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    <abstract>Multi-hop question answering (QA) often requires sequential retrieval (multi-hop retrieval), where each hop retrieves missing knowledge based on information from previous hops. To facilitate more effective retrieval, we aim to distill knowledge from a posterior retrieval, which has access to posterior information like an answer, into a prior retrieval used during inference when such information is unavailable. Unfortunately, current methods for knowledge distillation in one-time retrieval are ineffective for multi-hop QA due to two issues: 1) posterior information is often defined as the response (i.e. answers), which may not clearly connect to the query without intermediate retrieval; and 2) the large knowledge gap between prior and posterior retrievals makes distillation using existing methods unstable, even resulting in performance loss. As such, we propose MoPo (Momentum Posterior Regularization) with two key innovations: 1) Posterior information of one hop is defined as a query-focus summary from the golden knowledge of the previous and current hops; 2) We develop an effective training strategy where the posterior retrieval is updated along with the prior retrieval via momentum moving average method, allowing smoother and effective distillation. Experiments on HotpotQA and StrategyQA demonstrate that MoPo outperforms existing baselines in both retrieval and downstream QA tasks.</abstract>
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%0 Conference Proceedings
%T Momentum Posterior Regularization for Multi-hop Dense Retrieval
%A Xia, Zehua
%A Wu, Yuyang
%A Xia, Yiyun
%A Nguyen, Cam Tu
%Y Rambow, Owen
%Y Wanner, Leo
%Y Apidianaki, Marianna
%Y Al-Khalifa, Hend
%Y Eugenio, Barbara Di
%Y Schockaert, Steven
%S Proceedings of the 31st International Conference on Computational Linguistics
%D 2025
%8 January
%I Association for Computational Linguistics
%C Abu Dhabi, UAE
%F xia-etal-2025-momentum
%X Multi-hop question answering (QA) often requires sequential retrieval (multi-hop retrieval), where each hop retrieves missing knowledge based on information from previous hops. To facilitate more effective retrieval, we aim to distill knowledge from a posterior retrieval, which has access to posterior information like an answer, into a prior retrieval used during inference when such information is unavailable. Unfortunately, current methods for knowledge distillation in one-time retrieval are ineffective for multi-hop QA due to two issues: 1) posterior information is often defined as the response (i.e. answers), which may not clearly connect to the query without intermediate retrieval; and 2) the large knowledge gap between prior and posterior retrievals makes distillation using existing methods unstable, even resulting in performance loss. As such, we propose MoPo (Momentum Posterior Regularization) with two key innovations: 1) Posterior information of one hop is defined as a query-focus summary from the golden knowledge of the previous and current hops; 2) We develop an effective training strategy where the posterior retrieval is updated along with the prior retrieval via momentum moving average method, allowing smoother and effective distillation. Experiments on HotpotQA and StrategyQA demonstrate that MoPo outperforms existing baselines in both retrieval and downstream QA tasks.
%U https://aclanthology.org/2025.coling-main.550/
%P 8255-8271

Markdown (Informal)

[Momentum Posterior Regularization for Multi-hop Dense Retrieval](https://aclanthology.org/2025.coling-main.550/) (Xia et al., COLING 2025)

• Momentum Posterior Regularization for Multi-hop Dense Retrieval (Xia et al., COLING 2025)

ACL

• Zehua Xia, Yuyang Wu, Yiyun Xia, and Cam Tu Nguyen. 2025. Momentum Posterior Regularization for Multi-hop Dense Retrieval. In Proceedings of the 31st International Conference on Computational Linguistics, pages 8255–8271, Abu Dhabi, UAE. Association for Computational Linguistics.