I think "mathematics are" is a normal construction. "We have a new widget that does this, but the mathematics of mass production are troubling."
If you don't like something coming between "mathematics" and "are", how about "I can prove Fermat's Last Theorem, but the mathematics are pretty high level." One could argue that many people would say "the math is pretty high level", but I think I've heard each before. It doesn't feel odd to write at all.