Structure of Carrollian (conformal) superalgebra

In this work, we investigate possible supersymmetric extensions of the Carrollian algebra and the Carrollian conformal algebra in both $d=4$ and $d=3$. For the super-Carrollian algebra in $d=4$, we identify multiple admissible structures, depending on the representations of the supercharges with respect to the Carrollian rotation. Some of these structures can be derived by taking the speed of light $c\to 0$ limit from super-Poincar\'e algebra, but others are completely novel. In the conformal case, we demonstrate that the nontrivial Carrollian superconformal algebras for $d=4$ and $d=3$ are isomorphic to super-Poincar\'e algebra of $d=5$ and $d=4$ respectively. Remarkably, neither of these constructions requires R-symmetry to ensure the algebraic closure. Furthermore, we discover two distinct classes of super-BMS$_4$ algebras, i.e. one singlet super-BMS$_4$ algebra and two multiplet chiral super-BMS$_4$ algebras. The singlet case arises from extending the $3$D Carrollian superconformal algebra, whereas the multiplet cases do not admit this pathology due to their finite-dimensional subalgebra containing supercharges with conformal dimension $\Delta=\pm\frac{3}{2}$.