SNe II the rescue: A novel distance-ladder free determination of the Hubble constant

We present the development and proof-of-principle demonstration of a distance-ladder-independent method for determining the Hubble constant (H₀) using type II supernovae (SNe II). By leveraging advancements in spectral modeling through the tailored expanding photosphere method (EPM), we achieve precision comparable to leading H₀ determination techniques. This approach utilizes spectral emulators to efficiently interpolate radiative transfer models, allowing accurate fits to supernova spectra and the derivation of luminosity distances. Applied to a sample of ten SNe II with publicly available data, this method yields an independent H₀ value of 74.9 ± 1.9 (stat) km s⁻¹ Mpc⁻¹, consistent with recent local measurements. The study highlights the potential of SNe II as cosmological probes independent of traditional distance ladders. This talk will focus on the methodology and results of this proof-of-principle study, demonstrating the robustness and precision of the tailored EPM approach. A second talk (S. Taubenberger) will introduce the adH0cc project, which aims to refine and extend this methodology by utilizing a dedicated, larger dataset of over 20 SNe II optimized for cosmological applications. Additionally, a third talk (G. Csörnyei) will explore sibling supernovae as a path to test systematics in SN II cosmology, providing insights into controlling and understanding systematic uncertainties inherent to this approach.