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The first-order evolution of cosmic scalar perturbations

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Authors
Aalto, Tuomas
Date
2019
Discipline
Teoreettinen fysiikkaTheoretical Physics
Copyright
This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.

 
Nykytietämyksen mukaan kosminen inflaatio jätti pieniä häiriöitä lähes homogeeniseen varhaiseen maailmankaikkeuteen. Nykyään havaittavien kosmisten rakenteiden kehittyminen näistä häiriöistä on yksi kosmologian keskeisistä osa-alueista. Rakenteiden muodostumisen kannalta keskeisimpiä ovat skalaarityyppiset häiriöt, joihin maailmankaikkeuden energiatiheyden häiriöt pääasiallisesti kytkeytyvät. Tämä tutkielma on katsaus lineaarisen kosmologisen häiriöteorian antamaan hyvin tunnettuun kuvaukseen skalaarihäiriöiden kehittymiselle. Skalaarihäiriöiden kehittymistä kuvaavien yhtälöiden johto esitetään kosmologisesta häiriöteoriasta alkaen. Yhtälöt on johdettu newtonilaista mittaa käyttäen. Häiriöiden kehitystä kuvaaville yhtälöille esitetään sekä analyyttisillä approksimaatioilla että numeerisella laskennalla saatavia viitteellisiä ratkaisuja. Muodostuvassa mallissa rakenteiden syntyminen alkaa pimeän aineen kasautumisella säteilyn dominanssin aikana. Baryonisen aineen kasautuminen pääsee alkamaan vasta sen irtikytkeydyttyä fotoneista punasiirtymän z ≈ 1000 kohdalla. Häiriöteoriaan perustuvan menetelmän validisuutta tarkastellaan vertaamalla saatuja tuloksia rakenteenmuodostumisen pallomaisen romahdusmallin kanssa. Tämä entuudestaan tunnettu vertailu näyttää, kuinka lineaarinen häiriöteoria aliarvioi energiatiheyden häiriöiden kasvua. ...
 
According to the current understanding, the early universe was close to homogeneity with small perturbations left as remnants of the inflation. How these small perturbations evolved into the cosmic structures we observe today is one of the central topics in cosmology. Of different types of perturbations, it is the scalar ones that most dominantly couple to perturbations in energy density and lead to structure formation. This thesis is a review of the well-established evolution of the cosmic scalar perturbations within the context of linear cosmological perturbation theory. We present the derivation of the equations governing the evolution of the scalar perturbations starting from the cosmological perturbation theory. The derivation is done in the Newtonian gauge. Rudimentary solutions to the evolution equations are also presented, both through analytical approximations and numerical computations. In the emerging picture, the structure formation starts with the accumulation of dark matter in radiation dominance. Baryonic matter is prevented from accumulation until decoupling from the photons at the redshift z ≈ 1000. The validity of the perturbative method is examined through a comparison with the spherical collapse model of structure formation. This well known comparison shows how the linear perturbation theory underestimates the growth of perturbations in the energy density. ...
 
Keywords
large scale structure structure formation cosmological perturbation theory kosmologia cosmology
URI

http://urn.fi/URN:NBN:fi:jyu-201910234573

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