  We study the effects of Kondo correlations on the transmission phase shift of
a quantum dot coupled to two leads in comparison with the experimental
determinations made by Aharonov-Bohm (AB) quantum interferometry. We propose
here a theoretical interpretation of these results based on scattering theory
combined with Bethe ansatz calculations. We show that there is a factor of 2
difference between the phase of the S-matrix responsible for the shift in the
AB oscillations, and the one controlling the conductance. Quantitative
agreement is obtained with experimental results for two different values of the
coupling to the leads.
