Distribution amplitude for the photon-pion transition

The exclusive production of \pi\pi and \pi\rho in hard \gamma^{\star}\gamma scattering in the forward kinematical region where the virtual photon is highly off-shell are studied through the \gamma\to\pi^- Transition Distribution Amplitudes. The calculation is based on a covariant Bethe-Salpeter approach, applied to the Nambu - Jona-Lasinio model, for the determination of the pion bound state. In particular it is shown that the pion pole contribution produces a large enhancement of the differential cross section for the pion pair production with respect to previous estimates.Comment: To appear in the proceedings of Light Cone 2008: Relativistic Nuclear and Particle Physics (LC2008), Mulhouse, France, 7-11 Jul 200

The Pion-Photon Transition Distribution Amplitudes in the Nambu-Jona Lasinio Model

We define the pion-photon Transition Distribution Amplitudes (TDA) in a field theoretic formalism from a covariant Bethe-Salpeter approach for the determination of the bound state. We apply our formalism to the Nambu - Jona Lasinio model, as a realistic theory of the pion. The obtained vector and axial TDAs satisfy all features required by general considerations. In particular, sum rules and polynomiality condition are explicitly verified. We have numerically proved that the odd coefficients in the polynomiality expansion of the vector TDA vanish in the chiral limit. The role of PCAC and the presence of a pion pole are explicitly shown.Comment: 14 pag. and 6 fig, final version (to appear in Phys. Rev. D

Barter Economies and Centralized Merchants

The main goal of this essay is to analyze the emergence of a barter economy, and the rise of centralized merchants and a barter redistribution system out of a primitive barter system. The environment is a spatial general equilibrium model where exchange is costly. Since exchange becomes more complicated as the scope of the economy increases, we prove that, after the economy reaches a critical size, the cost of trade expansion surpasses its benefits. This imposes limitations on the scope of the economy and the production level. To overcome these limitations, rational individuals can develop a more advanced barter system leading to the appearance of centralized merchants. This more sophisticated system is the redistribution system. We also show that under some circumstances, in the presence of transaction costs it may be optimal for individuals to keep using barter instead of adopting a monetary system. This result explains why some primitive economies, like the Incas in Peru and ancient Egypt, did not evolve to a monetary system, and kept barter as their main exchange system.Barter, City, Exchange system, Market center, Merchant, Redistribution system, Transaction cost

The Appearance of Carriers and the Origins of Money

The main goal of this essay is to provide microfoundations in a spatial general equilibrium framework for the fact that individuals use money to make transactions, and hence microfoundations for the cash in advance constraint. We analyze the emergence of a monetary economy out of a redistribution barter system where goods are sent to a central market and then redistributed among individuals. We show that, as the population increases beyond a certain point, the barter exchange system becomes too expensive. To reduce the exchange system cost, and as a result of individuals’ rational behavior, a new specialized merchant, the carrier, appears and causes frictions among traders leading to the appearance of money. There are, however, certain conditions for this process to succeed. These conditions concern the economic characteristics of those goods chosen to act as money, and the level of economic development.Barter, Money, Carrier, Market center, City, Transaction cost

Semileptonic decays of charmed mesons in the effective action of QCD

Within the framework of phenomenological Lagrangians we construct the effective action of QCD relevant for the study of semileptonic decays of charmed mesons. Hence we evaluate the form factors of D -> P(0^-) l^+ nu_l at leading order in the 1/N_C expansion and, by demanding their QCD-ruled asymptotic behaviour, we constrain the couplings of the Lagrangian. The features of the model-independent parameterization of form factors provided and their relevance for the analysis of experimental data are pointed out.Comment: 1+24 pages, 1 figure. Updated version. Conclusions unchanged. Accepted for publication in The European Physical Journal

Non local lagrangians(I): the pion

We define a family of non local and chirally symmetric low energy lagrangians motivated by theoretical studies on Quantum Chromodynamics. These models lead to quark propagators with non trivial momentum dependencies. We define the formalism for two body bound states and apply it to the pion. We study the coupling of the photon and W bosons with special attention to the implementation of local gauge invariance. We calculate the pion decay constant recovering the Goldberger-Treiman and the Gell-Mann-Oakes-Renner relations. We recover a form of the axial current consistent with PCAC. Finally we study the pion form factor and we construct the operators involved in its parton distribution.Comment: Latex, 25 pages with 15 figures; added references for introduction and section

Strong Pionic Decays From a Spectroscopic Quark Model

From a refined non-relativistic quark model that fits the baryonic low-energy spectrum the study of strong pion decay processes within an elementary emission model scheme points out the need of incorporating size-contributing components into the baryon wave functions. In particular the effect of a (qqq qantiq) component is investigated in the framework of a quark pair creation model.Comment: 26 pages, 9 figures (1 postscript file), LaTe

Pion-to-vacuum vector and axial vector amplitudes and weak decays of pions in a magnetic field

We propose a model-independent parametrization for the one-pion-to-vacuum matrix elements of the vector and axial vector hadronic currents in the presence of an external uniform magnetic field. It is shown that, in general, these hadronic matrix elements can be written in terms of several gauge covariant Lorentz structures and form factors. Within this framework we obtain a general expression for the weak decay $\pi^- \to l\,\bar\nu_l$ and discuss the corresponding limits of strong and weak external magnetic fields.Comment: 33 page

Analysis of infrared optical polishing effluents and reduction of COD and TSS levels by ultrafiltration and coagulation/flocculation

Samples of polishing effluent produced during infrared optics manufacture were analyzed. Their particle size, composition, Zeta potential, chemical oxygen demand (COD), total suspended solids (TSS), and settleable solids were determined. Feasibility of treatment methods such as ultrafiltration (UF) and coagulation/flocculation was investigated to reduce both COD and TSS. It was found that effluents consisted of a suspension of micro- and nanoparticles. Effluent particle size distribution reflected the removal rate of the originating polishing process. Their composition was primarily germanium and other polished substrates as well as polishing abrasives. The effluent Zeta potential was highly negative and prevented particle settling. COD of all specimens was very high, which prevented sewage discharge. Laboratory-scale trials using UF showed substantial COD abatement of up to 74.1%. TSS was reduced to zero after UF. Comparable coagulation/flocculation COD abatement was demonstrated for the highest COD sample

Pion radiative weak decays in nonlocal chiral quark models

We analyze the radiative pion decay pi+ -> e+ nu_e gamma within nonlocal chiral quark models that include wave function renormalization. In this framework we calculate the vector and axial-vector form factors FV and FA at q^2=0 --where q^2 is the (e+ \nu_e) squared invariant mass-- and the slope a of FV(q^2) at q^2 -> 0. The calculations are carried out considering different nonlocal form factors, in particular those taken from lattice QCD evaluations, showing a reasonable agreement with the corresponding experimental data. The comparison of our results with those obtained in the (local) NJL model and the relation of FV and a with the form factor in pi^0 -> gamma* gamma decays are discussed.Comment: 14 pages, 1 figure, minor changes in text introduce