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.

Inflationary universe from perfect fluid and F ( R ) gravity and its comparison with observational data

Abstract: We investigate the descriptions for the observables of inflationary models, in particular, the spectral index of curvature perturbations, the tensor-to-scalar ratio, and the running of the spectral index, in the framework of perfect fluid models and $F(R)$ gravity theories through the reconstruction methods. Furthermore, the perfect fluid and $F(R)$ gravity descriptions of inflation are compared with the recent cosmological observations such as the Planck satellite and BICEP2 experiment. It is demonstrated with explicit examples that perfect fluid may lead to the inflationary universe consistent with the Planck data. It is also shown that several $F(R)$ gravity models, especially, a power-law model gives the best fit values compatible with the spectral index and tensor-to-scalar ratio within the allowed ranges suggested by the Planck and BICEP2 results.

Running G and \Lambda at low energies from physics at M_X: possible cosmological and astrophysical implications

Abstract: The renormalization group (RG) approach to cosmology is an efficient method to study the possible evolution of the cosmological parameters from the point of view of quantum field theory in curved space-time. In this work we continue our previous investigations of the RG method based on potential low-energy effects induced from physics at very high energy scales M_X near M_P. In the present instance we assume that both the Newton constant, G, and the cosmological term, \Lambda, can be functions of a scale parameter \mu. It turns out that G(\mu) evolves according to a logarithmic law which may lead to asymptotic freedom of gravity, similar to the gauge coupling in QCD. At the same time \Lambda(\mu) evolves quadratically with \mu. We study the consistency and cosmological consequences of these laws when \mu=H. Furthermore, we propose to extend this method to the astrophysical domain after identifying the local RG scale at the galactic level. It turns out that Kepler's third law of celestial mechanics receives quantum corrections that may help to explain the flat rotation curves of the galaxies without introducing the dark matter hypothesis. The origin of these effects (cosmological and astrophysical) could be linked, in our framework, to physics at M_X= 10^{16-17} GeV.

Large-scale structure tests of warm dark matter

Abstract: The nature of the dark matter critically affects the large-scale structure of the universe. Under the assumptions that the universe is spatially flat with zero cosmological constant and that primordial perturbations were adiabatic with a Harrison-Zeldovich spectrum, neither hot dark matter (HDM) nor cold dark matter (CDM) appears consistent with the observed large-scale structure. Warm dark matter (WDM) is an intriguing alternative from the point of view of both cosmology and particle physics. We consider a one-parameter family of WDM models. The linear power spectra for these models is calculated and compared with the corresponding spectra for CDM, HDM, and mixed dark matter (MDM), as well as the power spectrum derived from observations. Our linear analyses suggest that a model universe dominated by a particle whose mass-to-temperature ratio {ital m}{sub {ital x}}/{ital T}{sub {ital x}} is increased by a factor of 2 as compared with the standard HDM neutrino gives a reasonable fit to the data on large ({approx_gt}8{ital h}{sup {minus}1} Mpc) scales. {ital N}-body simulations for this particular WDM model show features of both HDM and CDM. As in HDM, the first objects to collapse are large pancake-like structures. The final matter distribution is rather smooth, and structures asmore » small as galaxy halos are excluded. However, there appear to be virialized rich clusters evident in the CDM but not in the HDM simulations. Unfortunately, a simple comparison of the matter distribution and its statistical properties with observations indicates that WDM, like CDM, has too much power at small scales. This is particularly evident in the small-scale pairwise velocity dispersion. The cluster multiplicity function has the wrong shape, with too many rich clusters being produced, although this conclusion is based on the simple assumption that light traces mass in groups of galaxies. {copyright} {ital 1996 The American Astronomical Society.}« less

Standard Big-Bang Nucleosynthesis up to CNO with an improved extended nuclear network

Abstract: Primordial or big bang nucleosynthesis (BBN) is one of the three strong pieces of evidence for the big bang model together with the expansion of the universe and cosmic microwave background radiation. In this study, we improve the standard BBN calculations taking into account new nuclear physics analyses and enlarge the nuclear network up to sodium. This is, in particular, important to evaluate the primitive value of CNO mass fraction that could affect Population III stellar evolution. For the first time we list the complete network of more than 400 reactions with references to the origin of the rates, including 270 reaction rates calculated using the TALYS code. Together with the cosmological light elements, we calculate the primordial beryllium, boron, carbon, nitrogen, and oxygen nuclei. We performed a sensitivity study to identify the important reactions for CNO, 9Be, and boron nucleosynthesis. We re-evaluated those important reaction rates using experimental data and/or theoretical evaluations. The results are compared with precedent calculations: a primordial beryllium abundance increase by a factor of four compared to its previous evaluation, but we note a stability for B/H and for the CNO/H abundance ratio that remains close to its previous value of 0.7 × 10–15. On the other hand, the extension of the nuclear network has not changed the 7Li value, so its abundance is still 3-4 times greater than its observed spectroscopic value.

Dark energy two decades after: observables, probes, consistency tests.

Abstract: The discovery of the accelerating universe in the late 1990s was a watershed moment in modern cosmology, as it indicated the presence of a fundamentally new, dominant contribution to the energy budget of the universe. Evidence for dark energy, the new component that causes the acceleration, has since become extremely strong, owing to an impressive variety of increasingly precise measurements of the expansion history and the growth of structure in the universe. Still, one of the central challenges of modern cosmology is to shed light on the physical mechanism behind the accelerating universe. In this review, we briefly summarize the developments that led to the discovery of dark energy. Next, we discuss the parametric descriptions of dark energy and the cosmological tests that allow us to better understand its nature. We then review the cosmological probes of dark energy. For each probe, we briefly discuss the physics behind it and its prospects for measuring dark energy properties. We end with a summary of the current status of dark energy research.