B %E2%88%92 L
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B %E2%88%92 L

In high energy physics, B - L (pronounced "bee minus ell") is the difference between the baryon number (B) and the lepton number (L).


This quantum number is the charge of a global/gauge U(1) symmetry in some Grand Unified Theory models, called U(1)BL. 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 exists as a symmetry, then for the seesaw mechanism to work 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 is always conserved. One hypothetical example is proton decay where a proton () would decay into a pion () and positron ().

The Weak hypercharge is related to via


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]


  1. ^ Wilczek, Frank; Zee, A. (1979). "Operator analysis of nucleon decay". Physical Review Letters. 43 (21): 1571-1573. Bibcode:1979PhRvL..43.1571W. doi:10.1103/PhysRevLett.43.1571.

See also

  This article uses material from the Wikipedia page available here. It is released under the Creative Commons Attribution-Share-Alike License 3.0.



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