Isocurvature Bound on a Bounce-Produced Dark Component

A dark component produced at a bounce need not share the primordial adiabatic perturbation; if its density fluctuates independently, it contributes isocurvature power that the microwave background tightly limits. This paper relates the isocurvature fraction to two quantities a bounce model controls: the fraction of the cold density carried by the bounce-produced component, and the relative density contrast imprinted on that component at production. Applying the published bound that uncorrelated cold-dark-matter isocurvature contributes less than about 3.8 percent of the total primordial power gives a product constraint on those quantities. A component carrying all of the cold density must be imprinted with a relative contrast below about a fifth of the adiabatic amplitude in power terms; components carrying a tenth of the density are constrained ten times more weakly in the same variable. Headline values are: beta bound = 3.8e-02, amp ratio full component = 1.987e-01, amp ratio tenth component = 1.987e+00, beta full order unity = 5.000e-01. This study is simulated and computed from stated assumptions; it is not a measurement.