  Complex question answering often requires finding a reasoning chain that
consists of multiple evidence pieces. Current approaches incorporate the
strengths of structured knowledge and unstructured text, assuming text corpora
is semi-structured. Building on dense retrieval methods, we propose a new
multi-step retrieval approach (BeamDR) that iteratively forms an evidence chain
through beam search in dense representations. When evaluated on multi-hop
question answering, BeamDR is competitive to state-of-the-art systems, without
using any semi-structured information. Through query composition in dense
space, BeamDR captures the implicit relationships between evidence in the
reasoning chain. The code is available at https://github.com/
henryzhao5852/BeamDR.
