Abstract
I show that General Relativity sets an absolute upper limit on the energy flux observed from a cosmological source as a function of its redshift. Detecting a brighter source in gravitational ...waves, neutrinos or light, would flag new physics. The derived flux limit can also be used to determine the maximum redshift possible for any source with an unknown origin.
Planck 2015 results Ade, P A R; Aghanim, N; Arnaud, M ...
Astronomy and astrophysics (Berlin),
10/2016, Letnik:
594
Journal Article
Recenzirano
Odprti dostop
This paper presents cosmological results based on full-mission Planck observations of temperature and polarization anisotropies of the cosmic microwave background (CMB) radiation. Our results are in ...very good agreement with the 2013 analysis of the Planck nominal-mission temperature data, but with increased precision. The temperature and polarization power spectra are consistent with the standard spatially-flat 6-parameter LambdaCDM cosmology with a power-law spectrum of adiabatic scalar perturbations (denoted "base LambdaCDM" in this paper). From the Planck temperature data combined with Planck lensing, for this cosmology we find a Hubble constant, H sub(0)= (67.8 + or - 0.9) km s super(-1) Mpc super(-1), a matter density parameter Omega sub(m)= 0.308 + or - 0.012, and a tilted scalar spectral index with n sub(s)= 0.968 + or - 0.006, consistent with the 2013 analysis. Note that in this abstract we quote 68% confidence limits on measured parameters and 95% upper limits on other parameters. We present the first results of polarization measurements with the Low Frequency Instrument at large angular scales. Combined with the Planck temperature and lensing data, these measurements give a reionization optical depth of T= 0.066 + or - 0.016, corresponding to a reionization redshift of (ProQuest: Formulae and/or non-USASCII text omitted). These results are consistent with those from WMAP polarization measurements cleaned for dust emission using 353-GHz polarization maps from the High Frequency Instrument. We find no evidence for any departure from base LambdaCDM in the neutrino sector of the theory; for example, combining Planck observations with other astrophysical data we find N sub(eff)= 3.15 + or - 0.23 for the effective number of relativistic degrees of freedom, consistent with the value N sub(eff)= 3.046 of the Standard Model of particle physics. The sum of neutrino masses is constrained to Sigma m sub(nu)< 0.23 eV. The spatial curvature of our Universe is found to be very close to zero, with Omega sub()K< 0.005. Adding a tensor component as a single-parameter extension to base LambdaCDM we find an upper limit on the tensor-to-scalar ratio of r sub(0.002)< 0.11, consistent with the Planck 2013 results and consistent with the B-mode polarization constraints from a joint analysis of BICEP2, Keck Array, and Planck(BKP) data. Adding the BKP B-mode data to our analysis leads to a tighter constraint of r 0.002 < 0.09 and disfavours inflationarymodels with a V(phi) proportional = to phi super(2) potential. The addition of Planck polarization data leads to strong constraints on deviations from a purely adiabatic spectrum of fluctuations. We find no evidence for any contribution from isocurvature perturbations or from cosmic defects. Combining Planck data with other astrophysical data, including Type Ia supernovae, the equation of state of dark energy is constrained to w= -1.006 + or - 0.045, consistent with the expected value for a cosmological constant. The standard big bang nucleosynthesis predictions for the helium and deuterium abundances for the best-fit Planck base LambdaCDM cosmology are in excellent agreement with observations. We also constraints on annihilating dark matter and on possible deviations from the standard recombination history. In neither case do we find no evidence for new physics. The Planck results for base LambdaCDM are in good agreement with baryon acoustic oscillation data and with the JLA sample of Type Ia supernovae. However, as in the 2013 analysis, the amplitude of the fluctuation spectrum is found to be higher than inferred from some analyses of rich cluster counts and weak gravitational lensing. We show that these tensions cannot easily be resolved with simple modifications of the base LambdaCDM cosmology. Apart from these tensions, the base LambdaCDM cosmology provides an excellent description of the Planck CMB observations and many other astrophysical data sets.
Abstract
We revisit Wagoner et al., a classic contribution in the development of Big Bang Nucleosynthesis. We demonstrate that it presents an incorrect expression for the temperature of the early ...universe as a function of time in the high temperature limit,
T
≳
10
10
K. As this incorrect expression has been reproduced elsewhere, we present a corrected form for the initial conditions required for calculating the formation of the primordial elements in the Big Bang.
Abstract
Ly
α
photons from the first radiating sources in the universe play a pivotal role in 21 cm radio detections of Cosmic Dawn and the Epoch of Reionization. Comments are provided on the effect ...of the hyperfine structure of hydrogen on the rate of heating or cooling of the Intergalactic Medium by Ly
α
photons.
ABSTRACT
The light-cone (LC) anisotropy arises due to cosmic evolution of the cosmic dawn (CD) 21-cm signal along the line-of-sight (LoS) axis of the observation volume. The LC effect makes the ...signal statistically non-ergodic along the LoS axis. The multifrequency angular power spectrum (MAPS) provides an unbiased alternative to the popular three-dimensional (3D) power spectrum as it does not assume statistical ergodicity along every direction in the signal volume. Unlike the 3D power spectrum which mixes the cosmic evolution of the 21-cm signal along the LoS k modes, MAPS keeps the evolution information disentangled. Here, we first study the impact of different underlying physical processes during CD on the behaviour of the 21-cm MAPS using simulations of various different scenarios and models. We also make error predictions in 21-cm MAPS measurements considering only the system noise and cosmic variance for mock observations of Hydrogen Epoch of Reionization Array (HERA), NenuFAR, and SKA-Low. We find that 100 h of HERA observations will be able to measure 21-cm MAPS at ≥3σ for ℓ ≲ 1000 with $0.1\, {\rm MHz}$ channel-width. The better sensitivity of SKA-Low allows reaching this sensitivity up to ℓ ≲ 3000. Note that due to the difference in the frequency coverage of the various experiments, the CD–epoch of reionization model considered for NenuFAR is different than those used for the HERA and SKA-Low predictions. Considering NenuFAR with the new model, measurements ≥2σ are possible only for ℓ ≲ 600 with $0.2\, {\rm MHz}$ channel-width and for a 10 times longer observation time of tobs = 1000 h. However, for the range 300 ≲ ℓ ≲ 600 and tobs = 1000 h more than 3σ measurements are still possible for NenuFAR when combining consecutive frequency channels within a 5 MHz band.
From Nobel Prize–winning physicist P. J. E. Peebles, the story of cosmology from Einstein to today Modern cosmology began a century ago with Albert Einstein's general theory of relativity and his ...notion of a homogenous, philosophically satisfying cosmos. Cosmology's Century is the story of how generations of scientists built on these thoughts and many new measurements to arrive at a well-tested physical theory of the structure and evolution of our expanding universe.In this landmark book, one of the world's most esteemed theoretical cosmologists offers an unparalleled personal perspective on how the field developed. P. J. E. Peebles was at the forefront of many of the greatest discoveries of the past century, making fundamental contributions to our understanding of the presence of helium and microwave radiation from the hot big bang, the measures of the distribution and motion of ordinary matter, and the new kind of dark matter that allows us to make sense of these results. Taking readers from the field's beginnings, Peebles describes how scientists working in independent directions found themselves converging on a theory of cosmic evolution interesting enough to warrant the rigorous testing it passes so well. He explores the major advances—some inspired by remarkable insights or perhaps just lucky guesses—as well as the wrong turns taken and the roads not explored. He shares recollections from major players in this story and provides a rare, inside look at how science is really done.A monumental work, Cosmology's Century also emphasizes where the present theory is incomplete, suggesting exciting directions for continuing research.
ABSTRACT
Unimodular gravity is an alternative theory of gravity to general relativity. The gravitational field equations are given by the trace-free version of Einstein’s field equations. Due to the ...structure of the theory, unimodular gravity admits a diffusion term that characterizes a possible non-conservation of the canonical energy–momentum tensor locally. Employing this feature of unimodular gravity, in this work, we explicitly show how to construct an inflationary phase that can be contrasted with current observations. In particular, we focus on three different inflationary scenarios of physical interest. An important element in these scenarios is that the accelerated expansion is driven by the diffusion term exclusively, i.e. there is no inflaton. Furthermore, the primordial spectrum during inflation is generated by considering inhomogeneous perturbations associated to standard hydrodynamical matter (modelled as a single ultra-relativistic fluid). For each of the scenarios, we obtain the prediction for the primordial spectrum and contrast it with recent observational bounds using Planck 2018 + Bicep2/KECK Array data.
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