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Steven S. Gubser

Publications and source records attributed to Steven S. Gubser.

At least 127 records · Page 7Linked to original sources
arXiv2000

The Hagedorn transition in non-commutative open string theory

The Hagedorn transition in non-commutative open string theory (NCOS) is relatively simple because gravity decouples. For NCOS theories in no more than five spacetime dimensions, the Hagedorn transition is second order, and the high temperature phase involves long, nearly straight fundamental strings separating from the D-brane on which the NCOS theory is defined. Above five spacetime dimensions interaction effects become important below the Hagedorn temperature. Although this complicates studies of the transition, we believe that the high temperature phase again involves long strings liberated from the bound state.

hep-th↗
arXiv2000

Instability of charged black holes in anti-de Sitter space

We exhibit a tachyonic mode in a linearized analysis of perturbations of large anti-de Sitter Reissner-Nordstrom black holes in four dimensions. In the large black hole limit, and up to a 0.7% discrepancy which is probably round-off error in the numerical analysis, the tachyon appears precisely when the black hole becomes thermodynamically unstable.

hep-th↗
arXiv2000

Curvature Singularities: the Good, the Bad, and the Naked

Necessary conditions are proposed for the admissibility of singular classical solutions with 3+1-dimensional Poincare invariance to five-dimensional gravity coupled to scalars. Finite temperature considerations and examples from AdS/CFT support the conjecture that the scalar potential must remain bounded above for a solution to be physical. Having imposed some restrictions on naked singularities allows us to comment on a recent proposal for solving the cosmological constant problem.

hep-th↗
arXiv2000

AdS/CFT and gravity

The radiation-dominated k=0 FRW cosmology emerges as the induced metric on a codimension one hypersurface of constant extrinsic curvature in the five-dimensional AdS-Schwarzschild solution. That we should get FRW cosmology in this way is an expected result from AdS/CFT in light of recent comments regarding the coupling of gravity to "boundary" conformal field theories. I remark on how this calculation bears on the understanding of Randall and Sundrum's "alternative to compactification." A generalization of the AdS/CFT prescription for computing Green's functions is suggested, and it is shown how gravity emerges from it with a strength G_4 = 2 G_5/L. Some numerical bounds are set on the radius of curvature L of AdS_5. One of them comes from estimating the rate of leakage of visible sector energy into the CFT. That rate is connected via a unitarity relation to deviations from Newton's force law at short distances. The best bound on L obtained in this paper comes from a match to the parameters of string theory. It is L < 1 nm if the string scale is 1 GeV. Higher string scales imply a tighter bound on L.

hep-th↗
arXiv1999

Non-conformal examples of AdS/CFT

Asymptotically anti-de Sitter spacetimes with Poincare invariance along the boundary can describe, via the AdS/CFT correspondence, either relevant deformations of a conformal field theory or non-conformal vacuum states. I consider examples of both types constructed in the framework of five-dimensional gauged supergravity. I explain the proof and motivation of a gravitational ``c-theorem'' which is independent of dimension. I show how one class of examples can be elevated to ten-dimensional geometries involving distributions of parallel D3-branes. For these cases some peculiar properties of two-point functions emerge, and I close with speculations on their physical origin.

hep-th↗
arXiv1999

Dynamics of D-brane Black Holes

We explore the interplay between black holes in supergravity and quantum field theories on the world-volumes of D-branes. A brief summary of black hole entropy calculations for D-brane black holes is followed by a detailed study of particle absorption by black holes whose string theory description involves D-branes intersecting along a string. A conformal field theory with large central charge describes the low-energy excitations of this string. The absorption cross-sections give rise to greybody factors in Hawking radiation processes which are characteristic of conformal field theory at finite temperature. Particle absorption by extremal three-branes is examined next, with particular attention to the implications for supersymmetric gauge theory in four dimensions. A fascinating duality between supergravity and gauge theory emerges from the study of these processes. Fields of supergravity are dual to local operators in the gauge theory. A non-renormalization theorem of N=4 gauge theory helps explain why certain aspects of the duality can be explored perturbatively. Anomalous dimensions of a large class of local operators in the gauge theory are shown to become large at strong 't Hooft coupling, signaling a possible simplification of N=4 gauge theory in this limit.

hep-th↗
arXiv1999

Exact absorption probabilities for the D3-brane

We consider a minimal scalar in the presence of a three-brane in ten dimensions. The linearized equation of motion, which is just the wave equation in the three-brane metric, can be solved in terms of associated Mathieu functions. An exact expression for the reflection and absorption probabilities can be obtained in terms of the characteristic exponent of Mathieu's equation. We describe an algorithm for obtaining the low-energy behavior as a series expansion, and discuss the implications for the world-volume theory of D3-branes.

hep-th↗
arXiv1999

Thermodynamic Stability and Phases of General Spinning Branes

We determine the thermodynamic stability conditions for near-extreme rotating D3, M5, and M2-branes with multiple angular momenta. Critical exponents near the boundary of stability are discussed and compared with a naive field theory model. From a partially numerical computation we conclude that outside the boundary of stability, the angular momentum density tends to become spatially inhomogeneous. Periodic Euclidean spinning brane solutions have been studied as models of QCD. We explain how supersymmetry is restored in the world-volume field theory in the limit of large spin and discuss the hierarchy of energy scales that develops as this limit is approached.

hep-th↗
arXiv1999

Dilaton-driven confinement

We derive a solution of type IIB supergravity which is asymptotic to AdS_5 x S^5, has SO(6) symmetry, and exhibits some of the features expected of geometries dual to confining gauge theories. At the linearized level, the solution differs from pure AdS_5 x S^5 only by a dilaton profile. It has a naked singularity in the interior. Wilson loops follow area law behavior, and there is a mass gap. We suggest a field theory interpretation in which all matter fields of N=4 gauge theory acquire a mass and the infrared theory is confining.

hep-th↗
arXiv1999

Phases of R-charged Black Holes, Spinning Branes and Strongly Coupled Gauge Theories

We study the thermodynamic stability of charged black holes in gauged supergravity theories in D=5, D=4 and D=7. We find explicitly the location of the Hawking-Page phase transition between charged black holes and the pure anti-de Sitter space-time, both in the grand-canonical ensemble, where electric potentials are held fixed, and in the canonical ensemble, where total charges are held fixed. We also find the explicit local thermodynamic stability constraints for black holes with one non-zero charge. In the grand-canonical ensemble, there is in general a region of phase space where neither the anti-de Sitter space-time is dynamically preferred, nor are the charged black holes thermodynamically stable. But in the canonical ensemble, anti-de Sitter space-time is always dynamically preferred in the domain where black holes are unstable. We demonstrate the equivalence of large R-charged black holes in D=5, D=4 and D=7 with spinning near-extreme D3-, M2- and M5-branes, respectively. The mass, the charges and the entropy of such black holes can be mapped into the energy above extremality, the angular momenta and the entropy of the corresponding branes. We also note a peculiar numerological sense in which the grand-canonical stability constraints for large charge black holes in D=4 and D=7 are dual, and in which the D=5 constraints are self-dual.

hep-th↗
arXiv1998

Thermodynamics of spinning D3-branes

Spinning black three-branes in type IIB supergravity are thermodynamically stable up to a critical value of the angular momentum density. Inside the region of thermodynamic stability, the free energy from supergravity is roughly reproduced by a naive model based on free N=4 super-Yang-Mills theory on the world-volume. The field theory model correctly predicts a limit on angular momentum density, but near this limit it does not reproduce the critical exponents one can compute from supergravity. Analogies with Bose condensation and modified matrix models are discussed, and a mean field theory improvement of the naive model is suggested which corrects the critical exponents.

hep-th↗
arXiv1998

Baryons and Domain Walls in an N = 1 Superconformal Gauge Theory

Coincident D3-branes placed at a conical singularity are related to string theory on $AdS_5\times X_5$, for a suitable five-dimensional Einstein manifold $X_5$. For the example of the conifold, which leads to $X_5=T^{1,1}=(SU(2)\times SU(2))/U(1)$, the infrared limit of the theory on $N$ D3-branes was constructed recently. This is ${\cal N}=1$ supersymmetric $SU(N)\times SU(N)$ gauge theory coupled to four bifundamental chiral superfields and supplemented by a quartic superpotential which becomes marginal in the infrared. In this paper we consider D3-branes wrapped over the 3-cycles of $T^{1,1}$ and identify them with baryon-like chiral operators built out of products of $N$ chiral superfields. The supergravity calculation of the dimensions of such operators agrees with field theory. We also study the D5-brane wrapped over a 2-cycle of $T^{1,1}$, which acts as a domain wall in $AdS_5$. We argue that upon crossing it the gauge group changes to $SU(N)\times SU(N+1)$. This suggests a construction of supergravity duals of ${\cal N}=1$ supersymmetric $SU(N_1)\times SU(N_2)$ gauge theories.

hep-th↗
arXiv1998

Coupling Constant Dependence in the Thermodynamics of N=4 Supersymmetric Yang-Mills Theory

The free energy of the maximally supersymmetric SU(N) gauge theory at temperature T is expected to scale, in the large N limit, as N^2 T^4 times a function of the 't Hooft coupling, f(g_{YM}^2 N). In the strong coupling limit the free energy has been deduced from the near-extremal 3-brane geometry, and its normalization has turned out to be 3/4 times that found in the weak coupling limit. In this paper we calculate the leading correction to this result in inverse powers of the coupling, which originates from the R^4 terms in the tree level effective action of type IIB string theory. The correction to 3/4 is positive and of order (g_{YM}^2 N)^{-3/2}. Thus, f(g_{YM}^2 N) increases as the 't Hooft coupling is decreased, in accordance with the expectation that it should be approaching 1 in the weak coupling limit. We also discuss similar corrections for other conformal theories describing coincident branes. In particular, we suggest that the coupling-independence of the near extremal entropy for D1-branes bound to D5-branes is related to the vanishing of the Weyl tensor of AdS_3\times S^3.

hep-th↗
arXiv1998

Einstein manifolds and conformal field theories

In light of the AdS/CFT correspondence, it is natural to try to define a conformal field theory in a large N, strong coupling limit via a supergravity compactification on the product of an Einstein manifold and anti-de Sitter space. We consider the five-dimensional manifolds T^{pq} which are coset spaces (SU(2) x SU(2))/U(1). The central charge and a part of the chiral spectrum are calculated, respectively, from the volume of T^{pq} and the spectrum of the scalar laplacian. Of the manifolds considered, only T^{11} admits any supersymmetry: it is this manifold which characterizes the supergravity solution corresponding to a large number of D3-branes at a conifold singularity, discussed recently in hep-th/9807080. Through a field theory analysis of anomalous three point functions we are able to reproduce the central charge predicted for the T^{11} theory by supergravity: it is 27/32 of the central charge of the N=2 Z_2 orbifold theory from which it descends via an RG flow.

hep-th↗
arXiv1998

Scalar Absorption and the Breaking of the World Volume Conformal Invariance

We investigate a version of fixed scalars for non-dilatonic branes which correspond to dilatations of the brane world-volume. We obtain a cross-section whose world-volume interpretation falls out naturally from an investigation of the breaking of conformal invariance by the irrelevant Born-Infeld corrections to Yang-Mills theory. From the same irrelevant world-volume operator we obtain the leading correction to the cross-sections of minimal scalars. This correction can be obtained in supergravity via an improved matching of inner and outer solutions to the minimal wave equation.

hep-th↗
arXiv1997

Absorption of photons and fermions by black holes in four dimensions

The absorption of photons and fermions into four-dimensional black holes is described by equations which in certain cases can be analyzed using dyadic index techniques. The resulting absorption cross-sections for near-extremal black holes have a form at low energies suggestive of the effective string model. A coupling to the effective string is proposed for spin-0 and spin-1/2 fields of pure N=4 supergravity which respects the unbroken supersymmetry of extreme black holes and correctly predicts dilaton, axion, and fermion cross-sections up to an overall normalization.

hep-th↗
arXiv1997

Can the effective string see higher partial waves?

The semi-classical cross-sections for arbitrary partial waves of ordinary scalars to fall into certain five-dimensional black holes have a form that seems capable of explanation in terms of the effective string model. The kinematics of these processes is analyzed in detail on the effective string and is shown to reproduce the correct functional form of the semi-classical cross-sections. But it is necessary to choose a peculiar value of the effective string tension to obtain the correct scaling properties. Furthermore, the assumptions of locality and statistics combine to forbid the effective string from absorbing more than a finite number of partial waves. The relation of this limitation to cosmic censorship is discussed.

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