Nucleon and gamma N -> Delta lattice form factors in a constituent quark model

A covariant quark model, based both on the spectator formalism and on vector meson dominance, and previously calibrated by the physical data, is here extended to the unphysical region of the lattice data by means of one single extra adjustable parameter - the constituent quark mass in the chiral limit. We calculated the Nucleon (N) and the gamma N -> Delta form factors in the universe of values for that parameter described by quenched lattice QCD. A qualitative description of the Nucleon and gamma N -> Delta form factors lattice data is achieved for light pions.Comment: To appear in J.Phys.

The Non-Mesonic Weak Decay of Double-Lambda Hypernuclei: A Microscopic Approach

The non--mesonic weak decay of double--$\Lambda$ hypernuclei is studied within a microscopic diagrammatic approach. Besides the nucleon--induced mechanism, $\Lambda N\to nN$, widely studied in single--$\Lambda$ hypernuclei, additional hyperon--induced mechanisms, $\Lambda \Lambda\to \Lambda n$, $\Lambda \Lambda\to \Sigma^0 n$ and $\Lambda \Lambda\to \Sigma^-p$, are accessible in double--$\Lambda$ hypernuclei and are investigated here. As in previous works on single--$\Lambda$ hypernuclei, we adopt a nuclear matter formalism extended to finite nuclei via the local density approximation and a one--meson exchange weak transition potential (including the ground state pseudoscalar and vector octets mesons) supplemented by correlated and uncorrelated two--pion--exchange contributions. The weak decay rates are evaluated for hypernuclei in the region of the experimentally accessible light hypernuclei $^{10}_{\Lambda\Lambda}$Be and $^{13}_{\Lambda\Lambda}$B. Our predictions are compared with a few previous evaluations. The rate for the $\Lambda \Lambda\to \Lambda n$ decay is dominated by $K$--, $K^*$-- and $\eta$--exchange and turns out to be about 2.5\% of the free $\Lambda$ decay rate, $\Gamma_{\Lambda}^{\rm free}$, while the total rate for the $\Lambda \Lambda\to \Sigma^0 n$ and $\Lambda \Lambda\to \Sigma^- p$ decays, dominated by $\pi$--exchange, amounts to about 0.25\% of $\Gamma_{\Lambda}^{\rm free}$. The experimental measurement of these decays would be essential for the beginning of a systematic study of the non--mesonic decay of strangeness $-2$ hypernuclei. This field of research could also shed light on the possible existence and nature of the $H$--dibaryon.Comment: 17 pages, 2 figure

Cross-Correlation in the Auditory Coincidence Detectors of Owls

Interaural time difference (ITD) plays a central role in many auditory functions, most importantly in sound localization. The classic model for how ITD is computed was put forth by Jeffress (1948). One of the predictions of the Jeffress model is that the neurons that compute ITD should behave as cross-correlators. Whereas cross-correlation-like properties of the ITD-computing neurons have been reported, attempts to show that the shape of the ITD response function is determined by the spectral tuning of the neuron, a core prediction of cross-correlation, have been unsuccessful. Using reverse correlation analysis, we demonstrate in the barn owl that the relationship between the spectral tuning and the ITD response of the ITD-computing neurons is that predicted by cross-correlation. Moreover, we show that a model of coincidence detector responses derived from responses to binaurally uncorrelated noise is consistent with binaural interaction based on cross-correlation. These results are thus consistent with one of the key tenets of the Jeffress model. Our work sets forth both the methodology to answer whether cross-correlation describes coincidence detector responses and a demonstration that in the barn owl, the result is that expected by theory

Spin and angular momentum in the nucleon

Using the covariant spectator theory (CST), we present the results of a valence quark-diquark model calculation of the nucleon structure function f(x) measured in unpolarized deep inelastic scattering (DIS), and the structure functions g1(x) and g2(x) measured in DIS using polarized beams and targets. Parameters of the wave functions are adjusted to fit all the data. The fit fixes both the shape of the wave functions and the relative strength of each component. Two solutions are found that fit f(x) and g1(x), but only one of these gives a good description of g2(x). This fit requires the nucleon CST wave functions contain a large D-wave component (about 35%) and a small P-wave component (about 0.6%). The significance of these results is discussed.Comment: 27 pages; 13 figure

Outer crust of a cold non-accreting magnetar

The outer crust structure and composition of a cold, non-accreting magnetar is studied. We model the outer crust to be made of fully equilibrated matter where ionized nuclei form a Coulomb crystal embedded in an electron gas. The main effects of the strong magnetic field are those of quantizing the electron motion in Landau levels and of modifying the nuclear single particle levels producing, on average, an increased binding of nucleons in nuclei present in the Coulomb lattice. The effect of an homogeneous and constant magnetic field on nuclear masses has been predicted by using a covariant density functional, in which induced currents and axial deformation due to the presence of a magnetic field that breaks time-reversal symmetry have been included self-consistently in the nucleon and meson equations of motion. Although not yet observed, for $B\gtrsim 10^{16}$G both effects contribute to produce different compositions and to enlarge the range of pressures typically present in common neutron stars. Specifically, in such a regime, the magnetic field effects on nuclei favor the appearance of heavier nuclei at low pressures. As $B$ increases, such heavier nuclei are also preferred up to larger pressures. In the most extreme case, the whole outer crust is almost made of ${}_{40}^{92}$Zr$_{52}$.Comment: Published versio

Covariant nucleon wave function with S, D, and P-state components

Expressions for the nucleon wave functions in the covariant spectator theory (CST) are derived. The nucleon is described as a system with a off-mass-shell constituent quark, free to interact with an external probe, and two spectator constituent quarks on their mass shell. Integrating over the internal momentum of the on-mass-shell quark pair allows us to derive an effective nucleon wave function that can be written only in terms of the quark and diquark (quark-pair) variables. The derived nucleon wave function includes contributions from S, P and D-waves.Comment: 13 pages and 1 figur

Monetary Policy after the Great Moderation

The interferences among some financial, economic and monetary variables are checked as an indicator of economic performance in the long run and for the monetary policy applied between the Great Moderation (GM) of 1987-2001 and the Global Financial Crisis of 2007-2009. For achieving this target, some Granger causality tests are applied to GDP growth, credit growth, and lending interest of 36 countries of the EU and the OECD for the full sample of 1987-2012 and the sub-sample of 2002-2007. Results corroborate the interferences among these variables for the discretionary monetary policy applied immediately after the GM, within the "Ad Hoc Era" or "lax period", and independence when monetary policy was correctly applied and rules-based

Efficient treatment of banking services under VAT

The efficiency of tax systems is an important topic for policy makers and academics. We focus on the efficiency of applying VAT to traditional banking services, a significant issue where a consensus has yet to be reached since the first debates more than two decades ago. This paper discusses one of the most relevant models of tax efficiency on banking services under VAT, the model developed by Jack (2000). This author shows that explicit fees and commissions should be taxable under VAT, while implicit fees covered by banking spreads should be zero-rated. An alternative theoretical approach is developed in this paper, proposing the taxation of both explicit and implicit fees of financial services under VAT at the same tax rate, which should also be the same rate applied to all other goods and services