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Oleg Lunin

Publications and source records attributed to Oleg Lunin.

At least 19 recordsLinked to original sources
arXiv2025

Gravitational Waves in the Myers-Perry Geometry

We analyze equations describing gravitational waves in the Myers-Perry and Gibbons-Lu-Page-Pope geometries with arbitrary rotation parameters. Assuming that at least one rotation parameter vanishes, we demonstrate full separability of equations for several polarizations of gravitational waves and analyze the resulting ODEs. We also construct some examples of separable solutions describing gravitational excitations of black holes with the maximal number of rotation parameters.

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arXiv2025

Gravitational analog of the Non-Abelian T-duality

Non-abelian T duality (NATD) is a symmetry of the worldsheet action that allows one to generate new solutions of string theory by performing algebraic transformations of known geometries. Applications of such transformations to spheres have been especially fruitful in the past, but the results did not reduce to the abelian transformation in the decompactification limit unless the dimension of sphere was equal to three. We propose a unique counterpart of NATD in classical gravity that reproduces the correct decompactification limit for all spheres $S^n$ but generates an n-form field strength and therefore cannot be naturally embedded in a worldsheet theory of NS-NS fields unless n=3. We also propose a non-abelian version of the TsT transformation which produces solutions of type II supergravity describing continuous deformations of geometries with $S^n\times S^n$ and $S^n\times T^n$ factors.

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arXiv2024

Rotating Einstein-Maxwell black holes in odd dimensions

To construct higher-dimensional counterparts of the Kerr-Newman black holes, we consider Einstein's equations sourced by a vector field and a negative cosmological constant. In contrast to the four-dimensional case, the Maxwell's equations are modified by sources generated by topological Chern-Simons couplings, the situation already encountered in the minimal five dimensional supergravity. After constructing explicit geometries in all odd dimensions, we demonstrate that the Klein-Gordon equation on the new backgrounds is fully separable.

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arXiv2024

Multi-charged geometries with cosmological constant

Motivated by gauged supergravities, we consider gravitational systems coupled to arbitrary numbers of fluxes and scalar fields. We show that simple ansatze for asymptotically AdS solutions in these systems fully determine the potential for the scalars, and we construct the black hole geometries which generalize the solutions known in gauged supergravities to an arbitrary number of dimensions. We also construct branes and brane intersections supported by an arbitrary number of higher-form fluxes and a correlated number of scalars.

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arXiv2024

Double Field Theory and $\alpha'$ corrections: explicit examples

We construct several solutions of effective actions for string theories beyond the supergravity approximation utilizing the framework of the Double Field Theory (DFT). The DFT effective actions, which are well suited for accommodating abelian and non-abelian T dualities, are naturally written in terms of modified connections and curvatures with torsion. We construct the most general solutions with vanishing modified torsion, and such geometries don't receive quantum corrections. We also compute the leading $\alpha'$ corrections to several supergravity solutions, including a pair of geometries related by a non-abelian T duality.

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arXiv2023

Geometries with twisted spheres and non-abelian T-dualities

Spectral flow in two-dimensional field theories is known to correspond to geometrical twisting between two circles in the gravity dual. We generalize this operation to the geometries which have SO(k+1) x SO(k+1) isometries with k>1 and perform various non-abelian T-dualities of the resulting twisted backgrounds. Combination of non-abelian twists and dualities leads to a new solution generating technique in supergravity, and we apply it to the geometries dual to supersymmetric states in N=4 super-Yang-Mills theory.

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arXiv2022

Charged wormholes in higher dimensions

We construct regular solutions of Einstein's equations connecting two copies of the $AdS_d$ space. Our geometries approach $AdS_{d-p} \times S^p$ in the interior, and topologically they have wormhole-like structures with non-contractible spheres $S^p$. Being inspired by charged branes, these solutions are supported by higher form gauge fields and a $d$-dimensional cosmological constant. Our ansatz also covers regular wormholes connecting two copies of $AdS_{q} \times S^{d-q}$ with various values of q, and we uncover an interesting phase structure of initial conditions leading to different interpolations.

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arXiv2022

Black branes with cosmological constant

We study neutral black branes with flat and curved worldvolumes in the presence of a negative cosmological constant. We reduce the equations governing the dynamics of such objects to one second--order ODE and perform various asymptotic expansions of the resulting equation. We also analyze regular geometries which have the same symmetries as the branes and interpolate between an empty interior and AdS asymptotics. We show that the dynamics of such spacetimes is governed by the Abel equation.

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arXiv2020

Separation of variables in the WZW models

We consider dynamics of scalar and vector fields on gravitational backgrounds of the Wess-Zumino-Witten models. For SO(4) and its cosets, we demonstrate full separation of variables for all fields and find a close analogy with a similar separation of vector equations in the backgrounds of the Myers--Perry black holes. For SO(5) and higher groups separation of variables is found only in some subsectors.

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arXiv2019

Excitations of the Myers-Perry Black Holes

We demonstrate separability of the dynamical equations for all p-form fluxes in the Myers-Perry-(A)dS geometry, extending the earlier results for electromagnetic field. In the physically important cases of p=(1,2,3,4), we explicitly write the ODEs governing the dynamics of separable solutions.

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arXiv2018

Scalar fields on λ-deformed cosets

We study dynamics of scalar fields on a large class of geometries described by integrable sigma models. Although equations of motion are not separable due to absence of isometries and Killing tensors, we completely determine the spectra using algebraic and group-theoretic methods.

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arXiv2017

Maxwell's Equations in the Myers-Perry Geometry

We demonstrate separability of the Maxwell's equations in the Myers-Perry-(A)dS geometry and derive explicit solutions for various polarizations. Application of our construction to the four-dimensional Kerr black hole leads to a new ansatz for the Maxwell field which has significant advantages over the previously known parameterization.

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arXiv2016

Generalized $λ$-deformations of AdS_p x S^p

We study analytical properties of the generalized $λ$-deformation, which modifies string theories while preserving integrability, and construct the explicit backgrounds corresponding to AdS_p x S^p, including the Ramond-Ramond fluxes. For an arbitrary coset, we find the general form of the R-matrix underlying the deformation, and prove that the dilaton is not modified by the deformation, while the frames are multiplied by a constant matrix. Our explicit solutions describe families of integrable string theories depending on several continuous parameters.

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arXiv2016

Supergravity background of the lambda-deformed AdS_3 x S^3 supercoset

We construct the solution of type IIB supergravity describing the integrable lambda-deformation of the AdS_3 x S^3 supercoset. While the geometry corresponding to the deformation of the bosonic coset has been found in the past, our background is more natural for studying superstrings, and several interesting features distinguish our solution from its bosonic counterpart. We also report progress towards constructing the lambda-deformation of the AdS_5 x S^5 supercoset.

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arXiv2015

Killing(-Yano) Tensors in String Theory

We construct the Killing(-Yano) tensors for a large class of charged black holes in higher dimensions and study general properties of such tensors, in particular, their behavior under string dualities. Killing(-Yano) tensors encode the symmetries beyond isometries, which lead to insights into dynamics of particles and fields on a given geometry by providing a set of conserved quantities. By analyzing the eigenvalues of the Killing tensor, we provide a prescription for constructing several conserved quantities starting from a single object, and we demonstrate that Killing tensors in higher dimensions are always associated with ellipsoidal coordinates. We also determine the transformations of the Killing(-Yano) tensors under string dualities, and find the unique modification of the Killing-Yano equation consistent with these symmetries. These results are used to construct the explicit form of the Killing(-Yano) tensors for the Myers-Perry black hole in arbitrary number of dimensions and for its charged version.

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arXiv2015

Bubbling geometries for AdS_2 x S^2

We construct BPS geometries describing normalizable excitations of AdS_2 x S^2. All regular horizon-free solutions are parameterized by two harmonic functions in R^3 with sources along closed curves. This local structure is reminiscent of the "bubbling solutions" for the other AdS cases, however, due to peculiar asymptotic properties of AdS_2, one copy of R^3 does not cover the entire space, and we discuss the procedure for analytic continuation, which leads to a nontrivial topological structure of the new geometries. We also study supersymmetric brane probes on the new geometries, which represent the AdS_2 x S^2 counterparts of the giant gravitons.

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arXiv2013

(Non)-Integrability of Geodesics in D-brane Backgrounds

Motivated by the search for new backgrounds with integrable string theories, we classify the D-brane geometries leading to integrable geodesics. Our analysis demonstrates that the Hamilton-Jacobi equation for massless geodesics can only separate in elliptic or spherical coordinates, and all known integrable backgrounds are covered by this separation. In particular, we identify the standard parameterization of AdS_p X S^q with elliptic coordinates on a flat base. We also find new geometries admitting separation of the Hamilton-Jacobi equation in the elliptic coordinates. Since separability of this equation is a necessary condition for integrability of strings, our analysis gives severe restrictions on the potential candidates for integrable string theories.

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