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.

The atacama cosmology telescope: a measurement of the primordial power spectrum

Abstract: We present constraints on the primordial power spectrum of adiabatic fluctuations using data from the 2008 Southern Survey of the Atacama Cosmology Telescope (ACT). The angular resolution of ACT provides sensitivity to scales beyond l = 1000 for resolution of multiple peaks in the primordial temperature power spectrum, which enables us to probe the primordial power spectrum of adiabatic scalar perturbations with wavenumbers up to k approx. = 0.2 Mp/c. We find no evidence for deviation from power-law fluctuations over two decades in scale. Matter fluctuations inferred from the primordial temperature power spectrum evolve over cosmic time and can be used to predict the matter power spectrum at late times; we illustrate the overlap of the matter power inferred from CMB measurements (which probe the power spectrum in thc linear regime) with existing probes of galaxy clustering, cluster abundances and weak lensing constraints on the primordial power. This highlights the range of scales probed by current measurement.s of the matter power spectrum.

The growth rate of cosmic structure from peculiar velocities at low and high redshifts

Abstract: Peculiar velocities are an important probe of the growth rate of mass density fluctuations in the universe. Most previous studies have focused exclusively on measuring peculiar velocities at intermediate (0.2 < z < 1) redshifts using statistical redshift-space distortions. Here, we emphasize the power of peculiar velocities obtained directly from distance measurements at low redshift (z 0.05), and show that these data break the usual degeneracies in the Ωm, 0- σ8, 0 parameter space. Using only peculiar velocity data, we find and σ8, 0 = 0.748 ± 0.035. Fixing the amplitude of fluctuations at very high redshift using observations of the cosmic microwave background, the same data can be used to constrain the growth index γ, with the strongest constraints coming from peculiar velocity measurements in the nearby universe. We find γ = 0.619 ± 0.054, consistent with ΛCDM. Current peculiar velocity data already strongly constrain modified gravity models and will be a powerful test as data accumulate.

Dynamical behavior in f (T, T G ) cosmology

Abstract: The class of gravitational modification, based on the quadratic torsion scalar T as well as on the new quartic torsion scalar TG, which is the teleparallel equivalent of the Gauss–Bonnet term, is a novel theory, different from both f (T) and ones. We perform a detailed dynamical analysis of a spatially flat universe governed by the simplest non-trivial model of 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 in a dark energy–dark matter scaling solution; 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.

Cosmology With Strong-lensing Systems

Abstract: In this paper, we assemble a catalog of 118 strong gravitational lensing systems from the Sloan Lens ACS Survey, BOSS emission-line lens survey, Lens Structure and Dynamics, and Strong Lensing Legacy Survey and use them to constrain the cosmic equation of state. In particular, we consider two cases of dark energy phenomenology: the XCDM model, where dark energy is modeled by a fluid with constant w equation-of-state parameter, and in the Chevalier–Polarski–Linder (CPL) parameterization, where w is allowed to evolve with redshift, . We assume spherically symmetric mass distribution in lensing galaxies, but we relax the rigid assumption of the SIS model in favor of a more general power-law index γ, also allowing it to evolve with redshifts . Our results for the XCDM cosmology show agreement with values (concerning both w and γ parameters) obtained by other authors. We go further and constrain the CPL parameters jointly with . The resulting confidence regions for the parameters are much better than those obtained with a similar method in the past. They are also showing a trend of being complementary to the Type Ia supernova data. Our analysis demonstrates that strong gravitational lensing systems can be used to probe cosmological parameters like the cosmic equation of state for dark energy. Moreover, they have a potential to judge whether the cosmic equation of state evolved with time or not.

Marginal evidence for cosmic acceleration from Type Ia supernovae

Abstract: The "standard" model of cosmology is founded on the basis that the expansion rate of the universe is accelerating at present --- as was inferred originally from the Hubble diagram of Type Ia supernovae. There exists now a much bigger database of supernovae so we can perform rigorous statistical tests to check whether these "standardisable candles" indeed indicate cosmic acceleration. Taking account of the empirical procedure by which corrections are made to their absolute magnitudes to allow for the varying shape of the light curve and extinction by dust, we find, rather surprisingly, that the data are still quite consistent with a constant rate of expansion.