For a start, I don't know how to type these on a keyboard.
Secondly, most people wouldn't know what these symbols are called. Granted, those looking at the code probably have a greater chance of knowing. But it isn't friendly code in my opinion. I think clarity is key, and "rho" or "sigma" are pretty clear.
Also, add in that there's a constant "n" and a constant "η". Just begging for confusion.