Accepted Friday Nov 06, 2009
We calculate the one-body temperature Green's (Matsubara) function of the unitary Fermi gas via Quantum Monte Carlo, and extract the spectral weight function A(p,w) using the methods of maximum entropy and singular value decomposition. From A(p,w) we determine the quasiparticle spectrum, which can be accurately parameterized by three functions of temperature: an effective mass m*, a mean-field potential U, and a gap D. Below the critical temperature Tc=0.15eF the results for m*, U and D can be accurately reproduced using an independent quasiparticle model. We find evidence of a pseudogap in the fermionic excitation spectrum for temperatures up to T* 0.20eF > Tc.