  We present a comprehensive theoretical study of the phase diagram of a system
of many Bose particles interacting with a two-body central potential of the
so-called Lennard-Jones form. First-principles path-integral computations are
carried out, providing essentially exact numerical results on the thermodynamic
properties. The theoretical model used here provides a realistic and remarkably
general framework for describing simple Bose systems ranging from crystals to
normal fluids to superfluids and gases. The interplay between particle
interactions on the one hand, quantum indistinguishability and delocalization
on the other, is characterized by a single quantumness parameter, which can be
tuned to engineer and explore different regimes. Taking advantage of the rare
combination of the versatility of the many-body Hamiltonian and the possibility
for exact computations, we systematically investigate the phases of the systems
as a function of pressure (P) and temperature (T), as well as the quantumness
parameter. We show how the topology of the phase diagram evolves from the known
case of He-4, as the system is made more (and less) quantum, and compare our
predictions with available results from mean-field theory. Possible realization
and observation of the phases and physical regimes predicted here are discussed
in various experimental systems, including hypothetical muonic matter.
