Role of the Dirac sea in the quenching of Gamow-Teller strength

The issue of the Gamow-Teller sum rule in atomic nuclei is reexamined in the framework of a relativistic description of nuclei. It is shown that the total Gamow-Teller strength in the nucleon sector is reduced by about 12% as compared to the prediction of a nonrelativistic description. This reduction is due to the antinucleon degrees of freedom.