C. Chiou-Lahanas

Tachyon field quantization and Hawking radiation.

We quantize the tachyon field in a static two dimensional dilaton gravity black hole background,and we calculate the Hawking radiation rate. We find that the thermal radiation flux, due to the tachyon field, is larger than the conformal matter one. We also find that massive scalar fields which do not couple to the dilaton, do not give any contribution to the thermal radiation, up to terms quadratic in the scalar curvature.

Five-dimensional black hole string backgrounds and brane universe acceleration

Abstract We examine background solutions of black hole type arising from the string effective action in five dimensions. We derive the unique metric — dilaton vacuum which is a Schwarzschild type black hole. It is found that it can be extended to incorporate electric charge without changing the topology of the three space. Kalb–Ramond charge may also be introduced if the three space is closed. The basic features of the cosmology induced on a three brane evolving in this background are also discussed.

Model for the nucleon structure function F2(x, Q2)☆

Abstract A particular j-plane singularity, leading to long-range effects in hadron scattering, is attributed to hard constituent quark interactions. A definite prediction for the nucleon structure function, including scaling violations consistent with QCD. is obtained, which is confronted with the available data.

Universe acceleration in brane world models

We examine the cosmology induced on a brane moving in the background of a five-dimensional black hole, solution of the string effective action. The evolution, determined by the Israel junction conditions is found to be compatible with an accelerating universe with the present day acceleration coming after a decelerating phase. The possible species of the energy–momentum tensor, localized on the brane, for these solutions to be valid are discussed.

KAHLER INVARIANCE OF N=1 QUANTUM SUPERGRAVITY

Abstract The Kahler invariance of the N = 1 supergravity theory is investigated beyond the classical level. In the popular gauge fixing condition emμ−eμm=0, γμψμ=0, ∂μ(√g gμν) = 0 one has a manifestly Kahler invariant theory at the quantum level and for that the form of the path integral measure is important. We show that Fujikawas measure is consistent with quantum Kahler invariance. The integration of the auxiliary fields of the closed algebra theory brings down local determinants ( det G zz ∗ ) − necessary for maintaining the Kahler symmetry at the quantum level. Owing to the gauge independence of the path integral measure Kahler invariance is a gauge independent property.

STATIC AND NONSTATIC QUANTUM EFFECTS IN TWO-DIMENSIONAL DILATON GRAVITY

We study back-reaction effects in two-dimensional dilaton gravity. The back-reaction comes from an R2 term which is a part of the one-loop effective action arising from massive scalar field quantization in a certain approximation. The peculiarity of this term is that it does not contribute to the Hawking radiation of the classical black hole solution of the field equations. In the static case we examine the horizon and the physical singularity of the new black hole solutions. Studying the possibility of time dependence we see the generation of a new singularity. The particular solution found still has the structure of a black hole, indicating that nonthermal effects cannot lead, at least in this approximation, to black hole evaporation.

Bounds on the top-quark mass in N=1 supergravity models

Abstract From the tree level study of the SU(3)×SU(2)×U(1) model arising as the flat limit of a spontaneously broken N =1 supergravity, via the super Higgs mechanism, we find particular directions of minima which lead to upper bound for the top-quark mass. These bounds on m t can also be of relevance to superstring-inspired low-energy models.