NEUTRINO SEARCHES WITH THE PIERRE AUGER OBSERVATORY: FROM NEW TECHNIQUES TO MULTI-MESSENGER OPPORTUNITIES

Parallel talk presented at the XXI International Workshop on Neutrino Telescopes - Padova 29 September - 3 October 2025 (https://agenda.infn.it/event/44606/) On behalf of the Pierre Auger Collaboration Abstract: The Pierre Auger Observatory, equipped with a vast Surface Detector (SD) array, is well suited to search for ultra-high-energy (UHE) neutrinos above 10 17 eV through the identification of deeply penetrating air showers. The Observatory has set some of the most stringent limits on both diffuse and point-like sources of UHE neutrinos and actively contributes to multi-messenger follow-up searches of transient astrophysical events, such as gamma-ray bursts and binary black hole mergers. The sensitivity to UHE neutrinos is continuously being enhanced through several approaches, including the implementation of two additional SD triggers---Time-over-Threshold-deconvolved (ToTd) and Multiplicity-of-Positive Steps (MoPS)---which have improved detection efficiency below 10 19 eV by a factor of 5-10 in the zenith angle range of 60° to 75°. In this contribution, we provide an overview of ongoing neutrino analyses at the Observatory, highlighting a novel identification strategy that incorporates these triggers within a blind search framework. Updated constraints on diffuse and point-source neutrino fluxes will be presented, alongside a discussion of other recent results. Funded by the Bundesministerium für Forschung, Technologie und Raumfahrt.