1. The Standard model is an SU(3)xSU(2)xU(1) symmetric theory. To me this means that if you choose any 3 members of the groups and act on the Lagrangian, it is invariant. However, not all terms in the Lagrangian have something for a group member to act on, for example terms that dont involve anything with colour charge aren't acted on by SU(3). Then such a term would only have SU(2)xU(1) symmetry. Do we just say that this term has the full symmetry, but there is nothing for the SU(3) part to act on?(adsbygoogle = window.adsbygoogle || []).push({});

2. In a chirally symmetric theory with (say) 2 massless fermions, the L and R handed parts of the Dirac equation can be separated leaving us with a U(2)xU(2) symmetry of the Dirac part. But now what is the symmetry of the bosonic part involving the field strength tensor? It isnt U(2)xU(2), it is the original SU(2) symmetry. How can the theory then said to be invariant under U(2)xU(2)

3. Finally, what are the symmetry transformations associated with the following conserved quantities:

baryon number

lepton number

strangeness

charmness

topness

bottomness

and why aren't there conserved upness and downness numbers?

**Physics Forums - The Fusion of Science and Community**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Standard model symmetries

Loading...

Similar Threads - Standard model symmetries | Date |
---|---|

A Conformal window | Jan 22, 2018 |

B Electroweak spontaneous symmetry breaking | Oct 15, 2017 |

A Custodial Symmetry in the Standard Model | Aug 22, 2016 |

Spontaneous symmetry breaking in the standard model | Feb 25, 2014 |

Exact Gauge Symmetry of the Standard Model | Sep 2, 2009 |

**Physics Forums - The Fusion of Science and Community**