Marcelo Hott

Derivative expansion at finite temperature.

In this Brief Report, we indicate the origin of nonanalyticity in the method of derivative expansion at finite temperature and discuss some of its consequences.

Thermal effects on the catalysis by a magnetic field.

We show that the formation of condensates in the presence of a constant magnetic field in 2+1 dimensions is extremely unstable. It disappears as soon as a heat bath is introduced with or without a chemical potential. We point out some new nonanalytic behavior that develops in this system at finite temperature.

Furry’s picture in the path integral framework

SummaryWe obtain the Feynman rules for QED in the presence of an external field in the path integral framework, establishing this way the path integral version of Furry’s picture. We illustrate our method by constructing explicitly the exact path integral expression for the propagator of a relativistic charged particle of spin one-half in the presence of a plane-wave external field.

Chiral invariance of massive fermions

We show that a massive fermion theory, while not invariant under the conventional chiral transformation, is invariant under a m-deformed chiral transformation. These transformations and the associated conserved charges are nonlocal but reduce to the usual transformations and charges when m=0. The m-deformed charges commute with helicity and satisfy the conventional chiral algebra.

ON THE WARD IDENTITIES AT FINITE TEMPERATURE

We show in both 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.

Perturbative bosonization from two-point correlation functions

Here we address the problem of bosonizing massive fermions without making expansions in the fermion masses in both massiveQED2 andQED3 with N fermion flavors including also a Thirring coupling. We start from two point correlators involving the U(1) fermionic current and the gauge field. From the tensor structure of those correlators we prove that the U(1) current must be identically conserved (topological) in the corresponding bosonized theory both in D = 2 and D = 3 dimensions. We find an effective generating functional in terms of bosonic fields which reproduces those two point correlators and from that we obtain a map of the =

SUPERSYMMETRIC THEORIES ON A NONSIMPLY CONNECTED SPACETIME

We study the Wess-Zumino theory on ℝ3×S1 where a spatial coordinate is compactified. We show that when the bosonic and fermionic fields satisfy the same boundary condition, the theory does not develop a vacuum energy or tadpoles. We work out the two-point functions at one-loop and show that their forms are consistent with the nonrenormalization theorem. However, the two-point functions are nonanalytic and we discuss the structure of this nonanalyticity.

Induced fractional valley number in graphene with topological defects

We report on the possibility of valley number fractionalization in graphene with a topological defect that is accounted for in Dirac equation by a pseudomagnetic field. The valley number fractionalization is attributable to an imbalance on the number of one particle states in one of the two Dirac points with respect to the other and it is related to the flux of the pseudomagnetic field. We also discuss the analog effect the topological defect might lead in the induced spin polarization of the charge carriers in graphene.

Virial coefficients from (2+1)-dimensional QED effective actions at finite temperature and density

From spinor and scalar (2 + 1)-dimensional QED effective actions at finite temperature and density in a constant magnetic field background, we calculate the corresponding virial coefficients for particles in the lowest Landau level. These coefficients depend on a parameter θ related to the time-component of the gauge field, which plays an essential role for large gauge invariance. The variation of the parameter θ might lead to an interpolation between fermionic and bosonic virial coefficients, although these coefficients are singular for θ = π/2.

Path integral solubility of a general two-dimensional model

The solubility of a general two dimensional model, which reduces to various models in different limits, is studied within the path integral formalism. Various subtleties and interesting features are pointed out.