We examine Hawking radiation from a Schwarzschild black hole in several reference frames using the quasi-classical tunneling picture. It is shown that when one uses, Γ ∝ exp(Im[ p dr]), rather than, Γ ∝ exp(2Im[ p dr]), for the tunneling probability/decay rate one obtains twice the original Hawking temperature. The former expression for Γ is argued to be correct since p dr is invariant under canonical transformations, while p dr is not. Thus, either the tunneling methods of calculating Hawking radiation are suspect or the Hawking temperature is twice that originally calculated.

We discuss peculiarities of quantum fields in de Sitter space on the example of the self-interacting massive real scalar, minimally coupled to the gravity background. Non-conformal quantum field theories in de Sitter space show very special infrared behavior, which is not shared by quantum fields neither in flat nor in anti-de-Sitter space: in de Sitter space loops are not suppressed in comparison with tree level contributions because there are strong infrared corrections. That is true even for massive fields. Our main concern is the interrelation between these infrared effects, the invariance of the quantum field theory under the de Sitter isometry and the (in)stability of de Sitter invariant states (and of dS space itself) under nonsymmetric perturbations.

The correspondence between the four-dimensional SU (N ), N = 4 SYM taken at large N and the type II B SUGRA on the AdS 5 ×S 5 background is considered. We argue that the classical equations of motion in the SUGRA picture can be interpreted as that of the renormalization group on the SYM side. In fact, when the D3-brane is slightly excited higher derivative terms in the field theory on its world-volume deform it form the conformal N = 4 SYM limit. We give arguments in favor of that the deformation goes in the way set by the SUGRA equations of motion. Concrete example of the s-wave dilaton is considered. Having in mind those facts, in this note we try to give a geometric interpretation of the renormalization group flow in the SYM theory. Our work is based on the proposed duality [10] between the four-dimensional large N SYM theory and type IIB SUGRA on a background which we describe below. Concretely, we argue that the classical equation of motion of the dilaton in the bulk SUGRA theory is nothing but the renormalization group equation for the SYM "coupling constant" on the D-brane world-volume [11]. As we discuss below, this fact is sensible if the dilaton -"coupling constant" -is excited and, hence, is a function of the four-dimensional coordinates. While if the dilaton is an arbitrary constant it remains to be the one at any energy scale. In the both cases the movement in the direction transversal to the D-brane is the renormalization group transformation [10,12] in the field theory on its world-volume.In fact, it is widely believed that super-strings suggest the regularization of field theory [13]. What is new in the D-brane case is that the regularization of their world-volume field theories can happen at much smaller energy scale than the Plank one, if some particular double scaling limit is taken [11,14,15]. The regularized theory should be considered as a vacuum in that of super-strings [10]. For after the regularization we are missing information 1

The quasi-classical method of deriving Hawking radiation is investigated. In order to recover the original Hawking temperature one must take into account a previously ignored contribution coming from the temporal part of the action. This contribution plus a contribution coming from the spatial part of the action gives the correct temperature.

Starting from the Abelian Higgs field theory, we construct the theory of quantum Abrikosov-Nielsen-Olesen strings. It is shown that in four space -time dimensions in the limit of infinitely thin strings, the conformal anomaly is absent, and the quantum theory exists. We also study an analogue of the Aharonov-Bohm effect: the corresponding topological interaction is proportional to the linking number of the string world sheet and the particle world trajectory. The creation operators of the strings are explicitly constructed in the path integral and in the Hamiltonian formulation of the theory. We show that the Aharonov-Bohm effect gives rise to several nontrivial commutation relations.

We present a simple and general procedure for calculating the thermal radiation coming from any stationary metric. The physical picture is that the radiation arises as the quasi-classical tunneling of particles through a gravitational barrier. We study three cases in detail: the linear accelerating observer (Unruh radiation), the non-rotating black hole (Hawking radiation), and the rotating/orbiting observer (circular Unruh radiation). For the linear accelerating observer we obtain a thermal spectrum with the usual Unruh temperature. For the non-rotating black hole we obtain a thermal spectrum, but with a temperature twice that given by the original Hawking calculations. We discuss possible reasons for the discrepancies in temperatures as given by the two different methods. For the rotating/orbiting case the quasi-classical tunneling approach indicates that there is no thermal radiation. This result for the rotating/orbiting case has experimental implications for the experimental detection of this effect via the polarization of particles in storage rings.

We study the expectation value of the energy momentum tensor during thin shell collapse for a massive, real, scalar field theory. At tree-level, we find thermal, Hawking-type, behaviour for the energy flux. Using the Schwinger-Keldysh technique, we calculate two-loop corrections to the tree-level correlation functions and show that they exhibit secular growth, suggesting the breakdown of the perturbation theory.Comment: 28 pages, but general physical explanation is given in the introduction; Final version that is going to appear in PR

We calculate one-loop corrections to the vertexes and propagators of photons and charged particles in the strong electric field backgrounds. We use the SchwingerKeldysh diagrammatic technique. We observe that photon's Keldysh propagator receives growing with time infrared contribution. As the result, loop corrections are not suppressed in comparison with tree-level contribution. This effect substantially changes the standard picture of the pair production. To sum up leading IR corrections from all loops we consider the infrared limit of the Dyson-Schwinger equations and reduce them to a single kinetic equation.