Dark matter in dense astrophysical objects

Tesis por compendio de publicaciones[ES] La materia oscura constituye la mayor parte de la materia en el modelo cosmológico aceptado para nuestro Universo. Las condiciones extremas en algunos objetos compactos tales como enanas blancas y estrellas de neutrones hacen de estos objetos muy buenos acretores de materia oscura debido al alto grado de compacidad, M/R, que presentan. Este hecho, unido a una sección eficaz de interacción finita entre la materia oscura y las partículas del modelo estándar, hace de estos objetos estelares sitios idóneos para encontrarla. En este trabajo de tesis doctoral se consideran diferentes modelos de materia oscura actualmente aceptados. En particular, se considera materia oscura fermiónica acretada en estrellas densas. Una vez dentro de estos objetos, dependiendo de la naturaleza de las partículas de materia oscura, éstas podrían proporcionar una fuente de energía que podría afectar a propiedades de las estrellas tales como el transporte de energía, la conductividad térmica, las emisividades o luminosidades de éstas. Además, si bien es cierto que el tema central de este trabajo es el estudio de distintos tipos de interacción de partículas de materia oscura dentro de objetos estelares compactos y analizar las posibles señales indirectas provenientes de ellos, también se ha analizado cómo puede eventualmente afectar el hecho de considerar una teoría general de gravedad modificada en las ecuaciones de estructura estelar. Considerando una aproximación perturbativa en el límite de campos gravitatorios débiles, se analizan los efectos de estas modificaciones de la gravedad en el radio, la masa y la luminosidad de estrellas de tipo solar y enanas blancas

Light dark matter scattering in outer neutron star crusts

We calculate for the first time the phonon excitation rate in the outer crust of a neutron star due to scattering from light dark matter (LDM) particles gravitationally boosted into the star. We consider dark matter particles in the sub-GeV mass range scattering off a periodic array of nuclei through an effective scalar-vector interaction with nucleons. We find that LDM effects cause a modification of the net number of phonons in the lattice as compared to the standard thermal result. In addition, we estimate the contribution of LDM to the ion-ion thermal conductivity in the outer crust and find that it can be significantly enhanced at large densities. Our results imply that for magnetized neutron stars the LDM-enhanced global conductivity in the outer crust will tend to reduce the anisotropic heat conduction between perpendicular and parallel directions to the magnetic field.Comment: 14 pages, 3 figure

Diffusion of dark matter in a hot and dense nuclear environment

We calculate the mean free path in a hot and dense nuclear environment for a fermionic dark matter particle candidate in the $\sim$GeV mass range interacting with nucleons via scalar and vector effective couplings. We focus on the effects of density and temperature in the nuclear medium in order to evaluate the importance of the final state blocking in the scattering process. We discuss qualitatively possible implications for opacities in stellar nuclear scenarios, where dark matter may be gravitationally accreted.Comment: 17 pages, 7 figure

Gamma rays from dark mediators in white dwarfs

[EN]We consider self-annihilation of dark matter, χ, into metastable mediators, Y, and their subsequent decay into photons inside white dwarfs. We focus on reactions of the type χχ→YY, where mediators, besides having a finite decay lifetime at rest τrest1 s, may suffer energy loss in the medium before they decay into photons, Y→γγ. We obtain attenuated gamma-ray luminosities arising from the combination of both effects. Using complementary sets of astrophysical measurements from cold white dwarfs in the M4 globular cluster as well as direct and indirect dark matter searches, we discuss further constraints on dark mediator lifetimes

Constraints from the duration of supernova neutrino burst on resonant light gauge boson production by neutrinos

In this article, we study the resonant production of low-mass vector mediators from neutrino-antineutrino coalescence in the core of proto-neutron stars. Taking into account the radial dependence of the density, energy, and temperature inside the proto-neutron star, we compute the neutrino-antineutrino interaction rate in the star interior in the well-motivated $U(1)_{L_{\mu}-L_{\tau}}$ model. First, we determine the values of the coupling above which neutrino-antineutrino interactions dominate over the Standard Model neutrino-nucleon scattering. We argue that, although in this regime a redistribution of the neutrino energies might take place, making low-energy neutrinos more trapped, this only affects a small part of the neutrino population and it cannot be constrained with the SN 1987A data. Thus, contrary to previous claims, the region of the parameter space where the $U(1)_{L_{\mu}-L_{\tau}}$ model explains the discrepancy in the muon anomalous magnetic moment is not ruled out. We then focus on small gauge couplings, where the decay length of the new gauge boson is larger than the neutrino-nucleon mean free path, but still smaller than the size of proto-neutron star. We show for the first time that in this regime, the resonant production of a long-lived $Z'$ and its subsequent decay into neutrinos can significantly reduce the duration of the neutrino burst, probing values of the coupling below ${\cal O}(10^{-7})$ for mediator masses between 10 and 100~MeV. This rules out new areas of the parameter space of the $U(1)_{L_{\mu}-L_{\tau}}$ model.Comment: 21 pages, 5 figures. Major changes: Confirming previous results but ruling out new ranges of parameter

Producción y comercialización de la piña cultivada en la meseta de los pueblos durante el período 97-98

Tesis (Licenciatura en Administración de Empresas)--Universidad Americana, Managua, 1998Nicaragua cuenta con muchos recursos naturales entre los que se destacan el suelo el clima, los cuales son propios para el cultivo del rubro de las frutas no tradicionales como es el caso de la piña. El documento siguiente muestra un estudio sobre cultivo, organización, distribución de la producción de piña de la variedad “Cayena Lisa”, así como un análisis de los factores que intervienen en la comercialización interna y externa, identificando los problemas que se presentan en ambos procesos y a su vez proponiendo alternativas que permitan mejorar los procesos productivos y comerciales de dicho rubro que se cultiva en la IV región del país

Factors controlling the community structure of picoplankton in contrasting marine environments

The effect of inorganic nutrients on planktonic assemblages has traditionally relied on concentrations rather than estimates of nutrient supply. We combined a novel dataset of hydrographic properties, turbulent mixing, nutrient concentration, and picoplankton community composition with the aims of (i) quantifying the role of temperature, light, and nitrate fluxes as factors controlling the distribution of autotrophic and heterotrophic picoplankton subgroups, as determined by flow cytometry, and (ii) describing the ecological niches of the various components of the picoplankton community. Data were collected at 97 stations in the Atlantic Ocean, including tropical and subtropical open-ocean waters, the northwestern Mediterranean Sea, and the Galician coastal upwelling system of the northwest Iberian Peninsula. A generalized additive model (GAM) approach was used to predict depth-integrated biomass of each picoplankton subgroup based on three niche predictors: sea surface temperature, averaged daily surface irradiance, and the transport of nitrate into the euphotic zone, through both diffusion and advection. In addition, niche overlap among different picoplankton subgroups was computed using nonparametric kernel density functions. Temperature and nitrate supply were more relevant than light in predicting the biomass of most picoplankton subgroups, except for Prochlorococcus and low-nucleic-acid (LNA) prokaryotes, for which irradiance also played a significant role. Nitrate supply was the only factor that allowed the distinction among the ecological niches of all autotrophic and heterotrophic picoplankton subgroups. Prochlorococcus and LNA prokaryotes were more abundant in warmer waters (>20 ∘C) where the nitrate fluxes were low, whereas Synechococcus and high-nucleic-acid (HNA) prokaryotes prevailed mainly in cooler environments characterized by intermediate or high levels of nitrate supply. Finally, the niche of picoeukaryotes was defined by low temperatures and high nitrate supply. These results support the key role of nitrate supply, as it not only promotes the growth of large phytoplankton, but it also controls the structure of marine picoplankton communities.Ministerio de Economía y Competitividad | Ref. CTM2012-30680Ministerio de Economía y Competitividad | Ref. CTM2008-0626I-C03-01Ministerio de Economía y Competitividad | Ref. REN2003-09532-C03-01Ministerio de Economía y Competitividad | Ref. CTM2004-05174 -C02Ministerio de Economía y Competitividad | Ref. CTM2011-25035Xunta de Galicia | Ref. 09MMA027604PRXunta de Galicia | Ref. EM2013/021European Commission | Ref. FP7, n. 261860Ministerio de Economía y Competitividad | Ref. FJCI-641 2015-2571

Nutrient supply does play a role on the structure of marine picophytoplankton communities

Conference communicationThe Margalef´s mandala (1978) is a simplified bottom-up control model that explains how mixing and nutrient concentration determine the composition of marine phytoplankton communities. Due to the difficulties of measuring turbulence in the field, previous attempts to verify this model have applied different proxies for nutrient supply, and very often used interchangeably the terms mixing and stratification. Moreover, because the mandala was conceived before the discovery of smaller phytoplankton groups (picoplankton <2 µm), it describes only the succession of vegetative phases of microplankton. In order to test the applicability of the classical mandala to picoplankton groups, we used a multidisciplinary approach including specifically designed field observations supported by remote sensing, database analyses, and modeling and laboratory chemostat experiments. Simultaneous estimates of nitrate diffusive fluxes, derived from microturbulence observations, and picoplankton abundance collected in more than 200 stations, spanning widely different hydrographic regimes, showed that the contribution of eukaryotes to picoautotrophic biomass increases with nutrient supply, whereas that of picocyanobacteria shows the opposite trend. These findings were supported by laboratory and modeling chemostat experiments that reproduced the competitive dynamics between picoeukaryote sand picocyanobacteria as a function of changing nutrient supply. Our results indicate that nutrient supply controls the distribution of picoplankton functional groups in the ocean, further supporting the model proposed by Margalef.Spanish Governmen

Role of internal waves on mixing, nutrient supply and phytoplankton community structure during spring and neap tides in the upwelling ecosystem of Ría de Vigo (NW Iberian Peninsula)

17 pages, 11 figures, 1 table, supporting information https://dx.doi.org/10.1002/lno.10482Despite evidence of internal waves in the NW Iberian upwelling region, their action and role on nutrient supply dynamics and phytoplankton community structure remain unexplored. A multidisciplinary approach, combining analysis of Synthetic Aperture Radar (SAR) images acquired during the summer months of 2008–2011, together with high-frequency samplings carried out in the Ría de Vigo in August 2013 during spring (CHAOS1) and neap tides (CHAOS2), was used to characterize: (1) the internal wave activity, (2) its influence on mixing and nutrient supply, and (3) its role on phytoplankton community. SAR images revealed that internal waves were more energetic during spring tides. Turbulent mixing was higher during CHAOS1-springs (Kz =1.3 [1.0–2.0, 95% confidence interval] × 10 m s) compared to CHAOS2-neaps (Kz = 0.7 [0.5–1.0] × 10 m s), and as a result nitrate diffusive fluxes were approximately fourfold higher (35 [17–73] mmol m d) during CHAOS1-springs. The sampling covered a transition from relaxation-stratification (CHAOS1-springs) to intensifying upwelling (CHAOS2-neaps) conditions, resulting in nitrate supply (including both diffusive and advective fluxes) being about 50% higher during CHAOS2-neaps. The phytoplankton community, which was overwhelmingly dominated by diatoms in both cruises, exhibited a shift in species composition, with an increase in the abundance of large Chaetoceros spp. during CHAOS2-neaps. About 50% of the primary production in the ecosystem during periods of upwelling relaxation-stratification could be sustained by enhanced nitrate diffusive fluxes during spring tides. Therefore, even in coastal upwelling regions, turbulent mixing driven by internal waves could play an important role in controlling phytoplankton productivity and community structureM. Villamaña acknowledges the receipt of a FPU fellowship (FPU014/05385) from the Spanish Ministry of Education, Culture and Sports. P. Cermeño thanks a Ramón y Cajal contract from Spanish Ministry of Economy and Competitiveness. J.M. Magalhaes is grateful for a Portuguese FCT research grant (SFRH/BPD/84420/2012). Funding for this study was provided by the Spanish Ministry of Economy and Competitiveness under the research project CTM2012-30680 to B. Mouriño-CarballidoPeer Reviewe