# Notation for Propability Amplitudes

I've recently stumbled upon a certain piece of notation that doesn't quite seem clear to me. When discussing the amplituhedron, my teacher mentioned the relation between the volume and the amplitude scattering, and then he wrote the following on the board: $$[1-,\,1+,\,3-,\,3+]$$ I assume these are probability amplitudes, but I don't quite what the integers and the signs mean.

• I know nothing about amplituhedra, so this may be entirely wrong: sometimes the notation 1+ is used to denote a real number that is indefinitely close to 1. as in lim (x-->O+) to mean the limit as x approaches zero from the right. Feb 19, 2014 at 16:45
• I would hope the instructor didn't just write that down in vacuo - was there some additional context?
– user10851
Feb 19, 2014 at 23:05
• FWIW, the $\pm$ are helicities of a 4-particle amplitude. Jan 5, 2019 at 18:33
• You know, I have had this on the back of my mind for four years; never quite returned to it. Now, it made sense haha. Thanks! Jan 7, 2019 at 21:29