We consider the M -> 0 limit for tagged particle diffusion in a 1-dimensional
Rayleigh-gas, studied originaly by Sinai and Soloveichik (1986), respectively
by Szasz and Toth (1986). In this limit we derive a new type of model for
tagged paricle diffusion, with Calogero-Moser-Sutherland (i.e. inverse
quadratic) interaction potential between the two central particles. Computer
simulations on this new model reproduce exactly the numerical value of the
limiting variance obtained by Boldrighini, Frigio and Tognetti (2002).Comment: Dedicated to Domokos Szasz on his 65th birthda
