Single Production of Fourth Family Sneutrino via RPV Couplings at Linear Colliders

The single production of fourth family sneutrino $\tilde{\nu}_{4}$ via R-parity violating interactions in electron-positron collisions has been investigated. We study the decays of $\tilde{\nu}_{4}$ into different flavor dilepton $e^{\pm}\mu^{\mp}$ via R-parity violation. It is shown that R-parity violating couplings $(\lambda_{411},\lambda_{412})$ down to 0.001 will be reachable at future linear colliders which would provide better accuracy comparing to the indirect measurements as complementary to the LHC results.Comment: 11 pages, 6 figure

Single Production of Fourth Family b' Quark at the Large Hadron electron Collider

We examined the single production of fourth family b' quarks at the Large Hadron electron Collider (LHeC).We have analyzed the background and the signal processes for the mass range 300-800 GeV. We find the discovery region for an optimal parametrization of the Vqb' matrix elements.Comment: 12 pages, 8 figures, 2 table

Effect of impurities on the mechanical and electronic properties of Au, Ag, and Cu monatomic chain nanowires

In this study, we have investigated the interaction of various different atomic and molecular species (H, C, O, H 2, and O 2) with the monatomic chains of Au, Ag, and Cu via total-energy calculations using the plane-wave pseudopotential method based on density functional theory. The stability, energetics, mechanical, and electronic properties of the clean and contaminated Au, Ag, and Cu nanowires have been presented. We have observed that the interaction of H, C, or O atoms with the monatomic chains are much stronger than the one of H 2 or O 2 molecules. The atomic impurities can easily be incorporated into these nanowires; they form stable and strong bonds with these one-dimensional structures when they are inserted in or placed close to the nanowires. Moreover, the metal-atomic impurity bond is much stronger than the metal-metal bond. Upon elongation, the nanowires contaminated with atomic impurities usually break from the remote metal-metal bond. We have observed both metallic and semiconducting contaminated nanowires depending on the type of impurity, whereas all clean monatomic chains of Au, Cu, and Ag exhibit metallic behavior. Our findings indicate that the stability and the electronic properties of these monatomic chains can be tuned by using appropriate molecular or atomic additives. © 2011 American Physical Society

First-principles study of thin TiOx and bulklike rutile nanowires

We have systematically investigated structural, electronic and magnetic properties of very thin TiOx (x=1,2) nanowires as well as bulklike (110) rutile nanowires by using the first-principles plane-wave pseudopotential calculations based on density functional theory. A large number of different possible structures have been searched via total-energy calculations in order to find the ground-state structures of these nanowires. Three-dimensional structures are more energetically stable than planar ones for both of the stoichiometries (i.e., x=1,2). The stability of TiOx nanowires is enhanced with its increasing radius as a result of reaching sufficient coordination number of Ti and O atoms. All stoichiometric TiO2 nanowires studied exhibit semiconducting behavior and have nonmagnetic ground state. There is a correlation between binding energy (Eb) and energy band gap (Eg) of TiO2 nanowires. In general, Eb increases with increasing Eg. In TiO nanowires, both metallic and semiconductor nanowires result. In this case, in addition to paramagnetic TiO nanowires, there are also ferromagnetic ones. We have also studied the structural and electronic properties of bulklike rutile (110) nanowires. There is a crossover in terms of energetics, and bulklike nanowires are more stable than the thin nanowires for larger radius wires after a critical diameter. These (110) rutile nanowires are all semiconductors. © 2009 The American Physical Society

Has the anomalous single production of the fourth SM family quarks decaying into light Higgs boson been observed by CDF?

Superjet events observed by the CDF Collaboration are interpreted as anomalous single production of the fourth SM family u_4 quark, decaying into a new light scalar particle. The specific predictions of the proposed mechanism are discussed.Comment: 5 pages, 1 tabl

First principles study of electronic and mechanical properties of molybdenum selenide type nanowires

Using the first-principles plane-wave pseudopotential method within density functional theory, we have systematically investigated structural, electronic, and mechanical properties of M2 Y6 X6, Y6 X6 (X=Se,Te,S; Y=Mo,Cr,W; and M=Li,Na) nanowires and bulk phase of M2 Y6 X6. We found that not only Mo6 X6, but also transition metal and chalcogen atoms lying in the same columns of Mo and Se can form stable nanowires consisting of staggered triangles of Y3 X3. We have shown that all wires have nonmagnetic ground states in their equilibrium geometry. Furthermore, these structures can be either a metal or semiconductor depending on the type of chalcogen element. All Y6 X6 wires with X=Te atom are semiconductors. Mechanical stability, elastic stiffness constants, breaking point, and breaking force of these wires have been calculated in order to investigate the strength of these wires. Ab initio molecular dynamic simulations performed at 500 K suggest that overall structure remains unchanged at high temperature. Adsorption of H, O, and transition metal atoms like Cr and Ti on Mo6 Se6 have been investigated for possible functionalization. All these elements interact with Mo6 Se6 wire forming strong chemisorption bonds, and a permanent magnetic moment is induced upon the adsorption of Cr or Ti atoms. Molybdenum selenide-type nanowires can be alternative for carbon nanotubes, since the crystalline ropes consisting of one type of (M2) Y6 X6 structures can be decomposed into individual nanowires by using solvents, and an individual nanowire by itself is either a metal or semiconductor and can be functionalized. © 2006 The American Physical Society

Gate induced monolayer behavior in twisted bilayer black phosphorus

Optical and electronic properties of black phosphorus strongly depend on the number of layers and type of stacking. Using first-principles calculations within the framework of density functional theory, we investigate the electronic properties of bilayer black phosphorus with an interlayer twist angle of 90°. These calculations are complemented with a simple k p model which is able to capture most of the low energy features and is valid for arbitrary twist angles. The electronic spectrum of 90° twisted bilayer black phosphorus is found to be x-y isotropic in contrast to the monolayer. However x-y anisotropy, and a partial return to monolayer-like behavior, particularly in the valence band, can be induced by an external out-of-plane electric field. Moreover, the preferred hole effective mass can be rotated by 90° simply by changing the direction of the applied electric field. In particular, a +0.4 (-0.4) V A-1 out-of-plane electric field results in a ~60% increase in the hole effective mass along the y (x) axis and enhances the m*y /m*x (m*x /m*y) ratio as much as by a factor of 40. Our DFT and k p simulations clearly indicate that the twist angle in combination with an appropriate gate voltage is a novel way to tune the electronic and optical properties of bilayer phosphorus and it gives us a new degree of freedom to engineer the properties of black phosphorus based devices. © 2017 IOP Publishing Ltd

Unparticle effects on top quark rare decays

In this work we study the flavor changing neutral current(FCNC) decays of the top quark, $t\to c\gamma$ and $t\to c g$. The Standard Model, predictions for the branching ratios of these decays are about $\sim 5\times 10^{-14}$, and $\sim 1\times 10^{-12}$, respectively. The recent study presented by the ATLAS Collaboration gives a sensitivity on these branching ratios about $\sim 10^{-5}$ at $$ C.L. The parameter space of $\lambda$, $\Lambda$, and $d$ where the branching ratios of $t\to c\gamma$ and $t\to c g$ decays exceed these predictions is obtained