A Note on Unparticle Decays

The coupling of an unparticle operator O_U to Standard Model particles opens up the possibility of unparticle decays into standard model fields. We study this issue by analyzing the pole structure (and spectral function) of the unparticle propagator, corrected to account for one-loop polarization effects from virtual SM particles. We find that the propagator of a scalar unparticle (of scaling dimension 1 < d_U < 2) with a mass gap m_g develops an isolated pole, m_p^2-i m_p Gamma_p, with m_p^2 < m_g^2 below the unparticle continuum that extends above m_g (showing that the theory would be unstable without a mass gap). If that pole lies below the threshold for decay into two standard model particles the pole corresponds to a stable unparticle state (and its width Gamma_p is zero). For m_p^2 above threshold the width is non zero and related to the unparticle decay rate into Standard Model particles. This picture is valid for any value of d_U in the considered range.Comment: 11 pages, 4 figure

Cosmological Properties of a Gauged Axion

We analyze the most salient cosmological features of axions in extensions of the Standard Model with a gauged anomalous extra U(1) symmetry. The model is built by imposing the constraint of gauge invariance in the anomalous effective action, which is extended with Wess-Zumino counterterms. These generate axion-like interactions of the axions to the gauge fields and a gauged shift symmetry. The scalar sector is assumed to acquire a non-perturbative potential after inflation, at the electroweak phase transition, which induces a mixing of the Stuckelberg field of the model with the scalars of the electroweak sector, and at the QCD phase transition. We discuss the possible mechanisms of sequential misalignments which could affect the axions of these models, and generated, in this case, at both transitions. We compute the contribution of these particles to dark matter, quantifying their relic densities as a function of the Stuckelberg mass. We also show that models with a single anomalous U(1) in general do not account for the dark energy, due to the presence of mixed U(1)-SU(3) anomalies.Comment: 29 pages, 5 figures. Revised version, accepted by Phys. Rev.

Momentum Distribution in Nuclear matter within a Perturbation Approximation

It is shown that the norm corrections, introduced to avoid the violation of the constraints on the depletion of the hole states in the standard perturbative 2p2h approach, leads in nuclear matter to a dependence of the momentum distribution with the total nucleon number. This unphysical behavior, which in turn makes the depletion to be non-extensive, arises from contributions of disconnected diagrams contained in the norm. It is found that the extensivity is again recovered when the 4p4h excitations in the ground state are included, and a reasonable value for the total number of nucleons promoted above the Fermi level is obtained.Comment: 11 pages, LaTeX, 5 figures, figures 1 to 3 included in the latex file, postscript files of figures 4 and 5 available from the Authors. Accepted for publication in Phys. Rev.

DETERMINATION OF OPTIMAL ALGAE CONCENTRATION FOR CONTINUOUS GROWTH OF Scenedesmus sp. IN CHU AND MODIFIED CHU MEDIA

The high cost of production in the cultivation of microalgae in photobioreactors is a barrier to be overcome, therefore is necessary to search to reduce the cost of cultivation. The objectives of this work are to compare the growth of the microalgae Scenedesmus sp. being cultivated in CHU medium and in an alternative medium composed mainly of fertilizer and to establish guidelines for growth under continuous mode. The research approach consisted on growing the microalgae in Erlenmeyer type photobioreactors and producing thegrowth curves for both media. The comparisons between the two, were made based upon three parameters: dry biomass, absorbance, and total lipid quantity. The experiments were made in triplicates in order to quantify the uncertainty in the measurements. The comparison of the cultivation in both media suggest that the modification of the chemical nutrients by fertilizer did not produce significant changes in the number of cells, dry biomass and lipids. In spite of that, the modification resulted in 20% cost reduction in the growth medium. In this way, the substitution of conventional nutrients by fertilizers, constitute an interesting alternative for the production of biomass from microalgae leading to a cost reduction. The results are used to develop strategies for continuous growth

Violation of the Ikeda sum rule and the self-consistency in the renormalized quasiparticle random phase approximation and the nuclear double-beta decay

The effect of the inclusion of ground state correlations into the QRPA equation of motion for the two-neutrino double beta ($\beta\beta_{2\nu}$) decay is carefully analyzed. The resulting model, called renormalized QRPA (RQRPA), does not collapse near the physical value of the nuclear force strength in the particle-particle channel, as happens with the ordinary QRPA. Still, the $\beta\beta_{2\nu}$ transition amplitude is only slightly less sensitive on this parameter in the RQRPA than that in the plain QRPA. It is argued that this fact reveals once more that the characteristic behaviour of the $\beta\beta_{2\nu}$ transition amplitude within the QRPA is not an artifact of the model, but a consequence of the partial restoration of the spin-isospin $SU(4)$ symmetry. It is shown that the price paid for bypassing the collapse in the RQRPA is the violation of the Ikeda sum rule.Comment: 16 pages, latex, 3 postscript figure

A new Fermi smearing approach for scattering of multi-GeV electrons by nuclei

The cross section for electron scattering by nuclei at high momentum transfers is calculated within the Fermi smearing approximation (FSA), where binding effects on the struck nucleon are introduced via the relativistic Hartree approximation (RHA). The model naturally preserves current conservation, since the response tensor for an off-shell nucleon conserves the same form that for a free one but with an effective mass. Different parameterizations for the inelastic nucleon structure function, are analyzed. The smearing at the Fermi surface is introduced through a momentum distribution obtained from a perturbative nuclear matter calculation. Recent CEBAF data on inclusive scattering of 4.05 GeV electrons on $^{56}$Fe are well reproduced for all measured geometries for the first time, as is evident from the comparison with previous calculations.Comment: 8 pages in Revtex4 style, 6 eps figures, to appear in Physical Review

On the energy-shell contributions of the three-particle~-~ three-hole excitations

The response functions for the extended second and third random phase approximation are compared. A second order perturbation calculation shows that the first-order amplitude for the direct $3p3h$ excitation from the ground state cancels with those that are engendered by the $1p1h$-$3p3h$ coupling. As a consequence nonvanishing $3p3h$ effects to the $1p1h$ response involve off energy shell renormalization only. On shell $3p3h$ processes are absent.Comment: 12 pages text (LaTex) and 1 figure included, to be published in Phys. Rev.

Effect of nickel in solid solution on hydrogen transport kinetics in low alloy steels

The use of low alloy steels (LAS) in H2S-containing environments in the oil and gas industry is governed by the ISO standard 15156-2 (NACE MR0175-2). One requirement, which has been disputed over the years, is that the nickel (Ni) content shall not exceed 1 wt%. This work investigated the effect of Ni in solid solution on hydrogen diffusion, solubility, and trapping in ferritic/pearlitic research-grade LAS with nominal Ni contents from 0 to 3 wt%. Hydrogen permeability experiments were carried out in a Devanathan-Stachurski setup at 15, 45 and 70 °C. The effective diffusion coefficients, calculated by the tlag method, decreased with increasing Ni content. The sub-surface hydrogen concentration in lattice and trap sites increased with increasing Ni content. There was no difference between the first and subsequent hydrogen permeation transients, suggesting that Ni in solid solution forms reversible traps. The effect of Ni in refining the microstructure may be superimposed on the effect of Ni in solid solution, and should be investigated in future work