New phases inCP-violatingBdecay asymmetries from mixing to singlet down quarks

Groups such as ${\mathrm{E}}_6$ with extra ${\mathrm{SU}\mathrm{}\left(2\right)\mathrm{}}_L$ 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 $B_d^0-{\overline{B}}_d^0$ and $B_s^0-{\overline{B}}_s^0$ mixing, within the allowed range of nonzero values for the four quark mixing parameters. These would then introduce new angles and phases into the $\mathrm{CP}$-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 $\mathrm{CP}$-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.