Search results for "Cosmological model"
showing 10 items of 26 documents
Status of Light Sterile Neutrino Searches
2020
A number of anomalous results in short-baseline oscillation may hint at the existence of one or more light sterile neutrino states in the eV mass range and have triggered a wave of new experimental efforts to search for a definite signature of oscillations between active and sterile neutrino states. The present paper aims to provide a comprehensive review on the status of light sterile neutrino searches in mid-2019: we discuss not only the basic experimental approaches and sensitivities of reactor, source, atmospheric, and accelerator neutrino oscillation experiments but also the complementary bounds arising from direct neutrino mass experiments and cosmological observations. Moreover, we r…
Cosmology with a very light Lμ − Lτ gauge boson
2019
In this paper, we explore in detail the cosmological implications of an abelian L − L gauge extension of the Standard Model featuring a light and weakly coupled Z′. Such a scenario is motivated by the longstanding ∼ 4σ discrepancy between the measured and predicted values of the muon’s anomalous magnetic moment, (g − 2) , as well as the tension between late and early time determinations of the Hubble constant. If sufficiently light, the Z′ population will decay to neutrinos, increasing the overall energy density of radiation and altering the expansion history of the early universe. We identify two distinct regions of parameter space in this model in which the Hubble tension can be significa…
The Redshift Distribution of Flat-Spectrum Radio Sources
2003
The redshift distribution of flat-spectrum radio sources with 5 GHz flux densities S>5 mJy is a key component in using current radio lens surveys to probe the cosmological model. We have constructed the first flat-spectrum radio sample in the flux density range 3-20 mJy. Our new sample has 33 sources; we have determined the redshifts of 14 of these (42% complete). The low mean redshift, ~0.75, of our faintest sample needs to be confirmed by further observations to improve the sample completeness. We also increased the redshift completeness of several surveys of brighter flat-spectrum sources. While the mean redshift, ~1.1 of flat-spectrum samples fainter than 1 Jy is nearly constant, the fr…
Running of featureful primordial power spectra
2017
Current measurements of the temperature and polarization anisotropy power spectra of the Cosmic Microwave Background (CMB) seem to indicate that the naive expectation for the slow-roll hierarchy within the most simple inflationary paradigm may not be respected in nature. We show that a primordial power spectra with localized features could in principle give rise to the observed slow-roll anarchy when fitted to a featureless power spectrum. Future CMB missions have the key to disentangle among the two possible paradigms and firmly establish the slow-roll mechanism as the responsible one for the inflationary period in the early universe. From a model comparison perspective, and assuming that …
Topological defects and large-scale structure
1990
Relativistic second-order perturbations of the Einstein-de Sitter universe
1998
We consider the evolution of relativistic perturbations in the Einstein-de Sitter cosmological model, including second-order effects. The perturbations are considered in two different settings: the widely used synchronous gauge and the Poisson (generalized longitudinal) one. Since, in general, perturbations are gauge dependent, we start by considering gauge transformations at second order. Next, we give the evolution of perturbations in the synchronous gauge, taking into account both scalar and tensor modes in the initial conditions. Using the second-order gauge transformation previously defined, we are then able to transform these perturbations to the Poisson gauge. The most important feat…
Current status of modified gravity
2014
We revisit the cosmological viability of the Hu-Sawicki modified gravity scenario. The impact of such a modification on the different cosmological observables, including gravitational waves, is carefully described. The most recent cosmological data, as well as constraints on the relationship between the clustering parameter ${\ensuremath{\sigma}}_{8}$ and the current matter mass-energy density ${\mathrm{\ensuremath{\Omega}}}_{m}$ from cluster number counts and weak lensing tomography, are considered in our numerical calculations. The strongest bound we find is $|{f}_{R0}|l3.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ at 95% C.L. Forthcoming cluster surveys covering $10\text{ …
Observation of direct CP violation in kaon decays
2019
A small matter-antimatter asymmetry of the weak force was experimentally established. This CP violation may be related to the small excess of matter from the big bang. The nature of CP violation in the K0 system has been clarified after 37 years of experimentation: it is due to a small part of the weak interaction (“milliweak interaction”). A non-trivial phase in the weak quark mixing matrix generates “direct CP violation” in the weak Hamiltonian. The experiments demonstrating direct CP violation are discussed.
Non-Linear Relativistic Evolution of Cosmological Perturbations in Irrotational Dust
2008
The galaxy power spectrum take on spatial curvature and cosmic concordance
2020
The concordance of the $\Lambda$CDM cosmological model in light of current observations has been the subject of an intense debate in recent months. The 2018 Planck Cosmic Microwave Background (CMB) temperature anisotropy power spectrum measurements appear at face value to favour a spatially closed Universe with curvature parameter $\Omega_K<0$. This preference disappears if Baryon Acoustic Oscillation (BAO) measurements are combined with Planck data to break the geometrical degeneracy, although the reliability of this combination has been questioned due to the strong tension present between the two datasets when assuming a curved Universe. Here, we approach this issue from yet another point…