Vector models are nothing but representation learning and applying the model out-of-domain usually gives worse results than plain old BM25. See https://arxiv.or

Vector models are nothing but representation learning and applying the model out-of-domain usually gives worse results than plain old BM25. See https://arxiv.org/abs/2104.08663 https://arxiv.org/abs/2104.08663 A concrete example is DPR which is a state of the art dense retriever model for wikipedia for question answering, when applying that model on MS Marco passage ranking it performs worse than plain BM25.