Lee-Weinberg bound

The Lee-Weinberg bound (aka Lee-Weinberg limit) refers to a lower limit of roughly 2 GeV on the mass of any possible heavy neutral lepton, i.e., any heavy neutrino. It does not exclude far lighter neutrinos and all currently known neutrino flavors have a mass less than an eV. The "heavy" lower limit was calculated by Benjamin Whisoh Lee and Steven Weinberg in 1977, their analysis sometimes called the Lee-Weinberg argument. A calculated upper limit termed the unitary bound, of a few TeV produces a range of possible heavy neutral leptons known as the Lee-Weinberg window. The fact that the total mass of such particles throughout the observable universe would be within the right order-of-magnitude to account for dark matter is termed the WIMP miracle, and the term WIMP is sometimes used specifically to mean such a lepton within this range.

Decades of searching for such particles has not detected any and there has been recent development of theories regarding why these limits may not apply to dark matter particles.