GLYPH<Minus> 4.0 GLYPH<Minus> 3.5 GLYPH<Minus> 3.0 GLYPH<Minus> 2.5 GLYPH<Minus> 2.0 GLYPH<Minus> 1.5 0.1 0.2 0.3 0.4 c for attractive bosons PSfrag replacements c µ/T FIG. 15: The scaling function c for attractive bosons as a function of µ/T . The origin of the axes is at (log . 33 , 0). modulus for instance, and it could simply be an artifact of our approximation, but let us take it as a hypothesis. Whereas a Wigner crystal phase occurs at low density in three dimensions, it occurs at high density in two dimensions[33]. The possibility of crystal phases for repulsive bosons was studied in [9]. For Coulomb repulsion with strength e $^{2}$, the thermodynamic state of a classical Coulomb system is determined by Γ = √$_{πn e}$ $^{2}$/k$_{B}$ T , where n is the density. Experimentally it was found that Γ ≈ 137[34], which gives a critical density On the other hand, since our model has point-like interactions, and is in the unitary limit, the conditions for a crystal phase are expected to be different. In particular our formula eq. (95) has no e 2 dependence, and this leads to a linear in T dependence. n$_{c}$ ≈ 2 . 15 × 10 $^{9}$T 2 1 cm $^{2}$K2 (96) 35