Publications (15)0 Total impact
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Article: Selected topics in string theory and black hole physics
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Article: Einstein y la Geometria
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ABSTRACT: This is a semipopular introduction to the Special and General Theory of Relativity, with special emphasis on the geometrical aspects of both theories and their physical implications. -
Article: Scaling Phenomena in Gravity from QCD
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ABSTRACT: We present holographic arguments to predict properties of strongly coupled gravitational systems in terms of weakly coupled gauge theories. In particular we relate the Choptuik critical exponent in black hole formation in five dimensions, \gamma_{5D}=0.408 \pm 2%, to the saturation exponent of four-dimensional Yang-Mills theory in the Regge limit, \gamma_{BFKL}=0.409552. -
Article: Introductory Lectures on Quantum Field Theory
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ABSTRACT: In these lectures we present a few topics in Quantum Field Theory in detail. Some of them are conceptual and some more practical. They have been selected because they appear frequently in current applications to Particle Physics and String Theory. -
Article: A cosmological interpretation of duality
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ABSTRACT: We study the cosmological meaning of duality symmetry by considering a two dimensional model of string cosmology. We find that as seen by an internal observer in this universe, the scale factor rebounds at the self-dual length. This rebound is a consequence of the adiabatic expansion. Furthermore, in this situation there are four mathematically different scenarios which describe physically equivalent universes which are in fact indistinguishable. We also stress that $R$-duality suffices to prove that all possible evolutions present a maximum temperature. -
Article: Topics in string theory and quantum gravity
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ABSTRACT: These are the lecture notes for the Les Houches Summer School on Quantum Gravity held in July 1992. The notes present some general critical assessment of other (non-string) approaches to quantum gravity, and a selected set of topics concerning what we have learned so far about the subject from string theory. Since these lectures are long (133 A4 pages), we include in this abstract the table of contents, which should help the user of the bulletin board in deciding whether to latex and print the full file. 1-FIELD THEORETICAL APPROACH TO QUANTUM GRAVITY: Linearized gravity; Supergravity; Kaluza-Klein theories; Quantum field theory and classical gravity; Euclidean approach to Quantum Gravity; Canonical quantization of gravity; Gravitational Instantons. 2-CONSISTENCY CONDITIONS: ANOMALIES: Generalities about anomalies; Spinors in 2n dimensions; When can we expect to find anomalies?; The Atiyah-Singer Index Theorem and the computation of anomalies; Examples: Green-Schwarz cancellation mechanism and Witten's SU(2) global anomaly. 3-STRING THEORY I. BOSONIC STRING: Bosonic string; Conformal Field Theory; Quantization of the bosonic string; Interaction in string theory and the characterization of the moduli space; Bosonic strings with background fields. Stringy corrections to Einstein equations; Toroidal compactifications. $R$-duality; Operator formalism 4-STRING THEORY II. FERMIONIC STRINGS: Fermionic String; Heterotic String; Strings at finite temperature; Is string theory finite? 5-OTHER DEVELOPMENTS AND CONCLUSIONS: String ``Phenomenology''; Black Holes and Related Subjects -
Article: On the stringy nature of winding modes in noncommutative thermal field theories
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ABSTRACT: We show that thermal noncommutative field theories admit a version of `channel duality' reminiscent of open/closed string duality, where non-planar thermal loops can be replaced by an infinite tower of tree-level exchanges of effective fields. These effective fields resemble closed strings in three aspects: their mass spectrum is that of closed-string winding modes, their interaction vertices contain extra moduli, and they can be regarded as propagating in a higher-dimensional `bulk' space-time. In noncommutative models that can be embedded in a D-brane, we show the precise relation between the effective `winding fields' and closed strings propagating off the D-brane. The winding fields represent the coherent coupling of the infinite tower of closed-string oscillator states. We derive a sum rule that expresses this effective coupling in terms of the elementary couplings of closed strings to the D-brane. We furthermore clarify the relation between the effective propagating dimension of the winding fields and the true codimension of the D-brane. -
Article: General Properties of Noncommutative Field Theories
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ABSTRACT: In this paper we study general properties of noncommutative field theories obtained from the Seiberg-Witten limit of string theories in the presence of an external B-field. We analyze the extension of the Wightman axioms to this context and explore their consequences, in particular we present a proof of the CPT theorem for theories with space-space noncommutativity. We analyze as well questions associated to the spin-statistics connections, and show that noncommutative N=4, U(1) gauge theory can be softly broken to N=0 satisfying the axioms and providing an example where the Wilsonian low energy effective action can be constructed without UV/IR problems, after a judicious choice of soft breaking parameters is made. We also assess the phenomenological prospects of such a theory, which are in fact rather negative. -
Article: Critical gravitational collapse: towards a holographic understanding of the Regge region
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ABSTRACT: We study the possible holographic connection between the Regge limit in QCD and critical gravitational collapse of a perfect fluid in higher dimensions. We begin by analyzing the problem of critical gravitational collapse of a perfect fluid in any number of dimensions and numerically compute the associated Choptuik exponent in d=5, 6 and 7 for a range of values of the speed of sound of the fluid. Using continuous self-similarity as guiding principle, a holographic correspondence between this process and the phenomenon of parton saturation in high-energy scattering in QCD is proposed. This holographic connection relates strong gravitational physics in the bulk with (nonsupersymmetric) QCD at weak coupling in four dimensions. -
Article: On nonanticommutative N=2 sigma-models in two dimensions
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ABSTRACT: We study nonanticommutative deformations of N=2 two-dimensional Euclidean sigma models. We find that these theories are described by simple deformations of Zumino's Lagrangian and the holomorphic superpotential. Geometrically, this deformation can be interpreted as a fuzziness in target space controlled by the vacuum expectation value of the auxiliary field. In the case of nonanticommutative deformations preserving Euclidean invariance, we find that a continuation of the deformed supersymmetry algebra to Lorentzian signature leads to a rather intriguing central extension of the ordinary (2,2) superalgebra. -
Article: Comments on "Noncommutative Field Theories"
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ABSTRACT: We discuss some aspects of noncommutative quantum field theories obtained from the Seiberg-Witten limit of string theories in the presence of an external B-field. General properties of these theories are studied as well as the phenomenological potential of noncommutative QED. -
Article: Dilute D-Instantons at Finite Temperature
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ABSTRACT: We discuss Dirichlet instanton effects on type IIB string thermodynamics. We review some general properties of dilute D-instanton gases and use the low energy supergravity solutions to define the normalization of the instanton measure, as well as the effects of long range interactions. Thermal singularities in the single instanton sector are due to tachyonic winding modes of Dirichlet open strings. Purely bosonic D-instantons induce in this way hard infrared singularities which ruin the weak coupling expansion in the microcanonical ensemble. Type IIB D-instantons however give smooth contributions at the Hagedorn temperature, and the induced mass and coupling of the axion field are insufficient to change the first order character of the phase transition in the mean field approximation. -
Article: Comments on noncommutative gravity
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ABSTRACT: We study the possibility of obtaining noncommutative gravity dynamics from string theory in the Seiberg-Witten limit. We find that the resulting low-energy theory contains more interaction terms than those proposed in noncommutative deformations of gravity. The role of twisted diffeomorphisms in string theory is studied and it is found that they are not standard physical symmetries. It is argued that this might be the reason why twisted diffeomorphisms are not preserved by string theory in the low energy limit. Twisted gauge transformations are also discussed. -
Article: Large N limit of extremal non-supersymmetric black holes
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ABSTRACT: The large N limit of extremal non-supersymmetric Type-I five-dimensional string black holes is studied from the point of view of D-branes. We find that the agreement between the D-brane and the black hole picture is due to an asymptotic restoration of supersymmetry in the large N limit in which both pictures are compared. In that limit Type-I string perturbation theory is effectively embedded into a Type-IIB perturbation theory with unbroken supersymmetric charges whose presence guarantees the non-renormalization of mass and entropy as the effective couplings are increased. In this vein, we also study the near-horizon geometry of the Type-I black hole using D5-brane probes to find that the low energy effective action for the probe is identical to the corresponding one in the auxiliary Type-IIB theory in the large N limit. -
Article: 12th International Conference on Elastic and Diffractive Scattering : Forward Physics and QCD
