## Publications

438 results found

Beccaria M, Tseytlin AA, 2024, Large N expansion of superconformal index of k = 1 ABJM theory and semiclassical M5 brane partition function, *Nuclear Physics B*, Vol: 1001, ISSN: 0550-3213

It was shown in arXiv:2309.10786 that the leading non-perturbative contribution to the large N expansion of the superconformal index of the (2,0) 6d theory (which describes low-energy dynamics of N coincident M5 branes) is reproduced by the semiclassical partition function of quantum M2 brane wrapped on S1×S2 in a twisted version of AdS×7S4 background. Here we demonstrate an analogous relation for the leading non-perturbative contribution to the large N expansion of the superconformal index of the N=8 supersymmetric level-one U(N)×U(N) ABJM theory (which describes low-energy dynamics of N coincident M2 branes). The roles of M2 and M5 branes get effectively interchanged. Namely, the large N correction to the ABJM index is found to be given by the semiclassical partition function of quantum M5 brane wrapped on S1×S5 in a twisted version of AdS×4S7 background. This effectively confirms the suggestion for the “M5 brane index” made in arXiv:2007.05213 on the basis of indirect superconformal algebra considerations.

Skrzypek T, Tseytlin AA, 2024, On AdS/CFT duality in the twisted sector of string theory on AdS<inf>5</inf>× S<sup>5</sup>/ℤ<inf>2</inf> orbifold background, *Journal of High Energy Physics*, Vol: 2024

We consider type IIB string theory on an AdS5 × S5/ℤ2 orbifold background, which should be dual to 4d N = 2 superconformal SU(N) × SU(N) gauge theory with two bi-fundamental hypermultiplets. The correlator of two chiral BPS operators from the twisted sector of this quiver CFT exhibits non-trivial dependence on the ’t Hooft coupling λ already in the planar limit. This dependence was recently determined using localisation and the expansion at large λ contains a subleading contribution proportional to ζ(3)λ−3/2. We address the question of how to reproduce this correction on the string theory side by starting with the ζ(3)α′3 term in the type IIB string effective action. We find a regular solution of type IIB supergravity which represents a resolution of the AdS5 × S5/ℤ2 orbifold and demonstrate that the relevant light twisted sector states may be identified as additional supergravity 2-form modes “wrapping” a finite 2-cycle in the resolution space. Reproducing the structure of the gauge theory result becomes more transparent in the large R-charge or BMN-like limit in which the resolved background takes a pp-wave form with the transverse space being a product of ℝ4 and the Eguchi-Hanson space.

Beccaria M, Giombi S, Tseytlin AA, 2024, (2,0) theory on S<sup>5</sup> × S<sup>1</sup> and quantum M2 branes, *Nuclear Physics B*, Vol: 998, ISSN: 0550-3213

The superconformal index Z of the 6d (2,0) theory on S5×S1 (which is related to the localization partition function of 5d SYM on S5) should be captured at large N by the quantum M2 brane theory in the dual M-theory background. Generalizing the type IIA string theory limit of this relation discussed in arXiv:2111.15493 and arXiv:2304.12340, we consider semiclassically quantized M2 branes in a half-supersymmetric 11d background which is a twisted product of thermal AdS7 and S4. We show that the leading non-perturbative term at large N is reproduced precisely by the 1-loop partition function of an “instanton” M2 brane wrapped on S1×S2 with S2⊂S4. Similarly, the (2,0) theory analog of the BPS Wilson loop expectation value is reproduced by the partition function of a “defect” M2 brane wrapped on thermal AdS⊂3 AdS7. We comment on a curious analogy of these results with similar computations in arXiv:2303.15207 and arXiv:2307.14112 of the partition function of quantum M2 branes in AdS×4S7/Zk which reproduced the corresponding localization expressions in the ABJM 3d gauge theory.

Seibold FK, Tseytlin AA, 2023, S-matrix on effective string and compactified membrane, *Journal of Physics A: Mathematical and Theoretical*, Vol: 56, ISSN: 1751-8113

Expanding Nambu-Goto action near infinitely long string vacuum one can compute scattering amplitudes of 2d massless fields representing transverse string coordinates. As was shown in (Dubovsky et al 2012 J. High Energy Phys. JHEP09(2012)044), the resulting S-matrix is integrable (provided appropriate local counterterms are added), in agreement with known free string spectrum and also with an interpretation of the static-gauge NG action as a T T ˉ deformation of a free massless theory. We consider a generalization of this computation to the case of a membrane, expanding its 3d action near an infinite membrane vacuum that has cylindrical R × S 1 shape (we refer to such membrane as ‘compactified’). Representing 3d fields as Fourier series in S 1 coordinate we get an effective 2d model in which the massless string modes are coupled to an infinite KK tower of massive 2d modes. We find that the resulting 2d S-matrix is not integrable already at the tree level. We also compute 1-loop scattering amplitude of massless string modes with all compactified membrane modes propagating in the loop. The result is UV finite and is a non-trivial function of the kinematic variables. In the large momentum limit or when the radius of S 1 is taken to infinity we recover the expression for the 1-loop scattering amplitude of the uncompactified R 2 membrane. We also consider a 2d model which is the T T ˉ deformation to the free theory with the same massless plus infinite massive tower of modes. The corresponding 2d S-matrix is found, as expected, to be integrable. Contribution to the special issue of Journal of Physics A: ‘Fields, Gravity, Strings and Beyond: In Memory of Stanley Deser’

Tseytlin AA, 2023, Comments on a 4-derivative scalar theory in 4 dimensions, *Theoretical and Mathematical Physics*, Vol: 217, Pages: 1969-1986, ISSN: 0040-5779

We review and elaborate on some aspects of the classically scale-invariant renormalizable 4-derivative scalartheory L = φ ∂4φ + g(∂φ)4. Similar models appear, e.g., in the context of conformal supergravity or inthe description of the crystalline phase of membranes. Considering this theory in Minkowski signature, wesuggest how to define Poincar´e-invariant scattering amplitudes by assuming that only massless oscillating(nongrowing) modes appear as external states. In such shift-symmetric interacting theory, there are no IRdivergences despite the presence of 1/q4 internal propagators. We discuss how nonunitarity of this theorymanifests itself at the level of the one-loop massless scattering amplitude.

Tseytlin AA, 2023, Quantum supermembranes and AdS/CFT duality, *Journal of Experimental and Theoretical Physics*, Vol: 137, Pages: 846-863, ISSN: 1063-7761

We review and extend some recent work on testing AdS/CFT correspondence between U(N)k × U(N)–k Chern-Simons-matter 3d gauge theory and M-theory in AdS4 × S7/Zk background. We demonstrate that 1-loop term in the quantum M2 brane partition function expanded near a classical solution correctly matches localization predictions on the gauge theory side in the case of BPS Wilson loop expectation value and instanton corrections to free energy.

Beccaria M, Giombi S, Tseytlin AA, 2023, Instanton contributions to the ABJM free energy from quantum M2 branes, *Journal of High Energy Physics*, Vol: 2023

We present a quantum M2 brane computation of the instanton prefactor in the leading non-perturbative contribution to the ABJM 3-sphere free energy at large N and fixed level k. Using supersymmetric localization, such instanton contribution was found earlier to take the form Finst(Nk)=−(sin22πk)−1exp(−2π2Nk)+.… The exponent comes from the action of an M2 brane instanton wrapped on S 3/ℤ k, which represents the M-theory uplift of the ℂP1 instanton in type IIA string theory on AdS4 × ℂP3. The IIA string computation of the leading large k term in the instanton prefactor was recently performed in arXiv:2304.12340. Here we find that the exact value of the prefactor (sin22πk)−1 is reproduced by the 1-loop term in the M2 brane partition function expanded near the S 3/ℤ k instanton configuration. As in the Wilson loop example in arXiv:2303.15207, the quantum M2 brane computation is well defined and produces a finite result in exact agreement with localization.

Beccaria M, Tseytlin AA, 2023, Comments on ABJM free energy on S3 at large N and perturbative expansions in M-theory and string theory, *Nuclear Physics B*, Vol: 994, ISSN: 0550-3213

We compare large N expansion of the localization result for the free energy F in the 3d N = 6 superconformal U(N)k × U(N)−k Chern-Simons-matter theory to its AdS/CFT counterpart, i.e. to the perturbativeexpansion of M-theory partition function on AdS4 × S7/Zk and to the weak string coupling expansionof type IIA effective action on AdS4 × CP3. We show that the general form of the perturbative expansions of F on the two sides of the AdS/CFT duality is indeed the same. Moreover, the transcendentalityproperties of the coefficients in the large N, large k expansion of F match those in the corresponding Mtheory or string theory expansions. To shed light on the structure of the 1-loop M-theory partition functionon AdS4 × S7/Zk we use the expression for the 1-loop 4-graviton scattering amplitude in the 11d supergravity. We also use the known information about the transcendental coefficients of the leading curvatureinvariants in the low-energy effective action of type II string theory. Matching of the remaining rationalfactors in the coefficients requires a precise information about currently unknown RR field strength termsin the corresponding superinvariants.

Beccaria M, Korchemsky GP, Tseytlin AA, 2023, Non-planar corrections in orbifold/orientifold <i>N</i>=2 superconformal theories from localization, *JOURNAL OF HIGH ENERGY PHYSICS*, ISSN: 1029-8479

Giombi S, Tseytlin AA, 2023, Wilson Loops at Large N and the Quantum M2-Brane, *PHYSICAL REVIEW LETTERS*, Vol: 130, ISSN: 0031-9007

Beccaria M, Korchemsky GP, Tseytlin AA, 2023, Exact strong coupling results in <i>N</i>=2 Sp(2<i>N</i>) superconformal gauge theory from localization, *JOURNAL OF HIGH ENERGY PHYSICS*, ISSN: 1029-8479

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Kurlyand SA, Tseytlin AA, 2022, Type IIB supergravity action on M5 x X5 solutions, *PHYSICAL REVIEW D*, Vol: 106, ISSN: 2470-0010

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Kurlyand SA, Tseytlin AA, 2022, Type IIB supergravity action on <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:msup><mml:mi>M</mml:mi><mml:mn>5</mml:mn></mml:msup><mml:mo>×</mml:mo><mml:msup><mml:mi>X</mml:mi><mml:mn>5</mml:mn></mml:msup></mml:math> solutions, *Physical Review D*, Vol: 106, ISSN: 2470-0010

Beccaria M, Korchemsky GP, Tseytlin A, 2022, Strong coupling expansion in <i>N</i>=2 superconformal theories and the Bessel kernel, *JOURNAL OF HIGH ENERGY PHYSICS*, ISSN: 1029-8479

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- Citations: 6

Hoare B, Seibold FK, Tseytlin AA, 2022, Integrable supersymmetric deformations of AdS(3)x S(3)x T-4, *The Journal of High Energy Physics*, Vol: 2022, Pages: 1-39, ISSN: 1029-8479

We construct a family of type IIB string backgrounds that are deformations of AdS3 × S3 × T4 with a “squashed” AdS3 × S3 metric supported by a combination of NSNS and RR fluxes. They have global SU(1, 1) × SU(2) symmetry, regular curvature, constant dilaton and preserve 8 supercharges. Upon compactification to 4 dimensions they reduce to N = 2 supersymmetric AdS2 × S2 solutions with electric and magnetic Maxwell fluxes. These type IIB supergravity solutions can be found from the undeformed AdS3 × S3 × T4 background by a combination of T-dualities and S-duality. In contrast to T-duality, S-duality transformations of a type IIB supergravity background do not generally preserve the classical integrability of the corresponding Green-Schwarz superstring sigma model. Nevertheless, we show that integrability is preserved in the present case. Indeed, we find that these backgrounds can be obtained, up to T-dualities, from an integrable inhomogeneous Yang-Baxter deformation (with unimodular Drinfel’d-Jimbo R-matrix) of the original AdS3 × S3 supercoset model.

Hoare B, Seibold FK, Tseytlin AA, 2022, Integrable supersymmetric deformations of AdS<inf>3</inf> × S<sup>3</sup> × T<sup>4</sup>, *Journal of High Energy Physics*, Vol: 2022

We construct a family of type IIB string backgrounds that are deformations of AdS3× S3× T4 with a “squashed” AdS3× S3 metric supported by a combination of NSNS and RR fluxes. They have global SU(1, 1) × SU(2) symmetry, regular curvature, constant dilaton and preserve 8 supercharges. Upon compactification to 4 dimensions they reduce to N = 2 supersymmetric AdS2× S2 solutions with electric and magnetic Maxwell fluxes. These type IIB supergravity solutions can be found from the undeformed AdS3× S3× T4 background by a combination of T-dualities and S-duality. In contrast to T-duality, S-duality transformations of a type IIB supergravity background do not generally preserve the classical integrability of the corresponding Green-Schwarz superstring sigma model. Nevertheless, we show that integrability is preserved in the present case. Indeed, we find that these backgrounds can be obtained, up to T-dualities, from an integrable inhomogeneous Yang-Baxter deformation (with unimodular Drinfel’d-Jimbo R-matrix) of the original AdS3× S3 supercoset model.

Beccaria M, Giombi S, Tseytlin A, 2022, Wilson loop in general representation and RG flow in 1d defect QFT

The generalized Wilson loop operator interpolating between the supersymmetric and the ordinary Wilson loop in N=4 SYM theory provides an interesting example of renormalization group flow on a line defect: the scalar coupling parameter ζ has a non-trivial beta function and may be viewed as a running coupling constant in a 1d defect QFT. In this paper we continue the study of this operator, generalizing previous results for the beta function and Wilson loop expectation value to the case of an arbitrary representation of the gauge group and beyond the planar limit. Focusing on the scalar ladder limit where the generalized Wilson loop reduces to a purely scalar line operator in a free adjoint theory, and specializing to the case of the rank k symmetric representation of SU(N), we also consider a certain semiclassical limit where k is taken to infinity with the product kζ2 fixed. This limit can be conveniently studied using a 1d defect QFT representation in terms of N commuting bosons. Using this representation, we compute the beta function and the circular loop expectation value in the large k limit, and use it to derive constraints on the structure of the beta function for general representation. We discuss the corresponding 1d RG flow and comment on the consistency of the results with the 1d defect version of the F-theorem.

Skrzypek T, Tseytlin AA, 2022, On type 0 string theory in solvable RR backgrounds, Publisher: ArXiv

Motivated by a possibility of solving non-supersymmetric type 0 string theoryin $AdS_5 \times S^5$ background using integrability, we revisit theconstruction of type 0 string spectrum in some solvable examples of backgroundswith RR fluxes that are common to type IIB and type 0B theories. The presenceof RR fluxes requires the use of a Green-Schwarz description for type 0 stringtheory. Like in flat space, the spectrum of type 0 theory can be derived fromthe type II theory spectrum by a $(-1)^F$ orbifolding, i.e. combining theuntwisted sector where GS fermions are periodic with the twisted sector whereGS fermions are antiperiodic (and projecting out all spacetime fermionicstates). This construction of the type 0 spectrum may also be implemented usinga Melvin background that allows to continuously interpolate between the type IIand type 0 theories. As an illustration, we discuss the type 0B spectrum in thepp-wave background which is the Penrose limit of $AdS_5 \times S^5$ with RR5-form flux and also in the pp-wave background which is the Penrose limit of$AdS_3 \times S^3 \times T^4$ supported by mixed RR and NSNS 3-form fluxes. Weshow that increasing the strength of the RR flux increases the value of theeffective normal ordering constant (which determines the mass of the type 0tachyon) and thus effectively decreases the momentum-space domain ofinstability of the ground state. We also comment on the semiclassical sector ofstates of type 0B theory in $AdS_5 \times S^5$.

Beccaria M, Tseytlin AA, 2022, 1/N expansion of circular Wilson loop in N = 2 superconformal SU(N) x SU(N) quiver (vol 265, JHEP04, 2021), *The Journal of High Energy Physics*, Vol: 115, ISSN: 1029-8479

Beccaria M, Giombi S, Tseytlin AA, 2022, Higher order RG flow on the Wilson line in N=4 SYM, *The Journal of High Energy Physics*, Vol: 2022, Pages: 1-28, ISSN: 1029-8479

Extending earlier work, we find the two-loop term in the beta-function for the scalar coupling ζ in a generalized Wilson loop operator of the N = 4 SYM theory, working in the planar weak-coupling expansion. The beta-function for ζ has fixed points at ζ = ±1 and ζ = 0, corresponding respectively to the supersymmetric Wilson-Maldacena loop and to the standard Wilson loop without scalar coupling. As a consequence of our result for the beta-function, we obtain a prediction for the two-loop term in the anomalous dimension of the scalar field inserted on the standard Wilson loop. We also find a subset of higher-loop contributions (with highest powers of ζ at each order in ‘t Hooft coupling λ) coming from the scalar ladder graphs determining the corresponding terms in the five-loop beta-function. We discuss the related structure of the circular Wilson loop expectation value commenting, in particular, on consistency with a 1d defect version of the F-theorem. We also compute (to two loops in the planar ladder model approximation) the two-point correlators of scalars inserted on the Wilson line

Beccaria M, Dunne G, Tseytlin AA, 2021, Strong coupling expansion of free energy and BPS Wilson loop in N=2 superconformal models with fundamental hypermultiplets, *The Journal of High Energy Physics*, Vol: 2021, Pages: 1-42, ISSN: 1029-8479

As a continuation of the study (in arXiv:2102.07696 and arXiv:2104.12625) of strong-coupling expansion of non-planar corrections in N = 2 4d superconformal models we consider two special theories with gauge groups SU(N) and Sp(2N). They contain N-independent numbers of hypermultiplets in rank 2 antisymmetric and fundamental representations and are planar-equivalent to the corresponding N = 4 SYM theories. These N = 2 theories can be realised on a system of N D3-branes with a finite number of D7-branes and O7-plane; the dual string theories should be particular orientifolds of AdS5 × S5 superstring. Starting with the localization matrix model representation for the N = 2 partition function on S4 we find exact differential relations between the 1/N terms in the corresponding free energy F and the 12-BPS Wilson loop expectation value ⟨W⟩ and also compute their large ’t Hooft coupling (λ » 1) expansions. The structure of these expansions is different from the previously studied models without fundamental hypermultiplets. In the more tractable Sp(2N) case we find an exact resummed expression for the leading strong coupling terms at each order in the 1/N expansion. We also determine the exponentially suppressed at large λ contributions to the non-planar corrections to F and ⟨W⟩ and comment on their resurgence properties. We discuss dual string theory interpretation of these strong coupling expansions.Download to read the full article text

Beccaria M, Dunne G, Tseytlin AA, 2021, BPS Wilson loop in N=2 superconformal SU(N) "orientifold" gauge theory and weak-strong coupling interpolation, *The Journal of High Energy Physics*, Vol: 2021, Pages: 1-30, ISSN: 1029-8479

We consider the expectation value ⟨W⟩ of the circular BPS Wilson loop in N = 2 superconformal SU(N) gauge theory containing a vector multiplet coupled to two hypermultiplets in rank-2 symmetric and antisymmetric representations. This theory admits a regular large N expansion, is planar-equivalent to N = 4 SYM theory and is expected to be dual to a certain orbifold/orientifold projection of AdS5 × S5 superstring theory. On the string theory side ⟨W⟩ is represented by the path integral expanded near the same AdS2 minimal surface as in the maximally supersymmetric case. Following the string theory argument in [5], we suggest that as in the N = 4 SYM case and in the N = 2 SU(N) × SU(N) superconformal quiver theory discussed in [19], the coefficient of the leading non-planar 1/N2 correction in ⟨W⟩ should have the universal λ3/2 scaling at large ’t Hooft coupling. We confirm this prediction by starting with the localization matrix model representation for ⟨W⟩. We complement the analytic derivation of the λ3/2 scaling by a numerical high-precision resummation and extrapolation of the weak-coupling expansion using conformal mapping improved Padé analysis.

Levine N, Tseytlin AA, 2021, Integrability vs. RG flow in G x G and G x G/H sigma models, *The Journal of High Energy Physics*, Vol: 2021, Pages: 1-32, ISSN: 1029-8479

We consider a class of 2d σ-models on products of group spaces that provide new examples of a close connection between integrability and stability under the RG flow. We first study the integrable G × G model derived from the affine Gaudin construction (for which the 1-loop β-functions were found in arXiv:2010.07879) and show that its condition of integrability is preserved also by the 2-loop RG flow. We then investigate the RG flow in the gauged G × G/H model, in particular the integrable T1,1 model found in arXiv:2010.05573. We also construct a new class of integrable G × G/H models in the case when the subgroup H is abelian. In the simplest case of G = SU2, H = U1 this leads to an integrable σ-model on the T1,q space (with a particular B-field). This model is also shown to be stable under the 2-loop RG flow, and we relate this property to its invariance under T-duality in an isometric U1 direction. This T1,q model may be interpreted as an integrable deformation of the GMM model (of two coupled WZW theories with generic levels) away from the conformal point.

Beccaria M, Tseytlin AA, 2021, 1/N expansion of circular Wilson loop in N=2 superconformal SU(N) x SU(N) quiver, *The Journal of High Energy Physics*, Vol: 2021, Pages: 1-33, ISSN: 1029-8479

Localization approach to N = 2 superconformal SU(N) × SU(N) quiver theory leads to a non-Gaussian two-matrix model representation for the expectation value of BPS circular SU(N) Wilson loop ⟨W⟩. We study the subleading 1/N2 term in the large N expansion of ⟨W⟩ at weak and strong coupling. We concentrate on the case of the symmetric quiver with equal gauge couplings which is equivalent to the ℤ2 orbifold of the SU(2N) N = 4 SYM theory. This orbifold gauge theory should be dual to type IIB superstring in AdS5 × (S5/ℤ2). We present a string theory argument suggesting that the 1/N2 term in ⟨W⟩ in the orbifold theory should have the same strong-coupling asymptotics λ3/2 as in the N = 4 SYM case. We support this prediction on the gauge theory side by a numerical study of the localization matrix model. We also find a relation between the 1/N2 term in the Wilson loop expectation value and the derivative of the free energy of the orbifold gauge theory on 4-sphere.

Beccaria M, Tseytlin AA, 2021, On the structure of non-planar strong coupling corrections to correlators of BPS Wilson loops and chiral primary operators, *The Journal of High Energy Physics*, Vol: 2021, Pages: 1-47, ISSN: 1029-8479

Starting with some known localization (matrix model) representations for correlators involving 1/2 BPS circular Wilson loop W in N = 4 SYM theory we work out their 1/N expansions in the limit of large ’t Hooft coupling λ. Motivated by a possibility of eventual matching to higher genus corrections in dual string theory we follow arXiv:2007.08512 and express the result in terms of the string coupling gs∼g2YM∼λ/N and string tension T∼λ−−√. Keeping only the leading in 1/T term at each order in gs we observe that while the expansion of ⟨W⟩ is a series in g2s/T, the correlator of the Wilson loop with chiral primary operators OJ has expansion in powers of g2s/T2. Like in the case of ⟨W⟩ where these leading terms are known to resum into an exponential of a “one-handle” contribution ∼g2s/T, the leading strong coupling terms in ⟨WOJ⟩ sum up to a simple square root function of g2s/T2. Analogous expansions in powers of g2s/T are found for correlators of several coincident Wilson loops and they again have a simple resummed form. We also find similar expansions for correlators of coincident 1/2 BPS Wilson loops in the ABJM theory.

Hoare B, Levine N, Tseytlin AA, 2020, Sigma models with local couplings: a new integrability-RG flow connection, *The Journal of High Energy Physics*, Vol: 20, ISSN: 1029-8479

We consider several classes of σ-models (on groups and symmetric spaces, η-models, ⋋-models) with local couplings that may depend on the 2d coordinates, e.g. on time τ . We observe that (i) starting with a classically integrable 2d σ-model, (ii) formally promoting its couplings hα to functions hα(τ ) of 2d time, and (iii) demanding that the resulting time-dependent model also admits a Lax connection implies that hα(τ ) must solve the 1-loop RG equations of the original theory with τ interpreted as RG time. This provides a novel example of an ‘integrability-RG flow’ connection. The existence of a Lax connection suggests that these time-dependent σ-models may themselves be understood as integrable. We investigate this question by studying the possibility of constructing non-local and local conserved charges. Such σ-models with D-dimensional target space and time-dependent couplings subject to the RG flow naturally appear in string theory upon fixing the light-cone gauge in a (D + 2)-dimensional conformal σ-model with a metric admitting a covariantly constant null Killing vector and a dilaton linear in the null coordinate.

Giombi S, Tseytlin AA, 2020, Strong coupling expansion of circular Wilson loops and string theories in AdS5 x S^5 and AdS4 x CP^3, *The Journal of High Energy Physics*, Vol: 2020, Pages: 1-27, ISSN: 1029-8479

We revisit the problem of matching the strong coupling expansion of the$\frac{1}{2}$ BPS circular Wilson loops in ${\cal N}=4$ SYM and ABJM gaugetheories with their string theory duals in ${\rm AdS}_5 \times S^5$ and ${\rmAdS}_4 \times CP^3$, at the first subleading (one-loop) order of the expansionaround the minimal surface. We observe that, including the overall factor$1/g_{\rm s}$ of the inverse string coupling constant, as appropriate for theopen string partition function with disk topology, and a universal prefactorproportional to the square root of the string tension $T$, both the SYM andABJM results precisely match the string theory prediction. We provide anexplanation of the origin of the $\sqrt T$ prefactor based on special featuresof the combination of one-loop determinants appearing in the string partitionfunction. The latter also implies a natural generalization $Z_\chi \sim (\sqrtT/g_{\rm s})^\chi$ to higher genus contributions with the Euler number $\chi$,which is consistent with the structure of the $1/N$ corrections found on thegauge theory side.

Pasarin O, Tseytlin AA, 2020, Generalised Schwarzschild metric from double copy of point-like charge solution in Born-Infeld theory, *Physics Letters B*, Vol: 807, Pages: 1-6, ISSN: 0370-2693

We discuss possible application of the classical double copy procedure to construction of a generalisation of the Schwarzschild metric starting from an -corrected open string analogue of the Coulomb solution. The latter is approximated by a point-like charge solution of the Born-Infeld action, which represents the open string effective action for an abelian vector field in the limit when derivatives of the field strength are small. The Born-Infeld solution has a regular electric field which is constant near the origin suggesting that corrections from the derivative terms in the open string effective action may be small there. The generalization of the Schwarschild metric obtained by the double copy construction from the Born-Infeld solution looks non-singular but the corresponding curvature invariants still blow up at . We discuss the origin of this singularity and comment on possible generalizations.

Drukker N, Giombi S, Tseytlin AA,
et al., 2020, Defect CFT in the 6d (2,0) theory from M2 brane dynamics in AdS7×S4, *The Journal of High Energy Physics*, Vol: 2020, ISSN: 1029-8479

Surface operators in the 6d (2,0) theory at large $N$ have a holographicdescription in terms of M2 branes probing the AdS$_7 \times S^4$ M-theorybackground. The most symmetric, 1/2-BPS, operator is defined over a planar orspherical surface, and it preserves a 2d superconformal group. This includes,in particular, an $SO(2,2)$ subgroup of 2d conformal transformations, so thatthe surface operator may be viewed as a conformal defect in the 6d theory. Thedual M2 brane has an AdS$_3$ induced geometry, reflecting the 2d conformalsymmetry. Here we use the holographic description to extract the defect CFTdata associated to the surface operator. The spectrum of transversefluctuations of the M2 brane is found to be in one-to-one correspondence with aprotected multiplet of operator insertions on the surface, which includes thedisplacement operator. We compute the one-loop determinants of fluctuations ofthe M2 brane, and extract the conformal anomaly coefficient of the sphericalsurface to order $N^0$. We also briefly discuss the RG flow from thenon-supersymmetric to the 1/2-BPS defect operator, and its consistency with a"$b$-theorem" for the defect CFT. Starting with the M2 brane action, we thenuse AdS$_3$ Witten diagrams to compute the 4-point functions of the elementarybosonic insertions on the surface operator, and extract some of the defect CFTdata from the OPE. The 4-point function is shown to satisfy superconformal Wardidentities, and we discuss a related subsector of "twisted" scalar insertions,whose correlation functions are constrained by the residual superconformalsymmetry.

Beccaria M, Jiang H, Tseytlin AA, 2020, Boundary correlators in WZW model on AdS2, *The Journal of High Energy Physics*, Vol: 2020, Pages: 1-37, ISSN: 1029-8479

Boundary correlators of elementary fields in some 2d conformal field theories defined on AdS2 have a particularly simple structure. For example, the correlators of the Liouville scalar happen to be the same as the correlators of the chiral component of the stress tensor on a plane restricted to the real line. Here we show that an analogous relation is true also in the WZW model: boundary correlators of the WZW scalars have the same structure as the correlators of chiral Kac-Moody currents. This is checked at the level of the tree and one-loop Witten diagrams in AdS2. We also compute some tree-level correlators in a generic σ-model defined on AdS2 and show that they simplify only in the WZW case where an extra Kac-Moody symmetry appears. In particular, the terms in 4- point correlators having logarithmic dependence on 1d cross-ratio cancel only at the WZW point. One motivation behind this work is to learn how to compute AdS2 loop corrections in 2d models with derivative interactions related to the study of correlators of operators on Wilson loops in string theory in AdS.

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