Flavor changing neutral currents with a fourth family of quarks

TL;DR

This paper explores the implications of a hypothetical fourth quark family on flavor changing neutral currents, predicting measurable deviations in top and strange quark decays that could be tested at collider experiments.

Contribution

It introduces a new analysis of flavor changing neutral currents in a four-quark family model, deriving experimental constraints and predicting observable rare decay rates.

Findings

|V_{tb}| significantly different from unity

Large rates for rare top decays t->cγ and t->cZ

Large rates for strange decays s->dγ and s->dg

Abstract

For a model with a fourth family of quarks, new sources of flavor changing neutral currents are identified by confronting the unitary 4x4 quark mixing matrix with the experimental measured values of the familiar 3x3 quark mixing matrix. By imposing as experimental constraints the known bounds for the flavor changing neutral currents, the largest mixing of the known quarks with the fourth family ones is established. The predictions are: a value for |V_{tb}| significantly different from unity, large rates for rare top decays as t->c\gamma and t->cZ, the last one reachable at the Large Hadrion Collider, and large rates for rare strange decays s->d\gamma and s->dg, where g stands for the gluon field.