33800044
Finite-size and dynamical effects in pair production by an external field.
We evaluate the rate of pair production in a uniform electric field confined to a bounded region in space. Using the Balian-Bloch expansion of Green's functions we obtain explicit expressions for finite-size corrections to Schwinger's formula. The case of a time-dependent boundary, relevant to describe energy deposition by quark-antiquark pair production in ultrarelativistic collisions, is also investigated. We find that finite-size effects are important in nuclear collisions. They decrease when the strength of the chromoelectric field between the nuclei is large. As a result, the rate of energy deposition increases sharply with the mass number {ital A} of the colliding nuclei.
8691879
Gauge Invariant Variables for SU ( 2 ) Yang-Mills Theory
We describe a nonperturbative calculation of the spectrum of SU(2) Yang-Mills theory based on a Hamiltonian formulation. Our approach exploits gauge invariant variables similar to those used in nuclear physics to describe collective motion in nuclei.
17246313
Variational Approximations for Correlation Functions in Quantum Field Theories
Abstract Applying the time-dependent variational principle of Balian and Veneroni, we derive variational approximations for multi-time correlation functions in Φ 4 field theory. We assume first that the initial state is given and characterized by a density operator equal to a Gaussian density matrix. Then, we study the more realistic situation where only a few expectation values are given at the initial time and we perform an optimization with respect to the initial state. We calculate explicitly the two-time correlation functions with two and four field operators at equilibrium in the symmetric phase.
17341915
Self similar solutions of the evolution equation of a scalar field in an expanding geometry
Abstract We consider the functional Schrodinger equation for a self interacting scalar field in an expanding geometry. By performing a time dependent scale transformation on the argument of the field we derive a functional Schrodinger equation whose hamiltonian is time independent but involves a time-odd term associated to a constraint on the expansion current. We study the mean field approximation to this equation and generalize in this case for interacting fields, the solutions worked out by Bunch and Davies for free fields.
17649647
Variational approximation for two-time correlation functions in Phi 4 theory: Optimization of the dynamics.
We apply the time-dependent variational principle of Balian and Veneroni to {Phi}{sup 4} theory. An appropriate parametrization for the variational objects allows us to write coupled dynamical equations from which we derive approximations for the two-time correlation functions involving two, three, or four field operators. {copyright} 1995 The American Physical Society.
16683941
Ground state properties and glueball spectrum in SU(2) Yang-Mills theory using gauge invariant variables
We describe a nonperturbative calculation of the spectrum of SU(2) Yang-Mills theory based on a Hamiltonian formulation. Our approach exploits gauge invariant variables similar to those used in nuclear physics to describe collective motion in nuclei.
15657072
Properties of the BFkl equation and structure function predictions for DESY HERA.
The general properties of the Lipatov or Balitskij-Fadin-Kuraev-Lipatov equation are reviewed. Modifications to the infrared region are proposed. Numerical predictions for the deep-inelastic electron-proton structure functions at small [ital x] are presented and confronted with recent DESY HERA measurements.
16919657
Decoupling of the epsilon -scalar mass in softly broken supersymmetry.
It has been shown recently that the introduction of an unphysical [epsilon]-scalar mass [ital [tilde m]] is necessary for the proper renormalization of softly broken supersymmetric theories by dimensional reduction (DR). In these theories, both the two-loop [beta] functions of the scalar masses and their one-loop finite corrections depend on [ital [tilde m]][sup 2]. We find, however, that the dependence on [ital [tilde m]][sup 2] can be completely removed by slightly modifying the DR renormalization scheme. We also show that previous DR calculations of one-loop corrections in supersymmetry which ignored the [ital [tilde m]][sup 2] contribution correspond to using this modified scheme.
15015533
QCD predictions for the transverse energy flow in deep-inelastic scattering in the DESY HERA small x regime.
The distribution of transverse energy [ital E][sub [ital T]], which accompanies deep-inelastic electron-proton scattering at small [ital x], is predicted in the central region away from the current jet and proton remnants. We use BFKL dynamics, which arises from the summation of multiple gluon emissions at small [ital x], to derive an analytic expression for the [ital E][sub [ital T]] flow. One interesting feature is an [ital x][sup [minus][epsilon]] increase of the [ital E][sub [ital T]] distribution with decreasing [ital x], where [epsilon]=(3[alpha][sub [ital s]]/[pi])2 ln2. We perform a numerical study to examine the possibility of using characteristics of the [ital E][sub [ital T]] distribution as a means of identifying BFKL dynamics at DESY HERA.
471847
Search for supersymmetry with a light gravitino at the Fermilab Tevatron and CERN LEP colliders.
We analyze the prospects for discovering supersymmetry at the Fermilab Tevatron and CERN LEP colliders in the scenario that the lightest supersymmetric particle is a gravitino of mass {approx_lt}1 keV. We consider in particular the case that the lightest neutralino has a nearly 100{percent} branching fraction into gravitino+photon within the detector. This implies that supersymmetric events should contain both missing (transverse) energy and two energetic photons. Therefore, one can search for supersymmetry simply through inclusive production of superpartners. We consider the exclusion and reach capabilities of the Tevatron in exploring the supersymmetric parameter space, and study the efficiencies which can be achieved in this search. We also consider the discovery reach and backgrounds at LEP with {radical}{ital s}=160, 175, and 190 GeV. {copyright} {ital 1996 The American Physical Society.}
36873731
Interference radiative phenomena in the production of heavy unstable particles.
We discuss the characteristic interference phenomena, including real as well as virtual radiative corrections, to the inclusive cross sections for production of heavy unstable systems such as {ital t{bar t}} or {ital W}{sup +}{ital W{minus}} pairs. We demonstrate explicitly the (fortunate) cancellation between emissions associated with the production of unstable particles and with their decays, and between emissions accompanying the decay stages. As a result the total interference effect is shown to be of {ital O}({alpha}{sub {ital i}}{Gamma}/{ital M}) or better (where {alpha}{sub {ital i}}={alpha} or {alpha}{sub {ital s}} as appropriate).