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The possible transition of large mass magnetic monopole solutions to monopole black hole solutions in Yang-Mills-Higgs theory with spontaneous symmetry breaking (SSB) coupled to the low energy effective theory of superstring with only…
Equations of motion of null cosmic strings near black holes, or other massive sources, are solved exactly in the weak field approximation. The stress-energy tensor of a null string in a curved spacetime is introduced and used to show how…
We give some examples in which neglecting the interactions between particles or truncating the description of a black hole to the spherically symmetric mode leads to unphysical results. The restoration of the interactions and higher angular…
String theory has strong implications for cosmology: it tells us that we cannot have a cosmological constant, that single-field slow-roll inflation is ruled out, and that black holes decay. We elucidate the origin of these statements within…
We discuss aspects of the possible transition between small black holes and highly excited fundamental strings. We focus on the connection between black holes and the self gravitating string solution of Horowitz and Polchinski. This…
We construct an exact black hole solution for the Einstein gravity coupled with the nonlinear electrodynamics (which corresponds to the Maxwell electrodynamics in the weak field limit) in the presence of a cloud of strings as the source. We…
We investigate the evolution of small perturbations around black strings and branes which are low energy solutions of string theory. For simplicity we focus attention on the zero charge case and show that there are unstable modes for a…
We argue that $(0,1)$ heterotic string models with 4 non-heterotic spacetime dimensions may provide an instability of the vacuum to gravitational polarization in globally strong gravitational fields. This instability would be triggered…
Quantum gravitational effects in black hole spacetimes with a cosmological constant $\Lambda$ are considered. The effective quantum spacetimes for the black holes are constructed by taking into account the renormalization group improvement…
The purpose of this thesis is to provide insights into different aspects of black hole physics, both at a quantum level and from an observational point of view. On the one hand, regarding their fundamental constitutive characteristics, we…
We study the stability of static black holes in Lovelock theory which is a natural higher dimensional generalization of Einstein theory. We show that Lovelock black holes are stable under vector perturbations in all dimensions. However, we…
In the light of recent blackhole solutions inspired by string theory, we review some old statements on field theoretic hair on blackholes. We also discuss some stability issues. In particular we argue that the two dimensional string…
This is a summary of a lecture I gave at the workshop on dynamics and thermodynamics of black holes and naked singularities at Politecnico Milano. It is directed to a non-expert audience and reviews several ways in which string theory…
Perturbative string amplitudes are correctly derived from the string geometry theory, which is one of the candidates of a non-perturbative formulation of string theory. In order to derive non-perturbative effects rather easily, we formulate…
We investigate the qualitative new features of charged dilatonic black holes which emerge when both the Yang-Mills and Gauss-Bonnet curvature corrections are included in the effective action. We consider perturbative effects by an expansion…
In this semi-technical review we discuss string theory (and all that goes by that name) as a framework for a quantum theory of gravity. This is a new paradigm in theoretical physics that goes beyond relativistic quantum field theory. We…
Thirty years of a deepening information paradox suggest the need to revise our basic physical framework. Multiple indicators point toward reassessment of the principle of locality: lack of a precise definition in quantum gravity, behavior…
We review the classical thermodynamics and the greybody factors of general (rotating) non-extreme black holes and discuss universal features of their near-horizon geometry. We motivate a microscopic interpretation of general black holes…
We propose a black hole thermodynamic description of highly excited charged and uncharged perturbative string states in 3+1 dimensional type II and 4+1 dimensional heterotic string theory. We also discuss the generalization to extremal and…
It is shown that there are large static black holes for which all curvature invariants are small near the event horizon, yet any object which falls in experiences enormous tidal forces outside the horizon. These black holes are charged and…