arXiv subjects

Per Kraus

Publications and source records attributed to Per Kraus.

At least 73 records · Page 4Linked to original sources

arXiv2009

Gravity Dual of a Quantum Hall Plateau Transition

We show how to model the transition between distinct quantum Hall plateaus in terms of D-branes in string theory. A low energy theory of 2+1 dimensional fermions is obtained by considering the D3-D7 system, and the plateau transition corresponds to moving the branes through one another. We study the transition at strong coupling using gauge/gravity duality and the probe approximation. Strong coupling leads to a novel kind of plateau transition: at low temperatures the transition remains discontinuous due to the effects of dynamical symmetry breaking and mass generation, and at high temperatures is only partially smoothed out.

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arXiv2009

Nonlinear Magnetohydrodynamics from Gravity

We apply the recently established connection between nonlinear fluid dynamics and AdS gravity to the case of the dyonic black brane in AdS_4. This yields the equations of fluid dynamics for a 2+1 dimensional charged fluid in a background magnetic field. We construct the gravity solution to second order in the derivative expansion. From this we find the fluid dynamical stress tensor and charge current to second and third order in derivatives respectively, along with values for the associated transport coefficients.

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arXiv2008

Precision Entropy of Spinning Black Holes

We construct spinning black hole solutions in five dimensions that take into account the mixed gauge-gravitational Chern-Simons term and its supersymmetric completion. The resulting entropy formula is discussed from several points of view. We include a Taub-NUT base space in order to test recent conjectures relating 5D black holes to 4D black holes and the topological string. Our explicit results show that certain charge shifts have to be taken into account for these relations to hold. We also compute corrections to the entropy of black rings in terms of near horizon data.

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arXiv2008

Quantum Hall Effect in AdS/CFT

Drawing on the connection with superconductivity, we give a simple AdS realization of the quantum Hall effect. The theory includes a statistical gauge field with a Chern-Simons term, in analogy with effective field theory models of the QHE.

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arXiv2008

String Theory Effects on Five-Dimensional Black Hole Physics

We review recent developments in understanding quantum/string corrections to BPS black holes and strings in five-dimensional supergravity. These objects are solutions to the effective action obtained from M-theory compactified on a Calabi-Yau threefold, including the one-loop corrections determined by anomaly cancellation and supersymmetry. We introduce the off-shell formulation of this theory obtained through the conformal supergravity method and review the methods for investigating supersymmetric solutions. This leads to quantum/string corrected attractor geometries, as well as asymptotically flat black strings and spinning black holes. With these solutions in hand, we compare our results with analogous studies in four-dimensional string-corrected supergravity, emphasizing the distinctions between the four and five dimensional theories.

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arXiv2007

Stringy NJL and Gross-Neveu models at finite density and temperature

Nonlocal stringy versions of the Nambu-Jona-Lasinio and Gross-Neveu models arise in a certain limit of holographic QCD. We analyze the phase structure at finite density and temperature at strong coupling in terms of probe branes in the gravity dual. Comparison with the phase structure of the local field theory models shows qualitative agreement with some aspects, and disagreement with others. Finally, we explain how to construct the Landau potentials for these models by taking the probe branes off-shell.

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arXiv2007

Fundamental Strings, Holography, and Nonlinear Superconformal Algebras

We discuss aspects of holography in the AdS_3 \times S^p near string geometry of a collection of straight fundamental heterotic strings. We use anomalies and symmetries to determine general features of the dual CFT. The symmetries suggest the appearance of nonlinear superconformal algebras, and we show how these arise in the framework of holographic renormalization methods. The nonlinear algebras imply intricate formulas for the central charge, and we show that in the bulk these correspond to an infinite series of quantum gravity corrections. We also makes some comments on the worldsheet sigma-model for strings on AdS_3\times S^2, which is the holographic dual geometry of parallel heterotic strings in five dimensions.

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arXiv2007

5D Black Holes and Strings with Higher Derivatives

We find asymptotically flat black hole and string solutions to 5D supergravity in the presence of higher derivative terms. In some cases, including the fundamental heterotic string solution, the higher derivative terms smooth out naked singularities into regular geometries carrying zero entropy. We also compute corrections to the entropy of 5D Calabi-Yau black holes, and discuss the relation to previous results.

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arXiv2007

5D Attractors with Higher Derivatives

We analyze higher derivative corrections to attractor geometries in five dimensions. We find corrected AdS_3xS^2 geometries by solving the equations of motion coming from a recently constructed four-derivative supergravity action in five dimensions. The result allows us to explicitly verify a previous anomaly based derivation of the AdS_3 central charges of this theory. Also, by dimensional reduction we compare our results with those of the 4D higher derivative attractor, and find complete agreement.

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arXiv2006

Lectures on black holes and the AdS_3 / CFT_2 correspondence

We present a detailed discussion of AdS_3 black holes and their connection to two-dimensional conformal field theories via the AdS/CFT correspondence. Our emphasis is on deriving refined versions of black hole partition functions, that include the effect of higher derivative terms in the spacetime action as well as non-perturbative effects. We include background material on gravity in AdS_3, in the context of holographic renormalization.

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arXiv2006

Generating Charge from Diffeomorphisms

We unravel some subtleties involving the definition of sphere angular momentum charges in AdS_q \times S^p spacetimes, or equivalently, R-symmetry charges in the dual boundary CFT. In the AdS_3 context, it is known that charges can be generated by coordinate transformations, even though the underlying theory is diffeomorphism invariant. This is the bulk version of spectral flow in the boundary CFT. We trace this behavior back to special properties of the p-form field strength supporting the solution, and derive the explicit formulas for angular momentum charges. This analysis also reveals the higher dimensional origin of three dimensional Chern-Simons terms and of chiral anomalies in the boundary theory.

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arXiv2006

Partition functions and elliptic genera from supergravity

We develop the spacetime aspects of the computation of partition functions for string/M-theory on AdS(3) xM. Subleading corrections to the semi-classical result are included systematically, laying the groundwork for comparison with CFT partition functions via the AdS(3)/CFT(2) correspondence. This leads to a better understanding of the "Farey tail" expansion of Dijkgraaf et. al. from the point of view of bulk physics. Besides clarifying various issues, we also extend the analysis to the N=2 setting with higher derivative effects included.

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arXiv2005

R^2 Corrections to Black Ring Entropy

Recently, Guica, Huang, Li, and Strominger considered an R^2 correction to the entropy of a black ring, and found a mismatch between supergravity and the CFT. However, such a comparison should take into account the subtle distinction between the asymptotic charges of the black ring and the charges entering the CFT description. We show that using the correct charges yields perfect agreement.

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arXiv2005

Holographic Gravitational Anomalies

In the AdS/CFT correspondence one encounters theories that are not invariant under diffeomorphisms. In the boundary theory this is a gravitational anomaly, and can arise in 4k+2 dimensions. In the bulk, there can be gravitational Chern-Simons terms which vary by a total derivative. We work out the holographic stress tensor for such theories, and demonstrate agreement between the bulk and boundary. Anomalies lead to novel effects, such as a nonzero angular momentum for global AdS(3). In string theory such Chern-Simons terms are known with exact coefficients. The resulting anomalies, combined with symmetries, imply corrections to the Bekenstein-Hawking entropy of black holes that agree exactly with the microscopic counting.

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arXiv2005

Massless black holes and black rings as effective geometries of the D1-D5 system

We compute correlation functions in the AdS/CFT correspondence to study the emergence of effective spacetime geometries describing complex underlying microstates. The basic argument is that almost all microstates of fixed charges lie close to certain "typical" configurations. These give a universal response to generic probes, which is captured by an emergent geometry. The details of the microstates can only be observed by atypical probes. We compute two point functions in typical ground states of the Ramond sector of the D1-D5 CFT, and compare with bulk two-point functions computed in asymptotically AdS_3 geometries. For large central charge (which leads to a good semiclassical limit), and sufficiently small time separation, a typical Ramond ground state of vanishing R-charge has the M=0 BTZ black hole as its effective description. At large time separation this effective description breaks down. The CFT correlators we compute take over, and give a response whose details depend on the microstate. We also discuss typical states with nonzero R-charge, and argue that the effective geometry should be a singular black ring. Our results support the argument that a black hole geometry should be understood as an effective coarse-grained description that accurately describes the results of certain typical measurements, but breaks down in general.

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arXiv2005

Microscopic Black Hole Entropy in Theories with Higher Derivatives

We discuss higher derivative corrections to black hole entropy in theories that allow a near horizon AdS_3 x X geometry. In arbitrary theories with diffeomorphism invariance we show how to obtain the spacetime central charge in a simple way. Black hole entropy then follows from the Euclidean partition function, and we show that this gives agreement with Wald's formula. In string theory there are certain diffeomorphism anomalies that we exploit. We thereby reproduce some recent computations of corrected entropy formulas, and extend them to the nonextremal, nonsupersymetric context. Examples include black holes in M-theory on K3 x T^2, whose entropy reproduces that of the perturbative heterotic string with both right and left movers excited and angular momentum included. Our anomaly based approach also sheds light on why exact results have been obtained in four dimensions while ignoring R^4 type corrections.

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arXiv2005

Microstates of the D1-D5-KK System

We find supergravity solutions corresponding to all U(1) x U(1) invariant chiral primaries of the D1-D5-KK system. These solutions are 1/8 BPS, carry angular momentum, and are asymptotically flat in the 3+1 dimensional sense. They can be thought of as representing the ground states of the four dimensional black hole constructed from the D1-D5-KK-P system. Demanding the absence of unphysical singularities in our solutions determines all free parameters, and gives precise agreement with the quantum numbers expected from the CFT point of view. The physical mechanism behind the smoothness of the solutions is that the D1-branes and D5-branes expand into a KK-monopole supertube in the transverse space of the original KK-monopole.

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arXiv2005

Black Rings in Taub-NUT

We construct the most generic three-charge, three-dipole-charge, BPS black-ring solutions in a Taub-NUT background. These solutions depend on seven charges and six moduli, and interpolate between a four-dimensional black hole and a five-dimensional black ring. They are also instrumental in determining the correct microscopic description of the five-dimensional BPS black rings.

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