The Lane–Emden inequality controls ∬ _ℝ^2dρ (x)ρ (y)|x-y|^-λ dx dy in terms of the L^1 and L^p norms of ρ . We provide a remainder estimate for this inequality in terms of a suitable distance of ρ to the manifold of optimizers.

The 1971 Fortuin–Kasteleyn–Ginibre inequality for two monotone functions on a distributive lattice is well known and has seen many applications in statistical mechanics and other fields of mathematics. In 2008, one of us (Sahi) conjectured an extended version of this inequality for all n > 2 monotone functions on a distributive lattice. Here, we prove the conjecture for two special cases: for monotone functions on the unit square in [Formula: see text] whose upper level sets are k-dimensional rectangles and, more significantly, for arbitrary monotone functions on the unit square in [Formula: see text]. The general case for [Formula: see text], remains open.

The Golden–Thompson trace inequality, which states that Tr eH+K ≤ Tr eHeK, has proved to be very useful in quantum statistical mechanics. Golden used it to show that the classical free energy is less than the quantum one. Here, we make this G–T inequality more explicit by proving that for some operators, notably the operators of interest in quantum mechanics, H = Δ or H=−−Δ+m and K = potential, Tr eH+(1−u)KeuK is a monotone increasing function of the parameter u for 0 ≤ u ≤ 1. Our proof utilizes an inequality of Ando, Hiai, and Okubo (AHO): Tr XsYtX1−sY1−t ≤ Tr XY for positive operators X, Y and for 12≤s,t≤1, and s+t≤32. The obvious conjecture that this inequality should hold up to s + t ≤ 1 was proved false by Plevnik [Indian J. Pure Appl. Math. 47, 491–500 (2016)]. We give a different proof of AHO and also give more counterexamples in the 32,1 range. More importantly, we show that the inequality conjectured in AHO does indeed hold in the full range if X, Y have a certain positivity property—one that does hold for quantum mechanical operators, thus enabling us to prove our G–T monotonicity theorem.

The Lieb–Oxford inequality provides a lower bound on the Coulomb energy of a classical system of N identical charges only in terms of their one-particle density. We prove here a new estimate on the best constant in this inequality. Numerical evaluation provides the value 1.58, which is a significant improvement to the previously known value 1.64. The best constant has recently been shown to be larger than 1.44. In a second part, we prove that the constant can be reduced to 1.25 when the inequality is restricted to Hartree–Fock states. This is the first proof that the exchange term is always much lower than the full indirect Coulomb energy.

In this chapter we first review the Levy-Lieb functional, which gives the lowest kinetic and interaction energy that can be reached with all possible quantum states having a given density. We discuss two possible convex generalizations of this functional, corresponding to using mixed canonical and grand-canonical states, respectively. We present some recent works about the local density approximation, in which the functionals get replaced by purely local functionals constructed using the uniform electron gas energy per unit volume. We then review the known upper and lower bounds on the Levy-Lieb functionals. We start with the kinetic energy alone, then turn to the classical interaction alone, before we are able to put everything together. An appendix is devoted to the Hohenberg-Kohn theorem and the role of many-body unique continuation in its proof.

The Gross-Pitaevskii(GP) equation is a nonlinear Schr odinger equation that was introduced in the early sixties [1]{[3]as a phenom enologicalequation forthe order param eter in super uid He4. It has com e into prom inence again because ofrecent experim ents on Bose-Einstein condensation ofdilute gases in m agnetic traps. The paper[4]bringsan up to datereview ofthesedevelopm ents. Oneoftheinputsneeded forthejusti cation oftheGP equation startingfrom the m any body Ham iltonian istheground stateenergy ofa a dilute,therm odynam ically in nite,hom ogeneousBose gas. The form ula forthisquantity isolderthan the GP equation butithasonlyveryrecentlybeen derived rigorouslyforsuitableinterparticle

We consider the inequality $f \geqslant f\star f$ for real integrable functions on $d$ dimensional Euclidean space where $f\star f$ denotes the convolution of $f$ with itself. We show that all such functions $f$ are non-negative, which is not the case for the same inequality in $L^p$ for any $1 0$, $\int e^{\epsilon|x|}f(x){\rm d}x < \infty$.

Received 4 October 2021DOI:https://doi.org/10.1103/PhysRevA.104.049904©2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasHard-core bosonsQuantum statistical mechanicsPhysical SystemsAtomic gasesBose gasesBose-Einstein condensatesUltracold gasesTechniquesApproximation methods for many-body systemsDiffusion quantum Monte CarloMany-body techniquesMonte Carlo methodsQuantum Monte CarloStatistical Physics

In a recent paper we studied an equation (called the "simple equation"") introduced by one of us in 1963 for an approximate correlation function associated with the ground state of an interacting Bose gas. Solving the equation yields a relation between the density rho of the gas and the energy per particle. Our construction of solutions gave a well-defined function rho (e) for the density as a function of the energy e. We had conjectured that rho (e) is a strictly monotone increasing function, so that it can be inverted to yield the strictly monotone increasing function e(rho). We had also conjectured that rho e(rho) is convex as a function of rho. We prove both conjectures here for small densities, the context in which they have the most physical relevance, and the monotonicity also for large densities. Both conjectures are grounded in the underlying physics, and their proof provides further mathematical evidence for the validity of the assumptions underlying the derivation of the simple equation, at least for low or high densities, if not intermediate densities, although the equation gives surprisingly good predictions for all densities rho. Another problem left open in our previous paper was whether the simple equation could be used to compute accurate predictions of observables other than the energy. Here, we provide a recipe for computing predictions for any oneor two-particle observables for the ground state of the Bose gas. We focus on the condensate fraction and the momentum distribution, and show that they have the same low density asymptotic behavior as that predicted for the Bose gas. Along with the computation of the low density energy of the simple equation in our previous paper, this shows that the simple equation reproduces the known and conjectured properties of the Bose gas at low densities.

Our recent work on the Burchard-Choksi-Topaloglu flocking problem showed that in the large mass regime the ground state density profile is the characteristic function of some set.Here we show that this set is, in fact, a round ball.The essential mathematical structure needed in our proof is a strict rearrangement inequality with a quantitative error estimate, which we deduce from recent deep results of M. Christ.

We discuss the Wehrl-type entropy inequality conjecture for the group SU(1,1) and for its subgroup AX+B (or affine group), their representations on L^2(ℝ_+), and their coherent states. For AX+B the Wehrl-type conjecture for L^p-norms of these coherent states (also known as the Rényi entropies) is proved in the case that p is an even integer. We also show how the general AX+B case reduces to an unsolved problem about analytic functions on the upper half plane and the unit disc.

In 1963, a Simple Approach was developed to study the ground state energy of an interacting Bose gas. It consists in the derivation of an Equation, which is not based on perturbation theory, and which gives the exact expansion of the energy at low densities. This Equation is expressed directly in the thermodynamic limit, and only involves functions of $3$ variables, rather than $3N$. Here, we revisit this approach, and show that the Equation yields accurate predictions for various observables for all densities. Specifically, in addition to the ground state energy, we have shown that the Simple Approach gives predictions for the condensate fraction, two-point correlation function, and momentum distribution. We have carried out a variety of tests by comparing the predictions of the Equation with Quantum Monte Carlo calculations, and have found remarkable agreement. We thus show that the Simple Approach provides a new theoretical tool to understand the behavior of the many-body Bose gas, not only in the small and large density ranges, which have been studied before, but also in the range of intermediate density, for which little is known.

We consider the inequality $f \geqslant f\star f$ for real integrable functions on $d$ dimensional Euclidean space where $f\star f$ denotes the convolution of $f$ with itself. We show that all such functions $f$ are non-negative, which is not the case for the same inequality in $L^p$ for any $1 &lt; p \leqslant 2$, for which the convolution is defined. We also show that all integrable solutions $f$ satisfy $\int f(x){\rm d}x \leqslant \tfrac12$. Moreover, if $\int f(x){\rm d}x = \tfrac12$, then $f$ must decay fairly slowly: $\int |x| f(x){\rm d}x = \infty$, and this is sharp since for all $r&lt; 1$, there are solutions with $\int f(x){\rm d}x = \tfrac12$ and $\int |x|^r f(x){\rm d}x &lt;\infty$. However, if $\int f(x){\rm d}x = : a &lt; \tfrac12$, the decay at infinity can be much more rapid: we show that for all $a&lt;\tfrac12$, there are solutions such that for some $\epsilon&gt;0$, $\int e^{\epsilon|x|}f(x){\rm d}x &lt; \infty$.

In 1963 a partial differential equation with a convolution non-linearity was introduced in connection with a quantum mechanical many-body problem, namely the gas of bosonic particles. This equation is mathematically interesting for several reasons. (1) Although the equation was expected to be valid only for small values of the parameters, further investigation showed that predictions based on the equation agree well over the {\it entire range} of parameters with what is expected to be true for the solution of the true many-body problem. (2) The novel nonlinearity is easy to state but seems to have almost no literature up to now. (3) The earlier work did not prove existence and uniqueness of a solution, which we provide here along with properties of the solution such as decay at infinity.

We study L-p inequalities that sharpen the triangle inequality for sums of N functions in L-p.

In 1963, a Simple Approach was developed to study the ground state energy of an interacting Bose gas. It consists in the derivation of an Equation, which is not based on perturbation theory, and which gives the exact expansion of the energy at low densities. This Equation is expressed directly in the thermodynamic limit, and only involves functions of $3$ variables, rather than $3N$. Here, we revisit this approach, and show that the Equation yields accurate predictions for various observables for all densities. Specifically, in addition to the ground state energy, we have shown that the Simple Approach gives predictions for the condensate fraction, two-point correlation function, and momentum distribution. We have carried out a variety of tests by comparing the predictions of the Equation with Quantum Monte Carlo calculations, and have found remarkable agreement. We thus show that the Simple Approach provides a new theoretical tool to understand the behavior of the many-body Bose gas, not only in the small and large density ranges, which have been studied before, but also in the range of intermediate density, for which little is known.

In 2006 Carbery raised a question about an improvement on the naïve norm inequality $$\Vert f+g\Vert _p^p \le 2^{p-1}(\Vert f\Vert _p^p + \Vert g\Vert _p^p)$$ for two functions f and g in $$L^p$$ of any measure space. When $$f=g$$ this is an equality, but when the supports of f and g are disjoint the factor $$2^{p-1}$$ is not needed. Carbery’s question concerns a proposed interpolation between the two situations for $$p>2$$ with the interpolation parameter measuring the overlap being $$\Vert fg\Vert _{p/2}$$ . Carbery proved that his proposed inequality holds in a special case. Here, we prove the inequality for all functions and, in fact, we prove an inequality of this type that is stronger than the one Carbery proposed. Moreover, our stronger inequalities are valid for all real $$p\ne 0$$ .

We give the first mathematically rigorous justification of the Local Density Approximation in Density Functional Theory. We provide a quantitative estimate on the difference between the grand-canonical Levy-Lieb energy of a given density (the lowest possible energy of all quantum states having this density) and the integral over the Uniform Electron Gas energy of this density. The error involves gradient terms and justifies the use of the Local Density Approximation in the situation where the density is very flat on sufficiently large regions in space.

We reprove a result by Ren and Wei concerning the periodicity of minimizers of a one-dimensional liquid drop model in the neutral case. Our proof works for general boundary conditions and also in the non-neutral case.