Spin Correlations in top quark pair production near threshold at the e−e+ e^- e^+ Linear Collider

We investigate the spin correlations in top quark pair production near threshold at the $e^- e^+$ linear collider. Comparing with the results above the threshold region, we find that near the threshold region the off-diagonal basis, the optimized decomposition of the top quark spins above the threshold region, does not exist, and the beamline basis is the optimal basis, in which there are the dominant spin components: the up-down (UD) component for $e_L^- e^+$ scattering and the down-up (DU) component for $e_R^- e^+$ scattering can make up more than 50% of the total cross section, respectively.Comment: 12 pages, 3 figures, minor modification

K-Inflation in Noncommutative Space-Time

The power spectra of the scalar and tensor perturbations in the noncommutative k-inflation model are calculated in this paper. In this model, all the modes created when the stringy space-time uncertainty relation is satisfied are generated inside the sound/Hubble horizon during inflation for the scalar/tensor perturbations. It turns out that a linear term describing the noncommutative space-time effect contributes to the power spectra of the scalar and tensor perturbations. Confronting the general noncommutative k-inflation model with latest results from \textit{Planck} and BICEP2, and taking $c_S$ and $\lambda$ as free parameters, we find that it is well consistent with observations. However, for the two specific models, i.e. the tachyon and DBI inflation models, it is found that the DBI model is not favored, while the tachyon model lies inside the $1\sigma$ contour, if the e-folds number is assumed to be around $50\sim60$.Comment: 9 pages, 2 figures. arXiv admin note: substantial text overlap with arXiv:1404.016