An author who has assigned his/her copyright in return for a continuing royalty interest is a “beneficial” owner of the copyright. As long as he/she has a continuing financial interest in the copyright, a beneficial owner is entitled to sue for infringement. A beneficial owner has only two rights in the work — the right to receive royalty payments and the right to sue.
For example, Alice, a songwriter, assigns her copyright in her composition to Bob, a music publisher in exchange for royalty payments. Despite this assignment, Alice can sue anyone who uses her composition without Bob’s authorization and obtain royalties.