On the Derivative Expansion at Finite Temperature
In this short note, we indicate the origin of nonanalyticity in the method of derivative expansion at finite temperature and discuss some of its consequences.
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arXiv subjects
Ashok Das
Publications and source records attributed to Ashok Das.
On the Ward Identities at Finite Temperature
We show both in 1+1 and 3+1 dimensions that, contrary to the recent suggestions, the contribution of the fermion loop to the polarization tensor is manifestly transverse at finite temperature. Some subtleties associated with the Ward identities at finite temperature are also pointed out.
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Gelfand-Dikii Brackets for Nonstandard Lax Equations
We generalize the construction of Gelfand-Dikii brackets to the case of nonstandard Lax equations. We also discuss the possible origin of Kac-Moody algebras present in such systems.
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Tests of Integrability of the Supersymmetric Nonlinear Schrodinger Equation
We apply various conventional tests of integrability to the supersymmetric nonlinear Schrödinger equation. We find that a matrix Lax pair exists and that the system has the Painlevé property only for a particular choice of the free parameters of the theory. We also show that the second Hamiltonian structure generalizes to superspace only for these values of the parameters. We are unable to construct a zero curvature formulation of the equations based on OSp(2$|$1). However, this attempt yields a nonsupersymmetric fermionic generalization of the nonlinear Schrödinger equation which appears to possess the Painlevé property.
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Duality of the Superstring in Superspace
The evolution of a closed NSR string is considered in the background of constant graviton and antisymmetric fields. The $σ$-model action is written in a manifestly supersymmetric form in terms of superfields. The first order formalism adopted for the closed bosonic string is generalised to implement duality transformations and the constant dual backgrounds are obtained for the dual theory. We recover the $G \rightarrow G^{-1}$ duality for the case when antisymmetric tensor field is set to zero. Next, the case when the backgrounds depend on one superfield, is also analysed. This scenario is similar to the cosmological case envisaged for the bosonic string. The explicit form of the duality transformation is given for this case.
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A New Class of Supersymmetric Theories
We construct a class of quantum mechanical theories which are invariant under fermionic transformations similar to supersymmetry transformations. The generators of the transformations in this case, however, satisfy a BRST-like algebra.
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Davey-Stewartson Equation from a Zero Curvature and a Self-Duality Condition
We derive the two equations of Davey-Stewartson type from a zero curvature condition associated with SL(2,{\bf R}) in $2+1$ dimensions. We show in general how a $2+1$ dimensional zero curvature condition can be obtained from the self-duality condition in $3+3$ dimensions and show in particular how the Davey-Stewartson equations can be obtained from the self-duality condition associated with SL(2,{\bf R}) in $3+3$ dimensions.
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On the Higher Order Corrections to Heavy Quark Effective Theory
We show that the different ways of deriving the Heavy Quark Effective Theory (HQET) lead to equivalent theories. The equivalence can be established through a careful redefinition of the field variables. We demonstrate the equivalence to order ${1 \over m^5}$ in the presence of a constant electric field.
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More on Symmetries in Heavy Quark Effective Theory
We present a general classification of all normal and ``chiral" symmetries of heavy quark effective theories. Some peculiarities and conondrums associated with the ``chiral" symmetries are discussed.
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Out of Equilibrium Phase Transitions and a Toy Model for Disoriented Chiral Condensates
We study the dynamics of a second order phase transition in a situation thatmimics a sudden quench to a temperature below the critical temperature in a model with dynamical symmetry breaking. In particular we show that the domains of correlated values of the condensate grow as $\sqrt{t}$ and that this result seems to be largely model independent.
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Nonleptonic Decays of Charmed Mesons into two Pseudoscalar Mesons
We investigate the nonleptonic decay of charmed meson into two pseudoscalar mesons using the vector--dominance model, and compare the results with those obtained from the factorization model. In particular, we discuss the role of the annihilation diagrams in the two models.
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δ-expansion and self-consistent calculation
We compare results from $δ$--expansion, in simple theories, with self--consistent calculations as well as calculations involving the principle of minimal sensitivity. We show that the latter methods give relatively more accurate results order by order.
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Feynman Parametrization and the Degenerate Electron Gas
We give an alternate derivation of Weldon's formula for combining products of factors with non identical analytic behavior. While such a formula would appear to be useful in finite temperature calculations, we give an example of a zero temperature calculation, namely, the degenerate electron gas, to justify the result.
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Self-Duality and the KdV Hierarchy
We derive the entire KdV hierarchy as well as the recursion relations from the self-duality condition on gauge fields in four dimensions.
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