The Shulchan Aruch paskens (OC 554) that it is forbidden to learn most parts of Torah on Tisha Beav, except for a few small sections about aveilut. The question is: the Shulchan Aruch doesn't explicitly mention Hilchot Teshuva, but would it be permissible to do so? The Rambam (Hilchot Taaniot) sa...