Random matrix averages and the impenetrable Bose gas in Dirichlet and Neumann boundary conditions

Source abstract

The density matrix for the impenetrable Bose gas in Dirichlet and Neumann boundary conditions can be written in terms of 〈∏l=1n|cos φ1−cos θl||cos φ2−cos θl|〉, where the average is with respect to the eigenvalue probability density function for random unitary matrices from the classical groups Sp(n) and O+(2n), respectively. In the large n limit log-gas considerations imply that the average factorizes into the product of averages of the form 〈∏l=1n|cos φ−cos θl|〉. By changing variables this average in turn is a special case of the function of t obtained by averaging ∏l=1n|t−xl|2q over the Jacobi unitary ensemble from random matrix theory. The latter task is accomplished by a duality formula from the theory of Selberg correlation integrals, and the large n asymptotic form is obtained. The corresponding large n asymptotic form of the density matrix is used, via the exact solution of a particular integral equation, to compute the asymptotic form of the low lying effective single particle states and their occupations, which are proportional to N.