D 0 − D̄ 0 Mixing in the Presence of Isosinglet Quarks

We analyse ∆C = 2 transitions in the framework of a minimal extension of the Standard Model where either a Q = 2/3 or a Q = −1/3 isosinglet quark is added to the standard quark spectrum. In the case of a Q = 2/3 isosinglet quark, it is shown that there is a significant region of parameter space where D 0 − ¯ D 0 mixing is sufficiently enhanced to be observed at the next round of experiments. On the contrary, in the case of a Q = −1/3 isosinglet quark, it is pointed out that obtaining a substancial enhancement of D 0 − ¯ D 0 mixing, while complying with the experimental constraints on rare kaon decays, requires a contrived choice of parameters.