Flexible Parametrization of Generalized Parton Distributions: The Chiral-Odd Sector

We present a physically motivated parameterization of the chiral-odd generalized parton distributions. The parametrization is an extension of our previous one in the chiral-even sector which was based on the reggeized diquark model. While for chiral even generalized distributions a quantitative fit with uncertainty estimation can be performed using deep inelastic scattering data, nucleon electromagnetic, axial and pseudoscalar form factors measurements, and all available deeply virtual Compton scattering data, the chiral-odd sector is far less constrained. While awaiting the analysis of measurements on pseudoscalar mesons exclusive electroproduction which are key for the extraction of chiral odd GPDs, we worked out a connection between the chiral-even and chiral-odd reduced helicity amplitudes using Parity transformations. The connection works for a class of models including two-components models. This relation allows us to estimate the size of the various chiral odd contributions and it opens the way for future quantitative fits.Comment: 35 pages, 18 figures, text changes, corrected typos, added fig.

Impact of Conditional Cash Transfers and Remittances on Credit Market Outcomes in Rural Nicaragua

The impact of public and private transfers on credit markets has not been sufficiently studied and understanding any spill over effects caused by these transfers may be useful for policy makers. This paper estimates the impact of Conditional Cash Transfers (CCTs) and remittances received by poor households in rural Nicaragua on their decision to request a loan. We find that, on average, CCTs did not affect the request of credit while remittances increased it, controlling for potential endogeneity. We argue the reduction in income risk provided by remittances changes borrowers’ expected marginal returns to a loan and/or their creditworthiness, as perceived by lenders. The successful enforcement of the use of CCTs on long-term investments seems to have avoided externalities on the use of short-term credit these households have access to and their creditworthiness.International Development, D14, F22, O15,

3D molecular line formation in dwarf carbon-enhanced metal-poor stars

We present a detailed analysis of the carbon and nitrogen abundances of two dwarf carbon-enhanced metal-poor (CEMP) stars: SDSS J1349-0229 and SDSS J0912+0216. We also report the oxygen abundance of SDSS J1349-0229. These stars are metal-poor, with [Fe/H] < -2.5, and were selected from our ongoing survey of extremely metal-poor dwarf candidates from the Sloan Digital SkySurvey (SDSS). The carbon, nitrogen and oxygen abundances rely on molecular lines which form in the outer layers of the stellar atmosphere. It is known that convection in metal-poor stars induces very low temperatures which are not predicted by `classical' 1D stellar atmospheres. To obtain the correct temperature structure, one needs full 3D hydrodynamical models. Using CO5BOLD 3D hydrodynamical model atmospheres and the Linfor3D line formation code, molecular lines of CH, NH, OH and C2 were computed, and 3D carbon, nitrogen and oxygen abundances were determined. The resulting carbon abundances were compared to abundances derived using atomic CI lines in 1D LTE and NLTE. There is not a good agreement between the carbon abundances determined from C2 bands and from the CH band, and molecular lines do not agree with the atomic CI lines. Although this may be partly due to uncertainties in the transition probabilities of the molecular bands it certainly has to do with the temperature structure of the outer layers of the adopted model atmosphere. We explore the influence of the 3D model properties on the molecular abundance determination. In particular, the choice of the number of opacity bins used in the model calculations and its subsequent effects on the temperature structure and molecular line formation is discussed. (Abridged)Comment: Poster presented at IAU JD 10, Rio de Janeiro, 10-11 August 2009, published in Memorie della Societa' Astronomica Italiana, Vol. 80 n.3 P.735. One reference corrected, matches the published versio

Transverse spin in exclusive experiments

We analyze a number of open questions in the application of the concept of generalized parton distribution to various high-energy exclusive processes. In particular we discuss the feasibility of global fits of the exclusive data, and provide a recursive procedure based on a physically motivated parametrization. By fixing the parameters to the Deeply Virtual Compton Scattering data we make predictions for chiral odd quantities, including transversity. All of our predictions include theoretical error

GPDs, their relationships with TMDs and related topics

Generalized Parton Distributions in the chiral odd sector are evaluated by examining their contribution to the quark proton helicity amplitudes, and by using Parity transformations to establish relations with the chiral even sector. The relations we find are valid in a spectator model where the recoiling system has total spin S=0,1. These relations allow us to fix the parameters for the chiral odd generalized parton distributions using results from a global analysis of unpolarized and longitudinally polarized experimental data in the kinematical region of intermediate Bjorken x and for Q2 in the multi-GeV region. Quantitative relations between chiral odd generalized parton distributions and transverse momentum dependent distributions are given, and their extension beyond spectator models is discussed. Contributions to the Generalized Transverse Momentum Distributions are obtained and considered in relation to observables. The related question about recoiling baryon polarizations is discussed

Solar analogs with and without planets: Tc_c trends and galactic evolution

We explore a sample of 148 solar-like stars to search for a possible correlation between the slopes of the abundance trends versus condensation temperature (known as the Tc slope) both with stellar parameters and Galactic orbital parameters in order to understand the nature of the peculiar chemical signatures of these stars and the possible connection with planet formation. We find that the Tc slope correlates at a significant level with the stellar age and the stellar surface gravity. We also find tentative evidence that the Tc slope correlates with the mean galactocentric distance of the stars (Rmean), suggesting that stars that originated in the inner Galaxy have fewer refractory elements relative to the volatile ones. We found that the chemical peculiarities (small refractory-to-volatile ratio) of planet-hosting stars is probably a reflection of their older age and their inner Galaxy origin. We conclude that the stellar age and probably Galactic birth place are key to establish the abundances of some specific elements.Comment: Proceedings of the GREAT-ITN conference: The Milky Way Unravelled by Gaia. Will be published in the "EAS Publications Series