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arXiv:2307.01257 · Physical review. D/Physical review. D.

Polyakov blocks for the 1D conformal field theory mixed-correlator bootstrap

Kausik Ghosh, Apratim Kaviraj, Miguel F. Paulos

Published Mar 29, 2024• 10 citations
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Abstract

We introduce manifestly crossing-symmetric expansions for arbitrary systems of 1D CFT correlators. These expansions are given in terms of certain Polyakov blocks which we define and show how to compute efficiently. Equality of operator product expansion and Polyakov block expansions leads to sets of sum rules that any mixed correlator system must satisfy. The sum rules are diagonalized by correlators in tensor product theories of generalized free fields. We show that it is possible to do a change of a basis that diagonalizes instead mixed correlator systems involving elementary and composite operators in a single field theory. As an application, we find the first nontrivial examples of optimal bounds, saturated by the mixed correlator system ϕ,ϕ2 in the theory of a single generalized free field. Published by the American Physical Society 2024

DOI
10.1103/physrevd.109.l061703

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We introduce manifestly crossing-symmetric expansions for arbitrary systems of 1D CFT correlators. These expansions are given in terms of certain Polyakov blocks which we define and show how to compute efficiently. Equality of operator product expansion and Polyakov block expansions leads to sets of sum rules that any mixed correlator system must satisfy. The sum rules are diagonalized by correlators in tensor product theories of generalized free fields. We show that it is possible to do a change of a basis that diagonalizes instead mixed correlator systems involving elementary and composite operators in a single field theory. As an application, we find the first nontrivial examples of optimal bounds, saturated by the mixed correlator system ϕ,ϕ2 in the theory of a single generalized free field. Published by the American Physical Society 2024
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We introduce a full set of rules to directly express all MMM-point conformal blocks in one- and two-dimensional conformal field theories, irrespective of the topology. The MMM-point conformal blocks are power series expansion in some carefully-chosen conformal cross-ratios. We then prove the rules for any topology constructively with the help of the known position space operator product expansion. To this end, we first compute the action of the position space operator product expansion on the most general function of position space coordinates relevant to conformal field theory. These results provide the complete knowledge of all MMM-point conformal blocks with arbitrary external and internal quasi-primary operators (including arbitrary spins in two dimensions) in any topology.
These lectures were given at the Weizmann Institute in the spring of 2019. They are intended to familiarize students with the nuts and bolts of the numerical bootstrap as efficiently as possible. After a brief review of the basics of conformal field theory in d>2 spacetime dimensions, we discuss how to compute conformal blocks, formulate the crossing equations as a semi-definite programming problem, solve this problem using SDPB on a personal computer, and interpret the results. We include worked examples for all steps, including bounds for 3d CFTs with Z2 or O(N) global symmetries. Each lecture includes a problem set, which culminate in a precise computation of the 3d Ising model critical exponents using the mixed correlator Z2 bootstrap. A Mathematica file is included that transforms crossing equations into the proper input form for SDPB.
We derive thermal Polyakov bootstrap equations for CFT two-point functions on Sβ1×Rd−1S^1_β\times\mathbb R^{d-1}Sβ1​×Rd−1. Combining the thermal OPE with a dispersion relation and the method of images gives a representation in blocks that satisfy Kubo-Martin-Schwinger (KMS) covariance. Their local expansions contain additional thermal blocks at classical double-twist dimensions. Matching the prescribed physical OPE requires cancellation of these generated contributions, yielding explicit linear equations for thermal OPE coefficients, including any compensating terms required by the reconstruction. We formulate the equations for bosonic scalar correlators and antiperiodic scalar structures extracted from fermion correlators, and find consistent solutions in analytically tractable thermal CFTs. The coefficient matrix, which we call the Polyakov matrix, connects the large-spin expansion to KMS consistency and reduces to minus the identity on the classical double-twist spectrum. This structure suggests a numerical approach to the three-dimensional Ising CFT that combines known low-lying vacuum data with a self-consistent large-spin tail.
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We consider conformal field theories around points of large twist degeneracy. Examples of this are theories with weakly broken higher spin symmetry and perturbations around generalized free fields. At the degenerate point we introduce twist conformal blocks. These are eigenfunctions of certain quartic operators and encode the contribution, to a given four-point correlator, of the whole tower of intermediate operators with a given twist. As we perturb around the degenerate point, the twist degeneracy is lifted. In many situations this breaking is controlled by inverse powers of the spin. In such cases the twist conformal blocks can be decomposed into a sequence of functions which we systematically construct. Decomposing the four-point correlator in this basis turns crossing symmetry into an algebraic problem. Our method can be applied to a wide spectrum of conformal field theories in any number of dimensions and at any order in the breaking parameter. As an example, we compute the spectrum of various theories around generalized free fields.