Excluded volume conditions in quasi-particle theories of superfluidity

Frederick Reif

V. Hui

Richard Norton

Jeffrey J. Prentis

This dissertation involves the renormalization group theory and its application to two systems exhibiting renormalization symmetry. Both the real space and the field theoretic formulations of the renormalization group theory are discussed. A continuum of real space renormalization transformations is used to study the critical behavior of the two-dimensional Ising model. We find that there exists an optimal transformation that produces sharply more accurate critical properties that the others. We establish a set of conditions that characterize the optimal transformation. These conditions suggest criteria that could enable one to control a given real space renormalization approximation. Field theory renormalization is used to exploit the renormalization symmetry in the excluded volume problem. We develop a self-contained formalism that incorporates the concepts and methods of field theory renormalization directly into the language of the excluded volume problem. This formalism avoids the Lagrangian model isomorphism, thereby providing a simpler and more natural framework for underst and ing the excluded volume problem from first principles. This formalism is used to investigate the spatial correlations in a large self-repelling ring polymer. In particular, we find that the ratio of the radius of gyration of a ring polymer to that of a linear polymer having the same number of monomers is a universal quantity whose value we calculate to first order in (epsilon) (TBOND) 4 - (dimension of space). In addition, we study the mutual excluded volume characterizing a system of two chains with different lengths. The renormalization of the polymer perturbation theory through two-loop order enables us to calculate the universal value of the interpenetration function to second order in (epsilon). Our renormalization group results are in very good agreement with the results obtained from numerical and experimental studies of rings and chains in three dimensional space. We also discuss the connection between real space and field theory renormalization. We outline the basic conceptual ideas that underlie the general theory of renormalization and illustrate how each of these ideas is realized in the real space and the field theoretic formulations.

Miki Wadati, Go Kato, Toshiaki Iida

Recent developments in statistical mechanics of quantum integrable systems are reviewed. Those studies are fundamental and have a renewed interest related to newly developing fields such as atomic Bose-Einstein condensations, photonic crystals and quantum computations. After a brief summary of the basic concepts and methods, the following three topics are discussed. First, by the thermal Bethe ansatz (TBA), a hard-core Bose gas is exactly solved. The model includes fully the effect of excluded volume and is identified to be a c=1 conformal field theory. Second, the cluster expansion method based on the periodic boundary condition for the Bethe wave function, which we call the Bethe ansatz cluster expansion (BACE) method, is developed for a δ-function gas and the XXX Heisenberg chain. This directly proves the TBA and reveals intrinsic properties of quantum integrable systems. Third, for a δ-function gas, the integral equations for the distribution functions of the quasi-momentum and the quasi-particle energy are solved in the form of power series. In the weak coupling case, the results reproduce those of Bogoliubov theory.

Weiyi Zhang