Understanding the cause of the accelerated expansion of the Universe is one of the most pressing issues in modern cosmology. An alternative to the LambdaCDM-model is bimetric gravity which is an extension of Einstein's theory of general relativity. In bimetric gravity there exists both a massive and massless graviton which gives rise to different phenomenology in a number of sectors. The LIGO observations of gravitational waves from binary mergers between black holes or neutron stars has opened up a new sector to test this theory in. We study the effects of the massive mode on the observed gravitational waveform. We place constraints on Fierz-Pauli mass, and the mixing angle between the massless and massive mode by using: (i) the observed LIGO waveform for GW150916 compared with the bimetric waveform which includes gravitational wave oscillations, (ii) absence of gravitational echoes, (iii) constraints on the luminosity distance, and (iv) constraints on the propagation speed of gravity. We note that the effects of dispersion on the massive wave packet which we detect as the echo can distort the waveform noticeably, hence it is possible that LIGO cannot detect it. Further investigation in this area is necessary. Lastly we investigate the stability of tensor perturbations in the early universe and the de Sitter point on sub- and superhorizon scales. The perturbations are found to be stable in all of these cases for all parameter values of the theory.

Inflation, the currently favoured solution to the grievous initial conditions problems of the Big Bang model of the universe, is a very general framework that can be constructed from any number of underlying theories. As inflation is meant to solve a problem of initial conditions, it is generally preferred that it not introduce its own initial conditions problem. The purpose of this thesis is to explore the sensitivity to initial conditions of solutions to two toy models of inflation. The models in and of themselves are not intended to explain inflation, but rather seek to begin to explore, in a controlled way, interesting properties that a full inflationary theory might have. The first model is one with a single scalar inflaton, but two compact extra dimensions. We find this model has two inflationary solutions that can be well understood analytically. These solutions are power laws in time. One is found to be marginally insensitive to its initial conditions, and the other is found to be highly sensitive to its initial conditions. We also find a solution to this model that exhibits 4D quasi-de Sitter space, but is difficult to understand analytically, and its sensitivity to initial conditions is not yet well known. The second model examines an n-scalar field Lagrangian that includes kinetic terms first-order in the derivatives of the fields (similar to certain ferromagnetic Lagrangians). It is found that this model can realize slow-roll inflation with arbitrarily steep potentials. A solution is constructed that can realize an exact de Sitter equation of state without saying anything about the slope of its potential. This solution is found to be marginally insensitive to its initial conditions for a certain range of parameters. Corrections from higher order terms in the Lagrangian are found to introduce a parameter space for which this solution is in fact highly insensitive to its initial conditions. We therefore make progress in understanding higher-dimensional inflation, slow-roll inflation with steep potentials, and the sensitivity of solutions in both those cases to their initial conditions. / Thesis / Master of Science (MSc)

This thesis examines Erasmus Darwin's poem The Loves of the Plants (1789) for its boundary crossing expression of ecological theory that takes into consideration the influence of religious cosmology on our understanding of the natural world. Darwin (1731-1802) was the grandfather of naturalist Charles Darwin, whose theories we recognize now as the foundation of an entire field of biological study. But Darwin harboured his own beliefs of evolutionary theory long before his grandson was born, those which asserted a relatedness of all forms of life and pressed against the conceptions of existence that were so deeply rooted in the Euro-Western mind. I intend to demonstrate here the originality and complexity of Darwin's work as an exploration of cosmology, wherein the animation of his vegetal world invites readers to consider both the continuities between states of organic existence and the categories which were established in an attempt to keep them apart. By investigating the origins of these conceptions, from biblical creation to the Aristotelean tradition into the time in which Darwin wrote, I explore the ways in which these ideologies pertaining to the natural order of being have come to be and continue to be. Based on his interpretation of Carl Linnaeus' system of taxonomic classification, a system which remains in use to this day, Darwin's Loves manipulates a structure shaped by European religious and ideological assumptions to unravel the binding understanding of a separate and distant nature, one that has been implemented to discourage ways of perceiving otherwise. Because of its incorporation of Linnaean thought, this early work of Darwin's is often disregarded by scholars in conversations of innovative natural philosophy. Yet, in employing a historicist rhetorical and cultural analysis, this thesis examines Darwin's botanical poem inclusively, engaging with his decentering of the Christian understanding of the hierarchy of species that has been maintained for centuries, to illustrate that in composing a realm of personified flora he is melding the believed to be distinct worlds of the human and nonhuman to unite our species with an all-encompassing naturalism. Though this research is culturally specific, its sentiment may be carried forward to acknowledge the ideological histories and inheritances that influence our conceptions of other biological beings and our understandings of our own species as well. / Thesis / Master of Arts (MA) / This project focuses on a reading of Erasmus Darwin's The Loves of the Plants (1789) that emphasizes its purpose as an exploration of cosmology and the influence of ideological histories. Taking inspiration from the metaphors of Carl Linnaeus' system of plant classification, Darwin is able to introduce his readers to the world of botany, all the while pointing to the implications of following approaches to understanding the natural world that rely on religious conceptions. Looking specifically at Darwin's manipulation of the origins of Euro-Western ideas pertaining to our planetary natural order, those which stem from the creation myths of Genesis and were passed on through antiquity into the Age of Reason, I intend for this thesis to demonstrate how Darwin's reimagining of nonhuman beings serves to illustrate the ways in which our cosmologies, even those we believe to be removed from, are able to affect our understandings of the worlds around us and all the beings within them.

No description available.

The data reduction software of CRIRES+, a new high-resolution spectrometer installed at VLT, features a calibration routine that uses data from a Fabry-Pérot étalon. The quality of this calibration mode is assessed in this project report. Two investigations are carried out: From a diagnostics data set, the physical spacing between the three detector chips is reconstructed, as well as the étalon gap size as a function of Fabry-Pérot order. Both provide a measure of internal coherence of the calibration solution. The reconstructed detector spacing values are irreconcilable with the actual measured values, hinting at a fault in the calibration routine. The reconstructed gap curve shows unphysical discontinuities. Further investigation shows that each detector chip’s calibration solution seems to be consistent across it, while the three chips’ solutions are inconsistent with each other at several hundred meters per second. Due to ESO’s top-level requirements, this does not pose a technical fault. Yet, it still indicates significant room for improvement of the calibration routine.

Coronal mass ejections (CMEs) are considered the most energetic phenomenon in the heliosphere. Originated in the solar corona, they are formed by ejected plasma driven by strong magnetic fields. Studying the effects of CMEs on Earth and the interplanetary medium has become priority, since ground- and space-based technology can be affected by strong CMEs. Modeling of CMEs can provide an estimation of the arrival time, and WSA-ENLIL + Cone model is one of the most used models in space weather forecasting around the world. The WSA-ENLIL + Cone model is based on the characterization of the observed coronagraph image of a CME as a projected cone in the plane-of-sky (POS), the use of a synoptic magnetogram and the magnetohydrodynamical approximation to model CME events. In this project, we will study a particular event occurred on the 2021-11-03 and compare it with simulated data using the WSA-ENLIL + Cone model. The main objective is to study the input parameters of the model and assess the forecasting ability of the simulations. To do so, we have used in-situ data obtained from the Solar Orbiter spacecraft (SolO) and WIND spacecraft, that at the time of the event were located over the same line-of-sight, being located at 0.8 AU and the L1 Lagrange point, respectively. A total of 144 runs (divided in 6 ensembles of 24 simulated runs) were provided by the Met Office (UK) for each spacecraft location. Each simulation run has been generated using preset input parameters with small random variations and a different background synoptic magnetogram. Statistical analysis has been carried out, showing a linear relationship between the half-width and the arrival velocity of the CME. No particular relationship has been found between the input parameters and the time of arrival (ToA) of simulated runs, probably due to the small range of variation. Late initialized synoptic maps seems to produce better ToA prediction.

The renowned Omega Centauri (NGC 5139) is one of the most massive and complex known globular clusters in terms of multiple populations. In this project, we aim to investigate the chemical abundance of lithium in RBG stars in this cluster in pursuit of unraveling the that govern the formation of these distinct populations. By analyzing spectroscopic and photometric data, we determine the necessary stellar parameters and produce an algorithm that yields the Li abundance for each star, as well as its errors and an upper limit for the content of this element. This is followed by a comparison with the results obtained in Mucciarelli et al.(2018). Finally, we investigate how Li behaves within the different stellar populations of Omega Centauri using data from Milone et al. (2017a).

No description available.

This licentiate thesis gives an overview of modified gravity and primordial magnetic fields,bridged by gravitational waves (GWs) as a phenomenological probe of both sectors. First we derive the GW equation in a homogeneous and isotropic background from general relativity.This is followed by a brief review of modified gravity -- its motivations and some common approaches.Within the vast theory space of modified gravity, however, only a handful of parameters enter at the level of the GW equation, in a relatively model-independent manner. We then discuss a range of possible mechanisms giving rise to GWs in the early universe -- from inflation to the early radiation era -- and note, in particular, that magnetically-driven turbulence could be present regardless of the orders of the phase transitions.Therefore, the anisotropic stress due to primordial magnetic fields could be an ubiquitous category of production mechanisms for GWs,whose present-day relic spectrum could then be used to constrain the parameters of modified gravity, in addition to inferring the nature of the primordial magnetic sources themselves.

No description available.