Deformations Of Conformal Field Theories Research Articles

Two-dimensional conformal field theory, full vertex algebra and current-current deformation

The main purpose of this paper is a mathematical construction of non-perturbative deformations of two-dimensional conformal field theories.We introduce the notion of a full vertex algebra which formulates a compact two-dimensional conformal field theory. Then, we construct a deformation family of full vertex algebras which serves as a current-current deformation of conformal field theory in physics. The parameter space of the deformations is expressed as a quotient of an orthogonal Grassmannian. This parameter space is a part of the CFT moduli space expected in physics. We demonstrate that nontrivial quotients of Grassmannians are obtained from holomorphic vertex operator algebras of central charge 24.

On the classification of UV completions of integrable Toverline{T} deformations of CFT

It is well understood that 2d conformal field theory (CFT) deformed by an irrelevant Toverline{T} perturbation of dimension 4 has universal properties. In particular, for the most interesting cases, the theory develops a singularity in the ultra-violet (UV), signifying a shortest possible distance, with a Hagedorn transition in applications to string theory. We show that by adding an infinite number of higher [ Toverline{T} ]s>1 irrelevant operators of positive integer scaling dimension 2(s+1) with tuned couplings, this singularity can be resolved and the theory becomes UV complete with a Virasoro central charge cUV> cIR consistent with the c-theorem. We propose an approach to classifying the possible UV completions of a given CFT perturbed by [ Toverline{T} ]s that are integrable. The main tool utilized is the thermodynamic Bethe ansatz. We study this classification for theories with scalar (diagonal) factorizable S-matrices. For the Ising model with cIR = frac{1}{2} we find 3 UV completions based on a single massless Majorana fermion description with cUV = frac{7}{10} and frac{3}{2} , which both have mathcal{N} = 1 SUSY and were previously known, and we argue that these are the only solutions to our classification problem based on this spectrum of particles. We find 3 additional ones with a spectrum of 8 massless particles related to the Lie group E8 appropriate to a magnetic perturbation with cUV = frac{21}{22},frac{15}{12} , and frac{31}{2} . We argue that it is likely there are more cases for this E8 spectrum. We also study simpler cases based on su(3) and su(4) where we can propose complete classifications. For su(3) the infrared (IR) theory is the 3-state Potts model with cIR = frac{4}{5} and we find 3 completions with frac{4}{5} < cUV≤ frac{16}{5} . For the su(4) case, which has 3 particles and cIR = 1, and we find 11 UV completions with 1 < cUV ≤ 5, most of which were previously unknown.

Thermodynamics of perturbations of some single particle field theories

We study the thermodynamic Bethe ansatz (TBA) equations for pure perturbations of some simple integrable quantum field theories with a single bosonic or fermionic particle, in particular the massive sinh-Gordon model and its ultraviolet (UV) limit which is a deformation of the conformally invariant free massless boson. Whereas the TBA equations for deformations of massive theories are in principle known, the TBA equations we propose for the deformations of conformal field theories are relatively new and require a special factorization in rapidity variables of the CDD factor for the scattering of the massless particles. The latter TBA equations can be solved exactly and reproduce the known results for the ground state energy on a cylinder of circumference R which were previously obtained using different methods based for instance on the Burgers differential equation. Special attention is paid to the c-theorem in this context which is discussed in some detail. For positive infra-red central charge c IR, for flows consistent with the c-theorem the ground state energy develops a (previously known) square-root singularity toward the UV, which strongly suggests the theories are UV incomplete in these physically important cases. We suggest that the singularity indicates a tachyonic vacuum instability. Other cases with c IR < 0 do not have this singularity are interpreted as being UV complete with c UV = 0. We extend our results to a continuously variable c IR by introducing a chemical potential and suggest this as a possible toy model for the perturbed Liouville theory.

Deformation of the Ising model and its ultraviolet completion

Pure deformations of conformal field theories are generally asymptotically incomplete in the ultra-violet (UV) due to square-root singularities in the ground state energy on a cylinder of circumference R, such that the theory is ill-defined for distances shorter than some critical R *. In this article we show how a theory can be completed if one includes an infinite number of additional irrelevant perturbations. This is fully demonstrated in the case of the Ising model at c IR = 1/2 in the infra-red (IR), where we find two completions with central charges c UV = 3/2 and c UV = 7/10, the latter being the tri-critical Ising model. Both of these UV completions have supersymmetry which is broken in the renormalization group flow to low energies. We also consider multiple deformations of a free massless boson, where we cannot find a UV completion that is consistent with the c-theorem. For negative coupling g, which violates the c-theorem, in both cases we find c UV = −c IR as g → −∞. Finally we also study pure deformations of the off-critical Ising model.

Very special TJ¯ deformed CFT

We study a very special class of $T\bar{J}$ deformations of conformal field theories in two dimensions. While the deformations break the Lorentz symmetry, they preserve the twisted Lorentz symmetry. The resulting theory has right-moving Virasoro as well as left-moving translation and left-moving (chiral) scale symmetry without left-moving special conformal symmetry (nor left-moving Virasoro symmetry). As in the original $T\bar{J}$ deformations, they may be regarded as an operator dependent non-local change of coordinates. We show concrete examples based on worldsheet string theory and discuss how the non-unitary nature enables us to circumvent various no-go theorems.

Wonder of sine-Gordon $Y$-systems

The sine-Gordon Y-systems and the reduced sine-Gordon Y-systems were introduced by Tateo in the 90's in the study of the integrable deformation of conformal field theory by the thermodynamic Bethe ansatz method. The periodicity property and the dilogarithm identities concerning these Y-systems were conjectured by Tateo, and only a part of them have been proved so far. In this paper we formulate these Y-systems by the polygon realization of cluster algebras of types A and D, and prove the conjectured periodicity and dilogarithm identities in full generality. As it turns out, there is a wonderful interplay among continued fractions, triangulations of polygons, cluster algebras, and Y-systems.

Conformal perturbation theory, dimensional regularization, and AdS/CFT correspondence

We study relevant deformations of conformal field theory on a cylinder using conformal perturbation theory, and in particular the one point function of the deformation operator and the energy in a system after a quench. We do the one point function calculation in both AdS and the conformal field theory and we show that the results match. Our calculations are done with arbitrary spacetime dimension, as well as arbitrary scaling dimension of the relevant operator. The only singularities that appear in the end calculation can be related to logarithmic singularities in dimensional regularization. We also study time dependent setups in the field theory and we show how the response of the system can be calculated in a Hamiltonian based approach. We use this procedure to explain certain short time universal results that have been found previously.

Multi-faced black Janus and entanglement

To the second order of the deformation parameter, we construct the black brane solutions, which are dual to the multiple interface deformations of conformal field theories. We compute their thermodynamic quantities from the gravity and the field theory sides, and find a precise agreement, confirming the validity of the AdS/CFT correspondence. The correlation of two separate interfaces induces a Casimir energy and an interesting form of correlated entropy contribution. We comment on the properties of the interface lattice system too.

Lifshitz from AdS at finite temperature and top down models

We construct analytically an asymptotically Lifshitz black brane with dynamical exponent z=1+epsilon^2 in an Einstein-Proca model, where epsilon is a small parameter. In previous work we showed that the holographic dual QFT is a deformation of a CFT by the time component of a vector operator and the parameter epsilon is the corresponding deformation parameter. In the black brane background this operator additionally acquires a vacuum expectation value. We explain how the QFT Ward identity associated with Lifshitz invariance leads to a conserved mass and compute analytically the thermodynamic quantities showing that they indeed take the form implied by Lifshitz invariance. In the second part of the paper we consider top down Lifshitz models with dynamical exponent close to one and show that they can be understood in terms of vector deformations of conformal field theories. However, in all known cases, both the conformal field theory and its Lifshitz deformations have modes that violate the Breitenlohner-Freedman bound.

Inflation and deformation of conformal field theory

It has recently been suggested that a strongly coupled phase of inflation may be describedholographically in terms of a weakly coupled quantum field theory (QFT). Here, we explore the possibility that the wave function of an inflationary universe may be given by the partition function of a boundary QFT. We consider the case when the field theory is a small deformation of a conformal field theory (CFT), by the addition of a relevant operator O, and calculate the primordial spectrum predicted in the corresponding holographic inflation scenario. Using the Ward-Takahashi identity associated with Weyl rescalings, we derive a simple relation between correlators of the curvature perturbation ζ and correlators of the deformation operator O at the boundary. This is done without specifying the bulk theory of gravitation, so that the result would also apply to cases where the bulk dynamics is strongly coupled. We comment on the validity of the Suyama-Yamaguchi inequality, relating the bi-spectrum and tri-spectrum of the curvature perturbation.

NS5‐branes, holography and CFT deformations

AbstractA few supergravity solutions representing configurations of NS5‐branes admit exact conformal field theory (CFT) description. Deformations of these solutions should be described by exactly marginal operators of the corresponding theories. We briefly review the essentials of these constructions and present, as a new case, the operators responsible for turning on angular momentum.

Supersymmetric deformations of F1-NS5-branes and their exact CFT description

We consider certain classes of operators in the exact conformal field theory SL(2,R) x SU(2) x U(1)^4 describing strings in an AdS(3) x S(3) x T4 geometry supported by Neveu--Schwarz 3-form fluxes. This background arises in the near-horizon limit of a system of NS5-branes wrapped on a 4-torus and F1-branes smeared on the 4-torus when both types of branes are located at the same point in their common transverse space. We find a class of operators that lead to spacetime supersymmetric deformations. It is remarkable that most of these operators are not chiral primary with respect to the N=2 superconformal algebra on the wordsheet. A subset of these worldsheet conformal field theory deformations admits an interpretation either as a geometric deformation of the brane system or as a deformation of the distribution of the F1-branes, viewed as smooth instantons, inside the wrapped NS5-brane worldvolume. The 2-dimensional conformal field theory, however, seems to lack operators corresponding to arbitrary NS5-brane deformations, in contrast to pure NS5-brane systems where all geometric deformations can be accounted for by chiral primary operators.

Current-current deformations of conformal field theories, and WZW models

Moduli spaces of conformal field theories corresponding to current-current deformations are discussed. For WZW models, CFT and sigma model considerations are compared. It is shown that current-current deformed WZW models have WZW-like sigma model descriptions with non-bi-invariant metrics, additional B-fields and a non-trivial dilaton.

Twistfield perturbations of vertex operators in the Bbb Z2-orbifold model

We apply Kadanoff's theory of marginal deformations of conformal field theories to twistfield deformations of Z_2 orbifold models in K3 moduli space. These deformations lead away from the Z_2 orbifold sub-moduli-space and hence help to explore conformal field theories which have not yet been understood. In particular, we calculate the deformation of the conformal dimensions of vertex operators for p^2<1 in second order perturbation theory.

D-PARTICLE RECOIL SPACE–TIMES AND "GLUEBALL" MASSES

We discuss the properties of matter in a D-dimensional anti-de Sitter-type space–time induced dynamically by the recoil of a very heavy D(irichlet)-particle defect embedded in it. The particular form of the recoil geometry, which from a world sheet view point follows from logarithmic conformal field theory deformations of the pertinent sigma-models, results in the presence of both infrared and ultraviolet (spatial) cutoffs. These are crucial in ensuring the presence of mass gaps in scalar matter propagating in the D-particle recoil space–time. The analogy of this problem with the Liouville-string approach to QCD, suggested earlier by John Ellis and one of the present authors, prompts us to identify the resulting scalar masses with those obtained in the supergravity approach based on the Maldacena's conjecture, but without the imposition of any supersymmetry in our case. Within reasonable numerical uncertainties, we observe that agreement is obtained between the two approaches for a particular value of the ratio of the two cutoffs of the recoil geometry. Notably, our approach does not suffer from the ambiguities of the supergravity approach as regards the validity of the comparison of the glueball masses computed there with those obtained in the continuum limit of lattice gauge theories.

Chiral deformations of conformal field theories

We study general perturbations of two-dimensional conformal field theories by holomorphic fields. It is shown that the genus one partition function is controlled by a contact term (pre-Lie) algebra given in terms of the operator product expansion. These models have applications to vertex operator algebras, two-dimensional QCD, topological strings, holomorphic anomaly equations and modular properties of generalized characters of chiral algebras such as the W 1+∞ algebra, that is treated in detail.

Finite deformations of conformal field theories using analytically regularized connections

We study some natural connections on spaces of conformal field theories using an analytical regularization method. The connections are based on marginal conformal field theory deformations. We show that the analytical regularization preserves conformal invariance and leads to integrability of the marginal deformations. The connections are shown to be flat and to generate well-defined finite parallel transport. These finite parallel transports yield formulations of the deformed theories in the state space of an undeformed theory. The restrictions of the connections to the tangent space are curved but free of torsion.

Classical matrix sine-Gordon theory

The matrix sine-Gordon theory, a matrix generalization of the well-known sine-Gordon theory, is studied. In particular, the A3 generalization where fields take values in SU(2) describes integrable deformations of conformal field theory corresponding to the coset SU(2) × SU(2)/SU(2). Various classical aspects of the matrix sine-Gordon theory are addressed. We find exact solutions, solitons and breathers which generalize those of the sine-Gordon theory with internal degrees of freedom, by applying the Zakharov-Shabat dressing method and explaining their physical properties. Infinite current conservation laws and then Backlund transformation of the theory are obtained from the zero curvature formalism of the equation of motion. From the Backlund transformation, we also derive exact solutions as well as a nonlinear superposition principle by making use of Bianchi's permutability theorem.

The space of local operators in perturbed conformal field theories

The space of local operators in massive deformations of conformal field theories is analysed. For several model systems it is shown that one can define chiral sectors in the theory, such that the chiral field content is in a one-to-one correspondence with that of the underlying conformal field theory. The full space of operators consists of the descendent spaces of all scalar fields. If the theory contains asymptotic states which satisfy generalised statistics, the form-factor equations admit in addition also solutions corresponding to the descendent spaces of the para-fermionic operators of the same spin as the asymptotic states. The derivation of these results uses q-sum expressions for the characters and q-difference equations used in proving Rogers-Ramanujan type identities.

Finite deformations of conformal field theory and spacetime geometry.

We demonstrate in detail how the space of two-dimensional quantum field theories can be parametrized by off-shell states of a free closed string moving in a flat background. The dynamic equation corresponding to the condition of conformal invariance includes an infinite number of higher order terms, and we give an explicit procedure for their calculation. The symmetries corresponding to equivalence relations of conformal field theory are described. In this framework we show how to perform a nonperturbative analysis in the low-energy limit and prove that it corresponds to the Brans-Dicke theory of gravity interacting with a skew symmetric tensor field.