arXiv subjects

George Georgiou

Publications and source records attributed to George Georgiou.

At least 19 recordsLinked to original sources

arXiv2026

Holographic interpolations of codimension-2 defect CFTs

We provide a comprehensive overview of the current status of higher-codimension defect systems. We review the holographic description and field theoretic properties of codimension-2 defects within the framework of defect Conformal Field Theories (dCFTs). Starting from the well-established classification of $1/2$-BPS supersymmetric defects, we examine their realisation through probe branes and bubbling supergravity geometries. Special emphasis is placed on recent developments involving non-supersymmetric D3/D5 configurations and their holographic interpolations. We discuss the calculation of important physical observables, such as one-point functions of the stress-energy tensor and chiral primary operators, across both weak and strong coupling regimes. The agreement of the results in the two regimes exhibits the full power of the holographic principle. This is a proceedings contribution to the Athens Workshop in Theoretical Physics: 10th Anniversary, held at the National and Kapodistrian University of Athens on December 17-19 2025.

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arXiv2026

Weyl Anomaly Coefficients of Holographic Defect CFTs at Weak and Strong Coupling

We determine the type-A Weyl anomaly coefficient $b$, associated with the intrinsic scalar curvature of the defect, for the class of holographically realised co-dimension two defect CFTs (dCFTs) introduced in arXiv: 2506.14505 and arXiv: 2512.14853. At strong coupling, we employ the dual D5-brane solutions in Euclidean signature, where the defect is supported on an $S^2$ submanifold of the Euclidean $AdS_3\times S^1$ boundary. At weak coupling, we use the classical solutions of the ${\cal N}=4$ SYM equations of motion, previously conjectured to describe the defects dual to the D5-brane configurations. Notably, the coefficient $b$ is found to be negative in a finite region of parameter space. To our knowledge, this constitutes the first explicit example of an {\it interacting} unitary dCFT with $b<0$. We also compute the type-B Weyl anomaly coefficients associated with the extrinsic curvature of the defects, first at strong coupling and subsequently at weak coupling. In a certain limit, we find agreement between the weak- and strong-coupling results for both the type-A and type-B anomaly coefficients.

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arXiv2025

Holographic interpolations of defect CFTs

We propose a new class of holographic dualities between certain, generically non supersymmetric, defect conformal field theories (dCFTs) and their gravity duals. Our construction interpolates between the 1/2-BPS D3-D3 system and its field theory dual at one end, and the holographic duality presented in arXiv: 2506.14505 at the other. On the gravity side, the defect is realised by a novel D5 probe brane embedded in the $AdS_5\times S^5$ geometry. The symmetry of the induced on the D5 brane metric is $AdS_3\times S^1\times S^2$. At a certain limit the D5 brane becomes singular and resembles the D3-D3 system. Consistency requires the presence of two D7 branes on which the D5 brane terminates. The existence of boundaries induces a gauge anomaly for the D5 brane which is cancelled through anomaly inflow from the D7 branes. The full system of the D5 and D7 branes is, thus, anomaly free. Also it does not have any tachyonic instabilities for a certain range of its parameters. On the field theory side, we determined the classical solution of the ${\cal N}=4$ SYM equations of motion which we conjecture to describe the defect dual to the D5-D7 system and comment on the identification of the parameters appearing at the two sides of the duality.

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arXiv2025

Holography of a novel codimension-2 defect CFT

We propose and study a new holographic duality between a non-supersymmetric defect conformal field theory (dCFT) and its gravity dual. On the gravity side, the defect is realised by a novel solution of a D5 probe brane embedded in the $AdS_5\times S^5$ geometry. The D5 brane wraps an $S^2\subset S^5$ and accommodates $k$ units of flux through the $S^2$. The symmetry of the induced on the brane metric is $AdS_3\times S^1\times S^2$. The brane ends on an $\mathbb{R}^{(1,1)}$ subspace of the 4-dimensional $AdS_5$ boundary resulting to a codimension-2 defect. We first prove that our brane configuration is stable by showing that the masses of all the fluctuations of the transverse to the brane coordinates respect the B-F bound. On the field theory side, the 2-dimensional defect is described by a classical solution whose precise form we determine. Subsequently, we calculate the one-point functions of the energy-momentum tensor and of the chiral primary operators (CPOs), first at strong and then at weak coupling. In an appropriate limit, we find compelling agreement between the weak and strong coupling results. Furthermore, we also extract one of the B-type Weyl anomaly coefficients.

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arXiv2025

The massless S-matrix of integrable $σ$-models

In contradistinction to the case of massive excitations, the connection between integrability and the tree-level massless scattering matrix of integrable $σ$-models is lost. Namely, in well-known 2-d integrable models the tree-level massless S-matrix exhibits particle production and fails to factorise. This is conjectured to happen due to IR ambiguities in the massless tree-level amplitudes. We present a definition of the massless S-matrix which has all the nice properties of integrable theories, there is no particle production and the S-matrix factorises. As an example, we present in detail the case of the $SU(2)$ principal chiral model (PCM).

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arXiv2023

Holographic three-point correlators at finite density and temperature

We calculate holographically three-point functions of scalar operators with large dimensions at finite density and finite temperature. To achieve this, we construct new solutions that involve two isometries of the deformed internal space. The novel feature of these solutions is that the corresponding two-point function depends not only on the conformal dimension but also on the difference between the two angular momenta. After identifying the dual operators, we systematically calculate three-point correlators as an expansion in powers of the temperature and the chemical potential. Our analytic perturbative results are in agreement with the exact numerical computation. The three point correlator (when the background contains either temperature or density but not both) is always a monotonic function of the temperature or the chemical potential. However, when both parameters are present the three point correlator is no longer a monotonic function. For fixed finite temperature and small values of the chemical potential a minimum of the three-point function appears. Surprisingly, contributions from the internal space do not depend on the chemical potential or the temperature, as long as those are treated as perturbations.

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arXiv2023

Holographic correlators of semiclassical states in defect CFTs

We set up the computation of correlation functions for operators that are dual to semiclassical string states in strongly coupled defect conformal field theories (dCFTs). In the dCFT that is dual to the D3-D5 probe-brane system, we calculate the correlation function of two heavy operators perturbatively, in powers of the conformal ratio. We find that the leading term agrees with the prediction of the operator product expansion (OPE). In the case of two heavy BMN operators, we find agreement in subleading orders as well.

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arXiv2022

Holographic correlation functions at finite density and/or finite temperature

We calculate holographically one and two-point functions of scalar operators at finite density and/or finite temperature. In the case of finite density and zero temperature we argue that only scalar operators can have non-zero VEVs. In the case in which both the chemical potential and the temperature are finite, we present a systematic expansion of the two-point correlators in powers of the temperature T and the chemical potential $Ω$. The holographic result is in agreement with the general form of the OPE which dictates that the two-point function may be written as a linear combination of the Gegenbauer polynomials $C_J^{(1)}(ξ)$ but with the coefficients depending now on both the temperature and the chemical potential, as well as on the CFT data. The leading terms in this expansion originate from the expectation values of the scalar operator $ϕ^2$, the R-current ${\cal J}^μ_{ϕ_3}$ and the energy-momentum tensor $T^{μν}$. By employing the Ward identity for the R-current and by comparing the appropriate term of the holographic result for the two-point correlator to the corresponding term in the OPE, we derive the value of the R-charge density of the background. Compelling agreement with the analysis of the thermodynamics of the black hole is found. Finally, we determine the behaviour of the two-point correlators, in the case of finite temperature, and in the limit of large temporal or spatial distance of the operators.

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arXiv2022

Scattering in integrable pp-wave backgrounds: S-matrix and absence of particle production

Particle production in integrable field theories may exist depending on the vacuum around which excitations are defined. To tackle this and analogous issues with conventional field theoretical tools, we consider the integrable $λ$-deformed model for $SU(2)$ together with a timelike coordinate. We construct the corresponding four-dimensional plane wave background keeping also post-plane wave corrections, as well as all the non-trivial $λ$-dependence. After imposing the light-cone gauge and the Virasoro constraints, we obtain an interacting field theory for the transverse physical modes which are massive. We explicitly demonstrate the absence of particle production to leading order in the large $k$-expansion. This is based crucially on the form of the interaction vertices and their dependence on the $λ$-deformation parameter. In addition, we compute the $S$-matrix for the two-particle elastic scattering exactly in $λ$ and to leading order in the large $k$-expansion. Our method can be applied to any integrable theory with at least one isometry.

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arXiv2022

Marginally deformed Schrödinger/dipole CFT correspondence

We construct and thoroughly study a new integrable example of the AdS/CFT correspondence with Schrödinger symmetry. On the gravity side, the supergravity solution depends on two parameters and is obtained by marginally deforming the internal space of the Schrödinger background through a series of TsT transformations. On the field theory side, we identify the dual field theory which also depends on two parameters. We find a point-like string solution and derive its dispersion relation. A non-trivial test of the correspondence is provided by using the Landau-Lifshitz coherent state approach to reproduce the leading, in the deformation parameters, terms of that relation. Then, we calculate the Wilson loop, describing the quark/anti-quark potential at strong coupling. It exhibits confining behaviour when the separation length is much less than the Schrödinger parameter. When the separation length is much greater than the Schrödinger parameter the behaviour is that of a conformal theory. Subsequently, we take the Penrose limit along a certain null geodesic of the constructed background and calculate the bosonic spectrum. Based on that spectrum, we make an educated guess for the exact, in the 't Hooft coupling, dispersion relation of the magnon excitations in the original doubly deformed background. This provides us with an exact prediction for the dimensions of the dual field theory operators.

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arXiv2021

Hamiltonian integrability of the webs of integrable theories

We present the Hamiltonian formulation of the recently constructed integrable theories of arXiv:2006.12525. These theories turn out to be canonically equivalent to the sum of an asymmetrically gauged CFT and of the most general $λ$-deformed model of arXiv:1812.04033. Using the Hamiltonian formalism, we prove that the full set of conserved charges of the models of arXiv:2006.12525 are in involution, ensuring their Hamiltonian integrability. Finally, we show that the equations of motion of these theories can be put in the form of zero curvature Lax connections.

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arXiv2021

Webs of integrable theories

We present an intuitive diagrammatic representation of a new class of integrable $\s$-models. It is shown that to any given diagram corresponds an integrable theory that couples $N$ WZW models with a certain number of each of the following four fundamental integrable models, the PCM, the YB model, both based on a group $G$, the isotropic $\s$-model on the symmetric space $G/H$ and the YB model on the symmetric space $G/H$. To each vertex of a diagram we assign the matrix of one of the aforementioned fundamental integrable theories. Any two vertices may be connected with a number of lines having an orientation and carrying an integer level $k_i$. Each of these lines is associated with an asymmetrically gauged WZW model at an arbitrary level $k_i$. Gauge invariance of the full action is translated to level conservation at the vertices. We also show how to immediately read from the diagrams the corresponding $\s$-model actions. The most generic of these models depends on at least $n^2+1$ parameters, where $n$ is the total number of vertices/fundamental integrable models. Finally, we discuss the case where the level conservation at the vertices is relaxed and the case where the deformation matrix is not diagonal in the space of integrable models.

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arXiv2020

Giant Gravitons in the Schrodinger holography

We construct and study new giant graviton configurations in the framework of the non-supersymmetric Schrodinger holography. We confirm in the original Schrodinger spacetime, the picture discovered previously in the pp-wave limit of the geometry, namely that it is the giant graviton that becomes the energetically favored stable configuration compared to the point graviton one. Furthermore, there is a critical value of the deformation above which the point graviton disappears from the spectrum. The former fact leads also to the possibility of tunnelling from the point graviton to the giant graviton configuration. We calculate, explicitly, the instanton solution and its corresponding action which gives a measure of the tunnelling probability. Finally, we evaluate holographically the three-point correlation function of two giant gravitons and one dilaton mode as a function of the Schrodinger invariant.

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arXiv2020

Asymmetric CFTs arising at the IR fixed points of RG flows

We construct a generalization of the cyclic $λ$-deformed models of \cite{Georgiou:2017oly} by relaxing the requirement that all the WZW models should have the same level $k$. Our theories are integrable and flow from a single UV point to different IR fixed points depending on the different orderings of the WZW levels $k_i$. First we calculate the Zamolodchikov's C-function for these models as exact functions of the deformation parameters. Subsequently, we fully characterize each of the IR conformal field theories. Although the corresponding left and right sectors have different symmetries, realized as products of current and coset-type symmetries, the associated central charges are precisely equal, in agreement with the valuesobtained from the C-function.

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arXiv2020

A free field perspective of $λ$-deformed coset CFT's

We continue our study of $λ$-deformed $σ$-models by setting up a $1/k$ perturbative expansion around the free field point for cosets, in particular for the $λ$-deformed $SU(2)/U(1)$ coset CFT. We construct an interacting field theory in which all deformation effects are manifestly encoded in the interaction vertices. Using this we reproduce the known $β$-function and the anomalous dimension of the composite operator perturbing away from the conformal point. We introduce the $λ$-dressed parafermions which have an essential Wilson-like phase in their expressions. Subsequently, we compute their anomalous dimension, as well as their four-point functions, as exact functions of the deformation and to leading order in the $k$ expansion. Correlation functions with an odd number of these parafermions vanish as in the conformal case.

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arXiv2020

Giant Gravitons on the Schrodinger pp-wave geometry

We construct a new giant graviton solution on the recently constructed pp-wave geometry of the non-supersymmetric Schrodinger background. That solution exhibits an intriguing behavior as the deformation parameter of the spacetime varies. Firstly, the degeneracy between the giant and the point graviton is lifted for the benefit of the giant graviton as soon as the deformation is turned on. Secondly, when the deformation parameter exceeds a critical value the barrier separating the point from the giant graviton disappears. This suggests that the mere presence of a D3-brane leads to the spontaneous breaking of conformal invariance. We perform a detailed analysis of the full bosonic spectrum, which reveals that the deformation induces a coupling between the scalar and the gauge field fluctuations. It is exactly this coupling that keeps the giant graviton free of tachyonic instabilities. Furthermore, the giant graviton configuration completely breaks the supersymmetry of the pp-wave background, as the Kappa-symmetry analysis suggests.

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arXiv2020

An exact symmetry in $λ$-deformed CFTs

We consider $λ$-deformed current algebra CFTs at level $k$, interpolating between an exact CFT in the UV and a PCM in the IR. By employing gravitational techniques, we derive the two-loop, in the large $k$ expansion, $β$-function. We find that this is covariant under a remarkable exact symmetry involving the coupling $λ$, the level $k$ and the adjoint quadratic Casimir of the group. Using this symmetry and CFT techniques, we are able to compute the Zamolodchikov metric, the anomalous dimension of the bilinear operator and the Zamolodchikov $C$-function at two-loops in the large $k$ expansion, as exact functions of the deformation parameter. Finally, we extend the above results to $λ$-deformed parafermionic algebra coset CFTs which interpolate between exact coset CFTs in the UV and a symmetric coset space in the IR.

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arXiv2020

Strong integrability of $λ$-deformed models

We study the notion of strong integrability for classically integrable $λ$-deformed CFTs and coset CFTs. To achieve this goal we employ the Poisson brackets of the spatial Lax matrix which we prove that it assumes the Maillet $r/s$-matrix algebra. As a consequence the system in question are integrable in the strong sense. Furthermore, we show that the derived Maillet $r/s$-matrix algebras can be realized in terms of twist functions, at the poles of which we recover the underlying symmetry algebras.

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