Isovector dipole resonances in {sup 4}He and neutrino-heating in supernova explosion

We studied transition strengths to isovector dipole resonances (GDR-1(-), SDR-1(-), and SDR-2(-)) in He-4 by using the He-4(Li-7,Be-7 gamma) reaction at 455 MeV and by comparing with shell-model calculations, in order to estimate cross sections of 4He for reactions induced by neutrinos emitting from a thermalized neutrino-sphere in the type-II supernova. Excitation of the SDR was dominant in the neutrino-heating of He-4. The He-4-excitation via neutral-current reactions of v(mu,tau) and (v) over bar (mu,tau) was found to be one order of magnitude stronger than that via charged-current reactions of v(e) and (v) over bar (e). The total energy-weighted cross section < omega sigma >(N) for neutrino-induced neutral-current reactions on He-4 was found to amount to about 1.0 x 10(-40) MeV.cm(2) which is comparable to those used in the previous simulations. The neutrino-heating effect of He-4 is small in the type-II supernova explosion.