Length scales for BEC in the dilute Bose gas

Lee-Huang-Yang能量用于稀薄玻色气体：一般势的上界

Lee-Huang-Yang Energy for Dilute Bose Gases: an Upper Bound for General Potentials

本文针对一般短程排斥势的稀薄玻色气体，扩展硬球方法，建立了基态能量密度的Lee-Huang-Yang上界。

Ground State Energy of Dilute Bose Gas in Small Negative Potential Case

It is well known that the ground state energy of a three dimensional dilute Bose gas in the thermodynamic limit is $E=4πa ρN$ when the particles interact via a non-negative, finite range, symmetric, two-body potential. Here, $N$ is the number of particles, $ρ$ is the density of the gas, and $a$ is the scattering length of the potential. In this paper, we prove the same result without the non-negativity condition on the potential, provided the negative part is small.

关于稀薄玻色气体试态构造的注记

A Note on the Construction of Trial States for the Dilute Bose Gas

本文通过局部粒子数截断方法构建试态，推导了Lee-Huang-Yang修正作为基态能量上限，揭示稀薄玻色气体的关联结构。

关于稀薄玻色气体低能研究中相互作用势的球对称性和有限程假设

On the spherical symmetry and finite-range assumptions of the interaction potential in the low energy study of dilute Bose gases

本文去除了格罗斯-皮塔耶夫斯基机制下三维环面上玻色气体证明玻色-爱因斯坦凝聚和激发谱收敛到博戈留波夫预测时对相互作用势的径向性和紧支撑假设。

低温下稀薄玻色气体的自由能

The free energy of dilute Bose gases at low temperatures

本文在热力学极限下研究低密度排斥势玻色气体，严格证明了低温自由能的Lee--Huang--Yang型下界公式，并揭示修正激发谱产生的二阶修正与基态能量修正同阶。

稀薄玻色气体的数学物理

Mathematical physics of dilute Bose gases

本文回顾了稀薄玻色气体数学分析的最新进展，重点探讨了各维度下基态能量密度的两项渐近展开（如三维的 Lee-Huang-Yang 公式），并概述了相关数学困难与遗留的开放问题。

Bose-Einstein Condensation of Dilute Gases in Traps

The ground state of a gas of Bosons confined in an external trap potential and interacting via repulsive two-body forces has recently been shown to exhibit complete Bose-Einstein condensation in the dilute limit, yielding for the first time a rigorous proof of this phenomenon in a physically realistic setting. We give here an account of this work about the Gross-Pitaevskii limit where the particle number $N$ goes to infinity with $Na$ fixed, where $a$ is the scattering length of the interparticle interaction, measured in units of the trap size.

Free Energies of Dilute Bose gases: upper bound

We derive a upper bound on the free energy of a Bose gas system at density $ρ$ and temperature $T$. In combination with the lower bound derived previously by Seiringer \cite{RS1}, our result proves that in the low density limit, i.e., when $a^3ρ\ll 1$, where $a$ denotes the scattering length of the pair-interaction potential, the leading term of $Δf$ the free energy difference per volume between interacting and ideal Bose gases is equal to $4πa (2ρ^2-[ρ-\rhoc]^2_+)$. Here, $\rhoc(T)$ denotes the critical density for Bose-Einstein condensation (for the ideal gas), and $[\cdot ]_+$ $=$ $\max\{\c…

The Ground State Energy of Dilute Bose Gas in Potentials with Positive Scattering Length

The leading term of the ground state energy/particle of a dilute gas of bosons with mass $m$ in the thermodynamic limit is $2π\hbar^2 a ρ/m$ when the density of the gas is $ρ$, the interaction potential is non-negative and the scattering length $a$ is positive. In this paper, we generalize the upper bound part of this result to any interaction potential with positive scattering length, i.e, $a>0$ and the lower bound part to some interaction potentials with shallow and/or narrow negative parts.

Calculation of the critical temperature of a dilute Bose gas in the Bogoliubov approximation

Following an earlier calculation in 3D, we calculate the 2D critical temperature of a dilute, translation-invariant Bose gas using a variational formulation of the Bogoliubov approximation introduced by Critchley and Solomon in 1976. This provides the first analytical calculation of the Kosterlitz-Thouless transition temperature that includes the constant in the logarithm.

稀薄玻色气体凝聚的指数界

Exponential bounds of the condensation for dilute Bose gases

本文研究单位环面上处于 Gross-Pitaevski 区域的 N 个玻色子，证明低温热平衡中玻色-爱因斯坦凝聚在强意义下成立，凝聚态外粒子数概率呈指数衰减。

Superfluidity in Dilute Trapped Bose Gases

A commonly used theoretical definition of superfluidity in the ground state of a Bose gas is based on the response of the system to an imposed velocity field or, equivalently, to twisted boundary conditions in a box. We are able to carry out this program in the case of a dilute interacting Bose gas in a trap. We prove that a gas with repulsive interactions is 100% superfluid in the dilute limit in which the Gross-Pitaevskii equation is exact. This is the first example in an experimentally realistic continuum model in which superfluidity is rigorously verified.

The energy of dilute Bose gases

For a dilute system of non-relativistic bosons interacting through a positive $L^1$ potential $v$ with scattering length $a$ we prove that the ground state energy density satisfies the bound $e(ρ) \geq 4πa ρ^2 (1+ \frac{128}{15\sqrtπ} \sqrt{ρa^3} +o(\sqrt{ρa^3}\,))$, thereby proving the Lee-Huang-Yang formula for the energy density.

A Lower Bound on the Ground State Energy of Dilute Bose Gas

Consider an N-Boson system interacting via a two-body repulsive short-range potential $V$ in a three dimensional box $Λ$ of side length $L$. We take the limit $N, L \to \infty$ while keeping the density $ρ= N / L^3$ fixed and small. We prove a new lower bound for its ground state energy per particle $$\frac{E(N, Λ)}{N} \geq 4 πa ρ[ 1 - O(ρ^{1/3} |\log ρ|^3) ],$$ as $ρ\to 0$, where $a$ is the scattering length of $V$.

The energy of dilute Bose gases II: The general case

For a dilute system of non-relativistic bosons interacting through a positive potential $v$ with scattering length $a$ we prove that the ground state energy density satisfies the bound $e(ρ) \geq 4πa ρ^2 (1+ \frac{128}{15\sqrtπ} \sqrt{ρa^3} +o(\sqrt{ρa^3}\,))$, thereby proving a lower bound consistent with the Lee-Huang-Yang formula for the energy density. The proof allows for potentials with large $L^1$-norm, in particular, the case of hard core interactions is included. Thereby, we solve a problem in mathematical physics that had been a major challenge since the 1960's.

稀薄 Bose 气体特定自由能的新上界

A new upper bound on the specific free energy of dilute Bose gases

本文提出了一种新的方法，用于确定稀薄 Bose 气体在热力学极限下的自由能上界，并改进了先前的结果。

Proof of Bose-Einstein Condensation for Dilute Trapped Gases

The ground state of bosonic atoms in a trap has been shown experimentally to display Bose-Einstein condensation (BEC). We prove this fact theoretically for bosons with two-body repulsive interaction potentials in the dilute limit, starting from the basic Schroedinger equation; the condensation is 100% into the state that minimizes the Gross-Pitaevskii energy functional. This is the first rigorous proof of BEC in a physically realistic, continuum model.

Critical Temperature of Dilute Bose Gases

We compute the critical temperature of Bose-Einstein condensation in dilute three-dimensional homogeneous Bose gases. Our method involves the models of spatial permutations and it should be exact to lowest order in the scattering length of the particle interactions. We find that the change in the critical temperature is proportional to a rho^{1/3} with constant c = -2.33; this contradicts the current consensus among physicists.

低温下通过强势相互作用的稀薄玻色气体的自由能

The free energy of dilute Bose gases at low temperatures interacting via strong potentials

本文研究了热力学极限下低温稀薄玻色气体的自由能，结合已有技术给出了更简短的证明，解决了包含硬核势在内的强相互作用情况，其下界与Lee-Huang-Yang猜想一致。

A new second order upper bound for the ground state energy of dilute Bose gases

We establish an upper bound for the ground state energy per unit volume of a dilute Bose gas in the thermodynamic limit, capturing the correct second order term, as predicted by the Lee-Huang-Yang formula. This result has been first established in J. Stat. Phys. 136(3) by H.-T. Yau and J. Yin. Our proof, which applies to repulsive and compactly supported $V \in L^3 (\mathbb{R}^3)$, gives better rates and, in our opinion, is substantially simpler.

通过Neumann局部化在稀薄 Bose 气体中传播凝结

Propagation of Condensation via Neumann Localization in the Dilute Bose Gas

本文通过Neumann局部化方法和自由能下界，将Gross-Pitaevskii尺度的强凝聚估计推广到更大的盒子中，建立了谱间隙估计。

The Ground State Energy of a Dilute Two-dimensional Bose Gas

The ground state energy per particle of a dilute, homogeneous, two-dimensional Bose gas, in the thermodynamic limit is shown rigorously to be $E_0/N = (2π\hbar^2ρ/m){|\ln (ρa^2)|^{-1}}$, to leading order, with a relative error at most ${\rm O} (|\ln (ρa^2)|^{-1/5})$. Here $N$ is the number of particles, $ρ=N/V$ is the particle density and $a$ is the scattering length of the two-body potential. We assume that the two-body potential is short range and nonnegative. The amusing feature of this result is that, in contrast to the three-dimensional case, the energy, $E_0$ is not simply $N(N-1)/2$ tim…

Free Energy of a Dilute Bose Gas: Lower Bound

A lower bound is derived on the free energy (per unit volume) of a homogeneous Bose gas at density $ρ$ and temperature $T$. In the dilute regime, i.e., when $a^3ρ\ll 1$, where $a$ denotes the scattering length of the pair-interaction potential, our bound differs to leading order from the expression for non-interacting particles by the term $4πa (2ρ^2 - [ρ-ρ_c]_+^2)$. Here, $ρ_c(T)$ denotes the critical density for Bose-Einstein condensation (for the non-interacting gas), and $[ ]_+$ denotes the positive part. Our bound is uniform in the temperature up to temperatures of the order of the critic…

The Ground State Energy of a Dilute Bose Gas

According to a formula that was put forward many decades ago the ground state energy per particle of an interacting, dilute Bose gas at density $ρ$ is $2π\hbar^2ρa/m$ to leading order in $ρa^3\ll 1$, where $a$ is the scattering length of the interaction potential and $m$ the particle mass. This result, which is important for the theoretical description of current experiments on Bose-Einstein condensation, has recently been established rigorously for the first time. We give here an account of the proof that applies to nonnegative, spherically symmetric potentials decreasing faster than $1/r^3$ …

Rigorous Upper Bound on the Critical Temperature of Dilute Bose Gases

We prove exponential decay of the off-diagonal correlation function in the two-dimensional homogeneous Bose gas when a^2 ρis small and the temperature T satisfies T > 4 πρ/ \ln |\ln(a^2ρ). Here, a is the scattering length of the repulsive interaction potential and ρis the density. To leading order in a^2 ρ, this bound agrees with the expected critical temperature for superfluidity. In the three-dimensional Bose gas, exponential decay is proved when ΔT_c / T_c^0 > 5 \sqrt{a ρ^{1/3}}, where T_c^0 is the critical temperature of the ideal gas. While this condition is not expected to be sharp, it g…

The free energy of the two-dimensional dilute Bose gas. I. Lower bound

We prove a lower bound for the free energy (per unit volume) of the two-dimensional Bose gas in the thermodynamic limit. We show that the free energy at density $ρ$ and inverse temperature $β$ differs from the one of the non-interacting system by the correction term $4 πρ^2 |\ln a^2 ρ|^{-1} (2 - [1 - β_{\mathrm{c}}/β]_+^2)$. Here $a$ is the scattering length of the interaction potential, $[\cdot]_+ = \max\{ 0, \cdot \}$ and $β_{\mathrm{c}}$ is the inverse Berezinskii--Kosterlitz--Thouless critical temperature for superfluidity. The result is valid in the dilute limit $a^2ρ\ll 1$ and if $βρ\gtr…

Dilute Bose gas in two dimensions: Density expansions and the Gross-Pitaevskii equation

A dilute two-dimensional (2D) Bose gas at zero temperature is studied by the method developed earlier by the authors. Low density expansions are derived for the chemical potential, ground state energy, kinetic and interaction energies. The expansion parameter is found to be a dimensionless in-medium scattering amplitude u obeying the equation 1/u+\ln u=-\ln(na^2π)-2γ, where na^2 and γare the gas parameter and the Euler constant, respectively. It is shown that the ground state energy is mostly kinetic in the low density limit; this result does not depend on a specific form of the pairwise inter…