There's a lot of research on recommender systems. There's a lot of other research that, while not directly mentioning recommenders, is very relevant, including research from decades ago.
A few of my favorite old papers that I think recommender systems researchers would do well to read (and perhaps cite):
Back to Bentham? Explorations of experienced utility (Kahneman et al., 1997) — how people experience and remember pain and pleasure. Strong implications for what ratings mean and what kind of utility our recommenders should optimize for.
User Modeling via Stereotypes (Rich, 1979) — the first computer-based recommender system that I know about.
A searching procedure for information retrieval (Goffman, 1964) — this early IR paper has the crucial insight that the relevance of an item in a search search result list (or recommendation list) is not independent of the items that appear before or after it. Rather, an item may be less relevant if it is (partially) redundant with a previous item.