Rewrite author_name

Rewrite author_name

I need to rewrite author_name to cat. I searched for hours but can't find
anything. I restrict the search results by author instead category because
of the performance, it's much faster.
For getting all posts from the user "alex" you have to type:
example.com/?author_name=alex, I just need to change the "author_name" to
"cat" it has nothing to do with the normal wordpress category structure.