The Mathematics of Poker by Bill Chen and Jerrod Ankenman is considered the standard setter in this area. However, it is a very dense book, not for the faint of heart. At least one training site had a series on understanding the book.
True story: I heard Chen interviewed on the old Poker Road podcast, where he said his book was aimed at the novice. So, considering that Chen had just won two WSOP
bracelets I ordered a copy as soon as it became available. Halfway through the introduction, I knew that I was over my head. So, it happens that one of the players in our regular home game was a math professor, known to lecture internationally. I assumed he would get something out of the book. He looked it over and came to the conclusion that he played poker for fun, preferring not to take his work home with him.
David Skalansky's Theory of Poker is a math based book, that is much more accessible. I think it's fair to say that a lot of current poker thinking grows out of Skalansky's work.