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SUMMARY:Anomalous propagators and the particle-particle channel of correla
 tion - Antoine Marie\, Universite Paul Sabatier
DTSTART:20240715T130000Z
DTEND:20240715T140000Z
UID:TALK219124@talks.cam.ac.uk
CONTACT:Alexander R Epstein
DESCRIPTION:Hedin's equations provide an elegant route to compute the exac
 t one-body Green's function (or propagator) via the self-consistent iterat
 ion of a set of non-linear equations. Its first-order approximation\, know
 n as _GW_\, corresponds to a resummation of ring diagrams and has shown to
  be extremely successful in physics and chemistry. Systematic improvement 
 is possible\, although challenging\, via the introduction of vertex correc
 tions. Considering anomalous propagators and an external pairing potential
 \, we derive a new self-consistent set of closed equations equivalent to t
 he famous Hedin equations but having as a first-order approximation the pa
 rticle-particle (pp) _T_-matrix approximation where one performs a resumma
 tion of the ladder diagrams (known as the pp random phase approximation (R
 PA)). This pp version of Hedin's equations offers a way to go systematical
 ly beyond the $T$-matrix approximation by accounting for low-order pp vert
 ex corrections. In particular\, we will show how to go beyond the pp-RPA-b
 ased _T_-matrix by formulating the Bethe-Salpeter equation for the two-par
 ticle propagator and discussing some of its approximations.
LOCATION:Yusuf Hamied Department of Chemistry\, Pfizer Lecture Theatre\; Z
 oom link: https://zoom.us/j/92447982065?pwd=RkhaYkM5VTZPZ3pYSHptUXlRSkppQT
 09
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