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The cold dark matter (CDM) paradigm underlying the standard <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5CLambda" />CDM model of cosmology is successful on large scales but faces potential problems on small scales partly related to a seeming overproduction of dwarf galaxies. This could be alleviated in exotic dark matter models that suppresses small-scale structure formation. One such attractive model is known as fuzzy dark matter (FDM). FDM positsthat dark matter is composed of ultra-light bosons with masses <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?m_%7B%5Crm%20FDM%7D%20%5Csim%2010%5E%7B-22%7D" /> eV. With such light particle masses, quantum effects become important. More specifically, a pressure-like term appears in the equations of motion that counteracts gravitational collapse on small scales. Because small galaxies form first in CDM, it follows that the early history ot galaxy formation predicted by FDM should be markedly different. One novel way to probe this effect would be to use the 21 cm line of hydrogen which acts as a sensitive probe of the epoch of reionization (EoR) and Cosmic Dawn — when the first galactic sources of X-rays started to reheat theintergalactic medium (IGM). In this thesis, the evolution of the 21 cm signal have been simulated for both CDM and FDM. These simulations indicate that the fluctuationsin the 21 cm signal amenable to future observations are extremely weak (<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Cll" /> 1 mK) — and probably unobservable — for FDM at high redshifts <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?z%20%5Csim%2015-16" /> compared to CDM (which tend to yield signals with amplitudes <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Cgg" /> 1 mK). This is mainly due to the delayed galaxy formation in FDM resulting in delayed Lyman-<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Calpha" /> coupling of the 21 cm spin temperature to the kinetic temperature of the IGM. A robust prediction from all FDM scenarios explored in this thesis is that any detection of a signal at <img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?z%20%5Csim%2015-16" /> would rule out interesting particle masses for FDM, and would be evidence for CDM-like structure formation. Future work that properly models ionization fluctuations during the EoR could also yield strong predictions at lower redshifts.

One method that can be used to identify the dynamic origin and specific parent bodies of Earth crossing meteoroids is the determination of the meteoroids’ orbital evolution. In this study, a Python-based program using the REBOUND software integration package to integrate meteoroid orbits backwards in time is developed. The program uses data from meteor observations made by the Swedish Allsky Meteor Network, and traces the distance and relative velocity between the meteoroid orbit and the orbits of selected parent body candidates backwards in time. The measure of these orbital differences is known as dissimilarity. The model is used to successfully reproduce the evolution of the Southworth-Hawkins dissimilarity criterion of the Annama meteorite and plausible parent body candidate 2014 UR116 presented by Trigo-Rodríguez et al (2015), as well as to determine plausible parent body associations of several meteors observed by the Swedish Allsky Meteor Network. Plausible parent bodies are presented in two new meteor cases, one of which confirms the parent body of the Geminid meteor shower. The model is concluded to be sufficiently accurate to motivate further use for meteoroid orbit integration purposes, and suggestions for future improvements are made. A new plausible parent body candidate for the Annama H5 meteorite is identified; the asteroid 2017 UZ44. In the case of one meteor event previously identified as a Perseid, the verification of the parent body is not successful using the developed model. In this case, no parent body candidate is found. Possible reasons for this are discussed. Moreover, the observational accuracy is found to be crucial if the program is to be used to study the meteor events observed by the network in detail, as the orbit has to be very well-constrained. / En metod som kan användas för att identifiera moderkroppar till meteoroider som äntrar jordens atmosfär är analys av meteoroidbanornas utveckling över tid. I denna studie har ett Python-baserat program som använder det numeriska integrationspaketet REBOUND för att följa meteoroidbanors utveckling över tid tagits fram. Programmet använder data från meteorobservationer som genomförts av det svenska meteornätverket Swedish Allsky Meteor Network och följer meteoroidbanors banutveckling i jämförelse med potentiella moderkroppars banutveckling över tid. För jämförelsen används Southworth-Hawkins-kriteriet. Modellen används för att framgångsrikt reproducera resultat presenterade av Trigo-Rodríguez et al (2015) genom att följa Annama-meteoritens banutveckling jämfört med banutvecklingen hos den möjliga moderkropp som presenteras i studien, asteroiden 2014 UR116. Modellen används också för att hitta möjliga moderkroppar för flertalet meteorer som observerats av det svenska meteornätverket. Möjliga moderkroppar presenteras i två fall, varav ett bekräftar moderkroppen för meteorregnet Geminiderna. Modellen verkar vara tillräckligt bra för att motivera användning vid integration av meteoroidbanor i syfte att identifiera moderkroppar genom att jämföra banornas utveckling över tid. En ny möjlig moderkropp presenteras för Annama-meteoriten; asteroiden 2017 UZ44. I ett fall har en meteor som observerats av det svenska meteornätverket tidigare klassificerats som en Perseid, men beräkningar genomförda med modellen framtagen i denna studie kan inte bekräfta resultatet. I detta fall återfinns ingen möjlig moderkropp för den specifika meteoren. Möjliga anledningar till detta diskuteras. Slutligen dras slutsatsen att mätosäkerheten i meteorobservationerna är vital för att meteoroidens bana ska vara tillräckligt välbestämd för att användas i syfte att analysera meteoroidbanornas utveckling över tid och hitta möjliga moderkroppar.

The Gaia space telescope is dedicated to monitor the sky, collect data and create the most precise 3D map consisting of more than 1.7 billion objects in the Milky Way. At the same time, the Radial Velocity Spectrometer (RVS) will collect spectra for ~150 million stars in the wavelength range 847 to 874 nm. This wave range is selected because it coincides with G-and K-type star energy-distribution peaks, as well as containing the strong Ca II infrared triplet lines (λ =8498, 8542, 8662 Å). The aim of this thesis is to create a grid of synthetic spectra in RVS wavelength range which later when compared to the real spectra can be used to determine the chemical composition of the star as well as precise atmospheric parameters. Calculations consist of 198 spectra ranging in effective temperature from Teff =4500 K to 7000 K with various steps, surface gravity log g = 2.5 to 4.5 with the step of 0.5and metallicities [M/H] = −0.5, 0.0 and 0.5 relative to the Solar composition. For calculations MARCS atmosphere models [3], a line list extracted from the VALD3 database [6] and the software SME [7] was used. Spectra calculations were conducted in both classical LTE and refined non-LTE modes for the line formation of calcium.

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In this project, we explore the area of black holes in String Theory. String Theory has had several successes in describing properties of black holes. Recent progress in String Theory points towards the possibility that black holes should not be thought of as fundamental objects, but rather as statistical descriptions of a huge number of smooth horizonless microstate geometries. We study this deep connection between the microscopic description of black holes and String Theory. The main goal is to understand and learn how some of the modern techniques in String Theory can be applied to model black holes, in particular, calculating an expression for the entropy. The main idea is to construct black hole solutions from intersecting certain types of branes, in the context of Supergravity theories that emerge as low-energy limits of Superstring theories. With this microscopic approach, the aim is to count the number of microstates and then compare with the macroscopic Bekenstein-Hawking entropies. We plan to construct such solutions, for both supersymmetric and non-supersymmetric black holes. Also, this microscopic origin of the black hole entropy could provide new insights to the black hole information paradox. / I detta projekt behandlar vi svarta hål i strängteori. Svarta hål är några av naturens mest fascinerande objekt. De är indirekt observerade, som mörka objekt av stjärnstorlek, vilka finns i binära system, eller som supermassiva objekt i galaxers centra. Svarta hål är vanligare förekommande i universum än vad vi tidigare har trott. Uppskattningsvis finns 100 miljoner mörka objekt enbart i Vintergatan. Svarta hål dyker upp i allmän relativitetsteori som klassiska materielösningar som gravitationellt har kollapsat till en punkt, en \textit{singularitet}.Från en teoretisk synvinkel  förser svarta hål oss med laboratorier för tankeexperiment, där nya teoretiska ideér kan testas. 1976 upptäckte Stephen Hawking att svarta hål inte är så svarta - de sänder ut värmestrålning motsvarande en karaktäristisk temperatur, Hawking-temperaturen. Termiska egenskaper, såsom Bekenstein-Hawking-entropi, associerades nu med svarta hål. 1996 härleddes denna entropi med strängteoretiska metoder. Man bestämde de mikroskopiska frihetsgraderna för ett speciellt slags svarta hål, och sedan dess har strängteori skördat många framgångar inom forskningsområdet. Här studerar vi detta djupa samband mellan strängteori och den mikroskopiska beskrivningen av svarta hål. Huvudmålet är att förstå hur vissa moderna strängteoretiska tekniker kan appliceras på svarta hålmodeller, framför allt när entropin ska beräknas.

There are four Period Luminosity relations from three sources, [3, 5, 9, 11], that are compared for theiraccuracy in calculating distances and to see how much uncertainty has to be considered when calculatingother distances based on these. Here, the relations are compared by using each to calculate and compare thedistances of the stars: BK Vir, L2 Pup, R Hor, R Hya, R Lep, and RR Aql; along with using data from AAVSOand SIMBAD in the calculations. The relations have an uncertainty that ranges from about 30%-40%, exceptfor the relation from [9] that has an uncertainty of 90%

The goal of this project is to gain a better understanding of the temperature fluctuations observed in the CMB. This goal is reached with the aid of a literature study. The report touches upon the origin of the CMB as well as how it is measured, mentioning and explaining relevant concepts such as recombination, photon decoupling, black body radiation, angular power spectrum etc. It is also specified that the temperature of the CMB is not uniform but varies slightly. The fact that these fluctuations show inhomogeneities at the early universe is emphasized as well as the need for a satisfying theory that explains said fluctuations. By presenting and employing inflation theory in combination with quantum mechanics, we show how such a theory can be obtained. Through extensive calculation we show how the primordial power spectrum for zero-point fluctuations during inflation is obtained and how it can be related to the time of recombination through a transfer function, thus explaining the existence of fluctuations in the CMB. / Målet med detta projekt är att få en bättre förståelse om observerade temperaturfluktuationer i CMB. Detta mål är uppnått med hjälp av en litteraturstudie. Rapporten nämner uppkomsten av CMB samt hur den mäts, nämner och förklarar relevanta koncept som rekombination, foton frikoppling, svartkroppstrålning, vinkelkraftspektrum etc. Det är också specificerat att temperaturen av CMB inte är enhetlig utan varierar en aning. Faktumet att dessa fluktuationer visar på inhomogeniteter i det tidiga universum är betonat samt behovet av en tillfredställande teori som förklarar dessa fluktuationer. Genom att presentera och använda inflationsteori i kombination med kvantmekanik visar vi hur en sådan teori kan erhållas. Genom omfattande beräkningar visar vi hur det ursprungliga kraftspektrumet för nollpunktsfluktuationer under inflation är erhållet och hur det kan relateras till tiden för rekombination genom en överföringsfunktion, som således förklarar existensen av fluktuationer i CMB.

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