs and Schenzle without invoking the wave function collapse. In this report it is proposed that the collapse does occur, and it can be explained by the `environment induced decoherence' theory. The environment here consists of the completely quantized field vacuum modes. The spontaneous emission life time of the atom sets a fundamental limit on the requirement of `continuous measurements' for QZE. This limit turns out to be related to the time-energy uncertainty relation discussed by Ghirardi et al.
Large mass Q-Qbar production from the Color Glass Condensate
F. Gelis,R. Venugopalan
Physics , 2003, DOI: 10.1103/PhysRevD.69.014019
Abstract: We compute quark-antiquark pair production in the context of the Color Glass Condensate model for central heavy-ion collisions. The calculation is performed analytically to leading order in the density of hard sources present in the projectiles, and is applicable to quarks with a mass large compared to the saturation momentum. The formulas derived in this paper are compared to expressions derived in the framework of collinearly factorized perturbative QCD and in kt factorization models. We comment on the breaking of kt factorization which occurs beyond leading order in our approach.
Universality of the saturation scale and the initial eccentricity in heavy ion collisions
T. Lappi,R. Venugopalan
Physics , 2006, DOI: 10.1103/PhysRevC.74.054905
Abstract: Recent estimates that Color Glass Condensate initial conditions may generate a larger initial eccentricity for noncentral relativistic heavy ion collisions (relative to the initial eccentricity assumed in earlier hydrodynamic calculations) have raised the possibility of a higher bound on the viscosity of the Quark Gluon Plasma. We show that this large initial eccentricity results in part from a definition of the saturation scale as proportional to the number of nucleons participating in the collision. A saturation scale proportional to the nuclear thickness function (and therefore independent of the probe) leads to a smaller eccentricity, albeit still larger than the value used in hydrodynamic models. Our results suggest that the early elliptic flow in heavy ion collisions (unlike multiplicity distributions) is sensitive to the universality of the saturation scale in high energy QCD.
Particle production in field theories coupled to strong external sources I. Formalism and main results
F. Gelis,R. Venugopalan
Physics , 2006, DOI: 10.1016/j.nuclphysa.2006.07.020
Abstract: We develop a formalism for particle production in a field theory coupled to a strong time-dependent external source. An example of such a theory is the Color Glass Condensate. We derive a formula, in terms of cut vacuum-vacuum Feynman graphs, for the probability of producing a given number of particles. This formula is valid to all orders in the coupling constant. The distribution of multiplicities is non--Poissonian, even in the classical approximation. We investigate an alternative method of calculating the mean multiplicity. At leading order, the average multiplicity can be expressed in terms of retarded solutions of classical equations of motion. We demonstrate that the average multiplicity at {\it next-to-leading order} can be formulated as an initial value problem by solving equations of motion for small fluctuation fields with retarded boundary conditions. The variance of the distribution can be calculated in a similar fashion. Our formalism therefore provides a framework to compute from first principles particle production in proton-nucleus and nucleus-nucleus collisions beyond leading order in the coupling constant and to all orders in the source density. We also provide a transparent interpretation (in conventional field theory language) of the well known Abramovsky-Gribov-Kancheli (AGK) cancellations. Explicit connections are made between the framework for multi-particle production developed here and the framework of Reggeon field theory.
Hard Thermal Loops and Beyond in the Finite Temperature World-Line Formulation of QED
R. Venugopalan,J. Wirstam
Physics , 2001, DOI: 10.1103/PhysRevD.63.125022
Abstract: We derive the hard thermal loop action for soft electromagnetic fields in the finite temperature world-line formulation at imaginary time, by first integrating out the hard fermion modes from the microscopic QED action. Further, using the finite T world-line method, we calculate all static higher order terms in the soft electromagnetic field. At high T, the leading non-linear terms are independent of the temperature and, except for a term quartic in the time component of the vector potential, they cancel exactly against the vacuum contribution. The remaining T-dependent non-linear terms become more strongly suppressed by the temperature as the number of soft fields increases, thus making the expansion reliable. Applications of this method to other theories and problems at the soft scale are also briefly discussed.
Multiparticle production at RHIC and LHC: a classical point of view
A. Krasnitz,R. Venugopalan
Physics , 2001,
Abstract: We report results of our ongoing nonperturbative numerical study of a classical effective theory describing low-x partons in the central region of a heavy-ion collision. In particular, we give estimates of the initial transverse energies and multiplicities for a wide range of collision regimes, including those at RHIC and at LHC.
Probing a color glass condensate in high energy heavy ion collisions
Krasnitz, A.;Nara, Y.;Venugopalan, R.;
Brazilian Journal of Physics , 2003, DOI: 10.1590/S0103-97332003000200010
Abstract: at very high energies, the partons in the nuclear wavefunction form a color glass condensate. since the occupation number of partons in the color glass condensate is large, classical methods can be used to compute multi-particle production in the initial instants of a high energy heavy ion collision. non-perturbative expressions are derived relating the distributions of produced partons to those of wee partons in the wavefunctions of the colliding nuclei. the time evolution of components of the stress-energy tensor is studied and the impact parameter dependence of elliptic flow is extracted. we discuss the space-time picture that emerges and interpret the rhic data within this framework.
Heavy flavor production in pA collisions
Fujii, H.;Gelis, F.;Venugopalan, R.
High Energy Physics - Phenomenology , 2007, DOI: 10.1088/0954-3899/34/8/S130
Abstract: Heavy quark production in high-energy proton-nucleus (pA) collisions is described in the framework of the Color Glass Condensate. kT factorization is broken even at leading order albeit a more general factorization in pA holds at this order in terms of 2, 3 and 4 point correlators of Wilson lines in the nuclear target. The x-evolution of these correlators is computed in the large A and large N mean field limit of the Balitsky-Kovchegov equation. We show results for heavy quark production at RHIC and LHC energies.
How particles emerge from decaying classical fields in heavy ion collisions: towards a kinetic description of the Glasma
Gelis, F.;Jeon, S.;Venugopalan, R.
High Energy Physics - Phenomenology , 2007, DOI: 10.1016/j.nuclphysa.2008.11.011
Abstract: We develop the formalism discussed previously in and to construct a kinetic theory that provides insight into the earliest ``Glasma'' stage of a high energy heavy ion collision. Particles produced from the decay of classical fields in the Glasma obey a Boltzmann equation whose novel features include an inhomogeneous source term and new contributions to the collision term. We discuss the power counting associated with the different terms in the Boltzmann equation and outline the transition from the field dominated regime to the particle dominated regime in high energy heavy ion collisions.
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