Weak-triplet, color-octet scalars, and the CDF dijet excess

We extend the standard model to include a weak-triplet and color-octet scalar. This octo-triplet'' field consists of three particles, two charged and one neutral, whose masses and renormalizable interactions depend only on two new parameters. The charged octo-triplet decay into a W boson and a gluon is suppressed by a loop factor and an accidental cancellation. Thus, the main decays of the charged octo-triplet may occur through higher-dimensional operators, mediated by a heavy vectorlike fermion, into quark pairs. For an octo-triplet mass below the t (b) over bar threshold, the decay into Wb (b) over bar or Wb (s) over bar through an off shell top quark has a width comparable to that into c (s) over bar or c (b) over bar. Pair production with one octo-triplet decaying into two jets and the other decaying into a W and two soft b jets may explain the dijet-plus-W excess reported by the CDF Collaboration. Using a few kinematic distributions, we compare two mechanisms of octo-triplet pair production: through an s-channel coloron and through the coupling to gluons. The higher-dimensional operators that allow dijet decays also lead to CP violation in B-s - (B) over bar (s) mixing.