Let phi(x) and phi_dagger(x) be field operators which satisfy the appropriate commutation relations.(adsbygoogle = window.adsbygoogle || []).push({});

Then is there any analytic approximation for the two particle density matrix given by

<phi_dagger(x)phi_dagger(x')phi(x')phi(x)>

Thanks!

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# Is there any approximation to the two particle density matrix

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