Deep-Research Agents: Retrieval, Fusion, Reranking, and Claim-Verification Algorithms
A deep-research agent's core is a set of IR and verification algorithms: lexical (BM25), dense, and hybrid retrieval; reciprocal rank fusion and diversity-aware (MMR) selection; cross-encoder reranking; and atomic, NLI-based claim verification with counter-evidence. This guide owns the algorithm layer — retrieval architecture, fusion math, reranking, and verification — and cross-links to its companion architecture pillar for the graph runtime, data model, and governance.