Forbidden Dark Matter at the Weak Scale via the Top Portal

TL;DR

This paper investigates a novel dark matter freezeout mechanism at the electroweak scale, where forbidden annihilations into top quarks dominate, leading to specific experimental signatures and model constraints.

Contribution

It introduces the forbidden annihilation mechanism for dark matter at the electroweak scale, emphasizing top quark coupling and exploring simplified models with collider and detection implications.

Findings

Forbidden annihilations can set the relic abundance.

Dark matter couples mainly to top quarks via mediators.

Models evade indirect detection but are testable by colliders.

Abstract

At the tail of its velocity distribution, cold dark matter (DM) can annihilate at finite temperature to states heavier than itself. We explore the possibility that DM freezeout is dictated by these "forbidden annihilations" at the electroweak scale. Demanding that annihilation products be Standard Model particles, we find that for the forbidden mechanism to primarily set the DM relic abundance, DM must couple predominantly, if not solely, to top quarks. This can be arranged by invoking a non-trivial flavor structure such as Minimal Flavor Violation. We avail two avenues to achieve the correct thermal cross-section, requiring a mediator exchanged in the $s$- or $t$-channel. These simplified models submit easily to direct detection and collider searches, and necessarily hide from indirect detection signals. Viable supersymmetric spectra involving the forbidden mechanism may be found if combined with co-annihilation.