ps -aux -U "user" not filtering on user as expected

I have a quick question. I would regularly like to list all the processes running under my account on Linux. After reading the manpage, I thought I'd have to write: ps -aux -U "joshua" to get all processes running under user account

. However, this command also lists processes running as root and other accounts. Am I missing something? Why does this happen? Thank you in advance, Joshua