Indirect constraints on third generation baryon number violation

Abstract

The non-observation of baryon number violation suggests that the scale of baryon-number violating interactions at zero temperature is comparable to the GUT scale. However, the pertinent measurements involve hadrons made of the first-generation quarks, such as protons and neutrons. One may therefore entertain the idea that new flavour physics breaks baryon number at a much lower scale, but only in the coupling to a third generation quark, leading to observable baryon-number violating $b$-hadron decay rates. In this paper we show that indirect constraints on the new physics scale $\Lambda_{\rm BNV}$ from the existing bounds on the proton lifetime do not allow for this possibility. For this purpose we consider the three dominant proton decay channels $p \to \ell^+ \nu_\ell \bar{\nu}$, $p \to \pi^+ \bar{\nu}$ and $p \to \pi^0 \ell^+$ mediated by a virtual bottom quark.