Quark Mixing Possibilities in Extensions of the Standard Model and the   Electromagnetic Current
  The existence of new quarks may lead to their mixing with ordinary quarks. We are particularly interested in studying the consequences such mixings could have upon the electromagnetic current. We find that new strong flavor and parity violating electromagnetic interactions may exist. To be specific, for our analysis we work with the model: $SU_2 \otimes U_1 \otimes \hat{SU}_2 \otimes \hat{U}_1$, which doubles the standard electroweak sector, both in gauge bosons and in quarks. 
A. Garcia (1), R. Huerta (2), and G. Sanchez-Colon (2,3) ((1)   CINVESTAV-Mexico, (2) CINVESTAV-Merida, (3) UC-Riverside)