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...
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...
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...
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...
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...
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...
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...
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...
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...
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
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...
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...
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...
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...
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...
Hey guys,
something that puzzles me everytime I stumble across spinors is the following:
I know that i can express Dirac spinors in terms of2-component Weyl spinors (dotted/undotted spinors).
Now, if i do that, i can reexpress for instance the Lorentz or conformal algebra in terms of Weyl...
Hey guys,
i'm stuck (yet again! :) )
I am somewhat confused by Dirac spinors u,\bar{u}. Take the product (where Einstein summation convention is assumed):
u^r u^s\bar{u}^s Is this the same as u^s\bar{u}^s u^r? Probably not cuz u^r is a vector while the other thing is a matrix, right...
Hi!
Quick question: Does it make a difference if i choose my dim reg. to be D=4-2epsilon or D=4+2epsilon (i suppose in both cases epsilon >0).
I mean opinion i should not matter but standard qft books normally don't touch this question very deeply...
Cheers,
earth2
Hey,
I've been reading a bit in the QFT book by Pierre Ramond about loops and i stumbled about some derivations in appendix B that I can't follow.
First Ramond derives a formula for integration of momenta in arbitrary dimensions
\int \frac{d^Nl}{(l^2+2p\cdot...
Homework Statement
Calculate the symmetry factor of a 4-point, 1-loop diagram in QCD. Two legs are external, two are not
Homework Equations
I don't know how to include pictures here, but lets try to describe it:
-It basically consists of 2 four-vertices connected by two propagators...
Hey guys,
I have a question about how to incorporate ghosts in practical calculations. So, from what I understand I have to add a factor of -1 for each closed gluon loop, right? But there are two ghost fields, c and \bar{c} appearing when I quantize the path integral. Does that mean that I also...
Hey guys,
i have the following situation:
I have a function which looks like
\frac{(a+bx)^3}{(x-y)^6(x-z)^6}
As one can easily see this function has poles at y and z of order 6. Now, I know how to calculate the residue of this function for instance at y, but how do I implement this into...
Hi guys,
i was just wondering if there is some book or whatever that has a list of loop integrals. More specifically, I am looking for one-loop integrals in the lightcone gauge with an arbitrary number of propagators. I found a paper by Leibbrandt which tells me how to calculate them, but I...
Hey guys,
i am looking for some primer on conformal, dual conformal symmetry, respectively. I have to read a lot of stuff about scattering amplitudes for uni and in recent papers people talk a lot about these symmetries.... unfortunately i am not so familiar with them, so does any of you know...
Question on Witten's paper: "Perturbative Gauge Theory As A String Theory..."
Hi guys,
I have a question regarding formula 2.12 of Witten's paper hep-th/0312171
"Perturbative Gauge Theory As A String Theory In Twistor Space". He just states this formula but i don't really understand his...
Hi there,
I have question about a gluon's wave function.
First of all, I thought it is just the vector potential A_\mu but I read several papers and they keep refering to the helicity \epsilon_\mu as the wave function. At least this is what I understand from the context. See for instance...
Hi folks,
I just read some stuff about Susy and encountered superfields and their expansion in terms of the supercoords x^\mu, \theta, \bar{\theta}. Reading that (e.g. in the script of Lykken), I found general expansions like
S(x,\theta,\bar{\theta})=...+ \theta\theta \psi +...
Hey guys,
I have a question about said spinors.
In supersymmetry introductions one finds (e.g. for two left-handed spinors \eta , \nu ) that \eta\nu=\nu\eta due to their Grassmannian character and the antisymmetry of the spinor product.
If I look, however, at modern field theoretical...
Hey folks,
i am reading about the BFKL equation and came across the reggezation of the exchanged gluons. Now, i understand what reggezation means but i don't see where it enters. Especially since most people simple write "virtual corrections enter via replacing the propagators by bla bla...