Samarth Bhargav

Learning to rank (LTR) traditionally requires large-scale training data to generalize effectively. In low-data domains where expert annotation is scarce, the performance of LTR methods degrades sharply. Foundation models have alleviated similar data dependencies in other domains via in-context learning, but a foundation model for ranking with tabular features has not been explored yet. We propose prior-data fitted networks (PFNs) as a strong method for ranking in low-data settings. First, we demonstrate that PFNs, which are originally trained for classification, successfully outperform classification baselines on ranking data. Next, we evaluate PFNs as rankers, showing that they surpass state-of-the-art tuned baselines in low-data regimes. We introduce a novel sampling and inference scheme to obtain pairwise predictions from PFNs' native pointwise architecture, analogous to pairwise LTR. To address the limited context window of the transformers underlying PFNs, we propose a dynamic support set selection strategy for queries that scales PFNs beyond random subsampling. Our experimental results show that PFNs are an effective foundation model for ranking that provides significant gains when data is limited.

Roxana Petcu, Samarth Bhargav, Maarten de Rijke, Evangelos Kanoulas. Findings of the Association for Computational Linguistics: EMNLP 2025. 2025.

In this paper we propose RecFusion, which comprise a set of diffusion models for recommendation. Unlike image data which contain spatial correlations, a user-item interaction matrix, commonly utilized in recommendation, lacks spatial relationships between users and items. We formulate diffusion on a 1D vector and propose binomial diffusion, which explicitly models binary user-item interactions with a Bernoulli process. We show that RecFusion approaches the performance of complex VAE baselines on the core recommendation setting (top-n recommendation for binary non-sequential feedback) and the most common datasets (MovieLens and Netflix). Our proposed diffusion models that are specialized for 1D and/or binary setups have implications beyond recommendation systems, such as in the medical domain with MRI and CT scans.

We present a study of Tip-of-the-tongue (ToT) retrieval for music, where a searcher is trying to find an existing music entity, but is unable to succeed as they cannot accurately recall important identifying information. ToT information needs are characterized by complexity, verbosity, uncertainty, and possible false memories. We make four contributions. (1) We collect a dataset - TOTMUSIC--of 2,278 information needs and ground truth answers. (2) We introduce a schema for these information needs and show that they often involve multiple modalities encompassing several Music IR sub-tasks such as lyric search, audio-based search, audio fingerprinting, and text search. (3) We underscore the difficulty of this task by benchmarking a standard text retrieval approach on this dataset. (4) We investigate the efficacy of query reformulations generated by a Large Language Model (LLM), and show that they are not as effective as simply employing the entire information need as a query--leaving several open questions for future research.

Entity disambiguation (ED) is the last step of entity linking (EL), when candidate entities are reranked according to the context they appear in. All datasets for training and evaluating models for EL consist of convenience samples, such as news articles and tweets, that propagate the prior probability bias of the entity distribution towards more frequently occurring entities. It was previously shown that the performance of the EL systems on such datasets is overestimated since it is possible to obtain higher accuracy scores by merely learning the prior. To provide a more adequate evaluation benchmark, we introduce the ShadowLink dataset, which includes 16K short text snippets annotated with entity mentions. We evaluate and report the performance of popular EL systems on the ShadowLink benchmark. The results show a considerable difference in accuracy between more and less common entities for all of the EL systems under evaluation, demonstrating the effects of prior probability bias and entity overshadowing.