Unveiling the Nature of Neutrinos: From Zero Mass to Majorana Fermions

The enigmatic nature of neutrinos, elementary particles that are key to understanding the universe, has been a subject of intense research and discussion. These intriguing particles were originally believed to be massless, classified as Weyl fermions. However, recent advancements in particle physics have shed light on the possibility that neutrinos can indeed gain mass, fundamentally altering our understanding of these elusive particles.

Neutrinos can acquire mass in two distinct ways within the Standard Model of particle physics. The first method involves engaging with the Higgs field once, resulting in the neutrinos becoming Dirac fermions, much like electrons and quarks. A Dirac fermion can be visualized as oscillating between two Weyl fermions, a behavior determined by its mass.

The second method of gaining mass involves neutrinos interacting with the Higgs field twice, transforming them into Majorana fermions. This fascinating transformation occurs when a Weyl fermion combines with its antiparticle. These Majorana fermions can only exist if the particle and antiparticle share identical properties.

The study and comprehension of neutrino masses, from their initial classification as zero-mass Weyl fermions to the potential as Majorana fermions, have significant implications for our understanding of the universe. These findings contribute to the broader knowledge of elementary particles, many of which display much smaller and more uncertain masses than neutrinos.

The SNO+ experiment, a revolutionary venture in detecting neutrinos, exemplifies the persistent drive to unravel the nature of these extraordinary particles. As we continue to explore the depths of particle physics, the neutrino's true nature remains a tantalizing mystery, holding the potential to reshape our view of the cosmos.

References: 

[1] The Standard Model More Deeply: The Nature of Neutrinos 

[2] Neutrino Masses from the Top Down 

[3] Neutrino Mass Hierarchy