IceCube collaboration has published two papers on ultrahigh energy neutrinos observation, recently. They have used the data collected in two years in their first publication, which reveals observation of two PeV energy neutrino events. The second pub
lication of the collaboration including more data has also confirmed main features of the former paper. In literature, various interpretations of the IceCube data have been proposed. In this study, it is shown that PeV energy neutrino events observed by the IceCube collaboration can be interpreted as resonance production of color octet neutrinos with masses in $500-800$ GeV range.
In this work we study the flavor changing neutral current(FCNC) decays of the top quark, $tto cgamma$ and $tto c g$. The Standard Model, predictions for the branching ratios of these decays are about $sim 5times 10^{-14}$, and $sim 1times 10^{-12}$,
respectively. The recent study presented by the ATLAS Collaboration gives a sensitivity on these branching ratios about $sim 10^{-5}$ at $%95$ C.L. The parameter space of $lambda$, $Lambda$, and $d$ where the branching ratios of $tto cgamma$ and $tto c g$ decays exceed these predictions is obtained.
We investigate the effects of unparticles on gamma gamma--> gamma gamma scattering for photon collider mode of the future multi-TeV e^+e^- linear collider. We show the effects of unparticles on the differential, and total scattering cross sections fo
r different polarization configurations. Considering 1-loop Standard Model background contributions from the charged fermions, and W^{+-} bosons to the cross section, we calculate the upper limits on the unparticle couplings lambda_0 to the photons for various values of the scaling dimension d(1<d<2) at sqrt{s}=0.5-5 TeV.
We study the single production of the fourth family quarks through the process pp--> QjX at the Large Hadron Collider (LHC). We have calculated the decay widths and branching ratios of the fourth family quarks (b and t) in the mass range 300-800 GeV.
The cross sections of signal and background processes have been calculated in a Monte Carlo framework. It is shown that the LHC can discover single t and b quarks if the CKM matrix elements |V_{tq}|,|V_{qb}|>=0.01.
