arXiv subjects

Alberto Guijosa

Publications and source records attributed to Alberto Guijosa.

At least 19 recordsLinked to original sources

arXiv2025

de Sitter Holography and Carrollian Brane Theories

It was discovered in recent months that the anti-de Sitter (AdS) backgrounds involved in all familiar top-down examples of AdS/CFT duality follow from applying a transverse nonrelativistic brane limit to string/M theory on (asymptotically) flat spacetime. In this note we show that an exactly analogous statement holds for de Sitter (dS) backgrounds relevant to particular instances of dS/CFT duality, which are obtained via a longitudinal Carrollian brane limit. This statement makes direct contact with the holographic duality inferred by Hull via temporal T-duality.

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arXiv2025

On the Underlying Nonrelativistic Nature of Relativistic Holography

Over the past quarter century, considerable effort has been invested in the study of nonrelativistic (NR) string theory, its U-dual NR brane theories, and their geometric foundations in (generalized) Newton-Cartan geometry. Many interesting results have been obtained, both for their intrinsic value and in the hope that they hold useful lessons for relativistic string/M theory. By synthesizing two strands of recent developments (especially, arXiv:2312.13243 and arXiv:2410.03591), we argue that this hope has already come to fruition, because standard, relativistic holography can now be recognized as a statement within a corresponding nonrelativistic brane theory. Our main conclusions are general, but in the familiar example of D3-brane based holography, they read as follows: (i) N=4 SYM is exactly the worldvolume theory of D3-branes within `NR D3-brane theory'; (ii) AdS_5*S^5 is exactly the corresponding RR black 3-brane, and includes an asymptotically flat-Newton-Cartan region; (iii) AdS/CFT duality is precisely synonymous with black-brane/D-brane (i.e., closed-string/open-string) duality within NR D3-brane theory; (iv) Newton-Cartan geometry is the underlying structure upon which entanglement of the D3-brane degrees of freedom builds relativistic spacetime.

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arXiv2024

Extrinsic Holographic Renormalization for a Scalar Field

In the context of the holographic correspondence, we introduce a purely extrinsic renormalization prescription, exemplified with the case of a minimally-coupled scalar field in AdS space. The counterterms depend only on the field and its radial derivatives. This would seem to conflict with the Dirichlet variational principle, but we show that consistency follows from the fact that the asymptotic structure of asymptotically locally AdS spacetimes requires not only the leading, but also all of the subleading non-normalizable modes to be fixed as a boundary condition. Crucially, as seen from a path integral definition of the bulk partition function involved in the standard GKPW formula, this condition is valid away from the saddle. We find that the extrinsic renormalization prescription is maximally efficient when the scalar field is massless, which is suggestive of a connection with the Kounterterm method for renormalization of pure gravity.

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arXiv2024

Asymptotically Nonrelativistic String Backgrounds

In recent years, interesting curved-space extensions of nonrelativistic (NR) string theory have been very actively pursued, where the background has a structure that is a stringy generalization of Newton-Cartan geometry. Here we show that the natural black branes of the NR theory, sourced by the familiar repertoire of stringy objects, generally have a different structure. The black string is our main example. We find that the source distorts the background significantly, generating a large throat within which physics is in fact relativistic. It is only far away from the throat that the background approaches the string Newton-Cartan form. We show that exactly the same is true for the longitudinal RR-charged black brane. On the other hand, the transverse RR-charged black brane turns out to have a proper string Newton-Cartan structure everywhere, not just asymptotically.

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arXiv2023

Geometry from D-branes in Nonrelativistic String Theory

Nonrelativistic (NR) string theory was discovered as a framework that underlies and unifies the various noncommutative open string (NCOS) theories, which were originally envisioned as surprising exceptions to the maxim that all string theories are gravitational in nature. In that view, the fact that NCOS has a gravitational dual was believed to be directly analogous to the AdS/CFT correspondence. When NCOS theories were understood to be simply the particular classes of states of the underlying NR theory that include longitudinal D-branes, it was suggested that the duality between NCOS and the corresponding gravitational theory is not an instance of gauge/gravity-type duality, but of open-string/closed-string duality between D-branes and black branes. The present paper provides direct evidence in support of this perspective, by starting from a stack of D-branes in NR string theory and deriving the long-distance profile of the curved geometry in the corresponding black brane.

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arXiv2022

Holographic Coarse-Graining: Correlators from the Entanglement Wedge and Other Reduced Geometries

There is some tension between two well-known ideas in holography. On the one hand, subregion duality asserts that the reduced density matrix associated with a limited region of the boundary theory is dual to a correspondingly limited region in the bulk, known as the entanglement wedge. On the other hand, correlators that in the boundary theory can be computed solely with that density matrix are calculated in the bulk via the GKPW or BDHM prescriptions, which require input from beyond the entanglement wedge. We show that this tension is resolved by recognizing that the reduced state is only fully identified when the entanglement wedge is supplemented with a specific infrared boundary action, associated with an end-of-the-world brane. This action is obtained by coarse-graining through a variant of Wilsonian integration, a procedure that we call holographic rememorization, which can also be applied to define other reduced density or transition matrices, as well as more general reduced partition functions. We find an interesting connection with AdS/BCFT, and, in this context, we are led to a simple example of an equivalence between an ensemble of theories and a single theory, as discussed in recent studies of the black hole information problem.

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arXiv2019

Renormalized AdS gravity and holographic entanglement entropy of even-dimensional CFTs

We derive a general formula for renormalized entanglement entropy in even dimensional CFTs holographically dual to Einstein gravity in one dimension higher. In order to renormalize, we adapt the Kounterterm method to asymptotically locally AdS manifolds with conical singularities. On the gravity side, the computation considers extrinsic counterterms and the use of the replica trick a la Lewkowycz-Maldacena. The boundary counterterm B_d is shown to satisfy a key property, in direct analogy to the Euler density: when evaluated on a conically singular manifold, it decomposes into a regular part plus a codimension-2 version of itself located at the conical singularity. The renormalized entropy thus obtained is shown to correspond to the universal part of the holographic entanglement entropy, which for spherical entangling surfaces is proportional to the central charge a that is the subject of the a-theorem. We also review and elucidate various aspects of the Kounterterm approach, including in particular its full compatibility with the Dirichlet condition for the metric at the conformal boundary, that is of standard use in holography.

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arXiv2018

Entanglement Wedge Reconstruction and Entanglement of Purification

In the holographic correspondence, subregion duality posits that knowledge of the mixed state of a finite spacelike region of the boundary theory allows full reconstruction of a specific region of the bulk, known as the entanglement wedge. This statement has been proven for local bulk operators. In this paper, specializing first for simplicity to a Rindler wedge of AdS$_3$, we find that generic curves within the wedge are in fact not fully reconstructible with entanglement entropies in the corresponding boundary region, even after using the most general variant of hole-ography, which was recently shown to suffice for reconstruction of arbitrary spacelike curves in the Poincare patch. This limitation is an analog of the familiar phenomenon of entanglement shadows, which we call 'entanglement shade'. We overcome it by showing that the information about the nonreconstructible curve segments is encoded in a slight generalization of the concept of entanglement of purification, whose holographic dual has been discussed very recently. We introduce the notion of 'differential purification', and demonstrate that, in combination with differential entropy, it enables the complete reconstruction of all spacelike curves within an arbitrary entanglement wedge in any 3-dimensional bulk geometry.

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arXiv2018

What's the Point? Hole-ography in Poincare AdS

In the context of the AdS/CFT correspondence, we study bulk reconstruction of the Poincare wedge of AdS$_3$ via hole-ography, i.e., in terms of differential entropy of the dual CFT$_2$. Previous work had considered the reconstruction of closed or open spacelike curves in global AdS, and of infinitely extended spacelike curves in Poincare AdS that are subject to a periodicity condition at infinity. Working first at constant time, we find that a closed curve in Poincare is described in the CFT by a family of intervals that covers the spatial axis at least twice. We also show how to reconstruct open curves, points and distances, and obtain a CFT action whose extremization leads to bulk points. We then generalize all of these results to the case of curves that vary in time, and discover that generic curves have segments that cannot be reconstructed using the standard hole-ographic construction. This happens because, for the nonreconstructible segments, the tangent geodesics fail to be fully contained within the Poincare wedge. We show that a previously discovered variant of the hole-ographic method allows us to overcome this challenge, by reorienting the geodesics touching the bulk curve to ensure that they all remain within the wedge. Our conclusion is that all spacelike curves in Poincare AdS can be completely reconstructed with CFT data, and each curve has in fact an infinite number of representations within the CFT.

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arXiv2016

QCD, with Strings Attached

In the nearly twenty years that have elapsed since its discovery, the gauge-gravity correspondence has become established as an efficient tool to explore the physics of a large class of strongly-coupled field theories. A brief overview is given here of its formulation and a few of its applications, emphasizing attempts to emulate aspects of the strong-coupling regime of quantum chromodynamics (QCD). To the extent possible, the presentation is self-contained, and in particular, it does not presuppose knowledge of string theory.

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arXiv2014

Branes from Light: Embeddings and Energetics for Symmetric $k$-Quarks in $\mathcal{N}=4$ SYM

We construct the D3-brane dual to a $k$-quark of $\mathcal{N}=4$ super-Yang-Mills theory in the totally symmetric representation of $SU(N)$, undergoing arbitrary motion. Our method of construction generalizes previous work by Mikhailov, and proceeds by shooting light rays inward from the anti-de Sitter boundary, to trace out the brane embedding. We expect this method to have wider relevance, and provide evidence for this by showing that it correctly reproduces the known D5-brane embeddings dual to totally antisymmetric $k$-quarks. As an application of our solutions, we compute the energy of the D3-brane and extract from it the $k$-quark's intrinsic energy and rate of radiation. The result matches expectations based on previous calculations, and makes contact with the exact Bremsstrahlung function for the fundamental representation.

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arXiv2014

Radiation and a dynamical UV/IR connection in AdS/CFT

We compute holographically the expectation value of the energy density sourced, in a strongly-coupled CFT, by a quark with large but finite mass (or equivalently, small but finite Compton radius) undergoing arbitrary motion. The resulting gluonic profile has two surprising features in the far region. First, besides the expected radiation, it contains a component that is attributable to the `intrinsic' or `near' field of the quark, and nevertheless falls off as the square of the distance. Second, even at distances much larger than the size of the quark, it differs from the profile set up by a pointlike quark. We explain how this second feature provides a useful case study for the UV/IR connection in a dynamical setting. We also examine some specific sample trajectories, including uniform circular motion and harmonic oscillation, where features such as the extent of the region with negative energy are found to vary with the quark mass.

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arXiv2013

Holographic EPR Pairs, Wormholes and Radiation

As evidence for the ER=EPR conjecture, it has recently been observed that the string that is holographically dual to an entangled quark-antiquark pair separating with (asymptotically) uniform acceleration has a wormhole on its worldsheet. We point out that a two-sided horizon and a wormhole actually appear for much more generic quark-antiquark trajectories, which is consistent with the fact that the members of an EPR pair need not be permanently out of causal contact. The feature that determines whether the causal structure of the string worldsheet is trivial or not turns out to be the emission of gluonic radiation by the dual quark and antiquark. In the strongly-coupled gauge theory, it is only when radiation is emitted that one obtains an unambiguous separation of the pair into entangled subsystems, and this is what is reflected on the gravity side by the existence of the worldsheet horizon.

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arXiv2012

No Line on the Horizon: On Uniform Acceleration and Gluonic Fields at Strong Coupling

We study a few assorted questions about the behavior of strings on anti-de Sitter spacetime (AdS), or equivalently, `flux tubes' in strongly-coupled conformal field theories (CFTs). For the case where the `flux tube' is sourced by a uniformly accelerated quark (or, more generally, a quark that asymptotes to uniform acceleration in the remote past), we point out that the dual string embedding known heretofore terminates unphysically at the worldsheet horizon, and identify the correct continuation, which is found to encode a gluonic shock wave. For arbitrary quark motion, we show that, contrary to common understanding, the worldsheet horizon does not in general represent a dividing line between the portions of the string respectively dual to the quark and to the gluonic radiation emitted by it.

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arXiv2012

On the Beaming of Gluonic Fields at Strong Coupling

We examine the conditions for beaming of the gluonic field sourced by a heavy quark in strongly-coupled conformal field theories, using the AdS/CFT correspondence. Previous works have found that, contrary to naive expectations, it is possible to set up collimated beams of gluonic radiation despite the strong coupling. We show that, on the gravity side of the correspondence, this follows directly (for arbitrary quark motion, and independently of any approximations) from the fact that the string dual to the quark remains unexpectedly close to the AdS boundary whenever the quark moves ultra-relativistically. We also work out the validity conditions for a related approximation scheme that proposed to explain the beaming effect though the formation of shock waves in the bulk fields emitted by the string. We find that these conditions are fulfilled in the case of ultra-relativistic uniform circular motion that motivated the proposal, but unfortunately do not hold for much more general quark trajectories.

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arXiv2011

Holographic Lessons for Quark Dynamics

We give a brief overview of recent results obtained through the gauge/gravity correspondence, concerning the propagation of a heavy quark in strongly-coupled conformal field theories (such as N=4 super-Yang-Mills), both at zero and finite temperature. In the vacuum, we discuss energy loss, radiation damping, signal propagation and radiation-induced fluctuations. In the presence of a thermal plasma, our emphasis is on early-time energy loss, screening and quark-antiquark evolution after pair creation. Throughout, quark dynamics is seen to be efficiently encapsulated in the usual string worldsheet dynamics.

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arXiv2011

The Gluonic Field of a Heavy Quark in Conformal Field Theories at Strong Coupling

We determine the gluonic field configuration sourced by a heavy quark undergoing arbitrary motion in N=4 super-Yang-Mills at strong coupling and large number of colors. More specifically, we compute the expectation value of the operator tr[F^2+...] in the presence of such a quark, by means of the AdS/CFT correspondence. Our results for this observable show that signals propagate without temporal broadening, just as was found for the expectation value of the energy density in recent work by Hatta et al. We attempt to shed some additional light on the origin of this feature, and propose a different interpretation for its physical significance. As an application of our general results, we examine when the quark undergoes oscillatory motion, uniform circular motion, and uniform acceleration. Via the AdS/CFT correspondence, all of our results are pertinent to any conformal field theory in 3+1 dimensions with a dual gravity formulation.

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arXiv2011

Early-Time Energy Loss in a Strongly-Coupled SYM Plasma

We carry out an analytic study of the early-time motion of a quark in a strongly-coupled maximally-supersymmetric Yang-Mills plasma, using the AdS/CFT correspondence. Our approach extracts the first thermal effects as a small perturbation of the known quark dynamics in vacuum, using a double expansion that is valid for early times and for (moderately) ultrarelativistic quark velocities. The quark is found to lose energy at a rate that differs significantly from the previously derived stationary/late-time result: it scales like T^4 instead of T^2, and is associated with a friction coefficient that is not independent of the quark momentum. Under conditions representative of the quark-gluon plasma as obtained at RHIC, the early energy loss rate is a few times smaller than its late-time counterpart. Our analysis additionally leads to thermally-corrected expressions for the intrinsic energy and momentum of the quark, in which the previously discovered limiting velocity of the quark is found to appear naturally.

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