  We report the theoretical evaluations of the static scalar polarizability of
the 133Cs ground state and of the black body radiation shift induced on the
transition frequency between the two hyperfine levels with m_F = 0. This shift
is of fundamental importance in the evaluation of the accuracy of the primary
frequency standards based on atomic fountains and employed in the realization
of the SI second in the International Atomic Time (TAI) scale at the level of
1e-15. Our computed value for the polarizability is alpha_0=6.600(16)e-39
Cm^2/V in agreement at the level of 1e-3 with recent theoretical and
experimental values. As regards the black body radiation shift we .nd for the
relative hyper.ne transition frequency beta=-1.49 (7)e-14 at T = 300 K in
agreement with frequency measurements reported by our group and by Bauch and
Schroder [Phys. Rev. Lett. 78, 622, (1997)]. This value is lower by 2e-15 than
that obtained with measurements based on the dc Stark shift and than the value
commonly accepted up to now.
