Biomorphous SiC ceramics prepared from cork oak as precursor

Porous ceramic materials of SiC were synthesized from carbon matrices obtained via pyrolysis of natural cork as precursor. We propose a method for the fabrication of complex-shaped porous ceramic hardware consisting of separate parts prepared from natural cork. It is demonstrated that the thickness of the carbon-matrix walls can be increased through their impregnation with Bakelite phenolic glue solution followed by pyrolysis. This decreases the material's porosity and can be used as a way to modify its mechanical and thermal characteristics. Both the carbon matrices (resulted from the pyrolysis step) and the resultant SiC ceramics are shown to be pseudomorphous to the structure of initial cork. Depending on the synthesis temperature, 3C-SiC, 6H-SiC, or a mixture of these polytypes, could be obtained. By varying the mass ratio of initial carbon and silicon components, stoichiometric SiC or SiC:C:Si, SiC:C, and SiC:Si ceramics could be produced. The structure, as well as chemical and phase composition of the prepared materials were studied by means of Raman spectroscopy and scanning electron microscopy

Locally periodic unfolding method and two-scale convergence on surfaces of locally periodic microstructures

In this paper we generalize the periodic unfolding method and the notion of two-scale convergence on surfaces of periodic microstructures to locally periodic situations. The methods that we introduce allow us to consider a wide range of non-periodic microstructures, especially to derive macroscopic equations for problems posed in domains with perforations distributed non-periodically. Using the methods of locally periodic two-scale convergence (l-t-s) on oscillating surfaces and the locally periodic (l-p) boundary unfolding operator, we are able to analyze differential equations defined on boundaries of non-periodic microstructures and consider non-homogeneous Neumann conditions on the boundaries of perforations, distributed non-periodically

B->gamma e nu Transitions from QCD Sum Rules

B->gamma e nu transitions have recently been studied in the framework of QCD factorization. The attractiveness of this channel for such an analysis lies in the fact that, at least in the heavy quark limit, the only hadron involved is the B meson itself, so one expects a very simple description of the form factor in terms of a convolution of the B meson distribution amplitude with a perturbative kernel. This description, however, does not include contributions suppressed by powers of the b quark mass. In this letter, we calculate corrections to the factorized expression which are induced by the ``soft'' hadronic component of the photon. We demonstrate that the power-suppression of these terms is numerically not effective for physical values of the $b$ quark mass and that they increase the form factor by about 30% at zero momentum transfer. We also derive a sum rule for lambda_B, the first negative moment of the B meson distribution amplitude, and find lambda_B = 0.6 GeV (to leading order in QCD).Comment: 13 pages, 5 figure

Associated production of H^{\pm} and W^{\mp} in high-energy e+e- collisions in the Minimal Supersymmetric Standard Model

We study the associated production of the charged Higgs boson and W^{\pm} gauge boson in high energy e+e- collisions in the Minimal Supersymmetric Standard Model (MSSM). This associated production, which first arises at the one loop level, offers the possibility of producing the charged Higgs boson at the e+e- collider with mass more than half the center-of-mass energy, when the charged Higgs pair production is kinematically forbidden. We present analytic and numerical results for the cross section for e+e- --> W+ H- in the full MSSM, taking into account the previously uncalculated contributions from supersymmetric (SUSY) particles. We find that the contributions of the SUSY particles enhance the cross section over most of SUSY parameter space, especially when the SUSY particles are light, ~200 GeV. With favorable SUSY parameters, at small tan beta, this process can yield more than ten W^{\pm}H^{\mp} events for m_{H^{\pm}} <~ 350 GeV in 500 fb-1 at a 500 GeV e+e- collider, or m_{H^{\pm}} <~ 600 GeV in 1000 fb-1 at a 1000 GeV collider. 80% left-handed polarization of the e- beam improves these reaches to m_{H^{\pm}} <~ 375 GeV and m_{H^{\pm}} <~ 670 GeV, respectively.Comment: v2: 21 pages, 9 figures, comments on Higgs search bounds and new references added, and minor changes; v3: 23 pages, 11 figures, review of literature moved from introduction to new Sec.5 and 2 plots added, references added, typos corrected; v4: bug fixed in nu nubar H0 cross section (Fig.11), version to appear in PR

Analysis of Ωb−(bss)\Omega_b^-(bss) and Ωc0(css)\Omega_c^0(css) with QCD sum rules

In this article, we calculate the masses and the pole residues of the ${1/2}^+$ heavy baryons $\Omega_c^0(css)$ and $\Omega_b^-(bss)$ with the QCD sum rules. The numerical values $M_{\Omega_c^0}=(2.72\pm0.18) \rm{GeV}$ (or $M_{\Omega_c^0}=(2.71\pm0.18) \rm{GeV}$) and $M_{\Omega_b^-}=(6.13\pm0.12) \rm{GeV}$ (or $M_{\Omega_b^-}=(6.18\pm0.13) \rm{GeV}$) are in good agreement with the experimental data.Comment: 18 pages, 18 figures, slight revisio

The B-Meson Distribution Amplitude in QCD

The B-meson distribution amplitude is calculated using QCD sum rules. In particular we obtain an estimate for the integral relevant to exclusive B-decays \lambda_B = 460 \pm 110 MeV at the scale 1 GeV. A simple QCD-motivated parametrization of the distribution amplitude is suggested.Comment: 17 pages, 8 figures, Latex styl

Mean-field description of ground-state properties of drip-line nuclei. (I) Shell-correction method

A shell-correction method is applied to nuclei far from the beta stability line and its suitability to describe effects of the particle continuum is discussed. The sensitivity of predicted locations of one- and two-particle drip lines to details of the macroscopic-microscopic model is analyzed.Comment: 22 REVTeX pages, 13 uuencoded postscript figures available upon reques

Associated charged Higgs and W boson production in the MSSM at the CERN Large Hadron Collider

We investigate the viability of observing charged Higgs bosons (H^+/-) produced in association with W bosons at the CERN Large Hadron Collider, using the leptonic decay H^+ -> tau^+ nu_tau and hadronic W-decay, within different scenarios of the Minimal Supersymmetric Standard Model (MSSM) with both real and complex parameters. Performing a parton level study we show how the irreducible Standard Model background from W+2 jets can be controlled by applying appropriate cuts and find that the size of a possible signal depends on the cuts needed to suppress QCD backgrounds and misidentifications. In the standard maximal mixing scenario of the MSSM we find a viable signal for large tan(beta) and intermediate H^+/- masses (~m_t) when using optimistic cuts whereas for more pessimistic ones we only find a viable signal for very large tan(beta) (>~50). We have also investigated a special class of MSSM scenarios with large mass-splittings among the heavy Higgs bosons where the cross-section can be resonantly enhanced by factors up to one hundred, with a strong dependence on the CP-violating phases. Even so we find that the signal after cuts remains small except for small masses (~< m_t) with optimistic cuts. Finally, in all the scenarios we have investigated we have only found small CP-asymmetries.Comment: 28 pages, 12 figures, version to appear in Euro. Phys. J.

Measurements of the SUSY Higgs self-couplings and the reconstruction of the Higgs potential

We address the issue of the reconstruction of the scalar potential of a two-Higgs doublet model having in mind that of the MSSM. We first consider the general CP conserving dim-4 effective potential. To fully reconstruct this potential, we show that even if all the Higgs masses and their couplings to the standard model particles are measured one needs not only to measure certain trilinear Higgs self-couplings but some of the quartic couplings as well. We also advocate expressing the Higgs self couplings in the mass basis. We show explicitly, that in the so-called decoupling limit, the most easily accessible Higgs self-couplings are given in terms of the Higgs mass while all other dependencies on the parameters of the general effective potential are screened. This helps also easily explain how, in the MSSM, the largest radiative corrections which affect these self couplings are reabsorbed by using the corrected Higgs mass. We also extend our analysis to higher order operators in the effective Higgs potential. While the above screening properties do not hold, we argue that these effects must be small and may not be measured considering the foreseen poor experimental precision in the extraction of the SUSY Higgs self-couplings.Comment: 25 pages, 3 figure

Lepton flavor violation decays τ−→μ−P1P2\tau^-\to \mu^- P_1 P_2 in the topcolor-assisted technicolor model and the littlest Higgs model with TT parity

The new particles predicted by the topcolor-assisted technicolor ($TC2$) model and the littlest Higgs model with T-parity (called $LHT$ model) can induce the lepton flavor violation ($LFV$) couplings at tree level or one loop level, which might generate large contributions to some $LFV$ processes. Taking into account the constraints of the experimental data on the relevant free parameters, we calculate the branching ratios of the $LFV$ decay processes $\tau^-\to\mu^- P_1 P_2$ with $P_1 P_2$ = $\pi^+\pi^-$, $K^+K^-$ and $K^0\bar{K^0}$ in the context of these two kinds of new physics models. We find that the $TC2$ model and the $LHT$ model can indeed produce significant contributions to some of these $LFV$ decay processes.Comment: 24 pages, 7 figure