Thursday, March 29, 2012

1102.4814 (R. van Leeuwen et al.)

Wick Theorem for General Initial States    [PDF]

R. van Leeuwen, G. Stefanucci
We present a compact and simplified proof of a generalized Wick theorem to calculate the Green's function of bosonic and fermionic systems in an arbitrary initial state. It is shown that the decomposition of the non-interacting $n$-particle Green's function is equivalent to solving a boundary problem for the Martin-Schwinger hierarchy; for non-correlated initial states a one-line proof of the standard Wick theorem is given. Our result leads to new self-energy diagrams and an elegant relation with those of the imaginary-time formalism is derived. The theorem is easy to use and can be combined with any ground-state numerical technique to calculate time-dependent properties.
View original: http://arxiv.org/abs/1102.4814

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