Abstract
"Dark quark nuggets", a lump of dark quark matter, can be produced in the early universe for a wide range of confining gauge theories and serve as a macroscopic dark matter candidate. The two necessary conditions, a nonzero dark baryon number asymmetry and a first-order phase transition, can be easily satisfied for many asymmetric dark matter models and QCD-like gauge theories with a few massless flavors. For confinement scales from 10 keV to 100 TeV, these dark quark nuggets with a huge dark baryon number have their masses vary from $10^{23}~\mathrm{g}$ to $10^{-7}~\mathrm{g}$ and their radii from $10^{8}~\mathrm{cm}$ to $10^{-15}~\mathrm{cm}$. Such macroscopic dark matter candidates can be searched for by a broad scope of experiments and even new detection strategies. Specifically, we have found that the gravitational microlensing experiments can probe heavier dark quark nuggets or smaller confinement scales around 10 keV; collision of dark quark nuggets can generate detectable and transient electromagnetic radiation signals; the stochastic gravitational wave signals from the first order phase transition can be probed by the pulsar timing array observations and other space-based interferometry experiments; the approximately massless dark mesons can behave as dark radiation to be tested by the next-generation CMB experiments; the free dark baryons, as a subcomponent of dark matter, can have direct detection signals for a sufficiently strong interaction strength with the visible sector.
Highlights
The theory of quantum chromodynamics (QCD) is an integral part of the Standard Model (SM) of elementary particles as it successfully explains hadron properties, nuclear structure, and phenomena
We have argued that the formation of dark quark nuggets is expected in confining gauge theories that generically admit a first-order phase transition and a dark baryon asymmetry
Depending on the confinement scale and the magnitude of the dark baryon asymmetry, a nugget’s mass and radius may span several orders of magnitude, MdQN ∼ 10−7–1023 g and RdQN ∼ 10−15–108 cm, and their cosmological abundance can match that of the dark matter
Summary
The theory of quantum chromodynamics (QCD) is an integral part of the Standard Model (SM) of elementary particles as it successfully explains hadron properties, nuclear structure, and phenomena. While QCD predicts that most matter in the current universe is in the form of hadrons, the theory admits an exotic phase of “quark matter” at high baryon-number density and low temperature [1] In his seminal work, Witten [2] proposed that “nuggets” of quark matter could have formed in the early universe at the epoch of quark confinement, and that these nuggets could survive in the universe today as a dark matter candidate. In Appendix A, we provide a calculation of the phase transition based on the effective sigma model for the dark chiral symmetry breaking
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