Reddit mentions of String Theory, Vol. 1 (Cambridge Monographs on Mathematical Physics)

This textbook is a standard I believe? Though I seriously doubt there’ll be any serious string theory textbooks at the undergraduate level. It’s a topic beyond the standard model, which is already seriously complex. I’m a PhD student but not in particle physics, so I doubt I could even get a good foundation in QFT by myself to begin with. There are plenty of YouTube videos going over the basic qualitative features, so I’d start with that, but I don’t think you should get too caught up on all the gory details.

For Stat Mech Daniel F. Styer's book and an assortment of lecture notes that I found doing a Google search.

For CFT here is one that I am finding helpful as a quick out line to help guide me: http://www.physics.iitm.ac.in/~suresh/sgtalk/talk_html/introcft.pdf. Also this book: http://www.amazon.com/String-Cambridge-Monographs-Mathematical-Physics/dp/0521672279/ref=pd_sim_b_5

String Theory, Vol. 1 (Cambridge Monographs on Mathematical Physics) by Joseph Polchinski assumes this result. Link - https://www.amazon.com/String-Cambridge-Monographs-Mathematical-Physics/dp/0521672279
Page 22 equation- 1.3.32. Also, why mathematics can't predict the functioning of the real world?

Cheers, Adeeb