Debris development in fretting contacts: debris particles and debris beds

In this study, the formation and destruction of compacted beds of oxidized debris particles are investigated. Fretting tests of steel specimens were conducted, employing a cylinder-on-flat geometry with displacement amplitude being varied. The debris was examined, both in the form of the debris beds and in the form of loose debris; together, these were characterized to better understand the mechanisms of debris bed formation and development throughout the fretting process. XRD was employed to determine the phase makeup of the debris, with SEM imaging and particle size analysis employed to understand the evolution of the debris from nanoparticles into agglomerates and then into sintered bed structures

Quantum Distillation Of Position Entanglement With The Polarization Degrees Of Freedom

Sources of entangled photon pairs using two parametric down-converters are capable of generating interchangeable entanglement in two different degrees of freedom. The connection between these two degrees of freedom allows the control of the entanglement properties of one, by acting on the other degree of freedom. We demonstrate experimentally, the quantum distillation of the position entanglement using polarization analyzers.Comment: Submitted for publication in Optics Communication

A numerical methodology for predicting tool wear in Friction Stir Welding

A novel methodology for predicting tool wear in FSW based on a CFD model, coupled with a modified Archard equation, is presented considering the effect of the deformation of the highly viscous flow around the tool on tool wear. A validation process is proposed to ensure robust results when using this methodology. A study was carried out to predict the wear on a dome shaped FSW tool, indicating that high wear was predicted at the shoulder edge due to rapidly changing flow, and that the interaction of the axial flow with the pin causes a bifurcation of the flow and an associated increase in pressure at the mid axial position of the pin, again leading to high wear in this location. The proposed approach could be used as a method for calculating tool wear and determining the effective limits of tool use, without the need for experimental trials

Seeking Evolution of Dark Energy

We study how observationally to distinguish between a cosmological constant (CC) and an evolving dark energy with equation of state $\omega(Z)$. We focus on the value of redshift Z* at which the cosmic late time acceleration begins and $\ddot{a}(Z^{*}) = 0$. Four $\omega(Z)$ are studied, including the well-known CPL model and a new model that has advantages when describing the entire expansion era. If dark energy is represented by a CC model with $\omega \equiv -1$, the present ranges for $\Omega_{\Lambda}(t_0)$ and $\Omega_m(t_0)$ imply that Z* = 0.743 with 4% error. We discuss the possible implications of a model independent measurement of Z* with better accuracy.Comment: 9 pages, LaTeX, 5 figure

On MSSM charged Higgs boson production in association with an electroweak W boson at electron positron colliders

We present a calculation of the cross section for the process e+ e- --> W+/- H-/+ in the minimal supersymmetric standard model (MSSM) and the Two Higgs Doublet Model (THDM). We study the basic features of the MSSM prediction for some distinctive parameter scenarios. We find large effects from virtual squarks for scenarios with large mixing in the stop sector which can lead to a cross section vastly different from a THDM with identical Higgs sector parameters. We investigate this interesting behaviour in more detail by thoroughly scanning the MSSM parameter space for regions of large cross section. For a charged Higgs boson too heavy to be pair-produced at such a machine, it turns out that a large MSSM cross section with a good chance of observation is linked to a squark mass scale below 600 GeV and a considerable amount of mixing in either the stop and sbottom sector.Comment: 25 pages, 10 figures (two in colour). Substantially improved on the MSSM parameter restrictions taken into account. Added some reference

Two-body Z′Z' decays in the minimal 331 model

The two-body decays of the extra neutral boson Z_2 predicted by the minimal 331 model are analyzed. At the three-level it can decay into standard model particles as well as exotic quarks and the new gauge bosons predicted by the model. The decays into a lepton pair are strongly suppressed, with $Br(Z_2 --> l^+l^-) ~ 10^{-2}$ and $Br(Z_2 --> \bar{\nu}_l \nu) ~ 10^{-3}$. In the bosonic sector, Z_2 would decay mainly into a pair of bilepton gauge bosons, with a branching ratio below the 0.1 level. The Z_2 boson has thus a leptophobic and bileptophobic nature and it would decay dominantly into quark pairs. The anomaly-induced decays $Z_2 --> Z_1\gamma$ and $Z_2 --> Z_1Z_1$, which occurs at the one-loop level are studied. It is found that $Br(Z_2 --> Z_1\gamma) ~ 10^{-9}$ and $Br(Z_2 --> Z_1Z_1) ~ 10^{-6}$ at most. As for the $Z_2 --> W^+W^-$ and $Z_2 --> Z_1H$ decays, with H a relatively light Higgs boson, they are induced via Z'-Z mixing. It is obtained that $Br(Z_2 --> W^+W^-) ~ 10^{-2}$ and $Br (Z_2 --> Z_1H) ~ 10^{-5}$. We also examine the flavor changing neutral current decays $Z_2 --> tc$ and $Z_2 --> tu$, which may have branching fractions as large as $10^{-3}$ and $10^{-5}$, respectively, and thus may be of phenomenological interest.Comment: 14 pages, 3 figures, submitted to Physical Review

Lepton Flavor Violating Processes and Muon g-2 in Minimal Supersymmetric SO(10) Model

In the recently proposed minimal supersymmetric SO(10) model, the neutrino Dirac Yukawa coupling matrix, together with all the other fermion mass matrices, is completely determined once free parameters in the model are appropriately fixed so as to accommodate the recent neutrino oscillation data. Using this unambiguous neutrino Dirac Yukawa couplings, we calculate the lepton flavor violating (LFV) processes and the muon g-2 assuming the minimal supergravity scenario. The resultant rates of the LFV processes are found to be large enough to well exceed the proposed future experimental bound, while the magnitude of the muon g-2 can be within the recent result by Brookhaven E821 experiment. Furthermore, we find that there exists a parameter region which can simultaneously realize the neutralino cold dark matter abundance consistent with the recent WMAP data.Comment: 18 pages, 10 figures. The version to be published in Phys. Rev.

Leptogenesis in Neutrino Textures with Two Zeros

The leptogenesis is studied in the neutrino textures with two zeros, which reduce the number of independent phases of the CP violation. The phenomenological favored neutrino textures with two zeros are decomposed into the Dirac neutrino mass matrix and the right-handed Majorana one in the see-saw mechanism. Putting the condition to suppress the $\mu \to e\gamma$ decay enough, the texture zeros of the Dirac neutrino mass matrix are fixed in the framework of the MSSM with right-handed neutrinos. These textures have only one CP violatig phase. The magnitude of each entry of the Dirac mass matrix is determined in order to explain the baryon asymmetry of the universe by solving the Boltzman equations. The relation between the leptogenesis and the low energy CP violation is presented in these textures.Comment: Latex file with 20 pages, 6 eps figure

Phenomenological Tests of Supersymmetric A_4 Family Symmetry Model of Neutrino Mass

Recently Babu, Ma and Valle proposed a model of quark and lepton mixing based on $A_4$ symmetry. Within this model the lepton and slepton mixings are intimately related. We perform a numerical study in order to derive the slepton masses and mixings in agreement with present data from neutrino physics. We show that, starting from three-fold degeneracy of the neutrino masses at a high energy scale, a viable low energy neutrino mass matrix can indeed be obtained in agreement with constraints on lepton flavour violating $\mu$ and $\tau$ decays. The resulting slepton spectrum must necessarily include at least one mass below 200 GeV which can be produced at the LHC. The predictions for the absolute Majorana neutrino mass scale $m_0 \geq 0.3$ eV ensure that the model will be tested by future cosmological tests and $\beta\beta_{0\nu}$ searches. Rates for lepton flavour violating processes $\ell_j \to \ell_i + \gamma$ in the range of sensitivity of current experiments are typical in the model, with BR(\mu \to e \gamma) \gsim 10^{-15} and the lower bound BR$(\tau \to \mu \gamma) > 10^{-9}$. To first approximation, the model leads to maximal leptonic CP violation in neutrino oscillations.Comment: 23 pages, 7 figure

Phantom Field with O(N) Symmetry in Exponential Potential

In this paper, we study the phase space of phantom model with O(\emph{N}) symmetry in exponential potential. Different from the model without O(\emph{N}) symmetry, the introduction of the symmetry leads to a lower bound $w>-3$ on the equation of state for the existence of stable phantom dominated attractor phase. The reconstruction relation between the potential of O(\textit{N}) phantom system and red shift has been derived.Comment: 5 pages, 3 figures, replaced with the version to appear on Phys. Rev.