ah, i think i got it.
yeah, since (as i just mentioned in my previous post :P) the end product is a scalar, it makes sense to write it this way and it really is just a index notation for a vector-many matrices-vector product. a normal scalar product of 2 vectors would have the same features...
Thanks for your answer!
At i thought it was the standard matrix multiplication, too. But as you wrote it, it already begins with an index. So its
w_i = \sum_j A_{ij} v_j instead of
w = \sum_j A_{ij} v_j, which just confuses me.
Yeah, i think so, too. Since its a scalar transposing it...
Homework Statement
The task is to show the invariance of a given Lagrangian (http://www.fysast.uu.se/~leupold/qft-2011/tasks.pdf" ), but my problem is just in one step (which i got from Peskin & Schröder, page 70) which i can not reproduce due to my lack of knowledge regarding spinors.
The...