Tesis postgrado Astrofísica

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Examinando Tesis postgrado Astrofísica por Autor "Candlish, Graeme"

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  • Miniatura
    Ítem
    The effect of non-gaussian primordial perturbations on large-scale structure
    (Universidad de Valparaíso, 2021-12) Peña Pinto, Greco; Candlish, Graeme
    The late-time effect of primordial non-Gaussianity offers a window into the physics of inflation and the very early Universe. In this thesis we study the conse- quences of a particular class of primordial non-Gaussianity that is fully characterized by initial density fluctuations drawn from a non-Gaussian probability density func- tion, rather than by construction of a particular form for the primordial bispectrum. We numerically generate multiple realisations of cosmological structure and use the late-time matter power spectrum, bispectrum and trispectrum to determine the ef- fect of these modified initial conditions. We show that the initial non-Gaussianity has only a small imprint on the first three polyspectra, when compared to a stan- dard Gaussian cosmology. Furthermore, some of our models present an interesting scale-dependent deviation from the Gaussian case in the bispectrum and trispectrum, although the signal is at most at the percent level. The majority of our models are consistent with CMB constraints, while the others are only marginally excluded. Finally, we discuss further possible extensions of our study.
  • Miniatura
    Ítem
    A momentum coupling between dark matter and dark energy : consequences at small scales
    (Universidad de Valparaíso, 2021-05) Palma Palma, Daniela; Candlish, Graeme
    Dark energy is frequently modelled as an additional dynamical scalar field component in the Universe, referred to as “quintessence,” which drives the late-time acceleration. Furthermore, the quintessence field may be coupled to dark matter and/or baryons, leading to a fifth force. In this thesis we explore the consequences for non-linear cosmological structure formation arising from a momentum coupling between the quintessence field and dark matter. The coupling leads to a modified Euler equation, which we implement in an N-body cosmological simulation. We then analyse the non- linear power spectrum, comparing with the standard ΛCDM cosmology, as well as the halo mass function, and various other dark matter halo properties. We find that, for certain quintessence potentials, a positive coupling leads to a large enhancement of structure formation at small scales.