Carroll fermions in two dimensions

TL;DR

This paper investigates fermions on two-dimensional null manifolds, revealing their Carroll symmetry, conformal structure, and algebraic classifications, and explores how these symmetries can be deformed or extended.

Contribution

It systematically analyzes 2D Carroll fermions, identifies two classes of Clifford algebras and fermion actions, and connects their symmetries to the BMS algebra and deformations.

Findings

2D free fermions exhibit 2D Conformal Carroll/BMS symmetry.

Two distinct classes of Clifford algebras are identified.

Fermion actions and symmetries can be deformed via infinite boosts.

Abstract

Carroll symmetry is a very powerful characteristic of generic null surfaces, as it replaces the usual Poincar\'e algebra with a vanishing speed of light version thereof. These symmetries have found universal applications in the physics of null manifolds as they arise in diverse situations ranging from black hole horizons to condensed matter systems with vanishing Fermi velocities. In this work, we concentrate on fermions living on two dimensional ($2d$) null manifolds and explore the Carroll invariant structure of the associated field theories in a systematic manner. The free massless versions of these fermions are shown to exhibit $2d$ Conformal Carroll or equivalently the $3d$ Bondi-Metzner-Sachs (BMS) algebra as their symmetry. Due to the degenerate nature of the manifold, we show the presence of two distinct classes of Clifford Algebras. We also find that in two dimensions there are two distinct fermion actions. We study discrete and continuous symmetries of both theories, and quantize them using highest weight representation of the vacuum. We also discuss how the symmetries of $2d$ free fermion CFTs can be continually deformed by infinite boosts or degenerate linear transformations on coordinates, leading to the corresponding BMS invariant theory at singular points.