abstract: Two ideas that extends on the theory of General Relativity are introduced and then the phenomenology they can offer is explored. The first idea shows how certain types of $f(R)$ gravity allows for traversable wormholes among its vacuum solutions. This is surprising to find in such simple setting as these type of solutions usually requires fairly complex constructions to satisfy the equations of motion of a gravitational theory. The second idea is the matter bounce description of the early universe where a fairly unique feature of the model is identified. Consequences of this feature could allow the paradigm to distinguish itself from other alternative descriptions, such as inflation, through late time observations. An explicit example of this claim is worked out by studying a model involving an interaction in the dark sector. Results of a more astrophysical nature, where a careful analysis of the morphology of blazar halos is performed, are also presented in the Appendix. The analysis determined that the $Q$-statistic is an appropriate tool to probe the properties of the intergalactic magnetic fields responsible for the halos formation. / Dissertation/Thesis / Doctoral Dissertation Physics 2017

The aim of this master thesis is to investigate the influence of intergalactic duston astronomical observations. The current cosmological paradigm of an acceleratingcosmic expansion is supported by observations of Type Ia supernovae. However, thelight emitted by these and other cosmological sources is not only redshifted by cosmicexpansion but will also interact with matter along the light path which affects the light.Especially intergalactic dust can lead to additional reddening and dimming of distantsources due to light scattering or absorption. This yields systematic contaminations tocosmological measurements. Using quasars as backlight sources we seek to estimate theattenuation of their observed spectra caused by intergalactic dust in order to determinethe existence and properties of the intergalactic dust. In this thesis we will analysethe methods and tools used as well as discussing the dust properties and how theyaffect the results. This thesis shows that intergalactic dust exist, and has a notableeffect on cosmological measurements and favors dust grains consisting of silicate witha size around 0.1 µm with Ωdust around 5 − 7 × 10^−6. The conclusion is in agreementwith previous studies of the same matter. With the increasing precision of cosmologicalmeasurements systematic effects such as intergalactic dust is a factor that has to betaken into account. / Syftet med denna masteruppsats är att undersöka de effekter intergalaktiskt stofthar på astronomiska observationer. Den ledande kosmologiska moddellen som säger attuniversum expanderar är stöttad av observationer av Typ 1a supernovor. Ljuset somkommer från supernovorna är däremot inte bara påverkade av den kosmiska expansionen men kommer också interagera med materia på vägen som påverkar ljuset. Specielltintergalaktiskt stoft kan leda till ytterligare dimning av ljuset och att ljuset blir rödare.Detta är på grund av spridningen eller absorptionen av ljuset när ljuset interagerar medstoftpartiklarna. Detta leder till systematiska fel i kosmologiska mätningar. Genomatt använda kvasarer som en ljuskälla försöker vi uppskatta ljusdämpningen på derasspektrum som orsakats av intergalaktiskt stoft. Detta görs för att bestämma ifall intergalaktiskt stoft existerar och vad dess egenskaper är. I denna uppsats gjordes enanalys av metoden, beräkningsverktygen som användes och några egenskaper hos stoft.Slutsatsen av denna analys visar på att intergalaktiskt stoft existerar och har en mätbar effekt på kosmologiska observationer. Resultatet visar att modellen föredrar stoftav silikat med storlekar runt 0.1 µm med Ωdust runt 5 − 7 × 10^−6vilket stämmer överens med tidigare studier. Med den ökade pressionen av kosmologiska mätningar blirsystematiska effekter, som den från intergalaktiskt stoft, ännu viktigare att ta i hänsyn.

We calculate the angular power spectrum of the cosmic microwave background temperature fluctuations induced by the kinetic Sunyaev-Zel'dovich (kSZ) effect from the epoch of reionization (EOR). We use detailed N-body+radiative-transfer simulations to follow inhomogeneous reionization of the intergalactic medium. For the first time, we take into account the "self-regulation" of reionization: star formation in low-mass dwarf galaxies or minihalos is suppressed if these halos form in the regions that were already ionized or Lyman-Werner dissociated. Some previous work suggested that the amplitude of the kSZ power spectrum from the EOR can be described by a two-parameter family: the epoch of half-ionization and the duration of reionization. However, we argue that this picture applies only to simple forms of the reionization history which are roughly symmetric about the half-ionization epoch. In self-regulated reionization, the universe begins to be ionized early, maintains a low level of ionization for an extended period, and then finishes reionization as soon as high-mass atomically cooling halos dominate. While inclusion of self-regulation affects the amplitude of the kSZ power spectrum only modestly (~10%), it can change the duration of reionization by a factor of more than two. We conclude that the simple two-parameter family does not capture the effect of a physical, yet complex, reionization history caused by self-regulation. When added to the post-reionization kSZ contribution, our prediction for the total kSZ power spectrum is below the current upper bound from the South Pole Telescope. Therefore, the current upper bound on the kSZ effect from the EOR is consistent with our understanding of the physics of reionization. / text

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