Special Colloquium
Yu-sik Kim	SCHEDULED

Ulsan National Institute of Science and Technology (UNIST), Korea

High-energy cosmic neutrinos, owing to their weak interactions with matter, offer a powerful means of probing extreme particle acceleration processes that cannot be directly accessed through electromagnetic observations. On 8 December 2021, the IceCube Neutrino Observatory reported the detection of a sub-PeV extragalactic neutrino event, IC-211208A. The blazar PKS 0735+178 lies within the localization region of this event and has therefore been considered a strong candidate neutrino-emitting source, joining a small group of extragalactic objects plausibly associated with TeV–PeV neutrinos. In this talk, I present a comprehensive investigation of the multi-wavelength variability and parsec-scale jet evolution of PKS 0735+178 across the neutrino detection epoch. This study combines radio VLBI observations with contemporaneous optical (ASAS-SN g and V bands), X-ray (Swift/XRT), and γ-ray (Fermi-LAT) data to trace the temporal and structural response of the jet. The neutrino arrival coincides with pronounced broadband flaring activity extending from radio to γ-ray energies. On VLBI scales, a newly ejected jet component appears shortly before IC-211208A and subsequently interacts with a quasi-stationary downstream feature at the time of the neutrino event. We interpret this temporal and spatial coincidence as evidence for efficient particle acceleration associated with a recollimation shock, where proton entrainment may occur. The inferred location of the neutrino-emitting region is at a projected distance exceeding approximately 6.5 pc from the central engine, supporting a scenario in which high-energy neutrino production takes place well downstream of the VLBI core. We will also then introduce recent and ongoing VLBI observations of PKS 1749+096, which is considered a new neutrino candidate. Finally, I will provide a concise overview of preparations for a KVN Key Science Program motivated by these investigations.

	Main Colloquium
Professor Axel Brandenburg	SCHEDULED

The Nordic Institute for Theoretical Physics (Nordita), Sweden

Current gamma-ray and radio observations constrain the present-day intergalactic magnetic field to be between 10^{-16} and 10^{-9} gauss on parsec to megaparsec scales. Their filling factors in the voids between galaxy clusters must have exceeded 10 to 30 percent, making it unlikely to be produced by astrophysical mechanisms. A magnetic field of primordial origin could have been generated in the first microseconds of the Universe during inflation or the subsequent electroweak or quark confinement epochs. Its comoving strength and typical scale are or will be reflected in the spectrum of relic gravitational waves on millihertz to nanohertz frequencies. Between generation and present-day observation, the magnetic field must have evolved on a specific track in a diagnostic diagram of comoving field strength versus length scale. This evolution is described by decaying homogeneous magnetically dominated turbulence. This is the subject of high-resolution direct numerical simulations covering over 28 orders of magnitude in cosmic time, augmented by an improved theoretical understanding of the turbulent decay. However, there are still some theoretical questions such as the effects of reconnection, and there are numerical challenges, so we need to ask when can we trust the simulations. Also, how are the results affected by additional physics such as the detailed generation mechanism, for example through axion-like particles, and during the time of recombination, they must include the interaction between photons, baryons, as well as dark matter, and of course the changing expansion of the universe. In my talk, I will review these recent developments and discuss ways of addressing them.