Talk:Flavor-changing neutral current

W0 boson would be a FCNC ??
The W+, W- bosons can alter 'flavor'. By implication, could not the W0 alter 'flavor', too? And, would not that, then, constitute a FCNC ?? 24.143.65.75 (talk) 09:18, 12 January 2012 (UTC)

No. Darktachyon (talk) 20:15, 4 January 2013 (UTC)

Lepton number violation in FCNC
Doesn't the standard model feynman diagram for a tau changing into an electron violate lepton number. There is a tau neutrino changing into an electron via a W boson.


 * Yes. I think this is allowed if you have neutrino oscillation. Total lepton number is conserved, but individual lepton numbers are not. -- Xerxes 14:48, 14 July 2006 (UTC)


 * True, but the caption claims that this is an example of a Standard Model FCNC, and traditionally, by the Standard Model, people often exclude neutrino oscillations. Maliz 12:16, 18 October 2006 (UTC)


 * No, the Standard Model tau decay into electron does NOT violate the lepton numbers (ignoring the possibility of neutrino oscillations). For example, a decay of a tau- into an e- is accompanied by a tau neutrino (which 'carries away' the original tau flavour) and an anti-electron-neutrino (which compensates the electron's flavour). See also this diagram from the tau article: http://upload.wikimedia.org/wikipedia/commons/thumb/1/11/Feynman_diagram_of_decay_of_tau_lepton.svg/260px-Feynman_diagram_of_decay_of_tau_lepton.svg.png Andre.holzner (talk) 10:32, 9 April 2011 (UTC)


 * Another thing I thought of: You don't have to use taus here. You could draw the same diagram without recourse to neutrino mixing in the quark sector with tau→s, mu→d, and nu→u. Of course, tau looks cleaner, because for the quarks, you would have some other hadronic bits to confine your quarks. On the other hand, the depicted tau decay (although allowed) has never been observed, while similar hadronic ones have.  -- Xerxes 15:08, 14 July 2006 (UTC)

Hi Xerxes, as mentioned above these examples are not good because they resort to lepton flavor violation instead of FCNCs. Can't you use a more classical example and one that has been observed? Originally the missing FCNCs in kaon decay were explained by introducing charm to cancel direct d->s transitions via the GIM mechanism. So a BSM diagram would show s -> FCNC_vertex -> d with a photon/Z0 radiating from the FCNC_vertex. And the SM diagram would be a loop-diagram like a penguin in B-physics: d fluctuates into a loop with a W on one side and u/c/t on the other. i think in the lepton sector you can't write such a diagram yet, because it hasn't been shown that theta_13 > 0 yet, which your picture shows. gbrandt 09:37, 2 February 2007 (UTC)

Even if theta_13 > 0, if the only source of LFV is from neutrino oscillations, the branching ratio for the decay for the tau penguin diagram shown as "SM tau decay" would be on the order of 10e-50, which is to say, as far as the SM is concerned, this process simply doesn't happen for all reasonable purposes. The tau penguin diagram is simply wrong, misleading, and needs to be replaced. It would work, however, if the fermion line were s -> t -> d, for example, instead of a tau -> neutrino -> electron.12.32.103.4 (talk) —Preceding undated comment added 21:06, 31 May 2012 (UTC)

Searches and Decays
Should there be coverage of the history of specific experimental: observations, searches and limits that have been published?

First Evidence for B0s→φφ Decay and Measurements of Branching Ratio and ACP for B+→φK+, Phys.Rev.Lett.95:031801,2005

Measurement of the B0s → φφ branching fraction and search for the decay B0 → φφ, arXiv:1508.00788v1

CLEO II:

Limits on Flavor Changing Neutral Currents in D0 Meson Decays, Phys. Rev. Lett. 76, 3065 — Preceding unsigned comment added by Timetraveler3.14 (talk • contribs) 17:22, 10 August 2015 (UTC)