# Homework Help: Some help needed

1. Sep 7, 2005

2. Sep 8, 2005

### Neitrino

Sorry but,

Could at least tell me why my question is not getting any replies???
Im very wondered.... its too nonsensical ? If so what do I say wrong?

3. Sep 8, 2005

### snooper007

I think the expresion $$<0|\phi(x)\phi(y)|0>$$
survives $$<0|a_p a_q^\dag|0>$$ means:
$$<0|a_p^\dag a_q^\dag|0>$$=0 and $$<0|a_p a_q|0>$$=0;
only $$<0|a_p a_q^\dag|0>$$ survives, of course p and q are arbitary,
not single p and single q. the final result will be an integral over all possible p or q.

(2) $$<0|\phi(x)|$$, is just complex conjugate of (2.41).
there is no special physical significance here, the author, I guess, just mentioned NR
case to make the formula be easily understood.

Last edited: Sep 8, 2005
4. Sep 8, 2005

### Neitrino

(as u posted in homework section)

Dear Snooper007 thks for ur reply..
$$<0|\phi(x)$$ it is a complex conjugation of $$\phi(x)|0>$$
So $$<0|\phi(x)=\int{\frac{d^3 p}{(2\pi)^3}\frac{1}{2E_p}e^{ipx}<p|$$

$$<0|\phi(x)=<x|$$ < - ?

and with regard to question 1) I still dont feel comfort with understanding..
seems I did no understand ur reply as it should be

5. Sep 8, 2005

### vanesch

Staff Emeritus
I wonder in what colleges one studies Peskin and Schroeder...