Tachyon Condensation and Brane Annihilation in Bose-Einstein Condensates: Spontaneous Symmetry Breaking in Restricted Lower-Dimensional Subspace

Abstract

In brane cosmology, the Big Bang is hypothesized to occur by the annihilation of the brane-anti-brane pair in a collision, where the branes are threedimensional objects in a higher-dimensional Universe. Spontaneous symmetry breaking accompanied by the formation of lower-dimensional topological defects, e.g. cosmic strings, is triggered by the so-called 'tachyon condensation', where the existence of tachyons is attributable to the instability of the brane-anti-brane system. Here, we discuss the closest analogue of the tachyon condensation in atomic Bose-Einstein condensates. We consider annihilation of domain walls, namely branes, in strongly segregated two-component condensates, where one component is sandwiched by two domains of the other component. In this system, the process of the brane annihilation can be projected effectively as ferromagnetic ordering dynamics onto a two-dimensional space. Based on this correspondence, three-dimensional formation of vortices from a domain-wall annihilation is considered to be a kink formation due to spontaneous symmetry breaking in the two-dimensional space. We also discuss a mechanism to create a 'vorton' when the sandwiched component has a vortex string bridged between the branes. We hope that this study motivates experimental researches to realize this exotic phenomenon of spontaneous symmetry breaking in superfluid systems.

Instability crossover of helical shear flow in segregated Bose-Einstein condensates

“…This instability plays an important role in nonequilibrium dynamics of phase-separated two-component BECs containing quantized vortices when there is a larger population imbalance between the two components. For example, numerous core-flow vortices are nucleated via an annihilation of two interfaces (a domain wall and an 063628-8 antidomain wall) [14][15][16][17]. In particular, tbe CFI must be cmcial to understand tbe dynamics and stability of a vorton [26,27], a loop of core-flow vortex.…”

“…Helical shear flows may naturally arise in turbulent or nonequilibrium states in segregated condensates with a large population imbalance between the two components (e.g., see Refs. [14][15][16][17]). A helical shear flow becomes dynamically unstable when the relative velocity along the vortex core exceeds a critical value.…”

Quantum nucleation of topological solitons

“…There are several other mechanisms for creating topological solitons such as bubble collisions [49][50][51], monopole pair creation under strong magnetic field (as a dual to the Schwinger mechanism) [52,53], and brane annihilations [54] (see Refs. [55][56][57][58] for condensed matter analogues). The purpose of this paper is to propose a yet another mechanism for a creation of topological solitons, that is, quantum nucleation through quantum tunneling.…”