Takashi Fujikawa,
Graduate School for Science, Chiba University, Chiba University, Yayoi-cho 1-33, Inage, Chiba 263-0022, JAPAN <

Research Center for a Photon Spectroscopy Theory Center is important to give a chance for theoretists working in XAFS, XPS and other related fields to communicate each other, and also for experimentalists to master how to use analytical tools to obtain reliable information.

Here a basic theoretical problem in XAFS will be discussed. At T=0K several useful formulas have been proposed to correctly describe X-ray absorption intensity by use of projection operator technique. However the above technique is inconvenient to extend to finite temperature XAFS analyses. Closed-time Green's function approach was successfully applied XPS analyses . In this work we use a systematic approach to XAFS theory based on the closed path Green's function ( Keldysh Green's function ) at T=0 and >0.

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