Search for single production of the vector-like top partner at the 14 TeV LHC

The new heavy vector-like top partner~($T$) is one of typical features of many new physics models beyond the standard model. In this paper we study the discovery potential of the LHC for the vector-like $T$-quark both in the leptonic $T\to bW$ and $T\to t_{\rm lep}Z_{\rm lep}$ (trilepton) channels at $\sqrt{s}= 14$ TeV in the single production mode. Our analysis is based on a simplified model including a $SU(2)_L$ singlet with charge $2/3$ with only two free parameters, namely the $TWb$ coupling parameter $g^{\ast}$ and the top partner mass $m_T$. The $2\sigma$ exclusion limits, $3\sigma$ evidence and the $5\sigma$ discovery reach in the parameter plane of $g^{\ast}-m_T$, are, respectively, obtained for some typical integrated luminosity at the 14 TeV LHC. Finally we analyze the projected sensitivity in terms of the production cross section times branching fraction for two decay channel.Comment: 15 pages, 10 figures, 2 tables. version in EPJ

Dilute magnetic semiconductor and half metal behaviors in 3d transition-metal doped black and blue phosphorenes: a first-principles study

We present first-principles density-functional calculations for the structural, electronic, and magnetic properties of substitutional 3d transition metal (TM) impurities in two-dimensional black and blue phosphorenes. We find that the magnetic properties of such substitutional impurities can be understood in terms of a simple model based on the Hund's rule. The TM-doped black phosphorenes with Ti, V, Cr, Mn, Fe and Ni impurities show dilute magnetic semiconductor (DMS) properties while those with Sc and Co impurities show nonmagnetic properties. On the other hand, the TM-doped blue phosphorenes with V, Cr, Mn and Fe impurities show DMS properties, those with Ti and Ni impurities show half-metal properties, whereas Sc and Co doped systems show nonmagnetic properties. We identify two different regimes depending on the occupation of the hybridized electronic states of TM and phosphorous atoms: (i) bonding states are completely empty or filled for Sc- and Co-doped black and blue phosphorenes, leading to non-magnetic; (ii) non-bonding d states are partially occupied for Ti-, V-, Cr-, Mn-, Fe- and Ni-doped black and blue phosphorenes, giving rise to large and localized spin moments. These results provide a new route for the potential applications of dilute magnetic semiconductor and half-metal in spintronic devices by employing black and blue phosphorenes.Comment: 9 pages, 7 figure