Apparent and effective mechanical properties of linear matrix-inclusion random composites: Improved bounds for the effective behavior

This paper is devoted to the derivation of improved bounds for the effective behavior of linear elastic matrix-inclusion composites based on a strategy which is inspired by both the works of Huet, 1990, Danielsson et al., 2007. As shown by the former author, the effective properties of random linear composites can be bounded by ensemble averages of their apparent elastic moduli defined on square (or cubic) volume elements (VEs) and computed with either affine displacement Boundary Conditions (BC) or uniform traction BC. However, in the case of a large contrast of the constituents, the discrepancy between the upper and lower bounds remains significant, even for large values of the VE size. This occurs because the contribution to the total potential (or complementary) energy of the particles (or pores) which intersect the edges of the VE becomes unphysically very large when uniform BC are directly applied to the particles. To avoid such limitations, we considerer non-square (or non-cubic) VEs consisting in simply connex assemblages of cells, each cell being composed of an inclusion surrounded by the matrix, thus forbidding any direct application of BC to the particles. Such VEs are generated by extending the scheme proposed by Danielsson et al. (2007) in the context of periodic random microstructures to fully random microstructures. By applying the classical energy bounding theorems to the non-square VEs, new bounds for the effective behavior are derived. Their application to a two-phase composite composed of an isotropic matrix and aligned identical fibers randomly distributed in the transverse plane leads to sharper bounds which converge quickly with the VE size, even for infinite contrasts.     

The higgs boson mass from precision electroweak data

We present a new global fit to precision electroweak data, including new low- and high-energy data and analyzing the radiative corrections arising from the minimal symmetry breaking sectors of the Standard Model (SM) and its supersymmetric extension (MSSM). It is shown that present data favor a Higgs mass ofO(M _z):M _H=76 _?50 ⁺¹⁵² GeV. We confront our analysis with (meta) stability and perturbative bounds on the SM Higgs mass, and the theoretical upper bound on the MSSM Higgs mass. Present data do not discriminate significantly between the SM and MSSM Higgs mass ranges. We comment in passing on the sensitivity of the Higgs mass determination to the values ofα(M _z) andα _s(M _z).     

Galaxy cluster number count data constraints on cosmological parameters

We use data on massive galaxy clusters (M _cluster>8×10¹⁴ h ^?1 M _?? within a comoving radius of R _cluster=1.5h ^?1?Mpc) in the redshift range 0.05?z?0.83 to place constraints, simultaneously, on the nonrelativistic matter density parameter ?? _m , on the amplitude of mass fluctuations ?? ₈, on the index n of the power-law spectrum of the density perturbations, and on the Hubble constant H ₀, as well as on the equation-of-state parameters (w ₀,w _a ) of a smooth dark energy component. For the first time, we properly take into account the dependence on redshift and cosmology of the quantities related to cluster physics: the critical density contrast, the growth factor, the mass conversion factor, the virial overdensity, the virial radius and, most importantly, the cluster number count derived from the observational temperature data. We show that, contrary to previous analyses, cluster data alone prefer low values of the amplitude of mass fluctuations, ?? ₈??0.69 (1?? C.L.), and large amounts of nonrelativistic matter, ?? _m ??0.38 (1?? C.L.), in slight tension with the ??CDM concordance cosmological model, though the results are compatible with ??CDM at 2??. In addition, we derive a ?? ₈ normalization relation, $\sigma_{8} \varOmega_{m}^{1/3} = 0.49 \pm 0.06$ (2?? C.L.). Combining cluster data with ?? ₈-independent baryon acoustic oscillation observations, cosmic microwave background data, Hubble constant measurements, Hubble parameter determination from passively evolving red galaxies, and magnitude?Credshift data of type Ia supernovae, we find $\varOmega_{m} = 0.28^{+0.03}_{-0.02}$ and $\sigma_{8} = 0.73^{+0.03}_{-0.03}$ , the former in agreement and the latter being slightly lower than the corresponding values in the concordance cosmological model. We also find $H_{0} = 69.1^{+1.3}_{-1.5}~\mbox {km}/\mbox {s}/\mbox {Mpc}$ , the fit to the data being almost independent on n in the adopted range [0.90,1.05]. Concerning the dark energy equation-of-state parameters, we show that the present data on massive clusters weakly constrain (w ₀,w _a ) around the values corresponding to a cosmological constant, i.e. (w ₀,w _a )=(?1,0). The global analysis gives $w_{0} = -1.14^{+0.14}_{-0.16}$ and $w_{a} = 0.85^{+0.42}_{-0.60}$ (1?? C.L. errors). Very similar results are found in the case of time-evolving dark energy with a constant equation-of-state parameter w=const (the XCDM parametrization). Finally, we show that the impact of bounds on (w ₀,w _a ) is to favor top-down phantom models of evolving dark energy.     

TBC and PML conditions for 2D and 3D BPM: a comparison

Any implementation of the beam propagation method, when used to analyse open problems, requires a procedure allowing radiation to leave the computational window. In this paper we present the results of a case study on the effectiveness of the classical Hadley's Transparent Boundary Conditions (TBC) and the Perfectly Matched Layer (PML) to handle strong radiation at the boundaries. A polished fibre coupler will be studied both in 2D and in 3D configurations using, in the former case, a scalar method and, in the latter, a full vectorial approach. Numerical results show that simple TBC can be used in 2D simulations also when high radiation occurs but they easily fail in 3D structures. Therefore, in these cases, the more complicated PML conditions should be preferred.     

About the isoscalar piece of the weak neutral current

The available neutral current induced one-pion production data at intermediate energy are analyzed in a model-independent way in the framework of a recent approach to the corresponding production mechanism. Clear indications about the structure of the isoscalar piece of the weak neutral current are obtained and more stringent evidence of agreement with the standard WS model is seen to emerge. For the first time the relative influence of the different amplitudes contributing to the production mechanism is analyzed, by adopting the neutral current parametrization provided by the WS model.     

Hints of theta13>0 from global neutrino data analysis

Nailing down the unknown neutrino mixing angle theta{13} is one of the most important goals in current lepton physics. In this context, we perform a global analysis of neutrino oscillation data, focusing on theta{13}, and including recent results [ (unpublished)]. We discuss two converging hints of theta{13}>0, each at the level of approximately 1sigma: an older one coming from atmospheric neutrino data, and a newer one coming from the combination of solar and long-baseline reactor neutrino data. Their combination provides the global estimate sin{2}theta{13}=0.016+/-0.010(1sigma), implying a preference for theta{13}>0 with non-negligible statistical significance ( approximately 90% C.L.). We discuss possible refinements of the experimental data analyses, which might sharpen such intriguing indications.     

Neutral current induced one-pion production: A new model and its comparison with experiment

In the framework of a recently presented model of weak one-pion production processes we analyze the neutral current induced $\text{ν}\text{and}\text{ν}$ channels, by assuming a Weinberg-Salam structure of the neutral currents. We find substantial agreement in the ν case, some discrepancy arising in the analysis of the $\text{ν}$ data. Predictions are given for the experiments requiring an improved statistics. In particular the relevance of the extension of the analyzed Nπ invariant-mass region up to 1.6 GeV/c², with the inclusion of the first $\text{I?}\text{1}\text{2}$ resonances, is stressed.     

Electroweak radiative corrections and parameters of the standard model: a comparative analysis

A comparative analysis of the effects induced by radiative corrections on the different sectors of the neutral current interactions at low momentum transfer (v?q, v?e ande?q interactions) and on the direct measurement of the vector boson masses is presented. In particular atomic parity violation is reviewed on the basis of new experimental data and more precise theoretical calculations. It is seen that the inclusion of radiative correction effects begins to become crucial in order to find an agreement between the parameters of the standard model extracted from the different sectors not only in the minimal version of the standard model, but also in two-parameter analysis.