62,853 research outputs found

    Discrete phase space - III: The Divergence-free S-matrix elements

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    In the arena of the discrete phase space and continuous time, the theory of S-marix is formulated. In the special case of Quantum-Electrodynamics (QED), the Feynman rules are precisely developed. These rules in the fourmomentum turn out to be identical to the usual QED, except for the vertex function. The new vertex function is given by an infinite series which can only be treated in an asymptotic approximation at the present time. Preliminary approximations prove that the second order self-energies of a fermion and a photon in the discrete model have convergent improper integrals. In the final section, a sharper asymptotic analysis is employed. It is proved that in case the number of external photon or fermion lines is at least one, then the S-matrix elements converge in all orders. Moreover, there are no infra-red divergences in this formulation.Comment: 31 pages, 3 figure

    Spherical Gravitating Systems of Arbitrary Dimension

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    We study spherically symmetric solutions to the Einstein field equations under the assumption that the space-time may possess an arbitrary number of spatial dimensions. The general solution of Synge is extended to describe systems of any dimension. Arbitrary dimension analogues of known four dimensional solutions are also presented, derived using the above scheme. Finally, we discuss the requirements for the existence of Birkhoff's theorems in space-times of arbitrary dimension with or without matter fields present. Cases are discussed where the assumptions of the theorem are considerably weakened yet the theorem still holds. We also discuss where the weakening of certain conditions may cause the theorem to fail.Comment: 14 pages with one fugure. Uses AMS fonts and Prog. Theor. Phys. style files. Added section on neutron star and anisotropic fluid star as well as Comments on Buchdahl's theorem and more analysis regarding the Birkhoff's theorem. Accepted for publication in Prog. Theor. Phy

    Effective Actions for 0+1 Dimensional Scalar QED and its SUSY Generalization at T‚Ȇ0T\neq 0

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    We compute the effective actions for the 0+1 dimensional scalar field interacting with an Abelian gauge background, as well as for its supersymmetric generalization at finite temperature.Comment: 5 pages, Latex fil

    Effective actions at finite temperature

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    This is a more detailed version of our recent paper where we proposed, from first principles, a direct method for evaluating the exact fermion propagator in the presence of a general background field at finite temperature. This can, in turn, be used to determine the finite temperature effective action for the system. As applications, we discuss the complete one loop finite temperature effective actions for 0+1 dimensional QED as well as for the Schwinger model in detail. These effective actions, which are derived in the real time (closed time path) formalism, generate systematically all the Feynman amplitudes calculated in thermal perturbation theory and also show that the retarded (advanced) amplitudes vanish in these theories. Various other aspects of the problem are also discussed in detail.Comment: 9 pages, revtex, 1 figure, references adde

    Specific heat at constant volume in the thermodynamic model

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    A thermodynamic model for multifragmentation which is frequently used appears to give very different values for specific heat at constant volume depending upon whether canonical or grand canonical ensemble is used. The cause for this discrepancy is analysed.Comment: Revtex, 7 pages including 4 figure
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