4/26/2023 0 Comments Neutrino massIntermediate scales, such as GeV, are motivatedīy grand unification and typically yield masses in the range (The latter two violateĬosmological bounds unless they decay rapidly and invisibly.) Lepton masses, so that one expects masses of orderĪnd, respectively. Typically, the Dirac massesĪre of the order of magnitude of the corresponding charged ![]() The TeV scale models are motivated, for example, by left-right Range anywhere from the TeV scale to the Planck scale. There are literally hundreds of versions of the Generating neutrino masses much smaller than the other fermion masses. Such models are a popular and natural way of Thus, there is one heavy neutrino and one neutrino much lighter than The physical particle content is given by two Majorana massĪn especialy interesting case is the seesaw limit The states are respectively active and sterile), while is aĭirac mass term. Transform as weak triplets and singlets, respectively (assuming that For two Weyl neutrinosĪre the two Weyl states. It is also possible to consider mixed models in which both MajoranaĪnd Dirac mass terms are present. The most familiar example is the seesaw model, to be discussed below. M is the scale of the new physics which generates the operator. Violation) is mainly a weak singlet ( invisible MajoronĮxpects, where C is a dimensionless constant and The Majoron (the Goldstone boson associated with lepton number Variant models involving explicit lepton number violation or in which Original GR model is now excluded by the LEP data on the Z In which lepton number is spontaneously broken by. Triplet or by an effective operator involving two Higgs doubletsįor an elementary triplet, where is a Yukawa If is active thenĪnd m must be generated by either an elementary Higgs Where is a self-conjugate two-component stateĬharge conjugation matrix. It can therefore lead to neutrinoless double beta decay. Equivalently, it can be viewedĪs the creation or annihilation of two neutrinos, and if present It is a transitionįrom an antineutrino into a neutrino. That leads to the question of why it is so small: one would requireĪ Majorana mass, which violates lepton number by two units, makes use of the right-handed antineutrino,, rather than a separate Weyl neutrino. Where the vacuum expectation value (VEV) ofĪ Dirac mass is just like the quark and charged lepton masses, but Interactions except those due to mixing). The charged current transitions then involveĪ leptonic mixing matrix (analogous to theĬabibbo-Kobayashi-Maskawa (CKM) quark mixing matrix), whichĬan lead to neutrino oscillations between the light neutrinos. To three or more families, in which case the masses become matrices. This and other types of mass terms can easily be generalized Thus aĭirac neutrino has four components (the CPT partner of ),Īnd the mass term allows a conserved lepton number. ![]() Is different from, the CPT partner of the Mass terms describe transitions between right ( R)Ī Dirac mass term, which conserves lepton number, involves transitions I give a brief survey of the principle classes. There are a confusing variety of models of neutrino mass. ![]() Looking further ahead, the workshop will also address prospects of extending the physics reach of current and next-generation experiments beyond the quest for neutrino masses by probing for the existence of light and medium-mass sterile neutrinos, searching for Lorentz invariance violation, or attempting detection of relic neutrinos.Next: Laboratory Limits Up: Implications of Neutrino Mass Previous: Motivations The objective of this workshop is to foster the discussion between theorists and experimentalists involved in the different projects at a time when large experiments are approaching the starting phase. This goal can only be achieved by bringing togetherĮxpertise from different fields such as nuclear and particle physics, atomic and molecular physics, theory and phenomenology. The mass scale of neutrinos is one of the fundamental open questions in modern physics, with far-reaching implications from cosmology to particle physics. Precision measurements of the kinematics of weak interactions, notably of the H-3 β-decay spectrum and the Ho-163 electron capture spectrum, represent the only model independent approach to address this question in a laboratory experiment.The next milestone is to reach sub-eV sensitivity with respect to the electron (anti-)neutrino mass.
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