Contemporary continuum QCD approaches to excited hadrons

Amongst the bound states produced by the strong interaction, radially excited meson and nucleon states offer an important phenomenological window into the long-range behavior of the coupling constant in Quantum Chromodynamics. We here report on some technical details related to the computation of the bound state's eigenvalue spectrum in the framework of Bethe-Salpeter and Faddeev equations.Comment: Proceedings of the 21st International Conference on Few-body Problems in Physics to be published in EPJ Web of Conference

Nucleation in the chiral transition with an inhomogeneous background

We consider an approximation procedure to evaluate the finite-temperature one-loop fermionic density in the presence of a chiral background field which systematically incorporates effects from inhomogeneities in the chiral field through a derivative expansion. Modifications in the effective potential and their consequences for the bubble nucleation process are discussed.Comment: 4 pages, 4 figures. To appear in the proceedings of I Latin American Workshop on High Energy Phenomenology (LAWHEP 2005), Porto Alegre, Brazil, 1-3 Dec 200

Excited hadrons and the analytical structure of bound-state interaction kernels

We highlight Hermiticity issues in bound-state equations whose kernels are subject to a highly asymmetric mass and momentum distribution and whose eigenvalue spectrum becomes complex for radially excited states. We trace back the presence of imaginary components in the eigenvalues and wave functions to truncation artifacts and suggest how they can be eliminated in the case of charmed mesons. The solutions of the gap equation in the complex plane, which play a crucial role in the analytic structure of the Bethe-Salpeter kernel, are discussed for several interaction models and qualitatively and quantitatively compared to analytic continuations by means of complex-conjugate pole models fitted to real solutions.Comment: Proceeding of the ECT* workshop "Nucleon Resonances From Photoproduction to High Photon Virtualities", talk given by B.E.; 8 pages, 2 figures with 6 graph

SMC west halo: a slice of the galaxy that is being tidally stripped? Star clusters trace age and metallicity gradients

(ABRIDGED) The evolution and structure of the Magellanic Clouds is presently under debate. The classical scenario where both the Large and Small Magellanic Clouds (LMC, SMC) are orbiting the Milky Way has been challenged by an alternative where the LMC and SMC are in their first close passage to our Galaxy. Detailed studies of stellar populations in the galaxies should constrain the proposed scenarios. In particular, the west halo of the SMC was recently characterized with radial trends in age and metallicity which indicates tidal disruption. We increase the sample of star clusters in the west halo of the SMC with homogeneous age, metallicity, and distance derivations, to determine better age and metallicity gradients. Comparisons of observed and synthetic V,(B-V) colour-magnitude diagrams are used to derive parameters for west halo star clusters. We derived age and metallicity for the reference cluster NGC 152 compatible with literature parameters. Age and metallicity gradients are confirmed in the west halo: 2.6 +/- 0.6 Gyr/deg and -0.19 +/- 0.09 dex/deg, respectively. Age-metallicity relation for the west halo has low dispersion in metallicity and it is compatible with a burst model of chemical enrichment. All WH clusters seem to follow the same predicted stellar distribution, with exception of AM-3 that should belong to the counter-bridge. Bruck 6 is only 130 +/- 40 Myr old and it could have been formed during a recent tidal interaction of the SMC-LMC. We suggest that it is crucial to split the SMC cluster population in groups: main body, wing/bridge, counter-bridge and west halo. This is the way to analyse the complex star formation and dynamical history of our neighbour. In particular we show that west halo has clear age and metallicity gradients and age-metallicity relation, also compatible with the dynamical model of tidal influence of the LMC over the SMC.Comment: 17 pages, 16 figures, 6 tables, in press in A&

Colour-Magnitude Diagrams of candidate age-gap filling LMC clusters

The LMC has a rich star cluster system spanning a wide range of ages and masses. One striking feature of the LMC cluster system is the existence of an age gap between 3-10 Gyrs. Four LMC clusters whose integrated colours are consistent with those of intermediate age simple stellar populations have been imaged with the Optical Imager (SOI) at the Southern Telescope for Astrophysical Research (SOAR). Their colour-magnitude diagrams (CMDs) reach V ~ 24. Isochrone fits, based on Padova evolutionary models, were carried out to these CMDs, after subtraction of field contamination. The preliminary results are as follows: KMK88-38 has an age of ~ 1.3 Gyr, assuming typical LMC metallicity and distance modulus, and a very low redenning. For OGLE-LMC0531, the best eye fits to isochrones yield an age ~ 1.6 Gyr and E(B-V)=0.03. BSDL917 is younger, ~ 150 yrs, and subjected to larger extinction (E(B-V)=0.08). The remaining cluster is currently under analysis. Therefore, we conclude that these clusers are unlikely to fill in the LMC cluster age gap, even when fitting uncertainties in the parameters are considered.Comment: 4 pages, 5 figures, compact form of the poster published online in the proceedings of IAUS256: The Magellanic System: Stars, Gas, and Galaxie

Mass spectrum and decay constants of radially excited vector mesons

We calculate the masses and weak decay constants of flavorless ground and radially excited $J^P=1^-$ mesons and the corresponding quantities for the K^*, within a Poincar\'e covariant continuum framework based on the Bethe-Salpeter equation. We use in both, the quark's gap equation and the meson bound-state equation, an infrared massive and finite interaction in the leading symmetry-preserving truncation. While our numerical results are in rather good agreement with experimental values where they are available, no single parametrization of the QCD inspired interaction reproduces simultaneously the ground and excited mass spectrum, which confirms earlier work on pseudoscalar mesons. This feature being a consequence of the lowest truncation, we pin down the range and strength of the interaction in both cases to identify common qualitative features that may help to tune future interaction models beyond the rainbow-ladder approximation

Signatures of natural selection in the adaptive immune system of primates

Tese de mestrado, Bioinformática e Biologia Computacional (Biologia Computacional), Universidade de Lisboa, Faculdade de Ciências, 2015O desenvolvimento de uma resposta imunitária adaptativa possibilitou aos vertebrados montar uma defesa mais eficaz em resposta a agentes patogénicos. O sistema imunitário adaptativo tem a capacidade de reconhecer e guardar memória de agentes patogénicos específicos, conferindo ao sistema um poder de resposta mais rápido e eficaz aquando de uma reinfecção. Com o sistema imunitário adaptativo surgem novas células, com o papel central na resposta imunitária. São exemplo dessas células, os linfócitos T e B, que produzem respectivamente os receptores das células T e B. Os receptores dos linfócitos T possuem grande capacidade de rearranjo das suas cadeias (α e β) e surgem de novo nos vertebrados mandibulados e em paralelo com o aparecimento dum novo órgão linfoide primário, o Timo. Este orgão é responsável pela maturação dos linfócitos T e tem a capacidade de eliminar linfócitos T autoreativos (isto é, que reconhecem o próprio).Dada a importância do sistema imunitário adaptativo nos vertebrados, foi objectivo do presente estudo a analise bioinformática de um conjunto de 38 genes intimamente ligados ao desenvolvimento do sistema imunitário adaptativo. Estes, estão compreendidos no “processo de desenvolvimento do timo” e “processo do sistema imunitário”, e foram analisados em busca de assinaturas de seleção positiva, através da aplicação de modelos estatísticos (PAML), que estimam pelo método de máxima verosimilhança, o rácio (ω) de mutações não sinónimas (dN) versus sinónimas (dS ) .No presente estudo, em genes ortólogos, de 11 espécies de primatas (incluindo Homo sapiens), encontraram-se sinais de seleção positiva em 7 genes que, após estudos complementares, foram reduzidos a 4 genes: CD4, IFNG, HOXA3 e PTCRA. O mapeamento dos aminoácidos selecionados positivamente, por inferência Bayesiana, nas suas estruturas terciárias ou quaternárias, revelou que os aminoácidos selecionados positivamente se encontravam predominantemente na região de superfície, da respectiva proteína. Isto leva à formulação da hipótese, de que a superfície da proteína poderá estar sujeita a menores pressões seletivas purificantes do que o seu interior. Neste cenário, uma mutação terá menor impacto na conformação tridimensional, aquando do enrolamento da estrutura primária. A ferramenta bioinformática SIFT, revelou que os aminoácidos selecionados positivamente surgem predominantemente em zonas putativamente menos conservadas. Os resultados do presente estudo, sugerem que os genomas tidos como completos apresentam ainda zonas com baixa qualidade, ou baixa cobertura, que irão beneficiar grandemente da integração de reads produzidas pelos sequenciadores de 4ª geração, como a tecnologia Nanopore.The emergence of an adaptive immune response has enabled vertebrates to respond more effectively to pathogenic infection. The adaptive immune system has the ability to recognize and memorize specific pathogens, allowing stronger responses each time the pathogen is encountered. In the adaptive immune system, T and B-lymphoid cells are central players, producing T-cell and B-cell receptors, respectively. The T-lymphoid cells arise a second time in vertebrates in the jawed lineage. These cells display a more random recombination process of the α and β chains of their receptors, which is followed by coevolution of a primary lymphoid organ (thymus), essential for the development T-lymphoid cells, allowing the elimination of self-reacting cells. Given the importance of the adaptive immune system in vertebrates, the present study aimed to analyze, from a bioinformatics perspective, a set of 38 genes annotated to “thymic development process” and “immune system process” GO terms. These genes were studied in order to find signatures of positive selection. To accomplish this, a statistical model (PAML) was applied to estimate the ratio (ω) of nonsynonymous (dN) versus synonymous substitutions (dS), through maximum likelihood. In the present study, in a set of orthologous genes, of 11 primate species (including Homo sapiens), signals of positive selection were found in 4 genes: CD4, IFNG, HOXA3 and PTCRA. The amino acids identified with positive selection, through Bayesian inference, were mapped to their tertiary and quaternary structures, revealing that these were predominantly located on the protein surface. This leads to the formulation of the hypothesis that the protein surface is under lower purifying selective pressure than its core, with the consequent reduction of impact on the protein folding. The positively selected amino acids were mainly in regions putatively non-damaging or less conserved as predicted by the SIFT tool. This study brings to light problems in the so called complete genomes, that still bear regions of low quality, or low coverage, which will greatly benefit from fourth generation sequencing technology, like Nanopore