Cosmology

About: Cosmology is a research topic. Over the lifetime, 18004 publications have been published within this topic receiving 631028 citations. The topic is also known as: physical cosmology & cosmologies.

Cosmological moduli and the post-inflationary universe: A critical review

Abstract: We critically review the role of cosmological moduli in determining the post-inflationary history of the universe. Moduli are ubiquitous in string and M-theory constructions of beyond the Standard Model physics, where they parametrize the geometry of the compactification manifold. For those with masses determined by supersymmetry (SUSY) breaking this leads to their eventual decay slightly before Big Bang nucleosynthesis (BBN) (without spoiling its predictions). This results in a matter dominated phase shortly after inflation ends, which can influence baryon and dark matter genesis, as well as observations of the cosmic microwave background (CMB) and the growth of large-scale structure. Given progress within fundamental theory, and guidance from dark matter and collider experiments, nonthermal histories have emerged as a robust and theoretically well-motivated alternative to a strictly thermal one. We review this approach to the early universe and discuss both the theoretical challenges and the observational implications.

Model independent tests of the standard cosmological model

Abstract: The dark energy problem has led to speculation that not only may $\ensuremath{\Lambda}\mathrm{CDM}$ be wrong, but that the Friedmann-Lema\^{\i}tre-Robertson-Walker models themselves may not even provide the correct family of background models. We discuss how direct measurements of $H(z)$ can be used to formulate tests of the standard paradigm in cosmology. On their own, such measurements can be used to test for deviations from flat $\ensuremath{\Lambda}\mathrm{CDM}$. When combined with supernovae distances, Hubble rate measurements provide a test of the Copernican principle and the homogeneity assumption of the standard model, which is independent of dark energy or a metric based the theory of gravity. A modification of this test also provides a model independent observable for flatness which decorrelates curvature determination from dark energy. We investigate these tests using Hubble rate measurements from age data, as well as from a Hubble rate inferred from recent measurements of the baryon acoustic oscillations. While the current data are too weak to say anything significant, these tests are exciting prospects for the future.

Dynamical behavior in $f(T,T_G)$ cosmology

Abstract: The $f(T,T_G)$ class of gravitational modification, based on the quadratic torsion scalar $T$, as well as on the new quartic torsion scalar $T_G$ which is the teleparallel equivalent of the Gauss-Bonnet term, is a novel theory, different from both $f(T)$ and $f(R,G)$ ones. We perform a detailed dynamical analysis of a spatially flat universe governed by the simplest non-trivial model of $f(T,T_G)$ gravity which does not introduce a new mass scale. We find that the universe can result in dark-energy dominated, quintessence-like, cosmological-constant-like or phantom-like solutions, according to the parameter choices. Additionally, it may result to a dark energy - dark matter scaling solution, and thus it can alleviate the coincidence problem. Finally, the analysis "at infinity" reveals that the universe may exhibit future, past, or intermediate singularities depending on the parameters.

Review of cosmic phase transitions: their significance and experimental signatures

Abstract: The study of cosmic phase transitions are of central interest in modern cosmology. In the standard model of cosmology the Universe begins in a very hot state, right after at the end of inflation via the process of reheating/preheating, and cools to its present temperature as the Universe expands. Both new and existing physics at any scale can be responsible for catalyzing either first, second or cross over phase transition, which could be either thermal or non-thermal with a potential observable imprints. Thus this field prompts a rich dialogue between gravity, particle physics and cosmology. It is all but certain that at least two cosmic phase transitions have occurred-the electroweak and the QCD phase transitions. The focus of this review will be primarily on phase transitions above such scales, We review different types of phase transitions that can appear in our cosmic history, and their applications and experimental signatures in particular in the context of exciting gravitational waves, which could be potentially be constrained by LIGO/VIRGO, Kagra, LISA, and Decigo.

Large-scale structure in a universe with mixed hot and cold dark matter

Abstract: A UNIVERSE whose density is dominated by cold dark matter (CDM) has been considered the standard model for large-scale structure formation1, but it has had difficulty in matching the relatively quiet velocity field of galaxies2 and the observed structure on very large scales3. By contrast, models with a mixture of COM and hot dark matter (HDM) have more power on large scales4–9, and seem more able to fit the excess large-scale power seen in galaxy surveys3 and the microwave background fluctuations recently measured by COBE10,11. Using high-resolution numerical simulations, we examine the formation of structure in a mixed dark matter model containing 70% COM and 30% HDM, the latter in the form of massive neutrinos. This model behaves like a CDM model in which the biasing factor (the relative magnitude of structure in the dark and visible components) varies from 2.5 on small scales to <1 on large scales, and can provide a consistent explanation of both the shape of the observed fluctuation spectrum and the difference in estimates of the cosmic density, Ω, on small and large scales.