Perturbative unitarity constraints on gauge portals

Abstract

Dark matter that was once in thermal equilibrium with the Standard Model is generally prohibited from obtaining all of its mass from the electroweak phase transition. This implies a new scale of physics and mediator particles to facilitate dark matter annihilation. In this work, we focus on dark matter that annihilates through a generic gauge boson portal. We show how partial wave unitarity places upper bounds on the dark gauge boson, dark Higgs and dark matter masses. Outside of well-defined fine-tuned regions, we find an upper bound of 9 TeV for the dark matter mass when the dark Higgs and dark gauge bosons both facilitate the dark matter annihilations. In this scenario, the upper bound on the dark Higgs and dark gauge boson masses are 10 TeV and 16 TeV, respectively. When only the dark gauge boson facilitates dark matter annihilations, we find an upper bound of 3 TeV and 6 TeV for the dark matter and dark gauge boson, respectively. Overall, using the gauge portal as a template, we describe a method to not only place upper bounds on the dark matter mass but also on the new particles with Standard Model quantum numbers. We briefly discuss the reach of future accelerator, direct and indirect detection experiments for this class of models.

How to save the WIMP: global analysis of a dark matter model with two s-channel mediators

“…We note that while such effects might be relevant in some parts of the parameter space, we do not expect these effects to significantly change our conclusions. 4 Our final result differs from the one in [51] by a factor of 2, because we find a factor 1/2 from phase space for two identical final-state particles (see also [52]). Note also that stronger bounds could be obtained by also considering the scattering of W + W − , ZZ and Z Z [53].…”

Powerful solar signatures of long-lived dark mediators

“…• Thermalization and Unitarity: Thermalization can be important for > 10 TeV DM, and unitarity issues exist for DM mass O(100) TeV [137,138] for a standard WIMP, which is reached at the edge of the DM mass range we consider. Furthermore bound state effects can be relevant if DM mass becomes too large [105].…”

Whac-a-constraint with anomaly-free dark matter models

“…The observed relic density is achieved for σv ≈ 10 −8 GeV, which implies that v S cannot be much larger than 10 TeV for g Y ≈ 1. Since, for gauge portal dark matter models, perturbative unitarity sets order one bounds on Yukawa couplings [60], the new fermionic states cannot be made heavier than a few tens of TeV in this limit. In the 'on-shell' region 2m χ 1 < m Z where collider searches are particularly sensitive, it is typically possible to make the anomaly cancelling fermions heavier than the Z since m Z = 2v S , m χ 2 /m χ ± 1 ∼ y φ / √ 2v S which will heavily suppress their pair production cross section.…”