Timeline for Standard Model Proton Decay Rate
Current License: CC BY-SA 3.0
14 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Oct 27, 2016 at 4:06 | comment | added | Thomas | Regarding $\pi^0\to 2\gamma$: There is a subtlety. QCD has global flavor symmetries, which are anomalous, hence the triangle anomaly that contributes to neutral pion decay. But in the SM these flavor currents are gauged, and there are no gauge anomalies. How can that be? At low energies the QCD flavor anomalies get represented by WZ terms that describe anomalous pion interactions, and in the SM these terms add to the flavor anomalies from leptons so that the total flavor anomaly cancels. | |
| Oct 27, 2016 at 4:02 | comment | added | Thomas | Well, 't Hooft is pretty careful .. | |
| Oct 27, 2016 at 3:41 | comment | added | anna v | @SeanLake I am not disputing that one needs anomalous channels to describe certain observations, I am saying that nowhere have I seen that anomalous channels exist within the standard model , at least to generate an amplitude for proton decay. It is indisputable that there are observations which are not describable in the standard model, which is why experiments are carried out searching for supersymmetry and GUTS signatures. I have not found on the net a standard model calculation for proton decay, whereas I found the link I gave that anomalies needed are not within the standard model. | |
| Oct 26, 2016 at 19:25 | comment | added | Sean E. Lake | See Peskin & Schoeder equation 19.119 and following:$$\Gamma(\pi^0\rightarrow 2\gamma) = \frac{\alpha^2}{64\pi^3} \frac{m_\pi^3}{f_\pi^2}.$$ "This relation, which provides a direct measure of the coefficient of the Adler-Bell-Jackiw anomaly, is satisfied experimentally to an accuracy of a few percent." | |
| Oct 26, 2016 at 19:05 | comment | added | Sean E. Lake | Please correct me if I'm wrong, but isn't the decay channel $\pi^0\rightarrow \gamma \gamma$ dominated by an anomalous channel? | |
| Oct 26, 2016 at 18:23 | comment | added | Thomas | 't Hooft studies a theory in which V-A is gauged, and there is a charm quark. Obviously, in the SM V-A is gauged (SU(2)_W), and the charm quark exists ('t Hooft cares about charm because he assumes that all fermions are weak doublets, and before the discovery of charm there was no particle to complete the weak doublet that contains the strange quark). 't Hooft did not know about (b,t), so in 1976 he concluded that in what we now call the standard model B violation by two units is allowed. We now know that B is violated by three units. | |
| Oct 26, 2016 at 18:18 | comment | added | Thomas | When people say that the SM is anomaly free they refer to gauge anomalies (color is trivially anomaly free, so they check SU(2)xU(1)). However, in the SM B+L is not gauged so it can (and indeed it does) have an anomaly. | |
| Oct 26, 2016 at 17:01 | comment | added | anna v | @Thomas I am not convinced. The link I gave for the specific lagrangian, called now the standard model, says that it has no anomalies. I have not been able to find proton decay in the standard model, proton decays are always in extensions of the SM like GUTs | |
| Oct 26, 2016 at 16:45 | comment | added | Thomas | The paper was written in 1976. What he calls "in models .. '' is what we now call "the standard model''. | |
| Oct 26, 2016 at 15:48 | comment | added | anna v | @Thomas imo it is an extension of the standard model, not what is "the standard model". Even in the abstract it says "in models ..." not, "in the standard model". | |
| Oct 26, 2016 at 13:11 | comment | added | Thomas | 'T Hooft's original paper Phys.Rev.Lett. 37 (1976) 8-11. | |
| Oct 26, 2016 at 5:13 | comment | added | anna v | @Thomas so, can you give a link where a proton decay is allowed within the standard model? The link I give is about anomalies in general. | |
| Oct 26, 2016 at 4:49 | comment | added | Thomas | They mean vanishing gauge anomalies. B+L is indeed anomalous. | |
| Oct 26, 2016 at 4:36 | history | answered | anna v | CC BY-SA 3.0 |