Reflection Equivariance and the Heisenberg Picture for Spaces of Conformal Blocks

TL;DR

This paper explores the concept of reflection equivariance in spaces of conformal blocks, extending algebraic structures related to surfaces and their mapping classes to include modified trace, with implications for non-semisimple modular categories and conformal field theories.

Contribution

It introduces reflection equivariance as a homotopy fixed point structure, linking orientation reversal to algebraic and topological properties of conformal blocks and skein modules.

Findings

Describes the effect of orientation reversal on conformal blocks and skein modules.

Shows that reflection equivariance implies the circle category is modular.

Generalizes results from rational to logarithmic conformal field theories.

Abstract

Monoidal product, braiding, balancing and weak duality are pieces of algebraic information that are well-known to have their origin in oriented genus zero surfaces and their mapping classes. More precisely, each of them correspond to operations of the cyclic framed $E_2$-operad. We extend this correspondence to include another algebraic piece of data, namely the modified trace, by showing that it amounts to a homotopy fixed point structure with respect to the homotopy involution that reverses the orientation of surfaces and dualizes the state spaces. We call such a homotopy fixed point structure reflection equivariance. As an application, we describe the effect of orientation reversal on spaces of conformal blocks and skein modules in the non-semisimple setting, throughout relying on their factorization homology description. This has important consequences: For a modular functor that is reflection equivariant relative to a rigid duality, i) the circle category is modular, and the resulting mapping class group representations are automatically the ones built by Lyubashenko, and ii) the modules over the internal skein algebras are generated by one simple representation, carrying a unique projective mapping class group representation making the action equivariant. While i) is a new topological characterization of not necessarily semisimple modular categories, ii) generalizes the implicit description of spaces of conformal blocks purely through the representation theory of moduli algebras given by Alekseev-Grosse-Schomerus from rational conformal field theories admitting a Hopf algebra description to finite rigid logarithmic conformal field theories. This also generalizes several results of Faitg from ribbon factorizable Hopf algebras to arbitrary modular categories.