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We calculate the long-distance matrix elements for the decays of the Upsilon(eta_b) and chi_b (h_b) states in lattice QCD with two flavors of lightdynamical quarks. We relate the lattice matrix elements to their continuumcounterparts through one-loop order in perturbation theory. In the case of theleading S-wave matrix element, we compare our result with a phenomenologicalvalue that we extract from the experimental leptonic decay rate by using thetheoretical expression for the decay rate, accurate through relative orderalpha_s. Whereas estimates of the leading S-wave matrix element from quenchedQCD are 40--45% lower than the phenomenological value, the two-flavor estimateof the same matrix element is close to the phenomenological value.Extrapolating to the real world of 2+1 light flavors, we find that this matrixelement is approximately 6% higher than the phenomenological value, but thatthe phenomenological value lies within our error bars. We also compute thecolor-singlet and color-octet matrix elements for P-wave decays. We find thevalue of the color-singlet matrix element for 2+1 flavors to be approximately70% larger than the quenched value and the value of the color-octet matrixelement for 2+1 flavors to be approximately 40% larger than the quenched value.Comment: 29 pages, REVTEX, 4 Postscript figures, more extensive discussion of  fitting procedures and uncertainties, minor additional revisions and  correction

Bottomonium decay matrix elements from lattice QCD with two light quarks