# Search results

1. ### Question on Tachyon Correlator (Green Schwarz Witten)

Thanks fzero! Since both - Trimok and you - suggested to look at Polchinksi I will do so :) To the Library...!
2. ### Question on Tachyon Correlator (Green Schwarz Witten)

Thanks Trimok for clearing that up :) As mentioned on phys stackexchange, I would like to understand this, since GSW say in the appendix that getting 7.A.17 is possible from 7.A.12 and 7.A.22... :)
3. ### Question on Tachyon Correlator (Green Schwarz Witten)

Hi fzero, Thanks for your answer but I'm not sure I understand it in the context of the equations above. Would you be so could to make it more precise w.r.t. the formulae I used above. That would be very nice since i'm banging my head against this for a while now. Moreover, this point is...
4. ### Question on Tachyon Correlator (Green Schwarz Witten)

I'm reading through chapter 7 of Green-Schwarz-Witten and I have a problem with the derivation of the M-tachyon correlation function. Basically I'm trying to get 7.A.17 from 7.A.12 and eq 7.A.22 in the appendix of the first volume. Basically I want to prove...
5. ### Amplitudes in CFT vanish. Why does N=4 have them?

Hi guys, one question in this growing amplitude business that i don't understand. Usually one says that conformal field theories do not have any non-trivial scattering amplitudes because one cannot define asymptotic states. But say we consider now N=4 Super Yang Mills and moreover treelevel...
6. ### Mathematica Streamlining Replace in Mathematica 8

Hi and thanks for your answer. Ok, i just realize i have been too vague. Acutally my expressions are of the type MP[X,a_1]...MP[X,a_{2n}] where MP is the Minkowski scalar product. Some of the a_n might be the some. This can be replaced in my case (under an integral over X) by...
7. ### Mathematica Streamlining Replace in Mathematica 8

Hi guys, i have expressions of the type (X*a)(X*b). I want replace this by X^2(a*b). So i tried building a block which does nothing but %//.(X*a_)(X*b_)->X^2(a*b). However, this works only if a is distinct from b. If a and b are equal if HAVE to use the replacement command...
8. ### Loop Integration in Spinor Language

Ah, thanks for the explanation. One more question about this: So coming back to the numerator, i could rewrite is in terms of a four-vector product as: \langle a |L|b]^2 = (2q\cdot L )^2 where q is a four-vector build from the spinors \langle a| and |b]. Under the integral sign i could...
9. ### Loop Integration in Spinor Language

Hi and thanks for your reply. Look for instance at hep-th/0612007. They never do the integrals (they reduce them to scalar integrals using PV) but i was wondering how to do them without reducing them. Look for instance at eq (3.9). If one is given such a type of integral but has no idea about...
10. ### Loop Integration in Spinor Language

Hi! Thanks for your reply! I understand how to treat these integrals if the numerator of the integrand is expressed in terms of four-vectors. But how do I proceed if the numerator is written in the spinor bra-ket language above? I don't really know how to handle these expressions if the loop...
11. ### Loop Integration in Spinor Language

Hi guys, i'm looking at one-loop calculations in terms of helicity spinor (basically a paper by Brandhuber, Travglini and others) language but i have no idea how to integrate them :) For instance \int FeynParam\int d^D L \frac{\langle a|L|b]^2}{(L^2-\Delta^2)^3} How would I do...
12. ### Self-Dual Field Strength in complex coordinates

Ah cool, i didn't know that i could just plug in numbers back :) Nice, thank you!
13. ### Self-Dual Field Strength in complex coordinates

Hi guys, I have to brush up my knowledge about self-dual Yang Mills and I'm reading an ancient paper by Yang about it...and of course I'm stuck...although Yang writes 'it is easy to see that'... Ok, so the self-duality condition of the YM field strength tensor is defined as...

15. ### 2Point Correlator in CFTs

Thank you for your answer! That is a nice way to understand this! From the book however I have the impression that the conclusion is much simpler to get and follows 'for free' from the invariance statements. But thanks a lot anyways! earth2 P.s. you were right, the \sim should be an...
16. ### 2Point Correlator in CFTs

Hi guys, i'm studying Conformal Field Theory using the big yellow book by Senechal et al. So far everything has been a smooth ride. I'm a bit stuck at the point where they derive the 2- and 3-point correlator for spinless fields. Based on invariance under rotations and translations the...
17. ### N=4 Susy for dummies

Hi guys, I'm under the impression that nowadays everything going on in hep-th is N=4 Susy stuff and that it has 20384093 awesome properties. Are there lecture notes where I can learn about all of that? I mean I know buzzwords but I don't see the whole picture. So, as I've said, are there...
18. ### Wick contraction and derivatives

Hey guys, one quick question about Wick contractions and derivatives: Suppose I want to write down all (non-vacuum) Wick contractions of two fields a, and one field A into a cubic QCD-like interaction term of the form \partial^\nu A^{\mu, a}(p_1) a_\mu^b(p_2) a_\nu^c(p_3) f^{abc} to...
19. ### Old vs new unitarity cut methods

Hey folks, I've been stumbeling recently about new unitarity methods to obtain one-loop amplitudes by cutting them in all possible channels thereby reducing the full amplitude to products of tree amplitudes (pioneered by Bern, Dixon, Kosower, Dunbar). From what I understand from my QFT...
20. ### Four vector made of Pauli matrices commute?

Hey guys There are those vectors made of Pauli matrices like \bar{\sigma}^\mu and {\sigma}^\mu. So if I have the product \bar{\sigma}^\mu {\sigma}^\nu I wonder if it is commutative? And if not, what is the commutator? Cheers, earth2
21. ### [Book?] Scattering processes in Condensed Matter

Thanks for the reply. I do already have this book and find it quite unsatisfactory somehow. The author is mainly concerned with Green's function and only mentions scattering amplitudes very very briefly without details... So thanks again! Other recommendations? Cheers
22. ### [Book?] Scattering processes in Condensed Matter

Hi guys, i know that there are Feynman diagrams in condensed matter around. As far as i understood it they are used to calculate Green's functions but as we all know from qft Feynman diagrams can also be used to calculated scattering amplitudes...so, i wonder if there is a book around with...
23. ### Real scalars for complex scalar results

Hi guys, I'm a bit puzzled. I'm just reading some offline lecture notes where the Feynman rules of real (!) scalars coupled to gluons are given. However, with these rules the amplitude for phi g -> \bar{phi} g is considered. There are no further instructions. I'm just wondering how one can...
24. ### Gamma matrices

Hi guys, i know this is a very old topic...so, sorry to reactivate it. But i would like to know if there is an example somewhere to prove this statement. I tried to write down the product of three different gamma matrices in this way, but i can't bring it into a form where each gamma matrix...
25. ### Feynman trick for linear propagators?

Hey guys, say i have some standard propagators then I know how to combine them using Feynman's parameter method. But what do I do if one of these propagators is linear? For instance: \int d^Dk \frac{1}{(k-p)^2(k \cdot q)} where q and p are some momenta. How do I combine them? Does...
26. ### Cross section energy dependence

Does that even make sense on physical grounds? In any case it is not true since the cross section of pp collisions and ppbar collision is the same at high energies, so your argument breaks down. Without being able to reproduce the full explanation, i think i remember that the increase has...
27. ### Cross section energy dependence

Concerning the increasing crosssection bit, there is a nice book by Forshaw and Ross called "Pomeron something something" (sorry, forgot the full title). Alternatively check http://arxiv.org/abs/hep-ph/9503226 Hope i could help! earth2
28. ### LSZ reduction and Renormalization constants

Hey folks, i have a question about LSZ and how to take into account the renormalization constants of the theory in question. In the derivation, only the field strength renormalization enters as a factor of Z (or square root thereof) but some mates said that also the vertex renormalization...
29. ### Closed Strings and Virasoro algebra

Hey, thanks for the answer. We had exactly this reasoning today in our lecture but we only DEFINED that L_n with n>0 vanishes. Is there a physical argument for that that makes this definition somehow intuitively accesible? I mean, why do we only require that n>0 vanishes and not all n? Cheers
30. ### Closed Strings and Virasoro algebra

Hey guys, i just started taking a course on ST and so far we discuss the closed string following Green, Schwarz, Witten. I don't see the point of constructing the Virasoro algebra (formula 2.1.85 in GSW) if the corresponding generators are zero due to the constraints. Or to put it differently...