  The lambda point in liquid He4 is a well established phenomenon acknowledged
as an example of Bose-Einstain condensation. This is generally accepted, but
there are serious discrepancies between the theory and experimental results,
namely the lower value of the transition temperature Tl and the negative value
of dTl /dP. These discrepancies can be explained in term of the quantum
stochastic hydrodynamic analogy (QSHA). The QSHA shows that at the
He4I\textregisteredHe4II superfluid transition the quantum coherence length lc
becomes of order of the distance up to which the wave function of a couple of
He4 atoms extends itself. In this case, the He42 state is quantum and the
quantum pseudo-potential brings a repulsive interaction that leads to the
negative dTl /dP behavior. This fact overcomes the difficulty to explain the
phenomenon by introducing a Hamiltonian inter-atomic repulsive potential that
would obstacle the gas-liquid transition.
