Reddit mentions of Treating Attachment Disorders, Second Edition: From Theory to Therapy

There are 2 lines of thought on RAD: mainstream science and a splinter group, mostly parents of adoptive children, who have very extreme views on RAD. They tend to think that every problem an adoptive kid has is RAD, they tend to hold very high behavioral expectations that most kids couldn't meet, and they tend to support the use of fairly extreme punishment. (As it happens, they're mostly evangelical christians who tend to be rigid parents regardless and often choose adoption because they believe it is a moral imperative, without necessarily being really ready for the reality of it.) Anyways, they've written a lot of books like Parenting the Difficult Child: A Biblical Perspective on Reactive Attachment Disorder. YOu might want those books if you're investigating parenting styles, but otherwise probably not.

There aren't any "gold standard" kinds of books that everyone reads, but there are some good ones. I like Treating Attachment Disorders and Reactive Attachment Disorder: A Case-Based Approach. They're from 2014 and 2012, respectively, though, so you'll have to look at the literature to get the most up-to-date stuff.