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1. • CommentRowNumber1.
   • CommentAuthorUrs
   • CommentTimeAug 27th 2014
   • (edited Aug 27th 2014)
   • PermaLink
   Author: Urs
   Format: MarkdownItexin the process of writing _[[zeta function regularization]]_ etc. I also created a stub for _[[Feynman propagator]]_/_[[Dirac propagator]]_ .This now has some key pointers, but the entry remains very stubby.

   in the process of writing zeta function regularization etc. I also created a stub for Feynman propagator/Dirac propagator .This now has some key pointers, but the entry remains very stubby.

2. • CommentRowNumber2.
   • CommentAuthorUrs
   • CommentTimeAug 4th 2017
   • (edited Aug 4th 2017)
   • PermaLink
   Author: Urs
   Format: MarkdownItexAm about to write up the rigorous definition of all things propagators (Feynman propagator, advanced/retarded propagator, etc.) for scalar fields on globally hyperbolic spacetimes. There is a beautiful graphical calculus in terms of wave front sets for this, which I finally grasped from [Radzikowski 96](https://ncatlab.org/nlab/show/Hadamard+distribution#Radzikowski96) (a remarkably pivotal reference for rigorous quantum field theory on curved spacetimes). The calculus without words is now tabulated [here](https://ncatlab.org/nlab/show/Klein-Gordon+equation#FundamentalSolutions). Have to call it quits for tonight. More later.

   Am about to write up the rigorous definition of all things propagators (Feynman propagator, advanced/retarded propagator, etc.) for scalar fields on globally hyperbolic spacetimes. There is a beautiful graphical calculus in terms of wave front sets for this, which I finally grasped from Radzikowski 96 (a remarkably pivotal reference for rigorous quantum field theory on curved spacetimes). The calculus without words is now tabulated here. Have to call it quits for tonight. More later.

3. • CommentRowNumber3.
   • CommentAuthorUrs
   • CommentTimeAug 5th 2017
   • (edited Aug 5th 2017)
   • PermaLink
   Author: Urs
   Format: MarkdownItexOkay, I have further fine tuned and then split off the table as a table for inclusion in related entries * _[[propagators - table]]_. Igor Khavkine kindly provided a correct picture of the wave front set for the Hadamard propagator, and we expanded a bit more the text at _[Klein-Gordon equation -- Fundamental solutions](https://ncatlab.org/nlab/show/Klein-Gordon+equation#FundamentalSolutions)_.

   Okay, I have further fine tuned and then split off the table as a table for inclusion in related entries

   • propagators - table.

   Igor Khavkine kindly provided a correct picture of the wave front set for the Hadamard propagator, and we expanded a bit more the text at Klein-Gordon equation – Fundamental solutions.

4. • CommentRowNumber4.
   • CommentAuthorUrs
   • CommentTimeSep 6th 2017
   • (edited Sep 6th 2017)
   • PermaLink
   Author: Urs
   Format: MarkdownItexI have given _[[Feynman propagator]]_ a decent Idea-section (or so I hope). Then I added statement and proof that the general formula expressing the Feynman propagator $\omega_F$ as the sum of the vacuum 2-point function $\omega$ with the advanced propagator $\Delta_A$ $$ \omega_F = \omega + i \Delta_A $$ yields the contour integral presentation that one finds in the standard textbooks ([this prop.](https://ncatlab.org/nlab/show/Feynman+propagator#ContourIntegralRepresentationOfStandardFeynmanPropagatorOnMinkowskiSpacetime))

   I have given Feynman propagator a decent Idea-section (or so I hope). Then I added statement and proof that the general formula expressing the Feynman propagator $\omega_F$ as the sum of the vacuum 2-point function $\omega$ with the advanced propagator $\Delta_A$

   $$\omega_F = \omega + i \Delta_A$$

   yields the contour integral presentation that one finds in the standard textbooks (this prop.)