Abstract
We use non-perturbative lattice calculations to investigate the finite-temperature confinement transition of stealth dark matter, focusing on the regime in which this early-universe transition is first order and would generate a stochastic background of gravitational waves. Stealth dark matter extends the standard model with a new strongly coupled SU(4) gauge sector with four massive fermions in the fundamental representation, producing a stable spin-0 'dark baryon' as a viable composite dark matter candidate. Future searches for stochastic gravitational waves will provide a new way to discover or constrain stealth dark matter, in addition to previously investigated direct-detection and collider experiments. As a first step to enabling this phenomenology, we determine how heavy the dark fermions need to be in order to produce a first-order stealth dark matter confinement transition.
Highlights
AND OVERVIEWThe confining gauge–fermion theory of quantum chromodynamics (QCD) produces the massive stable protons and nuclei of the visible Universe, making it compelling to hypothesize that new strong dynamics could underlie the dark sector
We have presented nonperturbative lattice investigations of the finite-temperature confinement transition of SU(4) stealth dark matter, motivated by the possibility that this early-Universe phase transition could have produced a stochastic background of gravitational waves that may be constrained or discovered by future searches
A firstorder transition is required to produce such a stochastic background of gravitational waves, so we have focused on determining the region of parameter space for which the stealth dark matter confinement transition is first order, considering relatively heavy dynamical fermions corresponding to the upper-right corner of the Columbia plot (Fig. 1)
Summary
The confining gauge–fermion theory of quantum chromodynamics (QCD) produces the massive stable protons and nuclei of the visible Universe, making it compelling to hypothesize that new strong dynamics could underlie the dark sector. In the context of strongly coupled composite models such as stealth dark matter, the transition of interest is the confinement transition through which the state of the system changes from a high-temperature deconfined plasma of “dark gluons” and dark fermions to stable SM-singlet dark baryons If this confinement transition was first order, its properties including the nucleation temperature and latent heat govern the stochastic spectrum of the gravitational waves it produced, making reliable knowledge of these properties a crucial ingredient to extract constraints from future observations [8,23,24]. IV we add those Nf 1⁄4 4 degenerate dynamical fermions and supplement our finite-temperature analyses with zero-temperature meson spectroscopy calculations These ingredients allow us to determine the ratio of dark pion and dark vector meson masses, MP=MV > 0.9, required for the stealth dark matter confinement transition to be first order. If we can assume TÃ ≃ Tc or estimate how they differ, our results for the mass dependence of the stealth dark matter transition will translate information on TÃ from gravitational-wave searches into predictions for both the approximate mass scale of the dark baryons as well as the minimum masses of the dark mesons being searched for at colliders
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