| Challenge: | Existing dense retrieval systems that use semantic embedding similarities can be effective across tasks and languages. |
| Approach: | They propose to pivot through Hypothetical Document Embeddings (HyDE) given a query, HyDE first zero-shot prompts an instruction-following language model to generate a hypothetical document. |
| Outcome: | The proposed method significantly outperforms the state-of-the-art unsupervised dense retriever Contriever and shows strong performance comparable to fine-tuned retrievers across tasks and languages. |
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| Challenge: | Zero-shot dense retrieval requires generic, pretrained DRs, which struggle to represent semantic differences between similar documents. |
| Approach: | They propose a training-free representation sharpening framework that augments a document’s representation with information that helps differentiate it from similar documents in the corpus. |
| Outcome: | The proposed framework is compatible with prior approaches to zero-shot dense retrieval and consistently improves their performance. |
AutoMIR: Effective Zero-Shot Medical Information Retrieval without Relevance Labels (2025.findings-emnlp)
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| Challenge: | Effective zero-shot dense retrieval in the medical domain remains difficult due to the scarcity of relevance-labeled data. |
| Approach: | They propose a framework that leverages large language models to generate hypothetical documents . they also propose 'CMIRB' to provide a rigorous evaluation suite . |
| Outcome: | The proposed framework outperforms HyDE in retrieval accuracy and generalization . it leverages large language models to generate hypothetical documents conditioned on a query . |
Scalable Zero-shot Entity Linking with Dense Entity Retrieval (2020.emnlp-main)
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| Challenge: | Existing methods for entity linking use manually curated mention tables and incoming Wikipedia link popularity. |
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Augmenting Document Representations for Dense Retrieval with Interpolation and Perturbation (2022.acl-short)
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| Challenge: | Existing sparse retrieval models rely on term-based matching to retrieve relevant documents. |
| Approach: | They propose a framework which augments the representations of documents with interpolation and perturbation. |
| Outcome: | The proposed framework significantly outperforms baselines on the dense retrieval of both the labeled and unlabeled documents. |
Dense Retrievers Can Fail on Simple Queries: Revealing The Granularity Dilemma of Embeddings (2025.findings-emnlp)
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| Challenge: | a limited number of text encoders are able to recognize fine-grained entities or events within encoded semantics. |
| Approach: | They propose a new evaluation dataset to examine embeddings' ability to recognize fine-grained entities or events within encoded semantics. |
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Issues with Entailment-based Zero-shot Text Classification (2021.acl-short)
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| Challenge: | Pre-trained BERT models with no fine-tuning can yield competitive performance against BERT fine- tuned for NLI. |
| Approach: | They propose to use any target label into a sentence of hypothesis and verify whether it could be entailed by the input. |
| Outcome: | The proposed models perform better than models fine-tuned for BERT, but the results are in general negative. |
PromptReps: Prompting Large Language Models to Generate Dense and Sparse Representations for Zero-Shot Document Retrieval (2024.emnlp-main)
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| Challenge: | Large language models (LLMs) excel in zero-shot document ranking tasks. |
| Approach: | They propose a prompt-based re-ranking method that requires no further training but is only feasible for reranking a handful of candidates due to computational costs. |
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A Thorough Examination on Zero-shot Dense Retrieval (2023.findings-emnlp)
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Ruiyang Ren, Yingqi Qu, Jing Liu, Xin Zhao, Qifei Wu, Yuchen Ding, Hua Wu, Haifeng Wang, Ji-Rong Wen
| Challenge: | Recent advances in dense retrieval (DR) models have been shown to be not as competitive as traditional sparse retrieval models in a zero-shot retrieval setting. |
| Approach: | They propose to examine the zero-shot capability of DR models by analyzing key factors related to source training set and potential bias from target dataset. |
| Outcome: | The proposed model is not as competitive as sparse retrieval models in a zero-shot retrieval setting. |
Relevance-assisted Generation for Robust Zero-shot Retrieval (2023.emnlp-industry)
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| Challenge: | Despite strong in-domain performance, dense retrievers have shown poor generalization to out-of-domain zero-shot tasks where no training queries are available. |
| Approach: | They propose to generate domain-specific pseudo queries for fine-tuning with domain-relevant relevance between PQ and documents. |
| Outcome: | The proposed approach is more robust to domain shifts, validated on BEIR zero-shot tasks. |
Exploring efficient zero-shot synthetic dataset generation for Information Retrieval (2024.findings-eacl)
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| Challenge: | Recent advances in large language models offer a new avenue of generating synthetic training data to train neural retrieval models for unlabelled data collections. |
| Approach: | They propose a method to generate high-quality synthetic datasets using a small language model and a filtering mechanism to ensure the quality of generated questions. |
| Outcome: | The proposed method outperforms unsupervised retrieval methods such as BM25 and pretrained monoT5. |