Radiative decays and the nature of heavy quarkonia

We argue that the photon spectra in radiative decays of various heavy quarkonium states provide important information on their nature. If two of these states are in the strong coupling regime, we are able to produce a parameter-free model independent formula, which holds at next-to-leading order and includes both direct and fragmentation contributions. When the formula is checked against recent CLEO data it favors Upsilon (2S) and Upsilon (3S) in the strong coupling regime and disfavors Upsilon (1S) in it.Comment: 5 pages, 3 figures. Clarifications introduced, including extra curve in plots. Journal versio

Semi-inclusive radiative decays of Upsilon 1S

We discuss in detail the photon spectrum of radiative Upsilon 1S decays taking into account a number of results that have recently appeared in the literature. In particular, we show how to consistently combine expressions which are valid in the upper end-point region, where NRQCD factorization breaks down, with those of the central region, where NRQCD factorization holds. An excellent description of data is achieved, but theoretical errors are large.Comment: 18 pages, 7 figures. Minor modifications. References added and corrected. Journal versio

María Zambrano y Pablo Neruda: la creación poética ante la Guerra Civil Española

This article proposes a philosophical reading of a militant power of the creation of poetry, based on works by María Zambrano and Pablo Neruda in the face of the Spanish Civil War. This analysis is presented in three sections: the first reviews the poet’s development towards a militant writing based on his biography; the second presents the political-poetic relationship between Zambrano and Neruda, based on their involvement in the Alliance of Anti-Fascist Intellectuals for the Defense of Culture; and the third analyzes the production of the philosophy that refers to Neruda and his work based on these aesthetic-political bonds, which allows to describe the political power (potentiae) of the poetic creation.Este artículo propone una lectura filosófica de la potencia militante de la creación poética, a partir de la interpretación que realiza María Zambrano de la obra de Pablo Neruda ante la Guerra Civil española. Este análisis de la obra de María Zambrano se aborda en tres apartados, en el primer se revisa desde su biografía el devenir del poeta hacia una escritura militante. En un segundo apartado se expone la relación político-poética entre Zambrano y Neruda, desde su participación en la “Alianza de intelectuales antifascistas por la defensa de la cultura”. Y en el tercero, se presenta la producción de la filósofa, que remite a Neruda y su obra, para describir la potencia (potentiae) política de la creación poética

The QCD static energy at NNNLL

We compute the static energy of QCD at short distances at next-to-next-to-next-to leading-logarithmic accuracy in terms of the three-loop singlet potential. By comparing our results with lattice data we extract the value of the unknown piece of the three-loop singlet potential.Comment: 25 pages, 16 figures. v2: Incorrect files for figure 7 replaced by the correct ones. One reference adde

Extraction of alpha_s from radiative Upsilon(1S) decays

We improve on a recent determination of alpha_s from Gamma(Upsilon(1S)-->X gamma)/Gamma(Upsilon(1S)-->X) with CLEO data by taking into account color octet contributions and avoiding any model dependence in the extraction. We obtain alpha_s(M_Upsilon(1S))= 0.184+0.015-0.014, which corresponds to alpha_s(M_Z)=0.119+0.006-0.005.Comment: 11 pages. v2: One reference added. v3: Minor modification in an error estimate. Journal versio

CAUSES OF LOW LEAF-SHREDDING INSECT DIVERSITY IN NEOTROPICAL STREAMS

Biological diversity peaks in tropical regions followed by a steady decline towards the poles. It is a pattern in γ-diversity that sometimes explains latitudinal patterns in local assemblages (α) and their species turnover (β), which suggests that similar ecological mechanisms might be operating at different latitudes. However, not all taxa have more species towards the equator. Aquatic shredder insect richness peaks in temperate streams relative to tropical streams, where local aquatic shredder insect assemblages have low α-diversity. Three mechanisms have been proposed as factors structuring aquatic shredder insect assemblages in tropical streams, leading to shredder assemblages with low α-diversity, 1) low dispersal capabilities, 2) environmental filtering, and 3) availability of low-quality leaf litter in tropical zones. Although several studies have described the pattern of low shredder α-diversity in tropical streams, few of them have tested the underlying mechanisms. Therefore, our understanding of the processes that generate local species-poor assemblages of shredders is incomplete, especially in Neotropical streams. In my dissertation, I tested how much environmental filtering and dispersal capabilities drove aquatic shredder assemblages along an elevation gradient in northern Central America. I tested how low-quality leaf litter influenced growth rates of a species in the genus Phylloicus, a pantropical aquatic shredder insect, with a field experiment of feeding manipulation to test. In Chapter 2, I show that distance decay relationships (DDR) between species assemblage similarity and spatial distance indicated lower dispersal capacity for shredder than non-shredder insects across the study river network. Shredder DDR decayed 1.6 times faster with Euclidean distance between pair of sites than with in-network distance between pair of sites, which suggests that overland dispersal may control variation among shredder assemblages. In Chapter 3, I show that phylogenetic diversity did not vary with increasing elevation for both, shredder and non-shredder insect assemblages. Phylogenetic divergence decreased with elevation for non-shredder insects while for shredder insects there was no change with increasing elevation, which suggest that the strength of environmental filtering was not changing with increasing elevation for shredder assemblages. Low elevation shredder assemblages had larger trait clustering and phylogenetic dispersion than high elevation shredder assemblages. Shredder assemblages had randomly dispersed phylogenetic and trait composition at all elevations. These findings suggest that ecological drift and competitive interactions may drive the observed phylogenetic patterns. In Chapter 4, I show that Phylloicus larvae had a potential N-P limitation when fed with leaf litter, both with high- and low-quality leaf litter. Instantaneous growth rate decreased with an increasing initial size of larvae, with a stronger decline in growth when larvae were fed with low-quality leaf litter in a warm stream. Given the high C:P and N:P among Neotropical plant species relative to invertebrates, it may be that the N-P limitation of shredders is common in Neotropical streams and support the hypothesis that leaf litter quality drives the low diversity of shredders in tropical streams. The results of my dissertation research supported the hypotheses of low dispersal capabilities and low-quality leaf litter as drivers of shredder insect assemblages but did not support the hypothesis of environmental filtering as a driver of the assemblage structure