#TITLE_ALTERNATIVE#

• Main Author: ABDAN MALIKUL MULKI (NIM: 20316009), FARGIZA
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/27160
• Institution: Institut Teknologi Bandung

The universe containing coupled scalar field has different dynamical evolution compared to uncoupled case. The significant difference can be expected to emerge during matter dominated era, where scalar field density mimics how matter density evolves (scaling solution), by becoming subdominant. Analysis of the dynamic is investigated both analytically and numerically through phase plane method then analyzing each of critical points which coresponds to specific conditions in universe. By studying all these points we obtain two attractor solutions which are compatible to late time cosmic acceleration as the ending of matter dominated era. Ordinary scalar field (coupled quintessence and coupled k-essence) gives the acceleration with stable attractor solution which converges to &#120596;&#120601; = &#120596;&#119890;&#119891;&#119891; &#8773; &#8722;1. <br /> <br /> Whereas, phantom scalar field allowed negatif values for its own energy (&#120596;&#119890;&#119891;&#119891; <&#8722;1 and &#937;&#120601; < 0), however, this is not stable. Then scalar field will be catched by attractor solutions which are stable to &#120596;&#120601; = &#120596;&#119890;&#119891;&#119891; &#8773; &#8722;1. In addition to these, we found cosmological parameters generated from both analytical exploration and numerical simulation, i.e. &#120596;&#120601;, &#937;&#120601; and &#120596;&#119890;&#119891;&#119891; , by assuming a flat universe. <br /> <br /> The existence of coupling constant &#119876; between scalar field and matter makes structure's growth different from uncoupled case and standard Cold Dark Matter (CDM) model. During matter dominated era, ordinary scalar field induced <br /> <br /> structure’s growth so it becomes faster than standard model does, whereas phantom scalar field, on the contrary, caused growth of structures evolves slower than standard model does. During scalar field dominated era (far in the future), we obtain that according to ordinary scalar field scenario, formed structures or density contrast will decay in a similar way as uncoupled case, whereas following phantom scenario, the decay of formed structures occurs faster and more drastic. This result is associated to background dynamics which show that big rip will be the relevant fate of our universe. <br /> <br /> In this Thesis, we also found transfer function for coupled scalar field model. On small scales, transfer function is simillar to CDM model. Coupled scalar field does not alter the systematic of structures formation, i.e. hierarchical growth of structure; the smaller structures form the larger structures. Based on numerical investigation, we obtain feasible signatures to distinguish phantom from ordinary scalar field, i.e. <br /> <br /> ISW rise and ISW plateau region in the CMB power spectrum due to good sensitivity of these regions to &#120596;&#119863;&#119864; , although the dynamics of dark energy affects the whole fitures in the CMB, included acoustic peaks and damping tail. However, &#119897; < 10 region is more sensitive to &#120596;&#119863;&#119864; variation than any other regions, so this will be a probable signatures for dark energy and to distinguish whether phantom or ordinary scalar field is compatible with future data.