Accepted Tuesday Nov 03, 2009
The expectation values of field operators are basic quantities of any interacting quantum theory, both for theoretical and experimental reasons. We present a novel method to compute, at zero and finite temperature, expectation values in the Lieb-Liniger model. These quantities, relevant in the physics of one-dimensional ultracold Bose gases, are expressed by a series that has a remarkable behavior of convergence. Among other results, we show the computation of the three-body expectation value at finite temperature, a quantity that rules the recombination rate of the Bose gas.