  I study the joint effect of dynamical friction, tidal torques and
cosmological constant on clusters of galaxies formation I show that within
high-density environments, such as rich clusters of galaxies, both dynamical
friction and tidal torques slows down the collapse of low-? peaks producing an
observable variation in the time of collapse of the perturbation and, as a
consequence, a reduction in the mass bound to the collapsed perturbation
Moreover, the delay of the collapse produces a tendency for less dense regions
to accrete less mass, with respect to a classical spherical model, inducing a
biasing of over-dense regions toward higher mass I show how the threshold of
collapse is modified if dynamical friction, tidal torques and a non-zero
cosmological constant are taken into account and I use the Extended Press
Schecter (EPS) approach to calculate the effects on the mass function Then, I
compare the numerical mass function given in Reed et al (2003) with the
theoretical mass function obtained in the present paper I show that the barrier
obtained in the present paper gives rise to a better description of the mass
function evolution with respect to other previous models (Sheth & Tormen 1999,
MNRAS, 308, 119 (hereafter ST); Sheth & Tormen 2002, MNRAS, 329, 61 (hereafter
ST1))
