Two papers were published by Zuckerman Postdoctoral Scholar Alumnus, Dr. Eric David Kramer, in collaboration with researchers at MIT and The Hebrew University of Jerusalem.
Paper Abstract: Thermal squeezeout of dark matter
We carry out a detailed study of the confinement phase transition in a dark sector with an SU(N) gauge group and a single generation of a dark heavy quark. We focus on heavy enough quarks such that their abundance freezes out before the phase transition, and the phase transition is of first order. We find that during this phase transition, the quarks are trapped inside contracting pockets of the deconfined phase and are compressed enough to interact at a significant rate, giving rise to a second stage of annihilation that can dramatically change the resulting dark matter abundance. As a result, the dark matter can be heavier than the often-quoted unitarity bound of ∼100 TeV. Our findings are almost completely independent of the details of the portal between the dark sector and the Standard Model. We comment briefly on possible signals of such a sector. Our main findings are summarized in a companion paper, while here we provide further details on different parts of the calculation.
Paper Abstract: Accidentally Asymmetric Dark Matter
We study the effect of a first-order phase transition in a confining SU(N) dark sector with heavy dark quarks. The baryons of this sector are the dark matter candidates. During the confinement phase transition the heavy quarks are trapped inside isolated, contracting pockets of the deconfined phase, giving rise to a second stage of annihilation that dramatically suppresses the dark quark abundance. The surviving abundance is determined by the local accidental asymmetry in each pocket. The correct dark matter abundance is obtained for O(1–100) PeV dark quarks, above the usual unitarity bound.