Carroll fermions in two dimensions

Abstract

Carroll symmetry is a very powerful characteristic of generic null surfaces, as it replaces the usual Poincaré 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 (2⁢𝑑) 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 2⁢𝑑 conformal Carroll or, equivalently the 3⁢𝑑 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 quantise them using the highest weight representation of the vacuum. We also discuss how the symmetries of 2⁢𝑑 free fermion conformal field theories can be continually deformed by infinite boosts or degenerate linear transformations on coordinates, leading to the corresponding BMS invariant theory at singular points.