Required Readings
 Rosenfeld's notes (estimation and information theory)
The goal of reading these notes is to know about some basic concepts in probability, statistics, and information theory. You should read at least Section 3 of the estimation note and all of the information theory note except for section 1.1.6. You should fully understand the derivation of the maximum likelihood estimate for the binomial distribution, and most of the contents in the information theory notes. If you can't understand these, you may want to read relevant discussions in a textbook on probability and statistics, and a book on information theory. Any book on these topics should be sufficient.

[Robertson and Zaragoza 2009]
This is a nice introduction to how one of the most effective retrieval functions, BM25, has been developed and extended later. As a minimum, read chapters 13, but try to read the entire review if you can.

SLMIR
This book has a chapter (Chapter 2) on a general survey of major retrieval models and an extensive coverage of statistical language models for IR, which might be useful if you want to have a good picture of all kinds of retrieval models in general. Chapters 36 are most useful for understanding language models for retrieval. Chapter 7 is useful for understanding topic models.
More to be posted later.