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The direct detection of the cosmic relic neutrino background (CnB) is an outstanding problem in particle physics and cosmology. There exist several proposals, but none of them is expected to be feasible anytime soon. After reviewing the challenges in CnB detection, we will discuss a new way to detect CnB via resonant scattering against cosmogenic neutrinos, which leads to a distinct absorption feature in the cosmogenic neutrino flux. This absorption feature may be observable in future radio-based neutrino observatories (such as IceCube-Gen2 radio), provided there exists a large CnB overdensity in the vicinity of the cosmogenic sources. This therefore provides a new probe of CnB clustering at large redshifts, complementary to the laboratory probes (such as KATRIN) at zero redshift. |