Dense Hierarchical Retrieval for Open-domain Question Answering Ye Liu author Kazuma Hashimoto author Yingbo Zhou author Semih Yavuz author Caiming Xiong author Philip Yu author 2021-11 text Findings of the Association for Computational Linguistics: EMNLP 2021 Marie-Francine Moens editor Xuanjing Huang editor Lucia Specia editor Scott Wen-tau Yih editor Association for Computational Linguistics Punta Cana, Dominican Republic conference publication liu-etal-2021-dense-hierarchical 10.18653/v1/2021.findings-emnlp.19 https://aclanthology.org/2021.findings-emnlp.19/ 2021-11 188 200