Dark QCD matters

Abstract

We investigate the nightmare scenario of dark sectors that are made of non-abelian gauge theories with fermions, gravitationally coupled to the Standard Model (SM). While testing these scenarios is experimentally challenging, they are strongly motivated by the accidental stability of dark baryons and pions, that explain the cosmological stability of dark matter (DM). We study the production of these sectors which are minimally populated through gravitational freeze-in, leading to a dark sector temperature much lower than the SM, or through inflaton decay, or renormalizable interactions producing warmer DM. Despite having only gravitational couplings with the SM these scenarios turn out to be rather predictive depending roughly on three parameters: the dark sector temperature, the confinement scale and the dark pion mass. In particular, when the initial temperature is comparable to the SM one these scenarios are very constrained by structure formation, ∆Neff and limits on DM self-interactions. Dark sectors with same temperature or warmer than SM are typically excluded.

Early-Universe Model Building

“…Once gauged, the same symmetry can also naturally serve as a portal between the dark and the visible sector with various interesting signals [169]. This portal can further give rise to an ADM scenario (see Sec.…”

“…Below we review different DM candidates in such sectors and some intriguing dynamics that can happen therein, see Refs. [167,169,170] for recent reviews of such models.…”

“…Refs. [166,169,[171][172][173][174][175][176][177][178][179][180][181]. These dark mesons are composed of a dark quark and a dark anti-quark and are always bosons, regardless of the spin of dark quarks.…”

“…The stability of dark mesons can also be guaranteed via accidental symmetries, see for instance Ref. [166], or thanks to lack of non-gravitational interactions between the SM and the dark sector [169,182]. In such models both dark mesons and dark baryons can be viable DM candidates.…”

Glueballs in a Thermal Squeezeout Model

“…Nonetheless, a portal is still required between the two sectors to allow the dark glueballs to decay to SM particles. If these glueballs were stable, they would have become the dominant fraction of the DM in such setups [56], and in the mass range where thermal squeezeout becomes relevant would lead to an overproduction of the DM abundance.…”