Create a text index on MongoDB schema which references another schema
I think, what you are looking for is the ability to join tables of data and perform a query against the sum of that data. That is something you need a relational database for, which MongoDB isn't.
So I recommend you change your approach in how you would like to preform your search, e.g. search for your keyword within both author and title instead of attempting to search the whole dataset at the same time.