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J. G. Russo

Publications and source records attributed to J. G. Russo.

62 records · Page 4Linked to original sources
arXiv1995

Exactly solvable string models of curved space-time backgrounds

We consider a new 3-parameter class of exact 4-dimensional solutions in closed string theory and solve the corresponding string model, determining the physical spectrum and the partition function. The background fields (4-metric, antisymmetric tensor, two Kaluza-Klein vector fields, dilaton and modulus) generically describe axially symmetric stationary rotating (electro)magnetic flux-tube type universes. Backgrounds of this class include both the dilatonic (a=1) and Kaluza-Klein (a=\sqrt 3) Melvin solutions and the uniform magnetic field solution, as well as some singular space-times. Solvability of the string sigma model is related to its connection via duality to a simpler model which is a ``twisted" product of a flat 2-space and a space dual to 2-plane. We discuss some physical properties of this model (tachyonic instabilities in the spectrum, gyromagnetic ratios, issue of singularities, etc.). It provides one of the first examples of a consistent solvable conformal string model with explicit D=4 curved space-time interpretation.

hep-th↗
arXiv1995

Constant magnetic field in closed string theory: an exactly solvable model

We consider a simple model describing a closed bosonic string in a constant magnetic field. Exact conformal invariance demands also the presence of a non-trivial metric and antisymmetric tensor (induced by the magnetic field). The model is invariant under target space duality in a compact Kaluza-Klein direction introduced to couple the magnetic field. Like open string theory in a constant gauge field, or closed string theory on a torus, this model can be straightforwardly quantized and solved with its spectrum of states and partition function explicitly computed. Above some critical value of the magnetic field an infinite number of states become tachyonic, suggesting a presence of phase transition. We also construct heterotic string generalisations of this bosonic model in which the constant magnetic field is embedded either in the Kaluza-Klein or internal gauge group sector.

hep-th↗
arXiv1994

Asymptotic level density in heterotic string theory and rotating black holes

We calculate the density of states with given mass and spin in string theory and obtain asymptotic formulas. We also compute the tree-level gyromagnetic couplings for arbitrary physical states in the heterotic string theory. These results are then applied to study whether fundamental strings can consistently describe the microphysics of the black hole horizon in the case of a general classical solution characterized by mass, charge and angular momentum.

hep-th↗
arXiv1993

On black hole singularities in quantum gravity

We show that absence of space-like boundaries in 1+1 dimensional dilaton gravity implies a catastrophic event at the end point of black hole evaporation. The proof is completely independent of the physics at Planck scales, which suggests that the same will occur in any theory of quantum gravity which only admits trivial space-time topologies.

gr-qc↗
arXiv1993

A theory of quantum black holes: non-perturbative corrections and no-veil conjecture

A common belief is that further quantum corrections near the singularity of a large black hole should not substantially modify the semiclassical picture of black hole evaporation; in particular, the outgoing spectrum of radiation should be very close to the thermal spectrum predicted by Hawking. In this paper we explore a possible counterexample: in the context of dilaton gravity, we find that non-perturbative quantum corrections which are important in strong coupling regions may completely alter the semiclassical picture, to the extent that the presumptive space-like boundary becomes time-like, changing in this way the causal structure of the semiclassical geometry. As a result, only a small fraction of the total energy is radiated outside the fake event horizon; most of the energy comes in fact at later retarded times and there is no information loss problem. Thus we propose that this may constitute a general characteristic of quantum black holes, that is, quantum gravity might be such as to prevent the formation of global event horizons. We argue that this is not unnatural from the viewpoint of quantum mechanics.

hep-th↗
arXiv1993

Discrete Strings and Deterministic Cellular Strings

A discrete string theory --a theory of embeddings from ${\bf Z}\times {\bf Z}_C\to {\bf R}^D$, where $C$ is the number of components of the string-- is explored. The closure of the algebra of constraints (`${\bf Z}_C$-Virasoro algebra') is exhibited. The ${\bf Z}_C$-Virasoro `algebra' is shown to be anomaly free in arbitrary number of target space dimensions. We prove the existence of a (manifestly unitary) light-cone gauge with anomaly free Lorentz algebra in any dimensions. The analog of vertex operators are introduced and the physical spectrum is analysed. There are an infinite number of higher-level states repeating a certain mass pattern and leading to an infinite degeneracy. The connection with the continuum string theory (in $D=26$) is investigated. Independently, following a method recently introduced by 't Hooft based on Hilbert-space extension of deterministic systems, a particular one-dimensional cellular automaton submitted to a deterministic evolution is shown to reduce to a massless scalar field theory at long distance scales. This automaton is utilized to define a (`cellular') string theory with world-sheet variables evolving under deterministic rules, which in the framework of `first-quantization' corresponds to the ${\bf Z}_C$ string theory mentioned above. We show that in this theory also the target space motion of free strings is governed by deterministic laws. Finally, we discuss a model for (off-shell) interacting strings where space-time determinism is fully restored.

hep-th↗
arXiv1992

Dilaton Quantum Cosmology in Two Dimensions

We consider a renormalizable two-dimensional model of dilaton gravity coupled to a set of conformal fields as a toy model for quantum cosmology. We discuss the cosmological solutions of the model and study the effect of including the backreaction due to quantum corrections. As a result, when the matter density is below some threshold new singularities form in a weak coupling region, which suggests that they will not be removed in the full quantum theory. We also solve the Wheeler-DeWitt equation. Depending on the quantum state of the Universe, the singularities may appear in a quantum region where the wave function is not oscillatory, i.e., when there is not a well defined notion of classical spacetime.

hep-th↗