From Galilei to Euclidean Carroll and the Alice Particle: The Times They Are a-Changin'
In generalized, also known as $p$-brane Galilei limits, the speed of light $c$ becomes infinite in the directions transverse to a $(p+1)$-dimensional Lorentzian worldvolume. In this paper, we explain that allowing the worldvolume to be Euclidean, and thus time to be transversal, $p$-brane Galilei limits turn into Carrollian ones, that we refer to as "Euclidean $p$-brane Carroll limits", in which $c$ goes to zero in the $p+1$ worldvolume directions. This leads to a unified approach to taking Galilean and Carrollian limits, whose consequences we explore for $p=0$. We show that the spacetime symmetries that arise from the Euclidean 0-brane Carroll limit can be centrally extended to what we will call the Alice algebra, similar to how the Bargmann algebra centrally extends the Galilei symmetries. This gives rise to the novel notion of an Alice particle, and we obtain the Bargmann and Alice particle actions from a unified limit of the action of a relativistic massive particle or tachyon, suitably coupled to a one-form gauge potential. In the presence of a cosmological constant, we find that the Bargmann and Alice particles undergo stable motion for negative and positive cosmological constant, respectively. Finally, we show that the Bargmann and Alice particle actions can be obtained from null reduction of a massless particle action in a relativistic spacetime with one and two times. Our results indicate that in 10 dimensions, the Alice particle is a decoupling limit of a D$0{}^*$-brane in Hull's type IIA${}^*$ theory, similar to how the Bargmann particle is related to a D$0$-brane in type IIA string theory.