arXiv subjects

Rodolfo Russo

Publications and source records attributed to Rodolfo Russo.

At least 55 records · Page 3Linked to original sources

arXiv2016

AdS3 Holography for 1/4 and 1/8 BPS geometries

Recently a new class of 1/8-BPS regular geometries in type IIB string theory was constructed in arXiv:1503.01463. In this paper we provide a precise description of the semiclassical states dual, in the AdS/CFT sense, to these geometries. In explicit examples we show that the holographic 1-point functions and the Ryu-Takayanagi's Entanglement Entropy for a single small interval match the corresponding CFT calculations performed by using the proposed dual states. We also discuss several new examples of such precision holography analysis in the 1/4-BPS sector and provide an explicit proof that the small interval derivation of the Entanglement Entropy used in arXiv:1405.6185 is fully covariant.

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arXiv2015

A microscopic description of absorption in high-energy string-brane collisions

We study the collision of a highly energetic light closed string off a stack of Dp-branes at (sub)string-scale impact parameters and in a regime justifying a perturbative treatment. Unlike at larger impact parameters - where elastic scattering and/or tidal excitations dominate - here absorption of the closed string by the brane system, with the associated excitation of open strings living on it, becomes important. As a first step, we study this phenomenon at the disk level, in which the energetic closed string turns into a single heavy open string at rest whose particularly simple properties are described.

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arXiv2015

Infrared divergences and harmonic anomalies in the two-loop superstring effective action

We analyze the pertubative contributions to the $D^4 R^4$ and $D^6 R^4$ couplings in the low-energy effective action of type II string theory compactified on a torus $T^d$, with particular emphasis on two-loop corrections. In general, it is necessary to introduce an infrared cut-off $Λ$ to separate local interactions from non-local effects due to the exchange of massless states. We identify the degenerations of the genus-two Riemann surface which are responsible for power-like dependence on $Λ$, and give an explicit prescription for extracting the $Λ$-independent effective couplings. These renormalized couplings are then shown to be eigenmodes of the Laplace operator with respect to the torus moduli, up to computable anomalous source terms arising in the presence of logarithmic divergences, in precise agreement with predictions from U-duality. Our results for the two-loop $D^6 R^4$ contribution also probe essential properties of the Kawazumi-Zhang invariant

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arXiv2015

Superdescendants of the D1D5 CFT and their dual 3-charge geometries

We describe how to obtain the gravity duals of semiclassical states in the D1-D5 CFT that are superdescendants of a class of RR ground states. On the gravity side, the configurations we construct are regular and asymptotically reproduce the 3-charge D1-D5-P black hole compactified on $S^1\times T^4$. The geometries depend trivially on the $T^4$ directions but non-trivially on the remaining 6D space. In the decoupling limit, they reduce to asymptotically AdS$_3 \times S^3 \times T^4$ spaces that are dual to CFT states obtained by acting with (exponentials of) the operators of the superconformal algebra. As explicit examples, we generalise the solution first constructed in arXiv:1306.1745 and discuss another class of states that have a more complicated dual geometry. By using the free orbifold description of the CFT we calculate the average values for momentum and the angular momenta of these configurations. Finally we compare the CFT results with those obtained in the bulk from the asymptotically $M^{1,4} \times S^1\times T^4$ region.

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arXiv2015

6D microstate geometries from 10D structures

We use the formalism of Generalised Geometry to characterise in general the supersymmetric backgrounds in type II supergravity that have a null Killing vector. We then specify this analysis to configurations that preserve the same supersymmetries as the D1-D5-P system compactified on a four-manifold. We give a set of equations on the forms defining the supergravity background that are equivalent to the supersymmetry constraints and the equations of motion. This study is motivated by the search of new microstate geometries for the D1-D5-P black hole. As an example, we rewrite the linearised three-charge solution of arXiv:hep-th/0311092 in our formalism and show how to extend it to a non-linear, regular and asymptotically flat configuration.

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arXiv2015

Entanglement Entropy and D1-D5 geometries

In Conformal Field Theories with a gravitational AdS dual it is possible to calculate the entanglement entropy of a region $A$ holographically by using the Ryu-Takayanagi formula. In this work we consider systems that are in a pure state that is not the vacuum. We study in particular the 2D Conformal Field Theory dual to type IIB string theory on AdS$_3 \times S^3 \times T^4$ and focus on the $1/4$-BPS states described holographically by the 2-charge microstate geometries. We discuss a general prescription for the calculation of the entanglement entropy in these geometries that are asymptotically AdS$_3 \times S^3$. In particular we study analytically the perturbative expansion for a single, short interval: we show that the first non-trivial terms in this expansion are consistent with the expected CFT structure and with previous results on the vevs of chiral primary operators for the $1/4$-BPS configurations.

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arXiv2015

Regge behavior saves String Theory from causality violations

Higher-derivative corrections to the Einstein-Hilbert action are present in bosonic string theory leading to the potential causality violations recently pointed out by Camanho et al. We analyze in detail this question by considering high-energy string-brane collisions at impact parameters $b \le l_s$ (the string-length parameter) with $l_s \gg R_p$ (the characteristic scale of the D$p$-brane geometry). If we keep only the contribution of the massless states causality is violated for a set of initial states whose polarization is suitably chosen with respect to the impact parameter vector. Such violations are instead neatly avoided when the full structure of string theory - and in particular its Regge behavior - is taken into account.

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arXiv2015

Multi-loop open string amplitudes and their field theory limit

We study the field theory limit of multi-loop (super)string amplitudes, with the aim of clarifying their relationship to Feynman diagrams describing the dynamics of the massless states. We propose an explicit map between string moduli around degeneration points and Schwinger proper-times characterizing individual Feynman diagram topologies. This makes it possible to identify the contribution of each light string state within the full string amplitude and to extract the field theory Feynman rules selected by (covariantly quantized) string theory. The connection between string and field theory amplitudes also provides a concrete tool to clarify ambiguities related to total derivatives over moduli space: in the superstring case, consistency with the field theory results selects a specific prescription for integrating over supermoduli. In this paper, as an example, we focus on open strings supported by parallel D-branes, and we present two-loop examples drawn from bosonic and RNS string theories, highlighting the common features between the two setups.

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arXiv2015

Two-loop Yang-Mills diagrams from superstring amplitudes

Starting from the superstring amplitude describing interactions among D-branes with a constant world-volume field strength, we present a detailed analysis of how the open string degeneration limits reproduce the corresponding field theory Feynman diagrams. A key ingredient in the string construction is represented by the twisted (Prym) super differentials, as their periods encode the information about the background field. We provide an efficient method to calculate perturbatively the determinant of the twisted period matrix in terms of sets of super-moduli appropriate to the degeneration limits. Using this result we show that there is a precise one-to-one correspondence between the degeneration of different factors in the superstring amplitudes and one-particle irreducible Feynman diagrams capturing the gauge theory effective action at the two-loop level.

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arXiv2015

Habemus Superstratum! A constructive proof of the existence of superstrata

We construct the first example of a superstratum: a class of smooth horizonless supergravity solutions that are parameterized by arbitrary continuous functions of (at least) two variables and have the same charges as the supersymmetric D1-D5-P black hole. We work in Type IIB string theory on T^4 or K3 and our solutions involve a subset of fields that can be described by a six-dimensional supergravity with two tensor multiplets. The solutions can thus be constructed using a linear structure, and we give an explicit recipe to start from a superposition of modes specified by an arbitrary function of two variables and impose regularity to obtain the full horizonless solutions in closed form. We also give the precise CFT description of these solutions and show that they are not dual to descendants of chiral primaries. They are thus much more general than all the known solutions whose CFT dual is precisely understood. Hence our construction represents a substantial step toward the ultimate goal of constructing the fully generic superstratum that can account for a finite fraction of the entropy of the three-charge black hole in the regime of parameters where the classical black hole solution exists.

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arXiv2014

Matching the $D^6 {\cal R}^4$ interaction at two-loops

The coefficient of the $D^6 {\cal R}^4$ interaction in the low energy expansion of the two-loop four-graviton amplitude in type II superstring theory is known to be proportional to the integral of the Zhang-Kawazumi (ZK) invariant over the moduli space of genus-two Riemann surfaces. We demonstrate that the ZK invariant is an eigenfunction with eigenvalue 5 of the Laplace-Beltrami operator in the interior of moduli space. Exploiting this result, we evaluate the integral of the ZK invariant explicitly, finding agreement with the value of the two-loop $D^6 {\cal R}^4$ interaction predicted on the basis of S-duality and supersymmetry. A review of the current understanding of the $D^{2p} {\cal R}^4$ interactions in type II superstring theory compactified on a torus $T^d$ with $p \leq 3$ and $d \leq 4$ is included.

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arXiv2013

Microscopic unitary description of tidal excitations in high-energy string-brane collisions

The eikonal operator was originally introduced to describe the effect of tidal excitations on higher-genus elastic string amplitudes at high energy. In this paper we provide a precise interpretation for this operator through the explicit tree-level calculation of generic inelastic transitions between closed strings as they scatter off a stack of parallel Dp-branes. We perform this analysis both in the light-cone gauge, using the Green-Schwarz vertex, and in the covariant formalism, using the Reggeon vertex operator. We also present a detailed discussion of the high energy behaviour of the covariant string amplitudes, showing how to take into account the energy factors that enhance the contribution of the longitudinally polarized massive states in a simple way.

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arXiv2013

The leading eikonal operator in string-brane scattering at high energy

In this paper we present two (a priori independent) derivations of the eikonal operator in string-brane scattering. The first one is obtained by summing surfaces with any number of boundaries, while in the second one the eikonal operator is derived from the three-string vertex in a suitable light-cone gauge. This second derivation shows that the bosonic oscillators present in the leading eikonal operator are to be identified with the string bosonic oscillators in a suitable light-cone gauge, while the first one shows that it exponentiates recovering unitarity. This paper is a review of results obtained in two previous publications of the same authors.

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arXiv2012

Perturbative superstrata

We study a particular class of D-brane bound states in type IIB string theory (dubbed "superstrata") that describe microstates of the 5D Strominger-Vafa black hole. By using the microscopic description in terms of open strings we probe these configurations with generic light closed string states and from there we obtain a linearized solution of six-dimensional supergravity preserving four supersymmetries. We then discuss two generalizations of the solution obtained which capture different types of non-linear corrections. By using this construction, we can provide the first explicit example of a superstratum solution which includes the effects of the KK-monopole dipole charge to first order.

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arXiv2012

Adding new hair to the 3-charge black ring

Motivated by the string theory analysis of arXiv:1108.6331, we construct a class of 1/8-BPS solutions of type IIB supergravity compactified on S^1 x T^4. In this duality frame our ansatz allows for a non-trivial NS-NS B-field which has been usually set to zero in previous studies of 1/8-BPS geometries. We provide a M-theory description of these new geometries and show that they can be interpreted as the lift of solutions of the N=2 5D supergravity with three vector multiplets and whose scalar manifold is the symmetric space SO(1,1) x (SO(1,2)/SO(2)). Finally we show that the non-minimal 5D black rings provide an explicit example of solutions falling in this ansatz. In particular we point out the existence of a black ring that has an extra dipole charge with respect to the solutions of the STU-model. In the near-horizon limit, this ring has an AdS_3 x S^3 geometry with the same radius as the one of the 3-charge black hole and thus its microstates should belong to the usual D1-D5 CFT.

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arXiv2011

New D1-D5-P geometries from string amplitudes

We derive the long range supergravity fields sourced by a D1-D5-P bound state from disk amplitudes for massless closed string emission. We suggest that since the parameter controlling the string perturbation expansion for this calculation decreases with distance from the bound state, the resulting asymptotic fields are valid even in the regime of parameters in which there is a classical black hole solution with the same charges. The supergravity fields differ from the black hole solution by multipole moments and are more general than those contained within known classes of solutions in the literature, whilst still preserving four supersymmetries. Our results support the conjecture that the black hole solution should be interpreted as a coarse-grained description rather than an exact description of the gravitational field sourced by D1-D5-P bound states in this regime of parameters.

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arXiv2010

The supergravity fields for a D-brane with a travelling wave from string amplitudes

We calculate the supergravity fields sourced by a D-brane with a null travelling wave from disk amplitudes in type IIB string theory compactified on T^4 x S^1. The amplitudes reproduce all the non-trivial features of the previously known two-charge supergravity solutions in the D-brane/momentum frame, providing a direct link between the microscopic bound states and their macroscopic descriptions.

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arXiv2010

High-energy string-brane scattering: leading eikonal and beyond

We extend previous techniques for calculations of transplanckian-energy string-string collisions to the high-energy scattering of massless closed strings from a stack of N Dp-branes in Minkowski spacetime. We show that an effective non-trivial metric emerges from the string scattering amplitudes by comparing them against the semiclassical dynamics of high-energy strings in the extremal p-brane background. By changing the energy, impact parameter and effective open string coupling, we are able to explore various interesting regimes and to reproduce classical expectations, including tidal-force excitations, even beyond the leading-eikonal approximation.

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