mathematical-physics / Quantum many-body theory; dilute Bose gases

Bose-Einstein condensation of the dilute hard-sphere Bose gas in the thermodynamic limit, at zero and small positive temperature

Positive temperature (October 5): for every a>0a>0 there is ρ∗(a)>0\rho_*(a)>0 such that for each fixed 0<ρ<ρ∗0<\rho<\rho_* some fixed T(a,ρ)>0T(a,\rho)>0 gives lim inf⁡N−1⟨u0,L,γN,L,T(1)u0,L⟩>0\liminf N^{-1}\langle u_{0,L},\gamma^{(1)}_{N,L,T}u_{0,L}\rangle>0 for the exact canonical hard-sphere Gibbs state as L→∞L\to\infty, N/L3→ρN/L^3\to\rho. Ground state (September 24 companion): absolute ε0,c0>0\varepsilon_0,c_0>0 with condensate fraction at least c0c_0 in every ground state when ρa3<ε0\rho a^3<\varepsilon_0. A further companion gives a density-uniform bound for bounded nonnegative finite-range potentials at temperatures up to ρ2\rho^2. Not shown: the transition temperature, condensation at moderate density, two dimensions, or potentials with attractive parts.

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mathematical-physicsOct 5, 2026Significance 58/100Registry: unreviewed

Bose-Einstein condensation of the dilute hard-sphere Bose gas in the thermodynamic limit, at zero and small positive temperature

Prior state unknown→proved

Positive temperature (October 5): for every a>0a>0 there is ρ∗(a)>0\rho_*(a)>0 such that for each fixed 0<ρ<ρ∗0<\rho<\rho_* some fixed T(a,ρ)>0T(a,\rho)>0 gives lim inf⁡N−1⟨u0,L,γN,L,T(1)u0,L⟩>0\liminf N^{-1}\langle u_{0,L},\gamma^{(1)}_{N,L,T}u_{0,L}\rangle>0 for the exact canonical hard-sphere Gibbs state as L→∞L\to\infty, N/L3→ρN/L^3\to\rho. Ground state (September 24 companion): absolute ε0,c0>0\varepsilon_0,c_0>0 with condensate fraction at least c0c_0 in every groun…

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Positive temperature (October 5): for every a>0a>0 there is ρ∗(a)>0\rho_*(a)>0 such that for each fixed 0<ρ<ρ∗0<\rho<\rho_* some fixed T(a,ρ)>0T(a,\rho)>0 gives lim inf⁡N−1⟨u0,L,γN,L,T(1)u0,L⟩>0\liminf N^{-1}\langle u_{0,L},\gamma^{(1)}_{N,L,T}u_{0,L}\rangle>0 for the exact canonical hard-sphere Gibbs state as L→∞L\to\infty, N/L3→ρN/L^3\to\rho. Ground state (September 24 companion): absolute ε0,c0>0\varepsilon_0,c_0>0 with condensate fraction at least c0c_0 in every ground state when ρa3<ε0\rho a^3<\varepsilon_0. A further companion gives a density-uniform bound for bounded nonnegative finite-range potentials at temperatures up to ρ2\rho^2. Not shown: the transition temperature, condensation at moderate density, two dimensions, or potentials with attractive parts.

Positive temperature (October 5): for every a>0a>0 there is ρ∗(a)>0\rho_*(a)>0 such that for each fixed 0<ρ<ρ∗0<\rho<\rho_* some fixed T(a,ρ)>0T(a,\rho)>0 gives lim inf⁡N−1⟨u0,L,γN,L,T(1)u0,L⟩>0\liminf N^{-1}\langle u_{0,L},\gamma^{(1)}_{N,L,T}u_{0,L}\rangle>0 for the exact canonical hard-sphere Gibbs state as L→∞L\to\infty, N/L3→ρN/L^3\to\rho. Ground state (September 24 companion): absolute ε0,c0>0\varepsilon_0,c_0>0 with condensate fraction at least c0c_0 in every ground state when ρa3<ε0\rho a^3<\varepsilon_0. A further companion gives a density-uniform bound for bounded nonnegative finite-range potentials at temperatures up to ρ2\rho^2. Not shown: the transition temperature, condensation at moderate density, two dimensions, or potentials with attractive parts.

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