Constraining models with vector-like fermions from FCNC in K and B physics

In this work, we update the constraints on tree level FCNC couplings in the framework of a theory with n isosinglet vector-like down quarks. In this context, we emphasize the sensitivity of the B -> J/psi K_S CP asymmetry to the presence of new vector-like down quarks. This CP asymmetry, together with the rare decays B -> X_{s,d} l bar{l} and K -> pi nu bar{nu} are the best options to further constrain the FCNC tree level couplings or even to point out, in the near future, the possible presence of vector-like quarks in the low energy spectrum, as suggested by GUT theories or models of large extra dimensions at the TeV scale.In this work, we update the constraints on tree level FCNC couplings in the framework of a theory with $\eta$ isosinglet vector-like down quarks. In this context, we emphasize the sensitivity of the $B \to J/\psi K_S CP$ asymmetry to the presence of new vector-like down quarks. This CP asymmetry, together with the rare decays $B \to X_{s,d} l \bar{l}$ and $K \to \pi \nu \bar{\nu}$ are the best options to further constrain the FCNC tree level couplings or even to point out, in the near future, the possible presence of vector-like quarks in the low energy spectrum, as suggested by GUT theories or models of large extra dimensions at the TeV scale