Competition of electron capture and beta-decay rates in supernova collapse

We calculate supernova electron capture and beta-decay rates for various pf-shell nuclei using large-scale shell-model techniques. We show that the centroid of the Gamow-Teller strength distribution was systematically misplaced in previous rate estimates. Our total electron capture rates are significantly smaller than currently adopted in core collapse calculations, while the total beta-decay rates change less. Our calculation shows that for electron-to-baryon ratios, Y-e = 0.42-0.46, beta-decay rates are larger than the competing electron capture rates.