FIMPzilla dark matter and conformal sectors

Abstract: We point out a dark matter candidate which arises in a minimal extension of solutions to the hierarchy problem based on compositeness. In such models, some or all of the Standard Model fields are composites of a conformal field theory (CFT) which confines near the electroweak scale. We posit an elementary scalar field, whose mass is expected to lie near the cutoff of the CFT, and whose couplings to the Standard Model are suppressed by the cutoff. Hence it can naturally be ultraheavy and feebly coupled. This scalar can constitute all of the dark matter for masses between $10^{10}$ GeV and $10^{18}$ GeV, with the relic abundance produced by the freeze-in mechanism via a coupling to the CFT. The principal experimental constraints come from bounds on the tensor-to-scalar ratio. We speculate about future detection prospects.