Inclusion Of Saturation Effects Research Articles

Saturation effects in exclusive ρ T,L meson electroproduction

Abstract We use recent results for the $ \gamma_L^{*}\to {\rho_L} $ and $ \gamma_T^{*}\to {\rho_T} $ impact factors, computed in the impact parameter representation within the collinear factorization scheme, to get predictions for the polarized cross-sections σ T and σ L of the diffractive leptoproduction of the ρ meson at high energy. In this approach the helicity amplitude is a convolution of the scattering amplitude of a color dipole with a target, together with the virtual gamma wave function and with the first moments of the ρ meson wave function (in the transverse momentum space), given by the distribution amplitudes up to twist 3 for the $ \gamma_T^{*}\to {\rho_T} $ impact factor and up to twist 2 for the $ \gamma_L^{*}\to {\rho_L} $ impact factor. Combining these results with recent dipole models fitted to DIS data, which include saturation effects, we show that the predictions are in good agreement with HERA data for photon virtuality (Q 2) larger than typically 5 GeV2, without free parameters and with a weak dependence on the choice of the factorization scale, i.e. the shape of the DAs, for both longitudinally and transversely polarized ρ meson. For lower values of Q 2, the inclusion of saturation effects is not enough to provide a good description of HERA data. We believe that it is a signal of a need for higher twist contributions in the ρ meson DAs. We also analyze the radial distributions of dipoles between the initial γ * and the final ρ meson states.

Fresh look at axions and SN 1987A

We re-examine the very stringent limits on the axion mass based on the strength and duration of the neutrino signal from SN 1987A, in the light of new measurements of the axial-vector coupling strength of nucleons, possible suppression of axion emission due to many-body effects, and additional emission processes involving pions. The suppression of axion emission due to nucleon spin fluctuations induced by many-body effects degrades previous limits by a factor of about 2. Emission processes involving thermal pions can strengthen the limits by a factor of 3-4 within a perturbative treatment that neglects saturation of nucleon spin fluctuations. Inclusion of saturation effects, however, tends to make the limits less dependent on pion abundances. The resulting axion mass limit also depends on the precise couplings of the axion and ranges from 0.5x10**(-3) eV to 6x10**(-3) eV.

A flux-limited treatment for the conductive evaporation of spherical interstellar gas clouds

In this work, we present and analyze a new analytic solution for the saturated (flux-limited) thermal evaporation of a spherical cloud. This work is distinguished from earlier analytic studies by allowing the thermal conductivity to change continuously from a diffusive to a saturated form, in a manner usually employed only in numerical calculations. This closed form solution will be of interest as a computational benchmark. Using our calculated temperature profiles and mass-loss rates, we model the thermal evaporation of such a cloud under typical interstellar medium (ISM) conditions, with some restrictions. We examine the ionization structure of the cloud-ISM interface and evaluate column densities of carbon, nitrogen, oxygen, neon, and silicon ions toward the cloud. In accord with other investigations, we find that ionization equilibrium is far from satisfied under the assumed conditions. Since the inclusion of saturation effects in the heat flux narrows the thermal interface relative to its classical structure, we also find that saturation effects tend to lower predicted column densities.

TM-polarized nonlinear guided waves in multilayer systems

The ability of various multilayer systems to support TM-polarized nonlinear guided waves is studied. A flexible numerical technique which includes the proper consideration of the nonlinear crossing conditions is used to calculate the field profiles and derive the dispersion relations. The fundamentals of the model are described, and the algorithm is applied to several nonlinear film configurations. For the sake of comparison with the finite-element method, a single linear film, embedded between two nonlinear materials, is treated. A three-film unit cell, consisting of a high-index linear film, sandwiched between two low-index nonlinear, ones is considered. This is the elementary unit cell of a composite geometry, a ten-unit-cell superlattice, which is then studied. It is found that unlike TE-polarized nonlinear guided waves in multilayer systems, the TM waves reveal a distinct power maximum. The inclusion of saturation effects in the analysis is straightforward.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Matrix Representation of Three-Phase N-Winding Transformers for Steady-State and Transient Studies

Detailed transformer representations are needed in the analysis of electromagnetic transients and in the analysis of unbalanced steady-state conditions. This paper describes the derivation of mdels for three- phase and single-phase N-winding transformers in the form of branch impedance or admittance matrices, which can be calculated from available test data of positive and zero sequence short-circuit and excitation tests. The models can be used for many types of studies as long as the frequencies are low enough so that capacitances in the transformer can be ignored. The inclusion of saturation effects is briefly discussed.