flavour (particle physics)




The fermion fundamental particles in the standard model of particle physics arrange in three “generation”. Between generations, particles differ in their mass and in further properties referred to as flavor quantum numbers, but otherwise their interactions are the same, to high accuracy. Hence flavor physics refers to the phenomenology of processes that do involve or depend on flavor quantum numbers, notably when flavor changes through interactions via the weak nuclear force and Yukawa interactions.

For the leptons these flavor quantum numbers are electron number, muon number and tauon number as well as the corresponding three neutrino numbers.

For the quarks the flavor quantum numbers are isospin, charm, strange-ness, bottom-ness and top-ness.

flavors of fundamental fermions in the
standard model of particle physics
generation of fermions1st generation2nd generation3d generation
up-typeup quarkcharm quarktop quark
down-typedown quarkstrange quarkbottom quark
neutralelectron neutrinomuon neutrinotau neutrino

See yotams for a good quick introduction.


Flavor anomalies

The flavor sector of the standard model of particle physics is maybe the least well understood in detail; in any case persistent flavor anomalies reflect a discrepancy between experiment (LHCb, Belle, BaBar) and theoretical computations.

See at flavour anomalies for more.

Geometric engineering on D8-branes

In geometric engineering of flavor physics in intersecting D-brane models, the flavour degrees of freedom come from open strings ending on spacetime-filling D-branes (Karch-Katz 02).

Specifically in the Sakai-Sugimoto model geometrically engineering something close to actual quantum chromodynamics (Sakai-Sugimoto 04, Sakai-Sugimoto 05), flavour is encoded in the presence of D8-branes in the model:

Here we are showing

  1. the color D4-branes;

  2. the flavor D8-branes;


    1. the 5d Chern-Simons theory on their worldvolume

    2. the corresponding 4d WZW model on the boundary

    both exhibiting the meson fields;

  3. the baryon D4-branes

    (see at WSS-model – Baryons);

  4. the Yang-Mills monopole D6-branes

    (see at D6-D8-brane bound state);

  5. the NS5-branes (often not considered here).



A good quick account is in

  • yotams, What is flavor? (pdf, pdf)

Lecture notes:

See also

Flavour anomalies

Outlook on the field of flavour physics in view of LHCb-measurement of flavour anomalies

Realization on intersecting D-brane models

geometric engineering of flavour physics in intersecting D-brane models (AdS/QCD) was originally understood in

and then developed in detail for QCD on D8-branes in the Sakai-Sugimoto model:

Last revised on November 20, 2019 at 02:38:27. See the history of this page for a list of all contributions to it.