The present and future status of heavy neutral leptons
Asli M. Abdullahi, Pablo Barham Alzás, Brian Batell, J. B. Beacham, Alexey Boyarsky, Saneli Carbajal, A. Chatterjee, J. I. Crespo-Anadón, Frank F. Deppisch, A. De Roeck, Marco Drewes, A. M. Gago, R. Gonzalez Suarez, E. Goudzovski, A. Hatzikoutelis, Josu Hernández-García, Matheus Hostert, Marco Hufnagel, P. Ilten, A. Izmaylov, Kevin J. Kelly, Juraj Klarić, Joachim Kopp, Suchita Kulkarni, M. Lamoureux, G. Lanfranchi, J. López-Pavón, Oleksii Mikulenko, M. Mooney, Miha Nemevšek, Maksym Ovchynnikov, Silvia Pascoli, Ryan Plestid, M. R. Darwish, F. Redi, Oleg Ruchayskiy, Richard Ruíz, Mikhail Shaposhnikov, L. Shchutska, Ian M. Shoemaker, Robert Shrock, Alex Sousa, N. Van Remortel, Vsevolod Syvolap, Volodymyr Takhistov, Jean‐Loup Tastet, Inar Timiryasov, Aaron C. Vincent, J. S. Yu
Abstract
Abstract The existence of nonzero neutrino masses points to the likely existence of multiple Standard Model neutral fermions. When such states are heavy enough that they cannot be produced in oscillations, they are referred to as heavy neutral leptons (HNLs). In this white paper, we discuss the present experimental status of HNLs including colliders, beta decay, accelerators, as well as astrophysical and cosmological impacts. We discuss the importance of continuing to search for HNLs, and its potential impact on our understanding of key fundamental questions, and additionally we outline the future prospects for next-generation future experiments or upcoming accelerator run scenarios.