Petra Wiederhold

Galactic collapse of scalar field dark matter

We present a scenario for core galaxy formation based on the hypothesis of scalar field dark matter. We interpret galaxy formation through the collapse of as calar field fluctuation. We find that a cosh potential for the self-interaction of the scalar field provides a reasonable scenario for the formation of a galactic core plus a remnant halo, which is in agreement with cosmological observations and phenomenological studies in galaxies. PACS numbers: 0425D, 9530S, 9535, 9862A, 9880 In the last few years, the quest concerning the nature of the dark matter in the universe has received much attention and has become of great importance for understanding the structure formation in the universe. Some candidates for dark matter have been discarded and some others have recently appeared. The standard candidates of the cold dark matter (CDM) model are axions and WIMP’S (weakly interacting massive particles), which are themselves not free of problems. Axions are massive scalar particles with no self interaction. In order for axions to be an essential component of the dark matter content of the universe, their mass should be m ∼ 10 −5 eV. With this axion mass, the scalar field collapses forming compact objects with masses of the order of Mcrit ∼ 0.6 m 2 m ∼ 10 −6 M� [1, 2], which corresponds to objects with the mass of a planet. Since the dark matte rm ass in galaxies is ten times higher than the luminous matter, we would need tenths of millions of such objects around the solar system, which is clearly not the case. On the other hand, there are many viable particles with nice features in super-symmetric theories, such a sW IMP’S, which behave just like standard CDM. However, a central debate nowadays is whether CDM can explain the observed scarcity of dwarf galaxies and the smoothness of the galactic-core matter densities, since high resolution numerical simulations with standard CDM predict an excess of dwarf galaxies and density

Contextual array grammars and array P systems

Contextual array grammars, with selectors not having empty cells, are considered. A P system model, called contextual array P system, that makes use of array objects and contextual array rules, is introduced and its generative power for the description of picture arrays is examined. A main result of the paper is that there is a proper infinite hierarchy with respect to the classes of languages described by contextual array P systems. Such a hierarchy holds as well in the case when the selector is also endowed with the #−sensing ability.

Thinning on quadratic, triangular, and hexagonal cell complexes

This paper deals with a thinning algorithm proposed in 2001 by Kovalevsky, for 2D binary images modelled by cell complexes, or, equivalently, by Alexandroff T0 spaces. We apply the general proposal of Kovalevsky to cell complexes corresponding to the three possible normal tilings of congruent convex polygons in the plane: the quadratic, the triangular, and the hexagonal tilings. For this case, we give a theoretical foundation of Kovalevskys thinning algorithm: We prove that for any cell, local simplicity is sufficient to satisfy simplicity, and that both are equivalent for certain cells. Moreover, we show that the parallel realization of the algorithm preserves topology, in the sense that the numbers of connected components both of the object and of the background, remain the same. The paper presents examples of skeletons obtained from the implementation of the algorithm for each of the three cell complexes under consideration.

A P System Model for Contextual Array Languages

A P system model, called Contextual array P system, that makes use of array objects and contextual array rules, is introduced and its generative power in the description of picture arrays is examined, by comparing it with certain other array generating devices.

CLASS OF EINSTEIN-MAXWELL-DILATON-AXION SPACE-TIMES

We use the harmonic maps ansatz to find exact solutions of the Einstein-Maxwell-dilaton-axion (EMDA) equations. The solutions are harmonic maps invariant to the symplectic real group in four dimensions Spð4;R Þ� Oð5Þ. We find solutions of the EMDA field equations for the one- and twodimensional subspaces of the symplectic group. Specially, for illustration of the method, we find spacetimes that generalize the Schwarzschild solution with dilaton, axion, and electromagnetic fields.

The Alexandroff Dimension of Digital Quotients of Euclidean Spaces

Alexandroff T0 -spaces have been studied as topological models of the supports of digital images and as discrete models of continuous spaces in theoretical physics. Recently, research has been focused on the dimension of such spaces. Here we study the small inductive dimension of the digital space X(W) constructed in [15] as a minimal open quotient of a fenestration W of Rn . There are fenestrations of Rn giving rise to digital spaces of Alexandroff dimension different from n , but we prove that if W is a fenestration, each of whose elements is a bounded convex subset of Rn , then the Alexandroff dimension of the digital space X(W) is equal to n .

Scalar Field Dark Matter and Galaxy Formation

We present a general description of the scalar field dark matter (SFDM) hypothesis in the cosmological context. The scenario of structure formation under such a hypothesis is based on Jeans instabilities of fluctuations of the scalar field. It is shown that it is possible to form stable long lived objects consisting of a wide range of typical galactic masses around 1012 M ⊙ once the parameters of the effective theory are fixed with the cosmological constraints. The energy density at the origin of such an object is smooth as it should.

SU(N)- and SO(N)-invariant chiral fields: One- and two-dimensional subspaces

Applying the harmonic map ansatz we find new classes of SU(N) and SO(N) chiral fields. We write the corresponding one-dimensional subgroups of SU(N) and SO(N) chiral fields in terms of one and two harmonic maps and the corresponding two-dimensional subgroups in terms of SU(2) and SO(3) chiral fields. In other words, we reduce the SU(N) and SO(N) chiral equations to harmonic maps in one- and two-dimensional spaces.

Automatic liver tissue segmentation in microscopic images using fusion color space and multiscale morphological reconstruction

In this paper we propose a new method for the segmentation of digital two-dimensional color liver tissue images acquired by an optical microscope from histological segments of the liver of hamster. The sections are acquired by cutting real livers of amoebic liver abscess. This work is part of a medical research project on studying the process of amoebiasis, which harms the human liver, being an important and dangerous disease. The new method is based on a fusion of various results of application of color histogram and multiscale morphological filter, which uses size and color characteristics. As a result, the images are segmented in four classes: the liver cell nuclei, the cytoplasm, stained cells, and the background. For the evaluation and for testing the reliability of the proposed segmentation algorithm, we use a set of real 2D color images of a hamsters liver provided through routine experimentation by the Experimental Pathology Unit at the National Autonomous University of Mexico.

SL(4, R)-invariant chiral fields

AbstractUsing a method developed before a set of exact solutions of the chiral equations