Benchmark Problems and Benchmark Datasets for the evaluation of Machine and Deep Learning methods on Photoplethysmography signals: the D4 report from the QUMPHY project. - Urs Hackstein; Jordi Alastruey; Philip J. Aston; Ciaran Bench; Peter H. Charlton; Loic Coquelin; Nando Hegemann; Vaidotas Marozas; Mohammad Moulaeifard; Manasi Nandi; Andrius Petrenas; Oskar Pfeffer; et al. (CoRR, 2026)