Type II and heterotic one loop string effective actions in four dimensions

We analyze the reduction to four dimensions of the R^4 terms which are part of the ten-dimensional string effective actions, both at tree level and one loop. We show that there are two independent combinations of R^4 present, at one loop, in the type IIA four dimensional effective action, which means they both have their origin in M-theory. The d=4 heterotic effective action also has such terms. This contradicts the common belief thathere is only one R^4 term in four-dimensional supergravity theories, given by the square of the Bel-Robinson tensor. In pure N=1 supergravity this new R^4 combination cannot be directly supersymmetrized, but we show that, when coupled to a scalar chiral multiplet (violating the U(1) $R$-symmetry), it emerges in the action after elimination of the auxiliary fields.Comment: v2: 22 pages. Discussion on the new R^4 term and extended supergravity has been abridged and improved. Published versio

Uma solução flexível para a etapa de pré-processamento em mineração de textos.

A mineração de textos é uma área de PD&I cujo objetivo é a busca por padrões, tendências e regularidades em documentos textuais. O primeiro e mais importante passo do processo de mineração de textos compreende um conjunto de procedimentos para leitura da coleção de documentos, identificação e a seleção dos atributos estatisticamente mais significantes para representar a coleção por meio de uma matriz atributo-valor. O objetivo deste trabalho é apresentar uma solução flexível e expansível para a tarefa de pré-processamento em mineração de textos, capaz de atender às necessidades de diferentes projetos de pesquisa envolvendo esta temática.CIIC 2012. No 12611

Delocalization in harmonic chains with long-range correlated random masses

We study the nature of collective excitations in harmonic chains with masses exhibiting long-range correlated disorder with power spectrum proportional to $1/k^{\alpha}$, where $k$ is the wave-vector of the modulations on the random masses landscape. Using a transfer matrix method and exact diagonalization, we compute the localization length and participation ratio of eigenmodes within the band of allowed energies. We find extended vibrational modes in the low-energy region for $\alpha > 1$. In order to study the time evolution of an initially localized energy input, we calculate the second moment $M_2(t)$ of the energy spatial distribution. We show that $M_2(t)$, besides being dependent of the specific initial excitation and exhibiting an anomalous diffusion for weakly correlated disorder, assumes a ballistic spread in the regime $\alpha>1$ due to the presence of extended vibrational modes.Comment: 6 pages, 9 figure

Mobility Edge in Aperiodic Kronig-Penney Potentials with Correlated Disorder: Perturbative Approach

It is shown that a non-periodic Kronig-Penney model exhibits mobility edges if the positions of the scatterers are correlated at long distances. An analytical expression for the energy-dependent localization length is derived for weak disorder in terms of the real-space correlators defining the structural disorder in these systems. We also present an algorithm to construct a non-periodic but correlated sequence exhibiting desired mobility edges. This result could be used to construct window filters in electronic, acoustic, or photonic non-periodic structures.Comment: RevTex, 4 pages including 2 Postscript figure

Geopolitical determinants of mental health and global health inequities

Geopolitical determinants of health have been well recognized by the World Health Organization and are increasingly being discussed across governments, institutions, academics, policy makers, and across global health sector. Geopolitical determinants of health are events, structures, processes, and factors that influence individual health including mental health, public and population mental health both directly and indirectly. Consequently, nation’s responses to these factors will affect short-term and long-term health outcomes. Geopolitical factors are becoming increasingly more important as they influence directly and indirectly social determinants of health. These factors clearly impact both physical and mental health leading to health inequities and inequalities. It is important to factor in geopolitical determinants in resource allocation and funding as well as policy making as has been highlighted by the recent pandemic and variable access to vaccines. Geopolitical determinants would be integral when addressing all global health inequities. These play a major role in resource allocation, policy and planning to meet today’s global health challenges

Magnon delocalization in ferromagnetic chains with long-range correlated disorder

We study one-magnon excitations in a random ferromagnetic Heisenberg chain with long-range correlations in the coupling constant distribution. By employing an exact diagonalization procedure, we compute the localization length of all one-magnon states within the band of allowed energies $E$. The random distribution of coupling constants was assumed to have a power spectrum decaying as $S(k)\propto 1/k^{\alpha}$. We found that for $\alpha < 1$, one-magnon excitations remain exponentially localized with the localization length $\xi$ diverging as 1/E. For $\alpha = 1$ a faster divergence of $\xi$ is obtained. For any $\alpha > 1$, a phase of delocalized magnons emerges at the bottom of the band. We characterize the scaling behavior of the localization length on all regimes and relate it with the scaling properties of the long-range correlated exchange coupling distribution.Comment: 7 Pages, 5 figures, to appear in Phys. Rev.