title: New field-theoretic method for the virial expansion.
abstract: We develop a graphical method for computing the virial expansion coefficients for a nonrelativistic quantum field theory. As an example we compute the third virial coefficient b3 for unitary fermions, a nonperturbative system. By calculating several graphs and performing an extrapolation, we arrive at b3=-0.2930, within 0.7% of a recent computation b3=-0.290 952 95 by Liu, Hu, and Drummond, which involved summing 10,000 energy levels for three unitary fermions in a harmonic trap.
authors.affiliation: Institute for Nuclear Theory, Box 351550, Seattle, Washington 98195-1550, USA. dbkaplan@uw.edu
authors.forename: David B
authors.initials: DB
authors.lastname: Kaplan
authors.forename: Sichun
authors.initials: S
authors.lastname: Sun