Английская Википедия:B − L
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Шаблон:Flavour quantum numbers
In particle physics, B − L (pronounced "bee minus ell") is a quantum number which is the difference between the baryon number (Шаблон:Mvar) and the lepton number (Шаблон:Mvar) of a quantum system.
Details
This quantum number is the charge of a global/gauge U(1) symmetry in some Grand Unified Theory models, called Шаблон:Math. Unlike baryon number alone or lepton number alone, this hypothetical symmetry would not be broken by chiral anomalies or gravitational anomalies, as long as this symmetry is global, which is why this symmetry is often invoked.
If Шаблон:Math exists as a symmetry, then for the seesaw mechanism to work Шаблон:Math has to be spontaneously broken to give the neutrinos a nonzero mass.
The anomalies that would break baryon number conservation and lepton number conservation individually cancel in such a way that Шаблон:Math is always conserved. One hypothetical example is proton decay where a proton (Шаблон:Math) would decay into a pion (Шаблон:Math) and positron (Шаблон:Math).
The weak hypercharge Шаблон:Math is related to Шаблон:Math via
<math display=block>X + 2\,Y_\text{W} = 5\,( B - L ),</math>
where X charge (not to be confused with the X boson) is the conserved quantum number associated with the global U(1) symmetry Grand Unified Theory.[1]
See also
References
Шаблон:Proton decay experiments
