Quantum vacuum Cherenkov emission as a solution to the pulsar death valley problem

The presence of numerous radio pulsars in the so-called ''death valley'' of the rotation period-magnetic field (P-B) diagram challenges the curvature-radiation assisted pair creation model and cascades in neutron star polar caps. We show that Cherenkov radiation from quantum vacuum, a strong field quantum electrodynamics (QED) phenomenon enabled by vacuum polarization, can dominate pair creation in neutron-star pulsar polar caps for magnetic fields B ≥ 10 ¹¹ Gauss, leading to neutron star radio emitters in this unexpected parameter window. Our analysis shows that Cherenkov photons dominate over curvature photons as seeds for pair production, setting a new death line that extends beyond the traditional limits. This result redefines the radio-loud landscape for neutron stars, opening a vast parameter space for long-period neutron star radio emitters previously considered inactive. Our predicted Cherenkov death line provides a physical basis for a population of neutron stars in a region of the P-B diagram where known pulsar models fail, offering a new interpretation for the existence of coherent radio emission at very long periods, and a new window for testing QED phenomena in astrophysical sources.