feeling European for the first time. Water pressure has gone to almost 0 today so I busted open that jar of mineral water

If you had access to a magic genie and could ask him 1 physics related question, what would it be?

@obliv How many angels can dance on the head of a pin if space really is 10 dimensional but 6 dimensions are compatified?

@obliv what is the probability that ACM is one of the angels mentioned in ZeroTheHero's question?

:-)

Using the Dyson's equation for summation of diagrams, it may be convenient to transform to k-space. Then we may handle an algebraic equation, instead of an integral equation. But if my system is on a lattice, and positions are discretized, I will have an algebraic equation either way, or?

If anyone is interested I've found a Chrome extension that allows me to enter the Unicode Greek letters without having to remember loads of alt-xxx sequences.

wassuuuup

chillin' like a villain, u?

@skillpatrol havin' fun like a dragon's son

Hi everyone. I am still getting crazy with the book of Itzykson&Zuber. This is the expression of the connected S-matrix for a 2->2 scattering of charged scalar particles. You can find it at page 246. Shouldn't be $\langle p_2| T \varphi(y)\varphi^\dagger(x)| p_1\rangle$ if $\varphi$ destroys a particle and creates an anti-particle?

@apt45 No, what's happening here is not that "$\phi$ creates a particle" - the field is not a creation or annihilation operator

They're using the LSZ formula here, and the LSZ formula says that you add a $\phi$ on the right for every in-state of a field and a $\phi^\dagger$ on the left for every out-state of that field (go to the derivation of LSZ to see why).

@ACuriousMind this is their derivation for real scalar field. In the case of a charged scalar field, you would have a $\varphi^\dagger(x)$ on the right

@ACuriousMind By "$\varphi$ destroys a particle" I mean that the field has a non-zero expectation value with a one-particle initial state

I checked the derivation, and $a^\dagger$ would be expressed in terms of $\varphi^\dagger$

ahh, you're right, the $a^\dagger$ is part of the $\phi^\dagger$, sorry

In that case I'd wager this is a typo :P

Ok great, thanks. So, I was checking with Weinberg's expression.

...and then you spent an hour trying to translate Weinberg into I&Z's notation? ;P

I like Weinberg's book but the non-standard notation gets on my nerves

ahah that's not so difficult

(in this case)

he has the dagger on the field corresponding to the out-state. That's the same formula I&Z (apart from the constant outside the integrals) in the opposite signature, i.e. with the metric $\eta \rightarrow \eta$

but we said there was a typo on I&Z

hmmm

I spent all day trying to figure out this discrepancy

*spending :)

BTW on the 10-page list of errata corrige of I&Z there is a reference to the text I have posted before. So, they change the usual convention to avoid to change all the equations... but the convention used in this section is not consistent with the rest of the book

yeah, I think this is just people getting confused with the conventions

there is no universal rule which of the c/a operators of a complex scalar field you call $a$ and which you call $b$, nor which of these you call the "particle" and which the "anti-particle"

so there's four possible combinations here. I'd just accept that you understand how the correct formula works for your convention and move on

yeah, I don't have any other choice If I don't want to get mad :)

the trouble with reading a math book by oneself: deciding whether your proofs are actually rigorous or not

This is like factors of $\mathrm{i}$ or $4\pi$ floating around - they're different between different texts, but we mostly just trust that the authors have worked it out correctly for their choice of convention

@ACuriousMind We trust the authors... except when there is a 10-pages list of errata corrige :) :)

Can you imagine how little I care that we got another few white Americans into space? The streets are on fire down here, the country is on fire along with the US Constitution, and the whole planet is burning up.

need the updated version of that

thenib.com/this-is-not-fine

@obliv Eyy you're back!