New phases in CP-violating B decay asymmetries from mixing to singlet down quarks

Groups such as E6 with extra SU(2)L singlet down quarks give rise to flavor-changing neutral currents (FCNC's) through the mixing of four or more down quarks. These currents may substantially contribute to the processes of Bd0-bar B d0 and Bs0-bar B s0 mixing, within the allowed range of nonzero values for the four quark mixing parameters. These would then introduce new angles and phases into the CP-violating B decay asymmetries. Other, negative FCNC experiments put limits on these angles. Using a maximum likelihood analysis with contributions from both the standard model and the FCNC's, we find large regions for new physics phases contributing to CP-violating B decay asymmetries. From the bound on the mixing elements, the new singlet down quark might have a mass above the 500 GeV range