arXiv subjects

G. C. Branco

Publications and source records attributed to G. C. Branco.

92 records · Page 6Linked to original sources

arXiv1995

$D^0 - \bar D^0$ Mixing in the Presence of Isosinglet Quarks

We analyse $ΔC=2$ 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 $D^0 - \bar D^0$ 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 $D^0 - \bar D^0$ mixing, while complying with the experimental constraints on rare kaon decays, requires a contrived choice of parameters.

hep-ph↗

arXiv1994

Supersymmetric Contributions to $\BB$ and $\KK$ Mixings

We show that in the supersymmetric standard model (SSM) box diagrams mediated by charginos and up-type squarks may give large contributions to $\BB$ and $\KK$ mixings. This is due to the fact that a heavy top quark mass allows large mass differences among the up-type squarks, which leads to a less efficient cancellation among the different squark diagrams. If the ratio of the vacuum expectation values of the Higgs bosons is of order of unity, box diagrams mediated by charged Higgs bosons also contribute appreciably. For sizable regions of the SSM parameter space, the SSM contributions could be sufficiently large to affect significantly the evaluation of the CKM matrix from the experimental values of the mixing parameter $x_d$ and the $CP$ violation parameter $ε$.

hep-ph↗