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Large-scale digital platforms generate billions of timestamped user-item interactions (events) that are crucial for predicting user attributes in, e.g., fraud prevention and recommendations. While self-supervised learning (SSL) effectively models the temporal order of events, it typically overlooks the global structure of the user-item interaction graph. To bridge this gap, we propose three model-agnostic strategies for integrating this structural information into contrastive SSL: enriching event embeddings, aligning client representations with graph embeddings, and adding a structural pretext task. Experiments on four financial and e-commerce datasets demonstrate that our approach consistently improves the accuracy (up to a 2.3% AUC) and reveals that graph density is a key factor in selecting the optimal integration strategy.
Many web-based datasets are characterized by multiway interactions of different categories, and can be modeled as edge-colored hypergraphs. We focus on clustering such datasets using the NP-hard edge-colored clustering problem, where the goal is to assign colors to nodes in such a way that node colors tend to match edge colors. A key focus in prior work has been to develop approximation algorithms for the problem that are combinatorial and easier to scale. In this paper, we present the first combinatorial approximation algorithm with an approximation factor better than 2.
We study the auto-bidding problem under a strict return-on-spend constraint (ROSC), where an online algorithm decides how much to bid for each ad slot based on a revealed value and hidden allocation and payment functions. The goal is to maximize cumulative expected utility (value times winning probability) while ensuring that total expected payment does not exceed total expected utility. We prove an impossibility result showing that no online algorithm can achieve sublinear regret even when values, allocations, and payments are drawn i.i.d. from an unknown distribution. For the special case of constant valuations, we design an algorithm that strictly satisfies the ROSC and achieves regret optimal up to logarithmic factors.
Audio deepfakes generated by modern TTS and voice conversion systems are increasingly difficult to distinguish from real speech, raising serious risks for security and online trust. While state-of-the- art self-supervised models provide rich multi-layer representations, existing detectors treat layers independently and overlook temporal and hierarchical dependencies critical for identifying synthetic arte- facts. We propose HierCon, a hierarchical layer attention framework combined with margin-based contrastive learning that models de- pendencies across temporal frames, neighbouring layers, and layer groups, while encouraging domain-invariant embeddings. Evalu- ated on ASVspoof 2021 DF and In-the-Wild datasets, our method achieves state-of-the-art performance (1.93% and 6.87% EER), im- proving over independent layer weighting by 36.6% and 22.5% re- spectively. The results and attention visualisations confirm that hierarchical modelling enhances generalisation to cross-domain generation techniques and recording conditions.
Large Language Models (LLMs) have shown significant potential for improving recommendation systems through their inherent reasoning capabilities and extensive knowledge base. Yet, existing studies predominantly address warm-start scenarios with abundant user-item interaction data, leaving the more challenging cold-start scenarios, where sparse interactions hinder traditional collaborative filtering methods, underexplored. To address this limitation, we propose novel reasoning strategies designed for cold-start item recommendations within the Netflix domain. Our method utilizes the advanced reasoning capabilities of LLMs to effectively infer user preferences, particularly for newly introduced or rarely interacted items. We systematically evaluate supervised fine-tuning, reinforcement learning-based fine-tuning, and hybrid approaches that combine both methods to optimize recommendation performance. Extensive experiments on real-world data demonstrate significant improvements in both methodological efficacy and practical performance in cold-start recommendation contexts. Remarkably, our reasoning-based fine-tuned models outperform Netflix's production ranking model by up to 8% in certain cases.
Personalized search ranking systems are critical for driving engagement and revenue in modern e-commerce platforms. Existing methods primarily model users' broad interests from historical behaviors but often fail to explicitly align these with real-time intent expressed in user queries. In this paper, we propose DiffusionGS, a scalable generative framework that treats user queries as explicit intent anchors to extract user interests from long-term, noisy behavior histories. Specifically, we formulate interest extraction as a conditional denoising task, where the user's query guides a conditional diffusion process to produce a robust, user intent-aware representation from their behavioral sequence. A User-aware Denoising Layer (UDL) further refines attention distribution using user-specific profiles. By reframing queries as intent priors and leveraging diffusion-based denoising, our method provides a powerful mechanism for capturing dynamic user interest shifts. Extensive offline and online experiments demonstrate the superiority of DiffusionGS over state-of-the-art methods.