Nikolaos Tsamis

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We derive the propagator for a massive vector field on a de Sitter background of arbitrary dimension. This propagator is de Sitter invariant and possesses the proper flat spacetime and massless limits. Moreover, the retarded Green's function inferred from it produces the correct classical response to a test source. Our result is expressed in a tensor basis(More)
OBJECTIVE During the last 5 years we observed a significant decrease in the incidence of newly established cases of Reiter's syndrome (reactive arthritis) in Greek Army personnel. Our study was initiated to validate this observation and to evaluate a possible change in the prevalence of Reiter's syndrome (RS) associated infections. METHODS The case(More)
We consider the quantum gravitational back-reaction on an initially inflating, homogeneous and isotropic universe whose topology is T 3 × ℜ. Although there is no secular effect at one loop, an explicit calculation shows that two-loop processes act to slow the rate of expansion by an amount which becomes non-perturbatively large at late times. By exploiting(More)
During inflation explicit perturbative computations of quantum field theories which contain massless, non-conformal fields exhibit secular effects that grow as powers of the logarithm of the inflationary scale factor. Starobinski˘ ı's technique of stochastic inflation not only reproduces the leading infrared logarithms at each order in perturbation theory,(More)
We stochastically formulate the theory of scalar quantum electrodynamics on a de Sitter background. This reproduces the leading infrared logarithms at each loop order. It also allows one to sum the series of leading infrared logarithms to obtain explicit, nonperturbative results about the late time behavior of the system. One consequence is confirmation of(More)
We prove that Weyl invariant theories of gravity possess a remarkable property which, under very general assumptions, explains the stability of flat space-time. We show explicitly how conformal invariance is broken spontaneously by the vacuum expectation value of an unphysical scalar field; this process induces general relativity as an effective long(More)