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Andreas Karch

Publications and source records attributed to Andreas Karch.

At least 91 records · Page 5Linked to original sources
arXiv2014

The holographic dual of a Hawking pair has a wormhole

In previous work, two of us constructed the holographic dual of a single Einstein-Podolsky-Rosen (EPR) pair in maximally supersymmetric Yang-Mills theory. Here we extend that work in two directions. First, we use a Randall-Sundrum brane to couple the entangled pair to dynamical gravity. Second, we consider the entangled pair in the background of a black hole with the particles on opposite sides of the horizon, turning the EPR pair into a Hawking pair. We give general arguments that ER=EPR should be understood as a duality between two equivalent descriptions of the same physical reality.

hep-th↗
arXiv2014

Generalized gravitational entropy of probe branes: flavor entanglement holographically

The notion of generalized gravitational entropy introduced by Lewkowycz and Maldacena allows, via the AdS/CFT correspondence, to calculate CFT entanglement entropies. We adapt the method to the case where flavor branes are present and treated in the probe approximation. This allows to calculate the leading flavor correction to the CFT entanglement entropy from the on-shell action of the probe, while dealing with the backreaction is avoided entirely and from the outset. As an application we give concise derivations for the contribution of massless and massive flavor degrees of freedom to the entanglement entropy in N=4 SYM theory.

hep-th↗
arXiv2014

Minimal area submanifolds in AdS x compact

We describe the asymptotic behavior of minimal area submanifolds in product spacetimes of an asymptotically hyperbolic space times a compact internal manifold. In particular, we find that unlike the case of a minimal area submanifold just in an asymptotically hyperbolic space, the internal part of the boundary submanifold is constrained to be itself a minimal area submanifold. For applications to holography, this tells us what are the allowed "flavor branes" that can be added to a holographic field theory. We also give a compact geometric expression for the spectrum of operator dimensions associated with the slipping modes of the submanifold in the internal space. We illustrate our results with several examples, including some that haven't appeared in the literature before.

hep-th↗
arXiv2014

Charged black holes in Horava gravity

We explore static spherically symmetric black hole solutions allowing a bulk U(1) vector field in the khronometric formulation of Horava gravity by way of Einstein-Aether. We examine analytic solutions and study numerical results in the limit that the khronon does not backreact on the metric.

hep-th↗
arXiv2013

Matrix Flavor Brane and Dual Wilson Line

We study a novel non-Abelian matrix configuration of probe D-branes in AdS5. This configuration gives rise to a new D-brane phenomenon related to the known "Myers effect" in the context of holography. It is dual to a deformation of the field theory by a Wilson line threaded fermion bilinear. We study the two point function of these short Wilson lines from both the non-Abelian DBI action and a classical string world sheet calculation and identify the region where they agree. We also study a related configuration where the non-Abelian nature of the embedding functions is enhanced by a background flux as in the Myers effect.

hep-th↗
arXiv2013

An ansatz for one dimensional steady state configurations

We conjecture a universal formula for the heat current of a steady state connecting two asymptotic equilibrium systems in d-dimensional conformal field theories. Our proposal is verified by comparing it to exact expressions in 1+1 dimensions and linear hydrodynamics as well as numerical simulations in an Israel-Stewart like theory of second order viscous hydrodynamics.

hep-th↗
arXiv2013

Entanglement Entropy for Probe Branes

We give a prescription for calculating the entanglement entropy in holographic probe brane systems by systematically taking the leading order backreaction of the probe brane into account. We find a simple compact double integral formula, which is insensitive to many details of the backreaction, most notably the internal space or the non-metric fields sourced by the probe. We validate our method by comparing to exact results in solvable toy models. We also determine the entanglement entropies for a sphere and a strip in the top-down D3/D7 and D3/D5 system. For the sphere the entanglement entropy has also been obtained by other methods and we find perfect agreement.

hep-th↗
arXiv2013

Higher-spin realization of a dS static patch/cut-off CFT correspondence

We derive a holographic relation for the dS static patch with the dual field theory defined on the observer horizon. The starting point is the duality of higher-spin theory on AdS_4 and the O(N) vector model. We build on a similar analytic continuation as used recently to obtain a realization of dS/CFT, and adapt it to the static patch. The resulting duality relates higher-spin theory on the dS_4 static patch to a cut-off CFT on the cylinder RxS^2. The construction permits a derivation of the finite thermodynamic entropy associated to the horizon of the static patch from the dual field theory. As a further brick we recover the spectrum of quasinormal frequencies from the correlation functions of the boundary theory. In the last part we incorporate the dS/dS correspondence as an independent proposal for holography on dS and show that a concrete realization can be obtained by similar reasoning.

hep-th↗
arXiv2013

The holographic dual of an EPR pair has a wormhole

We construct the holographic dual of two colored quasiparticles in maximally supersymmetric Yang-Mills theory entangled in a color singlet EPR pair. In the holographic dual the entanglement is encoded in a geometry of a non-traversable wormhole on the worldsheet of the flux tube connecting the pair. This gives a simple example supporting the recent claim by Maldacena and Susskind that EPR pairs and non-traversable wormholes are equivalent descriptions of the same physics.

hep-th↗
arXiv2012

Models of three-dimensional fractional topological insulators

Time-reversal invariant three-dimensional topological insulators can be defined fundamentally by a topological field theory with a quantized axion angle theta of zero or pi. It was recently shown that fractional quantized values of theta are consistent with time-reversal invariance if deconfined, gapped, fractionally charged bulk excitations appear in the low-energy spectrum due to strong correlation effects, leading to the concept of a fractional topological insulator. These fractionally charged excitations are coupled to emergent gauge fields which ensure that the microscopic degrees of freedom, the original electrons, are gauge-invariant objects. A first step towards the construction of microscopic models of fractional topological insulators is to understand the nature of these emergent gauge theories and their corresponding phases. In this work, we show that low-energy effective gauge theories of both Abelian or non-Abelian type are consistent with a fractional quantized axion angle if they admit a Coulomb phase or a Higgs phase with gauge group broken down to a discrete subgroup. The Coulomb phases support gapless but electrically neutral bulk excitations while the Higgs phases are fully gapped. The Higgs and non-Abelian Coulomb phases exhibit multiple ground states on boundaryless spatial 3-manifolds with nontrivial first homology, while the Abelian Coulomb phase has a unique ground state. The ground state degeneracy receives an additional contribution on manifolds with boundary due to the induced boundary Chern-Simons term.

cond-mat.str-el↗
arXiv2012

Non-relativistic holography from Horava gravity

Many non-relativistic Quantum Field Theories with conserved particle number share a common set of symmetries: time dependent spatial diffeomorphisms acting on the background metric and U(1) invariance acting on the background fields which couple to particle number. Here we use these symmetries to deduce a gravity dual for any such theory in terms of a non-relativistic theory of gravity, a variant of Horava gravity. This duality allows the extension of holography to generic non-relativistic field theories. As Horava gravity is presumed to be a consistent quantum theory, this duality also allows holography to move beyond the limit of a large number of colors, in principle. In the case when the field theory is conformally invariant, we prove that our proposal reproduces the form of the two point function demanded by this symmetry.

hep-th↗
arXiv2012

Hyperscaling-Violation on Probe D-Branes

For the field theories dual to D3/D7- and D3/D5-brane systems we find non-relativistic finite density fixed points exhibiting a violation of hyperscaling. This violation is measured by the critical exponent $θ=1$ while the dynamical critical exponent is $z=2$. At zero temperature we compute the thermodynamic potentials, the speed of normal sound, and the speed of zero sound for both these massive D3/D(2n+1)-brane systems near their non-relativistic fixed points. Moreover, we determine the first correction to the free energy for small temperatures yielding the critical exponents $α$ and $ν$.

hep-th↗
arXiv2012

Novel Solutions of Finite-Density D3/D5 Probe Brane System and Their Implications for Stability

In this article we present a novel set of solutions of the probe brane system consisting of Nf-D5 probe branes embedded in the near-horizon geometry generated by Nc-D3 branes, with the D5 worldvolume U(1) gauge fields turned on. Our system is holographically dual to a supersymmetric defect field theory at finite density in non-trivial vacua. We find that a large class of vacua turns out to satisfy a no-force condition, even with supersymmetry explicitly broken by the finite density; our solutions include configuration in which charge separates from the horizon and is instead carried by probe branes outside the horizon. The free energy is lowered in this process. Whether this corresponds to a genuine instability of the finite-density probe brane system remains to be seen.

hep-th↗
arXiv2012

SL(2,Z) Action on AdS/BCFT and Hall Conductivities

We study the response of a conserved current to external electromagnetic fields in a holographic system with boundaries using the recently proposed AdS/BCFT (boundary conformal field theory) framework. This, in particular, allows us to extract the Hall current, the Hall conductivity, plus some potentially novel transport coefficients, and relations among them. We also analyze the action of SL(2,Z) duality in the gravity bulk, which acts non-trivially on the conductivity of the BCFT. Finally we consider a type IIA string theory embedding of our setup.

hep-th↗
arXiv2012

Holographic realization of large-Nc orbifold equivalence with non-zero chemical potential

Recently, it has been suggested that large-Nc orbifold equivalences may be applicable to certain theories with chemical potentials, including QCD, in certain portions of their phase diagram. When valid, such an equivalence offers the possibility of relating large-Nc QCD at non-zero baryon chemical potential, a theory with a complex fermion determinant, to a related theory whose fermion determinant is real and positive. In this paper, we provide a test of this large Nc equivalence using a holographic realization of a supersymmetric theory with baryon chemical potential and a related theory with isospin chemical potential. We show that the two strongly-coupled, large-Nc theories are equivalent in a large region of the phase diagram.

hep-th↗
arXiv2011

Energy Loss Calculations of Moving Defects for General Holographic Metrics

We extend the ideas of using AdS/CFT to calculate energy loss of extended defects in strongly coupled systems to general holographic metrics. We find the equations of motion governing uniformly moving defects of various dimension and determine the corresponding energy loss rates in terms of the metric coefficients. We apply our formulae to the specific examples of both bulk geometries created by general Dp-branes, as well as to holographic superfluids. For the Dp-branes, we find that the energy loss of our defect, in addition to the expected quadratic dependence on velocity, depends on velocity only via an effective blueshifted temperature - despite the existence of a microscopic length scale in the theory. We also find, for a certain value of p and dimension of the defect, that the energy loss has no dependence on temperature or velocity other than the aforementioned quadratic dependence on velocity. For the superfluid example, we find agreement with previous results on the existence of a cutoff velocity, below which the probe experiences no drag force. For both examples we can easily extend the equations of motion and energy loss to defects of larger dimension.

hep-th↗
arXiv2011

Generating new dualities through the orbifold equivalence: a demonstration in ABJM and four-dimensional quivers

We show that the recently proposed large $N$ equivalence between ABJM theories with Chern-Simons terms of different rank and level, U(N_1)_{k_1}\times U(N_1)_{-k_1} and U(N_2)_{k_2}\times U(N_2)_{-k_2}, but the same value of N' =N_1 k_1=N_2 k_2, can be explained using planar equivalence in the mirror duals. The combination of S-dualities and orbifold equivalence can be applied to other cases as well, with very appealing results. As an example we show that two different quiver theories with k nodes can be easily shown to be Seiberg dual through the orbifold equivalence, but it requires order k^2 steps to give a proof when Seiberg duality is performed node by node.

hep-th↗