# In what sense are loop diagrams quantum corrections?

+ 3 like - 0 dislike
62 views

What's so not-quantum about tree-level diagrams?

This post has been migrated from (A51.SE)
From the tag of the question, you are already assuming "FIELD" theory, are you? So the queston is how classical the fields are?

This post has been migrated from (A51.SE)

+ 6 like - 0 dislike

The reasons were given here. Essentially, at tree level you recover classical results. Loop corrections are proportional to powers of $\hbar$ and these are quantum terms.

This post has been migrated from (A51.SE)
answered Dec 18, 2011 by (345 points)
It is a bit more obscure for particles with spin, because then the classical result has still an $\hbar$.

This post has been migrated from (A51.SE)
That is right, but classically spin does not exist and so, the result is consistent.

This post has been migrated from (A51.SE)
+ 2 like - 0 dislike

Tree level diagrams are one-particle relativistic quantum mechanics, but not quantum field theories.

The point is obscured by two reasonable details in modern QFT books: they avoid to speak of "2nd quantisation", and they set h=1 everywhere (so for instance it is not so clear how different the h->0 limit is for fermions than for scalar fields, or how bosons can add to build a classical electromagnetic field but fermions can not). It is expected that you go across a relativistic quantum mechanics textbook before jumping to QFT, but sometimes the career path is different.

This post has been migrated from (A51.SE)
answered Dec 19, 2011 by anonymous
There are relativistic quantum mechanics textbooks that are not quantum field theory texts?

This post has been migrated from (A51.SE)

 Please use answers only to (at least partly) answer questions. To comment, discuss, or ask for clarification, leave a comment instead. To mask links under text, please type your text, highlight it, and click the "link" button. You can then enter your link URL. Please consult the FAQ for as to how to format your post. This is the answer box; if you want to write a comment instead, please use the 'add comment' button. Live preview (may slow down editor)   Preview Your name to display (optional): Email me at this address if my answer is selected or commented on: Privacy: Your email address will only be used for sending these notifications. Anti-spam verification: If you are a human please identify the position of the character covered by the symbol $\varnothing$ in the following word:p$\hbar$y$\varnothing$icsOverflowThen drag the red bullet below over the corresponding character of our banner. When you drop it there, the bullet changes to green (on slow internet connections after a few seconds). To avoid this verification in future, please log in or register.