Shau-Jin Chang

Quantum Monte Carlo Studies of Superfluid Fermi Gases

We report results of quantum Monte Carlo calculations of the ground state of dilute Fermi gases with attractive short-range two-body interactions. The strength of the interaction is varied to study different pairing regimes which are characterized by the product of the s-wave scattering length and the Fermi wave vector, ak{sub F}. We report results for the ground-state energy, the pairing gap {delta}, and the quasiparticle spectrum. In the weak-coupling regime, 1/ak{sub F} 0, the interaction is strong enough to form bound molecules with energy E{sub mol}. For 1/ak{sub F} > or approx. 0.5, we find that weakly interacting composite bosons are formed in the superfluid gas with {delta} and gas energy per particle approaching E{sub mol}/2. In this region, we seem to have Bose-Einstein condensation (BEC) of molecules. The behavior of the energy and the gap in the BCS-to-BEC transition region, -0.5<1/ak{sub F}<0.5, is discussed.

Chiral vertex operators in off-conformal theory: Sine-Gordon example

We study chiral vertex operators in the sine-Gordon [SG] theory, viewed as an off-conformal system. We find that these operators, which would have been primary fields in the conformal limit, have interesting and, in some ways, unexpected properties in the SG model. Some of them continue to have scale- invariant dynamics even in the presence of the non-conformal cosine interaction. For instance, it is shown that the Mandelstam operator for the bosonic representation of the Fermi field does not develop a mass term in the SG theory, contrary to what the real Fermi field in the massive Thirring model is expected to do. It is also shown that in the presence of the non-conformal interactions, some vertex operators have unique Lorentz spins, while others do not.

High-Energy Elastic and Inelastic Scattering in ϕ 3 Theory

We study high-energy elastic and inelastic processes in a

Dilute Fermi Gases with Large Scattering Lengths: Atomic Gases and Neutron Matter

{\ensuremath{\phi}}^{3}

Iterative properties of a one-dimensional quartic map: Critical lines and tricritical behavior

theory based on the following model: For the elastic-scattering amplitude we first sum the leading terms in each order of perturbation of the

Quantum Field Theories in the Infinite-Momentum Frame. II. Scattering Matrices of Scalar and Dirac Fields

t

Existence of a second-order phase transition in a two-dimensional phi/sup 4/ field theory

-channel straight ladders, plus those obtained by interchange of the Mandelstam variables

Quantum fluctuations in a phi

s

sup 4

and

field theory: I. Stability of the vacuum

u