# What is the Twisted Trace Formula?

I am studying the trace formula using "An Introduction to the Trace Formula" by James Arthur. I would like to understand the twisted trace formula, but unfortunately I never came across a good article that mainly deals with it. For example, in Section 26 of the paper mentioned above, Arthur mentions how the formula looks like in the case of compact quotient, but that is it. I appreciate greatly if you could answer any of the following questions.

1. How is the kernel modified?
2. How do the coarse geometric and spectral expansions look like? How about the fine expansions?
3. How can the twisted trace formula be useful? Is there something that the twisted trace formula can detect, but the regular trace formula can not?

Thank you!

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See papers of Erez Lapid, and Herve Jacquet, and their collaborators. But, basically, there is an unfortunate apocryphal element built into many of these sources... –  paul garrett Feb 11 at 3:28