A student who alleges a Northwestern University professor sexually assaulted her doesn’t have a case against the school for allowing the man to remain on campus, a federal judge has ruled. In a written opinion, U.S. District Judge Harry D. Leinenweber granted judgment on the pleadings in favor of Northwestern in Yoona Ha’s lawsuit. Leinenweber rejected the argument that Northwestern’s failure to fire philosophy professor Peter Ludlow created a hostile environment that effectively deprived Ha of …