THE SMALL-SCALE CLUSTERING POWER SPECTRUM AND RELATIVISTIC DECAYS

We present constraints on decaying-particle models in which an enhance d relativistic density allows an Ohm = 1 Cold Dark Matter universe to be reconciled with acceptable values for the Hubble constant. Such mod els may contain extra small-scale power, which can have important cons equences for enhanced object formation at high redshifts. Small-scale galaxy clustering and abundances of high-redshift damped Lyman alpha a bsorption clouds give a preferred range for the mass of any such decay ing particle of 2 to 30 keV and a lifetime of 0.5 to 100 yr for models with a high Hubble constant (h > 0.75). A lower Hubble constant, h si milar or equal to 0.5, weakens the constraint to 0.5 < m < 30 keV, 0.2 < tau < 500 yr. In permitted versions of the model, reionization occu rs at redshifts similar to 10 - 200, and this feature may be of import ance in understanding degree-scale CMB anisotropies.