Fixed points of the Similarity Renormalization Group and the Nuclear Many-Body Problem

The Similarity Renormalization Group reduces the off-shellness by driving the evolved interaction towards a diagonal band. We analyze the infrared limit and the corresponding on-shell interactions and its consequences for light nuclei. Using a harmonic oscillator shell model we obtain a Tjon line B(4He)= 4B(3H)-3B(2H) which can be understood from a combinatorics counting of nucleon pairs and triplets in the triton and alpha-particle and compares favorably with realistic calculations.Comment: Presented by E.R.A. at the 22th European Conference On Few-Body Problems In Physics: EFB22 9 - 13 Sep 2013, Krakow (Poland), 5 pages, 3 figures (corrections and references added

Estrategias de mejoramiento de frijol para un sistema asociado con maiz, en el Valle Sagrado, Cusco-Peru

The improvement strategy of climbing bean in Cusco should take into account the importance of maize as a crop. In a recent study in 2 maize-growing communities of Valle Sagrado, 75 and 88 percent of the farmers considered beans as the main crop; however, only 57 and 22 percent of the maize-growing area was planted to beans. Furthermore, farmers usually plant beans at low densities, partly due to the high degree of competition with maize. This practice causes low bean yields (300-500 kg/ha). Considering these data, and to take advantage of the large areas planted to maize in Valle Sagrado and other areas, the improvement strategy has consisted in developing bean lines apt for associated cropping with maize. The new lines allow maize to maintain its yield level, while increasing bean production/ha. Using this strategy and on the basis of previous evaluations, 15 promising bean lines were selected at the Taray Exptl. Station for the 1988/89 cropping season. Of these, outstanding lines were ZAV 8382 (1354 kg beans and 7667 kg maize/ha), ZAV 8397 (1354 kg beans and 7395 kg maize/ha), and ZAV 8398 (1052 kg beans and 8156 kg maize/ha), compared with the local check Amarillo Gigante (1350 kg beans and 4500 kg maize/ha). The local check, due to its IVb growth habit (very aggressive), reduced maize yields significantly; the new lines, however, overcome this disadvantage, all being of growth habit IVa (less aggressive). (AS- CIAT

Low energy universality and scaling of Van der Waals forces

At long distances interactions between neutral ground state atoms can be described by the Van der Waals potential V(r) =-C6/r^6-C8/r^8 - ... . In the ultra-cold regime atom-atom scattering is dominated by s-waves phase shifts given by an effective range expansion p cot d0 (p) = -1/a0 + r0 p^2/2 + ... in terms of the scattering length a0 and the effective range r0. We show that while for these potentials the scattering length cannot be predicted, the effective range is given by the universal low energy theorem r0 = A + B/a0+ C/a0^2 where A,B and C depend on the dispersion coefficients Cn and the reduced di-atom mass. We confront this formula to about a hundred determinations of r0 and a0 and show why the result is dominated by the leading dispersion coefficient C6. Universality and scaling extends much beyond naive dimensional analysis estimates.Comment: 4 pages, 3 figure

Global superscaling analysis of quasielastic electron scattering with relativistic effective mass

We present a global analysis of the inclusive quasielastic electron scattering data with a superscaling approach with relativistic effective mass. The SuSAM* model exploits the approximation of factorization of the scaling function $f^*(\psi^*)$ out of the cross section under quasifree conditions. Our approach is based on the relativistic mean field theory of nuclear matter where a relativistic effective mass for the nucleon encodes the dynamics of nucleons moving in presence of scalar and vector potentials. Both the scaling variable $\psi^*$ and the single nucleon cross sections include the effective mass as a parameter to be fitted to the data alongside the Fermi momentum $k_F$. Several methods to extract the scaling function and its uncertainty from the data are proposed and compared. The model predictions for the quasielastic cross section and the theoretical error bands are presented and discussed for nuclei along the periodic table from $A=2$ to $A=238$: $^2$H, $^3$H, $^3$He, $^4$He, $^{12}$C, $^{6}$Li, $^{9}$Be, $^{24}$Mg, $^{59}$Ni, $^{89}$Y, $^{119}$Sn, $^{181}$Ta, $^{186}$W, $^{197}$Au, $^{16}$O, $^{27}$Al, $^{40}$Ca, $^{48}$Ca, $^{56}$Fe, $^{208}$Pb, and $^{238}$U. We find that more than 9000 of the total $\sim 20000$ data fall within the quasielastic theoretical bands. Predictions for $^{48}$Ti and $^{40}$Ar are also provided for the kinematics of interest to neutrino experiments.Comment: 26 pages, 20 figures and 4 table

Generalized Quark Transversity Distribution of the Pion in Chiral Quark Models

The transversity generalized parton distributions (tGPDs) of the the pion, involving matrix elements of the tensor bilocal quark current, are analyzed in chiral quark models. We apply the nonlocal chiral models involving a momentum-dependent quark mass, as well as the local Nambu--Jona-Lasinio with the Pauli-Villars regularization to calculate the pion tGPDs, as well as related quantities following from restrained kinematics, evaluation of moments, or taking the Fourier-Bessel transforms to the impact-parameter space. The obtained distributions satisfy the formal requirements, such as proper support and polynomiality, following from Lorentz covariance. We carry out the leading-order QCD evolution from the low quark-model scale to higher lattice scales, applying the method of Kivel and Mankiewicz. We evaluate several lowest-order generalized transversity form factors, accessible from the recent lattice QCD calculations. These form factors, after evolution, agree properly with the lattice data, in support of the fact that the spontaneously broken chiral symmetry is the key element also in the evaluation of the transversity observables.Comment: 17 pages, 17 figures, regular pape

Correlations between perturbation theory and power corrections in QCD at zero and finite temperature

The duality between QCD perturbative series and power corrections recently conjectured by Narison and Zakharov is analyzed. We propose to study correlations between both contributions as diagnostics tool. A very strong correlation between perturbative and non perturbative contributions is observed for several observables at zero and at finite temperature supporting the validity of the dual description.Comment: 7 pages, 5 figures, 7 table