J.-B. Bru, V. A. Zagrebnov
An exactly soluble model with non-conventional and non-extensive 
condensations
(100K, LATeX 2e)

ABSTRACT.  We present a new exactly soluble model which is motivated by the 
Michoel-Schr\"{o}der-Verbeure model [1] and our model [2]. It 
manifests two kinds of condensations which occur in two stages: 
for intermediate densities one has a non-conventional Bose 
condensation in the mode k=0 due to a diagonal perturbation of the 
Imperfect Bose Gas Hamiltonian, whereas for large densities  
it coexists with conventional (generalized, non-extensive) 
Bose-Einstein condensation corresponding to the standard mechanism of 
saturation.