On the interpretation of dark matter self-interactions in Abell 3827

Self-interactions of dark matter particles can potentially lead to an observable separation between the dark matter halo and the stars of a galaxy moving through a region of large dark matter density. Such a separation has recently been observed in a galaxy falling into the core of the galaxy cluster Abell 3827. We estimated the DM self-interaction cross section needed to reproduce the observed effects and find that the sensitivity of Abell 3827 has been significantly overestimated in a previous study. Our corrected estimate is $\tilde{\sigma}/m_\text{DM} \sim 3\:\text{cm}^2\:\text{g}^{-1}$ when self-interactions result in an effective drag force and $\sigma/m_\text{DM} \sim 1.5\:\text{cm}^2\:\text{g}^{-1}$ for the case of contact interactions, in some tension with previous upper bounds.Comment: 5 pages, 3 figures; v2: matches published versio

Simulations of core formation for frequent dark matter self-interactions

We present the first $N$-body simulations that adapt the equations of smoothed particle hydrodynamics to capture the effect of dark matter self-interactions which are too frequent to be resolved explicitly. The relevant energy transfer equations are derived, the appropriate thermal conductivity is determined and the effects of different smoothing kernels are studied. We apply our framework to simulate the formation of isothermal cores in isolated dark matter haloes and determine the core growth rate as a function of the self-scattering cross section. Our approach may be combined with explicit simulations of rare scatterings in order to simulate accurately the effects of arbitrary dark matter self-interactions in future cosmological simulations.Comment: 11 pages, 6 figures; v2: matches version published in MNRA

La NTE como agente de cambio ante problemas que agobian a la sociedad civil: un estudio de caso en la comunidad de Petaquillas, Guerrero, México

Ante la realidad agobiante que padece actualmente la gran mayoría de las naciones, como es el caso de México, donde se manifiesta una crisis socioeconómica desde diversas aristas, de manera oportuna y contestataria aparece la Nueva Teoría Estratégica (NTE) como respuesta a un reclamo multitudinario que aboga por encontrar soluciones ante la inoperancia de métodos empleados en circunstancias pasadas que hoy dejan de ser efectivos frente a una complejidad social sin precedentes. Desde esta visión enfocamos el presente trabajo a través de un estudio de caso en una comunidad mexicana, Petaquillas, ubicada en la periferia de Chilpancingo, capital del estado de Guerrero, donde sus habitantes acosados por el sistema de inseguridad prevaleciente, determinado por la presencia en su territorio de bandas del narcotráfico y ante el hartazgo por la respuesta ausente de las instancias gubernamentales y las fuerzas del orden establecidas, deciden organizarse como sociedad civil para encontrar solución a los graves problemas que les acechan y niegan el derecho a lograr una convivencia social en circunstancias seguras y en paz. El diseño de esta investigación se plantea desde el paradigma cualitativo basado en el enfoque de la Nueva Teoría Estratégica con rasgos de la Teoría Fundamentada desde donde se deriva un método apropiado a aplicar en una situación compleja en la que los actores sociales de una comunidad se integran en la búsqueda de estrategias novedosas, acordes al problema situacional complejo imperante. En este proceso, como lo establece la NTE, la comunicación asume un rol fundamental como recurso constituyente de la propia estrategia que permite el empleo de tácticas viables para, mediante la integración relacional mancomunada y consciente de los actores involucrados, resolver el problema socialmente afectivo

Radio Galaxy Classification with wGAN-Supported Augmentation

Novel techniques are indispensable to process the flood of data from the new generation of radio telescopes. In particular, the classification of astronomical sources in images is challenging. Morphological classification of radio galaxies could be automated with deep learning models that require large sets of labelled training data. Here, we demonstrate the use of generative models, specifically Wasserstein GANs (wGAN), to generate artificial data for different classes of radio galaxies. Subsequently, we augment the training data with images from our wGAN. We find that a simple fully-connected neural network for classification can be improved significantly by including generated images into the training set.Comment: 10 pages, 6 figures; accepted to ml.astro; v2: matches published versio

Evidence for dark matter self-interactions in Abell 3827?

Self-interactions of dark matter (DM) particles can potentially lead to an observable separation between the DM halo and the stars of a galaxy moving through a region of large DM density. Such a separation has recently been observed in a galaxy falling into the core of the galaxy cluster Abell 3827. We estimated the DM self-interaction cross-section needed to reproduce the observed effects and find that the sensitivity of Abell 3827 has been significantly overestimated in a previous study. Our corrected estimate is σ̃ /m_DM∼3cm^2 g^−1 when self-interactions result in an effective drag force and σ/m_DM ∼ 1.5 cm^2 g^−1 for the case of contact interactions, in some tension with previous upper bounds

Astrophysical Implications of Self-interacting Dark Matter

In this thesis we study the astrophysical implication of self-interacting dark matter. Observations on different scales suggest the existence of an additional form of matter which interacts gravitationally. This dark matter is assumed to be cold and collisionless in the standard model of cosmology. Discrepancies between observations and predictions of the $\Lambda$CDM model on cosmologically small scales motivate us to think beyond the assumptions of the model.Relaxing the assumption on the collisionality of dark matter leads to the idea of self-interacting dark matter, which may be able to resolve the small-scale issues. Studying astrophysical observables is a very promising avenue to understand the nature and the interactions of dark matter. Some signatures have the potential to test the standard cold and collisionless dark matter paradigm and could rule out many popular dark matter candidates. Self-interacting dark matter has striking consequences for colliding dark matter haloes such as an observable offset between the luminous and dark matter of an infalling halo. We demonstrate how a detection of such an offset leads to direct constraints on the self-interaction cross section. We distinguish between rare and frequent self-interactions and observe that it may be possible to gain knowledge about the fundamentals of the interaction from observations of merging systems. We also discuss a limitation of simulations of merging galaxy clusters with dark matter self-interactions, namely that commonly the galaxies are treated as collisionless test particles. However, the fact that galaxies reside in dark matter haloes makes the galaxies themselves collisional if dark matter self-interactions are implemented. We demonstrate how this effect diminishes observable offsets. Finally, we present the first implementation of frequent self-interactions in $N$-body simulations. Using smoothed particle hydrodynamics we find an effective description of energy transfer for the case that the interactions are too frequent to be resolved explicitly. Simulations of an isolated dark matter halo of a dwarf galaxy show that we are able to reproduce dark matter density profiles with an isothermal core

The Cosmological Constant in Theories with Finite Spacetime

We study the role of the cosmological constant in different theories with finite space- time. The cosmological constant appears both as an initial condition and as a constant of integration. In the context of the cosmological constant problem a new model will be presented. This modification of general relativity generates a small, non-vanishing cosmological constant, which is radiatively stable. The dynamics of the expansion of the universe in this model will be analyzed. Eventually, we try to solve the emergent problems concerning the generation of accelerated expansion using a quintessence model of dark energy