Is it permissible to add the names of researchers who did not actually participate in the research, and is it permissible for the principal author to receive financial compensation for this addition, given that the research is original and contains no fraud?

A Muslim must be truthful and avoid lying. Writing the name of a researcher on a book he did not participate in authoring is considered an explicit and impermissible lie. The intention behind this might be personal gain, such as obtaining a promotion, which falls under "being satiated with what one has not been given," or deceiving and defrauding the reader by increasing their trust in the book, which makes the matter worse.