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OP-3057OpenCondensed matter

Bose–Einstein condensation at fixed density

For a homogeneous three-dimensional Bose gas with a fixed nonnegative finite-range two-body potential, prove at zero temperature that the largest eigenvalue of the one-body density matrix is at least cNcN in the thermodynamic limit N/L3=ρN/L^3=\rho, for sufficient

Source-reported statusAs of 2026-09-04Source & evidence ↓

Problem statement

For a homogeneous three-dimensional Bose gas with a fixed nonnegative finite-range two-body potential, prove at zero temperature that the largest eigenvalue of the one-body density matrix is at least cNcN in the thermodynamic limit N/L3=ρN/L^3=\rho, for sufficiently small fixed gas parameter ρa3>0\rho a^3>0 and some c>0c>0.

Lean 4

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Background

Use periodic boxes, fixed kinetic-energy normalization and a potential with positive scattering length aa. The density and potential stay fixed as the box grows: this is not a mean-field or Gross–Pitaevskii scaling limit.

Established baseline: rigorous energy asymptotics and condensation theorems in other scaling regimes provide substantial progress but do not imply a macroscopic one-body eigenvalue in this homogeneous fixed-density limit. Solovej's 2025 account explicitly separates the energy expansion from this condensation question.

Positive-temperature condensation and quantitative depletion are further targets, not required for the zero-temperature existence benchmark.

Progress & source assessment

Source catalogue review: 4 September 2026. Improved indicates partial progress, including qualified preprint claims.

References
  1. [1]Solovej, original open questions on the dilute Bose gas (2025), sections 5 and 8 link

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