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The baryon number was defined long before the quark model was established, so rather than changing the definitions, ... global symmetry of the QCD Lagrangian. [3 ...
Baryon number violation is a necessary condition to produce an excess of baryons over anti-baryons. But C-symmetry violation is also needed so that the interactions which produce more baryons than anti-baryons will not be counterbalanced by interactions which produce more anti-baryons than baryons.
Baryon number violation is a necessary condition to produce an excess of baryons over anti-baryons. But C-symmetry violation is also needed so that the interactions which produce more baryons than anti-baryons will not be counterbalanced by interactions which produce more anti-baryons than baryons.
This quantum number is the charge of a global/gauge U(1) symmetry in some Grand Unified Theory models, called U(1) B−L.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.
The vector symmetry, U B (1) corresponds to the baryon number of quarks and is an exact symmetry. The axial symmetry U A (1) is exact in the classical theory, but broken in the quantum theory, an occurrence called an anomaly. Gluon field configurations called instantons are closely related to this anomaly.
Some beyond-the-Standard-Model grand unified theories (GUTs) explicitly break the baryon number symmetry, allowing protons to decay via the Higgs particle, magnetic monopoles, or new X bosons with a half-life of 10 31 to 10 36 years. For comparison, the universe is roughly 1.38 × 10 10 years old. [3]
By Noether's theorem, each symmetry above has an associated conservation law: the conservation of baryon number, [12] electron number, muon number, and tau number. Each quark is assigned a baryon number of , while each antiquark is assigned a baryon number of . Conservation of baryon number implies that the number of quarks minus the number of ...
There are also many approximate conservation laws, which apply to such quantities as mass, parity, [1] lepton number, baryon number, strangeness, hypercharge, etc. These quantities are conserved in certain classes of physics processes, but not in all.