arXiv subjects

Chiara Toldo

Publications and source records attributed to Chiara Toldo.

29 records · Page 2Linked to original sources

arXiv2018

Deforming black holes in AdS

We investigate how changes in the boundary metric affect the shape of AdS black holes. Most of our work is analytic and based on the AdS C-metric. Both asymptotically hyperbolic and compact black holes are studied. It has recently been shown that the AdS C-metric contains configurations of highly deformed black holes, and we show that these deformations are usually the result of similar deformations of the boundary metric. However, quite surprisingly, we also find cases where the horizon is insensitive to certain large changes in the boundary geometry. This motivates the search for a new family of black hole solutions with the same boundary geometry in which the horizon does respond to the changes in the boundary. We numerically construct these solutions and we (numerically) explore how the horizon response to boundary deformations depends on temperature.

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arXiv2017

Betti multiplets, flows across dimensions and c-extremization

We consider 4d N=1 SCFTs, topologically twisted on compact constant curvature Riemann surfaces, giving rise to 2d N=(0,2) SCFTs. The exact R-current of these 2d SCFT extremizes the central charge c_{2d}, similarly to the 4d picture, where the exact R-current maximizes the central charge a_{4d}. There are global currents that do not mix with the R-current in 4d but their mixing becomes non trivial in 2d. In this paper we study the holographic dual of this process by analyzing a 5d N=2 truncation of T^{1,1} with one Betti vector multiplet, dual to the baryonic current on the CFT side. The holographic realization of the flow across dimensions connects AdS_5 to AdS_3 vacua in the supergravity picture. We verify the existence of the flow to AdS_3 solutions and we retrieve the field theory results for the mixing of the Betti vector with the graviphoton. Moreover, we extract the central charge from the Brown-Henneaux formula, matching with the results obtained in field theory. We develop a general formalism to obtain the central charge of a 2d SCFT from 5d N=2 gauged supergravity with a generic number of vector multiplets, showing that its extremization corresponds to an attractor mechanism for the scalars in the supergravity picture.

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arXiv2017

Black holes with halos

We present new AdS4 black hole solutions in N = 2 gauged supergravity coupled to vector and hypermultiplets. We focus on a particular consistent truncation of M-theory on the homogeneous Sasaki-Einstein seven-manifold M111, characterized by the presence of one Betti vector multiplet. We numerically construct static and spherically symmetric black holes with electric and magnetic charges, corresponding to M2 and M5 branes wrapping non-contractible cycles of the internal manifold. These configurations have nonzero temperature and are moreover surrounded by a massive vector field halo. For these solutions we verify the first law of black hole mechanics and we analyze the thermodynamics and phase transitions in the canonical ensemble, interpreting the process in the corresponding dual field theory.

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arXiv2016

Thermodynamics of spinning AdS4 black holes in gauged supergravity

In this paper we study the thermodynamics of rotating black hole solutions arising from four-dimensional gauged N=2 supergravity. We analyze two different supergravity models, characterized by prepotentials $F = -i X^0 X^1$ and $F= -2i \sqrt{X^0 (X^1)^3}$. The black hole configurations are supported by electromagnetic charges and scalar fields with different kinds of boundary conditions. We perform our analysis in the canonical ensemble, where we find a first order phase transition for a suitable range of charges and angular momentum. We perform the thermodynamic stability check on the configurations. Using the holographic dictionary we interpret the phase transition in terms of expectation values of operators in the dual field theory, which pertains to the class of ABJM theories living on a rotating Einstein universe. We extend the analysis to dyonic configurations as well. Lastly, we show the computation of the on-shell action and mass via holographic renormalization techniques.

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arXiv2015

Segmented Strings in $AdS_3$

We study segmented strings in flat space and in $AdS_3$. In flat space, these well known classical motions describe strings which at any instant of time are piecewise linear. In $AdS_3$, the worldsheet is composed of faces each of which is a region bounded by null geodesics in an $AdS_2$ subspace of $AdS_3$. The time evolution can be described by specifying the null geodesic motion of kinks in the string at which two segments are joined. The outcome of collisions of kinks on the worldsheet can be worked out essentially using considerations of causality. We study several examples of closed segmented strings in $AdS_3$ and find an unexpected quasi-periodic behavior. We also work out a WKB analysis of quantum states of yo-yo strings in $AdS_3$ and find a logarithmic term reminiscent of the logarithmic twist of string states on the leading Regge trajectory.

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arXiv2014

Static nonextremal AdS4 black hole solutions

We find new static nonextremal black hole solutions that asymptote to AdS_4 in D=4 gauged N=2 supergravity. Solutions include electric and magnetic black holes with constant scalars that in the BPS limit reduce to naked singularities, but also magnetic black holes with running scalars that at extremality reduce to BPS black holes with finite horizon area. For all these solutions we compute area product formulae and show they are independent of the mass. Finally, we also find new examples of nonextremal magnetic black branes.

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arXiv2013

Rotating black holes in 4d gauged supergravity

We present new results towards the construction of the most general black hole solutions in four-dimensional Fayet-Iliopoulos gauged supergravities. In these theories black holes can be asymptotically AdS and have arbitrary mass, angular momentum, electric and magnetic charges and NUT charge. Furthermore, a wide range of horizon topologies is allowed (compact and noncompact) and the complex scalar fields have a nontrivial radial and angular profile. We construct a large class of solutions in the simplest single scalar model with prepotential $F = -i X^0 X^1$ and discuss their thermodynamics. Moreover, various approaches and calculational tools for facing this problem with more general prepotentials are presented.

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arXiv2013

Phase transitions of magnetic AdS4 black holes with scalar hair

We determine the thermodynamic properties of a class of spherically symmetric and static black holes in AdS4 with magnetic charges and scalar hair. These black holes are solutions in 4d N=2 gauged supergravity that can arise from eleven-dimensional supergravity compactified on S^7. At zero temperature, they preserve supersymmetry and hence are stable. At non-zero temperatures, we explore in detail the canonical ensemble and stability of solutions and find a first order phase transition between small and large hairy black holes. The transition emerges as a liquid-gas phase transition in the dual three-dimensional field theory on R x S^2 with magnetic flux through S^2.

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arXiv2013

On the non-BPS first order flow in N=2 U(1)-gauged Supergravity

We consider theories of N=2 supergravity with Fayet-Iliopoulos gauging, and describe a procedure to obtain non-BPS extremal black hole solutions in asymptotically AdS_4 space, in a fully symplectic covariant framework. By considering both electric as well as magnetic gauging, we are able to find new extremal purely magnetic and dyonic solutions. We consistently impose the Dirac quantization condition as a constraint on the black hole and gravitinos charges. This additional requirement allows to parameterize the black hole entropy in terms of an integer and of the entropy of the corresponding black hole in the ungauged model. We also find the nonextremal generalization of the dyonic solution and we compute the product of the areas. For all the configurations with asymptotic supersymmetry we furthermore compute the mass.

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arXiv2012

Black branes in AdS: BPS bounds and asymptotic charges

We focus on black branes and toroidal black holes in N=2 gauged supergravities that asymptote to AdS_4, and derive formulas for the mass and central charge densities. We derive the corresponding BPS bound from the superalgebra of the asymptotic vacuum and illustrate our procedure with explicit examples of genuine black brane solutions with non-trivial scalars.

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arXiv2011

On BPS bounds in D=4 N=2 gauged supergravity

We determine the BPS bounds in minimal gauged supergravity in four spacetime dimensions. We concentrate on asymptotically anti-de Sitter (AdS) spacetimes, and find that there exist two disconnected BPS ground states of the theory, depending on the presence of magnetic charge. Each of these ground states comes with a different superalgebra and a different BPS bound, which we derive. As a byproduct, we also demonstrate how the supersymmetry algebra has a built-in holographic renormalization method to define finite conserved charges.

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