The electro-weak force is known to contain a <A HREF="https://en.wikipedia.org/wiki/Chiral_anomaly#An_example:_baryonic_charge_non-conservation">chiral anomaly that breaks $B+L$ conservation</A>. In other words, it allows for the sum of baryons and leptons to change, but still conserves the difference between the two. This means that the standard model could have a channel for [protons to decay](http://en.wikipedia.org/wiki/Proton_decay), for example into a pion and a positron. Does anyone know what the total proton decay rate through standard model channels is?