Non-linear clustering during the BEC dark matter phase transition

TL;DR

This paper investigates the non-linear collapse of Bose-Einstein Condensate dark matter during phase transitions, analyzing how it compares to standard dark matter on various scales through numerical simulations.

Contribution

It provides an analytical study of BEC dark matter collapse during phase transitions, extending previous numerical results and exploring the dependence on model parameters.

Findings

Collapse behavior similar to CDM on small scales before phase transition

Differences between BEC and CDM appear only on large astrophysical scales

BEC model evolution is nearly indistinguishable from standard dark matter for cluster-scale structures

Abstract

Spherical collapse of the Bose-Einstein Condensate (BEC) dark matter model is studied in the Thomas Fermi approximation. The evolution of the overdensity of the collapsed region and its expansion rate are calculated for two scenarios. We consider the case of a sharp phase transition (which happens when the critical temperature is reached) from the normal dark matter state to the condensate one and the case of a smooth first order phase transition where there is a continuous conversion of "normal" dark matter to the BEC phase. We present numerical results for the physics of the collapse for a wide range of the model's space parameter, i.e. the mass of the scalar particle $m_{\chi}$ and the scattering length $l_s$. We show the dependence of the transition redshift on $m_{\chi}$ and $l_s$. Since small scales collapse earlier and eventually before the BEC phase transition the evolution of collapsing halos in this limit is indeed the same in both the CDM and the BEC models. Differences are expected to appear only on the largest astrophysical scales. However, we argue that the BEC model is almost indistinguishable from the usual dark matter scenario concerning the evolution of nonlinear perturbations above typical clusters scales, i.e., $\gtrsim 10^{14}M_{\odot}$. This provides an analytical confirmation for recent results from cosmological numerical simulations [H.-Y. Schive {\it et al.}, Nature Physics, {\bf10}, 496 (2014)].