  We give reasons in support of the use of an effective intensity-dependent
pion-nucleon coupling Hamiltonian for describing the properties of the pion
multiplicity distribution and the corresponding factorial moments within the
thermal-density matrix approach.We explain the appearance of the
negative-binomial (NB) distribution for pions and the well-known empi- rical
relation of Wroblewski.Our model Hamiltonian is written as a linear combination
of the generators of the SU(1,1) group.We find the generating function for the
pion multiplicity distribution at finite temperature T and discuss the
properties of the second-order factorial moment.Also, we show that an
intensity-dependent pion-nucleon coupling generates the squeezed states of the
pion field. At T=0, these squeezed states become an inherent property of the NB
distribution.
