We prove the following formula for the ground state energy density of a dilute Bose gas with density
ρ in
2 dimensions in the thermodynamic limit \begin{align*} e^{\rm{2D}}(ρ) = 4πρ^2 Y\left(1 - Y \vert \log Y \vert + \left( 2Γ+ \frac{1}{2} + \log(π) \right) Y \right) + o(ρ^2 Y^{2}). \end{align*} Here
Y=∣log(ρa2)∣−1 and
a is the scattering length of the two-body potential. This result in
2 dimensions corresponds to the famous Lee-Huang-Yang formula in
3 dimensions. The proof is valid for essentially all positive potentials with finite scattering length, in particular it covers the crucial case of the hard core potential.
Abstract We prove the following formula for the ground state energy density of a dilute Bose gas with density
ρ ρ in 2 dimensions in the thermodynamic limit
e2D(ρ)=4πρ2Y(1−Y∣logY∣+(2Γ+21+log(π))Y)+o(ρ2Y2), e 2D ( ρ ) = 4 π ρ 2 Y ( 1 - Y | log Y | + ( 2 Γ + 1 2 + log ( π ) ) Y ) + o ( ρ 2 Y 2 ) , as
ρa2→0 ρ a 2 → 0 . Here
Y=∣log(ρa2)∣−1 Y = | log ( ρ a 2 ) | - 1 and a is the scattering length of the two-body potential. This result in 2 dimensions corresponds to the famous Lee–Huang–Yang formula in 3 dimensions. The proof is valid for essentially all positive potentials with finite scattering length, in particular, it covers the crucial case of the hard core potential.
We study interacting bosons on a three-dimensional Bravais lattice with positive hopping amplitudes and on-site repulsive interactions. We prove that, in the dilute limit
ρ→0, the ground state energy density satisfies
e0(ρ)=4πaρ2(1+O(ρ1/6)), where
a is the lattice scattering length defined through the corresponding two-body problem. This establishes the analogue of the Dyson and Lieb-Yngvason theorems for the Bose-Hubbard gas. Our result shows that the leading-order energy is universal: although the lattice geometry affects the microscopic dispersion relation, it enters the leading order asymptotics only through the scattering length. In particular, it is independent of other features of the underlying Bravais lattice.