Talk:Propagator

message: The Feynman propagator pictures in the article seem a little confused. The propagator only depends on the distance between the spacetime points x and y, so a 2d graph over the whole range of x and y seems a complete waste, as it sacrifices the ability to represent the actual value of GF(x-y) in anything other than a color shade, for a degree of freedom which GF does not depend on, that is, x+y.
Eudoxie (talk) 09:05, 6 August 2010 (UTC)
replies: text: Agreed... also x and y are four-component vectors, so a plot treating them as single variables makes no sense. Even if it did make sense, plots with no explanation of what the axes are or what the shadings represent are pretty pointless anyway. Removed. 92.11.114.194 (talk) 10:06, 19 September 2012 (UTC)
thread_title:  The feynman propagator images 

message: In the section on non-relativistic propagators, the symbol D[q(t)] is introduced. Anyone who can clarify the meaning? Thanks, 99.93.47.26 (talk) 14:04, 15 August 2010 (UTC)
thread_title:  undefined symbol 

message: I am unconvinced by the level of detail and the explicitness of the derivations provided in this article. While what exists is fairly detailed, the derivations are difficult to follow (For reference, I hold a Masters' degree in physics with a heavy dose of theory). For example, comparing the derivation of the position-space scalar field propagator to my textbook (the recommended one), I can't match the starting point in the book to the implied jump in the article - it simply mentions 'by Fourier transformation' (a Fourier transform of what?) with no elaboration, whereas the book (Quantum Field Theory, Mandl F and Shaw G, Wiley, 1993) starts with the scalar field commutators and proceeds through a long-winded sequence of (admittedly poorly-explained) steps. Yet the derivation takes several lines to define the 'box operator' and the Dirac delta - which anyone with any education in field theory should recognise and be able to remind themselves of in seconds, even if they haven't memorised them implicitly.
While I realise that demanding extensive derivation is not entirely reasonable, neither is it reasonable to assume that this article's quite limited audience - those of the population positioned in between 'total incomprehension' and 'comfortable professional familiarity' - would be able to gain much useful insight from derivations which assume too much prior understanding. Most modestly-knowledgeable people in the field (read: students) simply aren't capable of parsing this much jargon and extracting detailed understanding from it, myself included. If anyone sufficiently-knowledgeable feels like expanding this, I would suggest that at least a couple of intermediate steps and/or a couple of lines of prose explaining same in words would be beneficial. Sojourner001 (talk) 18:27, 11 October 2010 (UTC)
thread_title: Detail and usefulness

message: So what do you call the propagator that results from going over the left pole and under the right pole? 173.165.239.237 (talk) 06:04, 27 February 2012 (UTC)
replies: text: Dyson? YohanN7 (talk) 19:55, 25 January 2013 (UTC)
thread_title: Question

message: The propagator D(x-y) is defined as an integral in p-space, in 4 dimensions. The integrand is exp(i(k*(x-y)) times a function that, 
for p-->infinity, goes like 1/p^2.
Doesn't this imply that D=infinity?!?!?
Indeed, the integrated function should vanish faster than 1/p^5 to get a finite integral in d=4.
I probably missed a point or two.  — Preceding unsigned comment added by 94.161.219.216 (talk) 21:47, 21 August 2012 (UTC)
replies: text: The propagator is a distribution. From its Fourier transform one can split off a suitable polynomial such that the remainder has an absolutely convergent Fourier transform. The Fourier transform of the polynomial yields distributions. I prefer the precise determination of the propagator in Bogoliubov's book. Norbert Dragon (talk) 17:38, 5 March 2020 (UTC)
thread_title:  Is the propagator infinite? 

message: This article refers readers to textbooks for certain calculations, e.g. This choice of contour is equivalent to calculating the limit (see Huang p. 30) in the section Relativistic propagators.  
In my opinion this is not at all helpful to an unfamiliar reader. Either some explanation of the calculation should be given or the reference should be cited in the canonical way. That is to say, the references should be properly formatted at the bottom of the page, with enough information for a novice to understand them. Simply writing Huang may not be sufficient for a reader who doesn't know anything about the books Huang has authored. PhysicsSean (talk) 04:27, 9 February 2018 (UTC)
replies: text: OK, relegated to ref in refute, a superior format. You may improve by formatting in ref template, if you consider it necessary. Pls review WP referencing rules: Author in parenthesis suffices, unless there is a year ambiguity involved, and it always refers to the eponymous text in the reflist. So, consideration of Huang's collected works is a non-sequitur.  You appear confused about the reason for these refs. Firstly they are "defensive", i.e., they block obstreperous editors from peremptorily junking material as "unsourced", or "OR", an acrimonious  procedural problem in WP editing. Secondly they send the patient aggrieved readers to the original text, if a moment's reflection failed them.  There is no problem with dropping in useful explanatory works in the footnote, which you are welcome to, but "unfunded mandate" exhortations to what others should do are unconventional. Cuzkatzimhut (talk) 13:41, 9 February 2018 (UTC)
thread_title:  Inline Referencing of Textbooks 

message: Just very poor. Another academic failing to explain something!
This is how you do it: https://www.youtube.com/watch?v=uPsTGIkWKjA&t=1912s
:@User:Koitus~nlwiki you should sign your posts with 4 tildes, being a register user. This page is not a forum. You fail to propose concrete improvements to the article, which is not a tutorial, in any case! It is unclear what your sour hectorings are meant to achieve,  or how subpar video links elicit improvements.  Cuzkatzimhut (talk) 17:03, 15 November 2020 (UTC)
thread_title:  No derivation or explanation of the propagator AT ALL!