Cosmic thermal neutrino background: Can it be detected?

The detection of the Cosmic Thermal Neutrino Background (CTNB) would provide the “cleanest” evidence for the hot big bang model of the early Universe. I discuss some recent thoughts on the possibility of detecting the CTNB (especially if neutrinos have a small mass of ~ few eV) by looking for certain CTNB-induced features in the extremely high energy (E ≳ 10²⁰ eV) cosmic neutrino spectrum that may become measurable in the future by some of the large-area extensive air-shower detectors being built for detecting extremely high energy cosmic rays. NAS/NRC Senior Research Associate on sabbatical leave from Indian Institute of Astrophysics, Bangalore 560 034, India.