PLEnuM: A world-wide monitoring system of high-energy astrophysical neutrinos

The IceCube discovery of high-energy astrophysical neutrinos, with TeV-PeV energies, has bolstered neutrino astronomy. However, because the detection rate of high-energy astrophysical neutrinos remains low, various important questions about them, notably their origin, remain unanswered or answered only uncertainly. This situation will improve when new neutrino telescopes will come online in the next years: KM3NeT, Baikal-GVD, and P-ONE in the Northern Hemisphere, and IceCube-Gen2 in the Southern Hemisphere. Individually, they will offer important improvements; combined, their reach will be transformative. To achieve this, we propose the Planetary Neutrino Monitoring System (PLEνM), a concept for a combined repository of worldwide high-energy neutrino observations. PLEνM can reach more than four times the exposure available today by combining the exposures of the current and future neutrino telescopes distributed around the world. Depending on the declination, spectral index, and flavor, PLEνM will improve the sensitivity to astrophysical neutrinos by up to two orders of magnitude. We present first estimates on the capability of PLEνM to discover Galactic and extragalactic sources of astrophysical neutrinos and to characterize the diffuse flux of high-energy neutrinos in unprecedented detail.