QCD Corrections to Squark Production in <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> Annihilation in the MSSM with Complex Parameters

We discuss the pair production of scalar quarks in e ⁺ e ⁻ annihilation within the MSSM with complex parameters. We calculate the SUSY-QCD corrections to the cross section and show that the effect of the CP phases of these complex parameters on the cross section can be quite strong in a large region of the MSSM parameter space. This could have important implications for squarks searches and the MSSM parameter determination in future collider experiments. PACS number(s): 14.80. Ly, 12.60. Jv, 13.10. + q, 13.88. +e.     

Comparative Study of Light Manipulation in Three-Level Systems Via Spontaneously Generated Coherence and Relative Phase of Laser Fields *

We present a comparative study of the control of-group velocity in three-level atomic systems including $\Lambda{}$-, Ladder-, and-V-types via spontaneously generated coherence (SGC) and relative phase of laser-fields. In the steady regime, expressions of group index are derived as an-analytical function of controllable parameters related to SGC and relative phase.-It is shown that the group velocity can be further slowed down or speeded up-under SGC in which modifications of group velocity due to the SGC in $\Lambda{}$--and V-systems are stronger than that in Ladder-system. In particular, when-interference strength of SGC p increases from 0.7 to 1.0, the light-propagation is switched from superluminal to subluminal modes (for $\Lambda{}$--and Ladder-systems) or from subluminal to superluminal modes (for V-system). In-the presence of relative phase, the group velocity changes between subluminal and-superluminal modes with a period of 2$\pi{}$. In resonant region, the largest-positive value of group index reaches at the relative phase $\varphi{}$ = $\pi{}$-while the largest negative value of group index reaches at $\varphi{}$ = 0 and-2$\pi{}$ for the $\Lambda{}$- and Ladder-systems, otherwise, for the V-system the-largest positive group index occurs at $\varphi{}$ = 0 and 2$\pi{}$, and the largest-negative group index occurs at $\varphi{}$ = $\pi{}$.     

Electrical and magnetic properties of TmCoIn5 and YbCoIn5 single crystals

Electrical and magnetic properties of TmCoIn₅ and YbCoIn₅ single crystals were investigated by means of electrical resistivity and magnetization measurements in the temperature range from 300 to 0.5 K under the magnetic field up to 5 T. TmCoIn₅ is an antiferromagnetic metal with a Néel temperature T_N=2.6 K. YbCoIn₅ shows non-magnetic behavior, reflecting of divalent Yb ion.     

Tikhonov regularization method for a backward problem for the inhomogeneous time-fractional diffusion equation

Fractional (nonlocal) diffusion equations replace the integer-order derivatives in space and time by their fractional-order analogs and they are used to model anomalous diffusion, especially in physics. In this paper, we study a backward problem for an inhomogeneous time-fractional diffusion equation with variable coefficients in a general bounded domain. Such a backward problem is of practically great importance because we often do not know the initial density of substance, but we can observe the density at a positive moment. The backward problem is ill-posed and we propose a regularizing scheme by using Tikhonov regularization method. We also prove the convergence rate for the regularized solution by using an a priori regularization parameter choice rule. Numerical examples illustrate applicability and high accuracy of the proposed method.     

A note on the derivation of filter regularization operators for nonlinear evolution equations

Despite the strong focus of regularization on ill-posed problems, the general construction of such methods has not been fully explored. Moreover, many previous studies cannot be clearly adapted to handle more complex scenarios, albeit the greatly increasing concerns on the improvement of wider classes. In this note, we rigorously study a general theory for filter regularized operators in a Hilbert space for nonlinear evolution equations which have occurred naturally in different areas of science. The starting point lies in problems that are in principle ill-posed with respect to the initial/final data – these basically include the Cauchy problem for nonlinear elliptic equations and the backward-in-time nonlinear parabolic equations. We derive general filters that can be used to stabilize those problems. Essentially, we establish the corresponding well-posed problem whose solution converges to the solution of the ill-posed problem. The approximation can be confirmed by the error estimates in the Hilbert space. This work improves very much many papers in the same field of research.     

Raman spectroscopy of Cu doping in Zn1−xCoxO diluted magnetic semiconductor

The room‐temperature ferromagnetism and the Raman spectroscopy of the Cu‐doped Zn_1−xCo_xO powders prepared by the sol–gel method are reported. The x‐ray diffraction (XRD) data confirmed that the wurtzite structure of ZnO is maintained for ZnO doped with Co below 10 at%. The magnetization–field curves measured at room temperature demonstrated that all Co‐doped ZnO powders were paramagnetic. Ferromagnetic ordering is observed for the samples doped with Cu in Zn_0.98Co_0.02O and strongly depends on the concentration of Cu. The relative strength of the second‐order LO peak to the first‐order one in the Raman spectra, which is related to the carrier concentration, of the Cu‐doped Zn_0.98Co_0.02O powder is strongly correlated with the saturation magnetic moment of the system. This seems to be in favor of the Ruderman‐Kittel‐Kasuya‐Yosida (RKKY) or double exchange mechanism of the ferromagnetism in this system. Copyright © 2009 John Wiley & Sons, Ltd.     

Magnetic Kronig-Penney-type graphene superlattices: finite energy Dirac points with anisotropic velocity renormalization

We study the energy band structure of magnetic graphene superlattices with delta-function magnetic barriers and zero average magnetic field. The dispersion relation obtained using the T-matrix approach shows the emergence of an infinite number of Dirac-like points at finite energies, while the original Dirac point is still located at the same place as that for pristine graphene. The carrier group velocity at the original Dirac point is isotropically renormalized, but at finite energy Dirac points it is generally anisotropic. An asymmetry in the width between the wells and the barriers of the periodic potential induces a shift of the original Dirac point in the zero-energy plane, keeping the velocity renormalization isotropic.