Macro-orbitals and microscopic theory of a system of interacting bosons
  Macro-orbital representation of a particle (detailed account given in cond-mat/0603784) has been used to develop the microscopic theory of a system of interacting bosons. It concludes that: (i) below certain temperature (say, $T_{\lambda}$), particles assume a state of (q, -q) bound pairs, (ii) the $\lambda-$transition is a consequence of inter-particle quantum correlations clubbed with zero-point repulsion and inter-particle attraction and represents an onset of the order-disorder of particles in their $\phi-$space followed simultaneously by their BEC as (q, -q) bound pairs in a state of q = $q_o = \pi/d$ and K = 0, (iii) particles at $T \le T_{\lambda}$ acquire collective binding which locks them at <k> = 0, <r> = $\lambda/2$ and $\Delta\phi = 2n\pi$ (with n = 1, 2, 3, ...), (iv) the entire system assumes mechanical strain in inter-particle bonds and behaves like a single macroscopic molecule, (v) there exists an energy gap between the superfluid and normal fluid phases of the system, (vi) the $\lambda-$transition represents the twin phenomena of broken gauge symmetry and phase coherence, (vii) the system does not have p = 0 condensate, (viii) a new kind of quantum quasi-particle "omon" (a phononlike wave of the oscillations of the momentum coordinates of particles) exists in superfluid phase, etc. It explains the properties of He-II, including the origin of quantized vortices, critical velocities, logarithmic singularity of specific heat, etc. at quantitative level and provides microscopic foundation to two fluid theory, $\Psi-$theory, idea of macroscopic wave function, etc. The framework of the theory can unify the physics of interacting bosons and fermions. 
Yatendra S. Jain