Truncatable bootstrap equations in algebraic form and critical surface exponents

TL;DR

This paper introduces algebraic truncations of conformal bootstrap equations that reveal exact spectra and surface critical exponents in boundary conformal field theories, notably applied to the 3d Ising model.

Contribution

It presents a novel algebraic approach to bootstrap equations that simplifies analysis and accurately estimates surface critical exponents in boundary CFTs.

Findings

Exact spectra for boundary operators in 3d Ising model

Precise estimates of surface renormalization group exponents

Algebraic identities among conformal block derivatives

Abstract

We describe examples of drastic truncations of conformal bootstrap equations encoding much more information than that obtained by a direct numerical approach. A three-term truncation of the four point function of a free scalar in any space dimensions provides algebraic identities among conformal block derivatives which generate the exact spectrum of the infinitely many primary operators contributing to it. In boundary conformal field theories, we point out that the appearance of free parameters in the solutions of bootstrap equations is not an artifact of truncations, rather it reflects a physical property of permeable conformal interfaces which are described by the same equations. Surface transitions correspond to isolated points in the parameter space. We are able to locate them in the case of 3d Ising model, thanks to a useful algebraic form of 3d boundary bootstrap equations. It turns out that the low-lying spectra of the surface operators in the ordinary and the special transitions of 3d Ising model form two different solutions of the same polynomial equation. Their interplay yields an estimate of the surface renormalization group exponent, $y_{h}=0.72558(18)$ for the ordinary universality class and $y_{h}=1.646(2)$ for the special universality class, which compare well with the most recent Monte Carlo calculations. Estimates of other surface exponents as well as OPE coefficients are also obtained.