On the temperature dependence of the absorption cross section for black holes in string theory

We study the low frequency absorption cross section of spherically symmetric nonextremal d-dimensional black holes. In the presence of α′ corrections, this quantity must have an explicit dependence on the Hawking temperature of the form 1/TH. This property of the low frequency absorption cross section is shared by the D1-D5 system from type IIB superstring theory already at the classical level, without α′ corrections. We apply our formula to the simplest example, the classical d-dimensional Reissner-Nordstr¨om solution, checking that the obtained formula for the cross section has a smooth extremal limit. We also apply it for a d-dimensional Tangherlini-like solution with α′3 corrections.This work has been supported by FEDER funds through Programa Operacional Fatores de Competitividade – COMPETE and by Funda¸c˜ao para a Ciˆencia e a Tecnologia through projects Est-C/MAT/UI0013/2011 and CERN/FP/123609/2011

String Corrections to Supergravity Theories

In this thesis, we study the leading quantum corrections to supergravity theories in four dimensions, given by the fourth power of the Riemann tensor (R 4). We write, in four-dimensional superspace, the N = 1 minimal action which contains the fourth power of the Weyl tensor with a coupling constant. Starting from the superspace action, we fully compute the x-space action, keeping the auxiliary fields. In order to find their field equations, we work in superspace. Starting from iii the off-shell solution of the Bianchi identities, we compute the on-shell torsions and curvatures with this term. We show that their complete solution includes, for some of them, an infinite series in the coupling constant, which can only be computed iteratively. We explicitly compute the superspace torsions and curvatures up to second order in this coupling constant