Recent content by JosephButler

The momentum operator acting to the left on the vacuum gives zero since the vacuum is assumed to be Lorentz invariant . -JB

I figure it might be helpful if I offered some literature which I found very, very helpful when I was learning about renormalization for the first time: * Zee, Chapter III. At the very least III.1. A very user-friendly explanation of what is meant by bare and physical/renormalized paramters...

Hi there Cordovan -- renormalization can indeed be a slippery subject. Here are my best attempts at (perhaps partial) answers from a fellow student. To be precise, regularization is the somewhat arbitrary prescription for extracting a finite number from an infinite number. Renormalization...

Hi there StatusX 00 is the \nabla_\mu a covariant derivative or a partial derivative? Should the \partial_\mu also be a covariant derivative? Thanks, Joe

Other useful references are: * Cahn's semisimple lie algebras book. It's now available free from the author at http://phyweb.lbl.gov/~rncahn/www/liealgebras/book.html , or alternately via a very inexpensive Dover edition. * Jan Gutowski's "Part III: Symmetries and Particle Physics" notes...

Hi xfshi, in quantum mechanics it's a bit ill-posed to ask if a particle ever `arrives' somewhere. The meaningful thing to ask is whether or not you observe the particle. Zero probability density indeed means zero chance of observing the particle in that state (e.g. at that position). It is...

Hello everyone, I'm not sure if these questions are really trivial or of they're a little subtle... but here goes. 1. In Ramond's text (Field Theory: A Modern Primer), he explains that the Lagrangian for fermions should have the derivative operator antisymmetrized in order for the kinetic...

Thanks for the reply. There is further insight in on the nature of the SUSY covariant derivative in a few of the older books on SUSY/SUGRA, but it appears to be hidden in sections about differential forms. The point, I believe, that that the [differential] geometric interpretation of the SUSY...

Lykken's SUSY lectures (hep-th/9612114) say a few words about this, see equations (55) and (56) on page 17. It's still a little vague to me; the point seems that flat superspace may have no curvature, but it still has torsion. Thus the vielbeins are non-trivial even in the flat case. In this...

Hi there, Mr. Hyde. I'm not an expert in this, so I'll necessarily be a little hand-wavy... but I'll do my best to get the flavor of the idea as I understand it. Part of the reason why it's hard to find a good explanation for "hidden sectors" are that they're a fairly loosely defined tool...

Hi everyone -- I have a question about the relation between the spin connection and the Christoffel connection. The spin connection comes from the local (gauge) Lorentz symmetry of how we orient vielbeins at each point in space, it contains a manifold index and two tangent space indices. The...

Thanks Sam! I eagerly await your reply. I understand now that the D's are 'covariant' in the sense of (anti)commuting with the Q's... but I don't understand what this means from a, say, Riemannian geometry perspective. (I.e. thinking of the covariant derivative in terms of parallel...

I don't mean to be pedantic, but I'm not sure if this is true. One can certainly write down a Lagrangian for gravity, the Einstein-Hilbert action, \mathcal L = \sqrt{-g}(M_{Pl}^2 R) Further, one could go ahead and quantize this as a theory for a spin-2 graviton, i.e. by writing the...

Hello once again. I'm trying to understand the relation between the superspace representation of the SUSY generators Q_\alpha,\overline Q_{\dot\beta} and the covariant derivatives on superspaces D_\alpha, \overline D_{\dot\beta}: Q_\alpha = \frac{\partial}{\partial\theta^\alpha} -...

Hi Hamster -- I think that answers my question exactly. So even if the vacuum were set to be a superposition of the two states, a measurement by an observer in the universe will yield a definite state. Would it be correct to say that the choice of vacuum (up or down) is an observable that...