Finite Temperature and Large Gauge Invariance

We discuss the problem of large gauge invariance at finite temperature.Comment: Talk presented at the Second School on Field Theory and Gravitation in Vitoria, to be published in the proceeding

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.Comment: 17 pages, UR-1325, ER-40685-77

The response of laser interferometers to a gravitational wave

Laser interferometer detectors are now widely used in an attempt to detect gravitational waves (gw). The interaction of the gw with the light circulating in the interferometer is usually explained in terms of the motion of the "free" mirrors that form the interferometer arms. It is however instructive to show that the same result can be obtained by simply calculating the propagation of an electromagnetic plane wave between "free mirrors" in the curved space-time induced by the gw. One finds that the plane wave acquires frequency modulation sidebands at the gw frequency, as would be expected from the absorption and emission of gravitons from and to the gw. Such sidebands are completely equivalent to the time-dependent phase shift imposed on the plane wave, that follows from the conventional calculation

Thermal effective action for 1+1 dimensional massive QED

In continuation of our earlier proposal for evaluating thermal effective actions, we determine the exact fermion propagator in 1+1 dimensional massive QED. This propagator is used to derive the finite temperature effective action of the theory which generates systematically all the one loop Feynman amplitudes calculated in thermal perturbation theory. Various aspects of the effective action including its imaginary part are discussed.Comment: revtex 12 pages, 6 figure

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.Comment: 12 pages, UR-1361, ER40685-81