arXiv subjects

Pablo Bueno

Publications and source records attributed to Pablo Bueno.

72 records · Page 4Linked to original sources

arXiv2016

Entanglement equilibrium for higher order gravity

We show that the linearized higher derivative gravitational field equations are equivalent to an equilibrium condition on the entanglement entropy of small spherical regions in vacuum. This extends Jacobson's recent derivation of the Einstein equation using entanglement to include general higher derivative corrections. The corrections are naturally associated with the subleading divergences in the entanglement entropy, which take the form of a Wald entropy evaluated on the entangling surface. Variations of this Wald entropy are related to the field equations through an identity for causal diamonds in maximally symmetric spacetimes, which we derive for arbitrary higher derivative theories. If the variations are taken holding fixed a geometric functional that we call the generalized volume, the identity becomes an equivalence between the linearized constraints and the entanglement equilibrium condition. We note that the fully nonlinear higher curvature equations cannot be derived from the linearized equations applied to small balls, in contrast to the situation encountered in Einstein gravity. The generalized volume is a novel result of this work, and we speculate on its thermodynamic role in the first law of causal diamond mechanics, as well as its possible application to holographic complexity.

hep-th↗

arXiv2016

Einsteinian cubic gravity

We drastically simplify the problem of linearizing a general higher-order theory of gravity. We reduce it to the evaluation of its Lagrangian on a particular Riemann tensor depending on two parameters, and the computation of two derivatives with respect to one of those parameters. We use our method to construct a D-dimensional cubic theory of gravity which satisfies the following properties: 1) it shares the spectrum of Einstein gravity, i.e., it only propagates a transverse and massless graviton on a maximally symmetric background; 2) the relative coefficients of the different curvature invariants involved are the same in all dimensions; 3) it is neither trivial nor topological in four dimensions. Up to cubic order in curvature, the only previously known theories satisfying the first two requirements are the Lovelock ones: Einstein gravity, Gauss-Bonnet and cubic-Lovelock. Of course, the last two theories fail to satisfy requirement 3 as they are, respectively, topological and trivial in four dimensions. We show that, up to cubic order, there exists only one additional theory satisfying requirements 1 and 2. Interestingly, this theory is, along with Einstein gravity, the only theory which also satisfies 3.

hep-th↗

arXiv2016

f(Lovelock) theories of gravity

f(Lovelock) gravities are simple generalizations of the usual f(R) and Lovelock theories in which the gravitational action depends on some arbitrary function of the corresponding dimensionally-extended Euler densities. In this paper we study several aspects of these theories in general dimensions. We start by identifying the generalized boundary term which makes the gravitational variational problem well-posed. Then, we show that these theories are equivalent to certain scalar-tensor theories and how this relation is characterized by the Hessian of f. We also study the linearized equations of the theory on general maximally symmetric backgrounds. Remarkably, we find that these theories do not propagate the usual ghost-like massive gravitons characteristic of higher-derivative gravities on such backgrounds. In some non-trivial cases, the additional scalar associated to the trace of the metric perturbation is also absent, being the usual graviton the only dynamical field. In those cases, the linearized equations are exactly the same as in Einstein gravity up to an overall factor, making them appealing as holographic toy models. We also find constraints on the couplings of a broad family of five-dimensional f(Lovelock) theories using holographic entanglement entropy. Finally, we construct new analytic asymptotically flat and AdS/dS black hole solutions for some classes of f(Lovelock) gravities in various dimensions.

hep-th↗

arXiv2016

Bounds on corner entanglement in quantum critical states

The entanglement entropy in many gapless quantum systems receives a contribution from corners in the entangling surface in 2+1d. It is characterized by a universal function $a(θ)$ depending on the opening angle $θ$, and contains pertinent low energy information. For conformal field theories (CFTs), the leading expansion coefficient in the smooth limit $θ\to π$ yields the stress tensor 2-point function coefficient $C_T$ . Little is known about $a(θ)$ beyond that limit. Here, we show that the next term in the smooth limit expansion contains information beyond the 2- and 3-point correlators of the stress tensor. We conjecture that it encodes 4-point data, making it much richer. Further, we establish strong constraints on this and higher order smooth-limit coefficients. We also show that $a(θ)$ is lower-bounded by a non-trivial function multiplied by the central charge $C_T$ , e.g. $a(π/2) \geq (π^2 \ln 2)C_T /6$. This bound for 90-degree corners is nearly saturated by all known results, including recent numerics for the interacting Wilson-Fisher quantum critical points (QCPs). A bound is also given for the Rényi entropies. We illustrate our findings using O(N) QCPs, free boson and Dirac fermion CFTs, strongly coupled holographic ones, and other models. Exact results are also given for Lifshitz quantum critical points, and for conical singularities in 3+1d.

cond-mat.str-el↗

arXiv2016

Universal entanglement for higher dimensional cones

The entanglement entropy of a generic $d$-dimensional conformal field theory receives a regulator independent contribution when the entangling region contains a (hyper)conical singularity of opening angle $Ω$, codified in a function $a^{(d)}(Ω)$. In arXiv:1505.04804, we proposed that for three-dimensional conformal field theories, the coefficient $σ$ characterizing the smooth surface limit of such contribution ($Ω\rightarrow π$) equals the stress tensor two-point function charge $C_{ T}$, up to a universal constant. In this paper, we prove this relation for general three-dimensional holographic theories, and extend the result to general dimensions. In particular, we show that a generalized coefficient $σ^{ (d)}$ can be defined for (hyper)conical entangling regions in the almost smooth surface limit, and that this coefficient is universally related to $C_{ T}$ for general holographic theories, providing a general formula for the ratio $σ^{ (d)}/C_{ T}$ in arbitrary dimensions. We conjecture that the latter ratio is universal for general CFTs. Further, based on our recent results in arXiv:1507.06997, we propose an extension of this relation to general Rényi entropies, which we show passes several consistency checks in $d=4$ and $d=6$.

hep-th↗

arXiv2015

Universal corner entanglement from twist operators

The entanglement entropy in three-dimensional conformal field theories (CFTs) receives a logarithmic contribution characterized by a regulator-independent function $a(θ)$ when the entangling surface contains a sharp corner with opening angle $θ$. In the limit of a smooth surface ($θ\rightarrowπ$), this corner contribution vanishes as $a(θ)=σ\,(θ-π)^2$. In arXiv:1505.04804, we provided evidence for the conjecture that for any $d=3$ CFT, this corner coefficient $σ$ is determined by $C_T$, the coefficient appearing in the two-point function of the stress tensor. Here, we argue that this is a particular instance of a much more general relation connecting the analogous corner coefficient $σ_n$ appearing in the $n$th Rényi entropy and the scaling dimension $h_n$ of the corresponding twist operator. In particular, we find the simple relation $h_n/σ_n=(n-1)π$. We show how it reduces to our previous result as $n\rightarrow 1$, and explicitly check its validity for free scalars and fermions. With this new relation, we show that as $n\rightarrow 0$, $σ_n$ yields the coefficient of the thermal entropy, $c_S$. We also reveal a surprising duality relating the corner coefficients of the scalar and the fermion. Further, we use our result to predict $σ_n$ for holographic CFTs dual to four-dimensional Einstein gravity. Our findings generalize to other dimensions, and we emphasize the connection to the interval Rényi entropies of $d=2$ CFTs.

hep-th↗

arXiv2015

Corner contributions to holographic entanglement entropy

The entanglement entropy of three-dimensional conformal field theories contains a universal contribution coming from corners in the entangling surface. We study these contributions in a holographic framework and, in particular, we consider the effects of higher curvature interactions in the bulk gravity theory. We find that for all of our holographic models, the corner contribution is only modified by an overall factor but the functional dependence on the opening angle is not modified by the new gravitational interactions. We also compare the dependence of the corner term on the new gravitational couplings to that for a number of other physical quantities, and we show that the ratio of the corner contribution over the central charge appearing in the two-point function of the stress tensor is a universal function for all of the holographic theories studied here. Comparing this holographic result to the analogous functions for free CFT's, we find fairly good agreement across the full range of the opening angle. However, there is a precise match in the limit where the entangling surface becomes smooth, i.e., the angle approaches $π$, and we conjecture the corresponding ratio is a universal constant for all three-dimensional conformal field theories. In this paper, we expand on the holographic calculations in our previous letter arXiv:1505.04804, where this conjecture was first introduced.

hep-th↗

arXiv2015

Universality of corner entanglement in conformal field theories

We study the contribution to the entanglement entropy of (2+1)-dimensional conformal field theories coming from a sharp corner in the entangling surface. This contribution is encoded in a function $a(θ)$ of the corner opening angle, and was recently proposed as a measure of the degrees of freedom in the underlying CFT. We show that the ratio $a(θ)/C_T$, where $C_T$ is the central charge in the stress tensor correlator, is an almost universal quantity for a broad class of theories including various higher-curvature holographic models, free scalars and fermions, and Wilson-Fisher fixed points of the $O(N)$ models with $N=1,2,3$. Strikingly, the agreement between these different theories becomes exact in the limit $θ\rightarrow π$, where the entangling surface approaches a smooth curve. We thus conjecture that the corresponding ratio is universal for general CFTs in three dimensions.

hep-th↗

arXiv2015

Resolution of SU(2) monopole singularities by oxidation

We show how "colored" SU(2) BPS monopoles (that is: SU(2) monopoles satisfying the Bogomol'nyi equation whose Higgs field and magnetic charge vanish at infinity and which are singular at the origin) can be obtained from the BPST instanton by a singular dimensional reduction, explaining the origin of the singularity and implying that the singularity can be cured by the oxidation of the solution. We study the oxidation of other monopole solutions in this scheme.

hep-th↗

arXiv2015

Non-extremal branes

We prove that for arbitrary black brane solutions of generic Supergravities there is an adapted system of variables in which the equations of motion are exactly invariant under electric-magnetic duality, i.e. the interchange of a given extended object by its electromagnetic dual. We obtain thus a procedure to automatically construct the electromagnetic dual of a given brane without needing to solve any further equation. We apply this procedure to construct the non-extremal (p, q)-string of Type-IIB String Theory (new in the literature), explicitly showing how the dual (p, q)-five-brane automatically arises in this construction. In addition, we prove that the system of variables used is suitable for a generic characterization of every double-extremal Supergravity brane solution, which we perform in full generality.

hep-th↗

arXiv2014

Higher-curvature corrections to holographic entanglement entropy in geometries with hyperscaling violation

We study the effects of including higher-curvature corrections to the Einstein gravity bulk action on the holographic entanglement entropy (HEE) expression for geometries with hyperscaling violation (hvLf). For $θ< 0$ we show that one single new divergence arises for general curvature-squared gravities, which allows us to conjecture the general expression of HEE for any higher-order gravity action. For $0<θ<d$, we assume the hvLf geometry to arise above some intermediate scale $r_F$, becoming AdS in the UV and perform a similar analysis for $R^n$ gravities. For negative values of $θ$ we find that new logarithmic contributions show up in the HEE formula for any $n$th-order gravity when $θ=d(d-1)/(d-2(n-1))$ and $d<2(n-1)$. In the range $0\leq θ<d$ we do not find additional logarithmic contributions appearing at any order except for $n=1$, which corresponds to the famous case $θ=d-1$ encountered in Einstein gravity.

hep-th↗

arXiv2014

N=2 Einstein-Yang-Mills' static two-center solutions

We construct bona fide one- and two-center supersymmetric solutions to N=2, d=4 supergravity coupled to SU(2) non-Abelian vector multiplets. The solutions describe black holes and global monopoles alone or in equilibrium with each other and exhibit non-Abelian hairs of different kinds.

hep-th↗

arXiv2013

The violation of the No-Hair Conjecture in four-dimensional ungauged Supergravity

By choosing a particular, String Theory inspired, Special Kähler manifold, we are able to find a N=2 four-dimensional ungauged Supergravity model that contains supersymmetric black hole solutions that violate the folk uniqueness theorems that are expected to hold in ungauged Supergravity. The black hole solutions are regular in the sense that they have a positive mass and a unique physical singularity hidden by an event horizon. In contradistinction to most examples already known in the literature, we find our solutions in a theory without scalar potential, gaugings or higher order curvature terms.

hep-th↗

arXiv2013

Non-perturbative black holes in Type-IIA String Theory vs. the No-Hair conjecture

We obtain the first black hole solution to Type-IIA String Theory compactified on an arbitrary self-mirror Calabi Yau manifold in the presence of non-perturbative quantum corrections. Remarkably enough, the solution involves multivalued functions, which could lead to a violation of the No-Hair conjecture. We discuss how String Theory forbids such secenario. However the possibility still remains open in the context of four-dimensional ungauged Supergravity.

hep-th↗

arXiv2013

Agujeros negros cuánticos en la teoría de cuerdas tipo-IIA

In the context of Type-IIA String Theory compactified to four dimensions on a Calabi-Yau manifold (CY), we study the effect of considering perturbative and non-perturbative corrections (in alpha prime) to the prepotential of the resulting effective Supergravity theory on the space of black hole solutions. Considering the large volume limit of the CY, in which the non-perturbative corrections are exponentially suppressed, we define a new class of solutions which turn out to be genuinely quantum, in the sense that not only their classical limit is not well defined, but also the truncation under consideration becomes inconsistent in such a limit. Next, we construct the first non-extremal black hole solution with non-constant scalars in the presence of perturbative corrections. Right after, restricting ourselves to the case of self-mirror CY, we study the case in which the sub-dominant contribution has a non-perturbative origin, obtaining the first family of explicit supersymmetric solutions of this kind. Surprisingly enough, these solutions turn out to involve multivalued functions, which opens the door for a possible violation of the No-Hair conjecture. We discuss how this cannot be accomplished in our String Theory set up, but how the possibility remains open in the context of N=2, d=4 ungauged Supergravity. Fully in Spanish.

hep-th↗

arXiv2013

On hvLif-like solutions in gauged Supergravity

We perform a thorough investigation of Lifshitz-like metrics with hyperscaling violation (hvLif) in four-dimensional theories of gravity coupled to an arbitrary number of scalars and vector fields, obtaining new solutions, electric, magnetic and dyonic, that include the known ones as particular cases. After establishing some general results on the properties of purely hvLif solutions, we apply the previous formalism to the case of \mathcal{N}=2, d=4 Supergravity in the presence of Fayet-Iliopoulos terms, obtaining particular solutions to the t^3-model, and explicitly embedding some of them in Type-IIB String Theory.

hep-th↗

arXiv2012

Quantum black holes in Type-IIA String Theory

We study black hole solutions of Type-IIA Calabi-Yau compactifications in the presence of perturbative quantum corrections. We define a class of black holes that only exist in the presence of quantum corrections and that, consequently, can be considered as purely quantum black holes. The regularity conditions of the solutions impose the topological constraint h^{1,1}>h^{2,1} on the Calabi-Yau manifold, defining a class of admissible compactifications, which we prove to be non-empty for h^{1,1}=3 by explicitly constructing the corresponding Calabi-Yau manifolds, new in the literature.

hep-th↗

arXiv2012

Lifshitz-like solutions with hyperscaling violation in ungauged supergravity

In this note we describe several procedures to construct, from known black-hole and black-brane solutions of any ungauged supergravity theory, non-trivial gravitational solutions whose "near-horizon" and "near-singularity" limits are Lifshitz-like spacetimes with dynamical critical exponent z, "hyperscaling violation" exponent θand Lifshitz radius \ell that depends on the physical parameters of the original black-hole solution. Since the new Lifshitz-like solutions can be constructed from any black-hole solution of any ungauged supergravity, many of them can be easily embedded in String Theory. Some of the procedures produce supersymmetric Lifshitz-like solutions.

hep-th↗