Dense passage retrieval has become the mainstream method in the first stage of open-domain question answering, which usually adopts a bi-encoder structure to learn the dense representation of questions and passages for semantic matching. One of the main challenges currently is to effectively utilize more informative hard negatives. Many efforts have been made to address this challenge by reducing the discrepancy between training and inference and training expensive cross-encoder for mining hard negatives. However, none of these approaches consider the theme information regarding the candidate ...
