Who is the world's greatest authority on anxiety disorders? You know the greatest psychiatrist?

Not one best answer. For treatment, in my opinion there is no one best psychiatrist. There are various styles of practice, and what works for one patient may not work for another. Of note, us news and world report has a list of recommended hospital psychiatry departments, and could serve as a guide. Johns hopkins and massachusetts general hospital are highly rated.
Funny Q&A. After more than 25 years of expert witness work, one becomes cautious about declaring any person or source as authoritative or the greatest. The true mark of knowledge is understanding they nor we know everything. The greatest psychiatrist or psychologist may be the one who takes a good history, performs a good assessment, listens to you and establishes what we call a good working relationship.