A primordial cosmological magnetic field induces and supports vorticity or Alfvén waves, which in turn generate cosmic microwave background (CMB) anisotropies. A homogeneous primordial magnetic field with fixed direction induces correlations between the al-1,m and al+1,m multipole coefficients of the CMB temperature anisotropy field. We discuss the constraints that can be placed on the strength of such a primordial magnetic field using CMB anisotropy data from the Wilkinson Microwave Anisotropy Probe experiment. We place 3 σ upper limits on the strength of the magnetic field of B < 15 nG for vector perturbation spectral index n = -5 and B < 1.7 nG for n = -7.
We use measurements of the peak photon energy and bolometric fluence of 119 gamma-ray bursts (GRBs) extending over the redshift range of $0.3399 \leq z \leq 8.2$ to simultaneously determine cosmological and Amati relation parameters in six different cosmological models. The resulting Amati relation parameters are almost identical in all six cosmological models, thus validating the use of the Amati relation in standardizing these GRBs. The GRB data cosmological parameter constraints are consistent with, but significantly less restrictive than, those obtained from a joint analysis of baryon acoustic oscillation and Hubble parameter measurements.
We formulate a functional approach to scalar quantum field theory in (n+1)-dimensional de Sitter spacetime and solve the functional Schr\"odinger equation for the conformally and minimally coupled scalar fields in both the k=0 and k=1 gauges. We show that there is a natural initial condition, the requirement that the field energy remain finite as the scale factor a becomes small, which specifies a unique, time-dependent, de Sitter vacuum state. This initial condition is closely related to Hawking's prescription of including in the functional integral only those field configurations which are regular on the Euclidean section. The Green's functions constructed using this initial condition are explicitly shown to be the analytic continuation of those derived using the Euclidean path-integral formalism and the regularity (boundary) condition. These Green's functions are used to study the Hawking effect and the restoration of continuous symmetries. In particular we study the restoration of a broken O(2) symmetry of a ${\ensuremath{\Phi}}^{4}$ theory. We argue that spontaneously broken continuous symmetries are always dynamically restored in de Sitter spacetime.
A primordial cosmological magnetic field induces Faraday rotation of the cosmic microwave background polarization. This rotation produces a curl-type polarization component even when the unrotated polarization possesses only gradient-type polarization, as expected from scalar density perturbations. We compute the angular power spectrum of curl-type polarization arising from small Faraday rotation due to a weak stochastic primordial magnetic field with a power-law power spectrum. The induced polarization power spectrum peaks at arcminute angular scales. Faraday rotation is one of the few cosmological sources of curl-type polarization, along with primordial tensor perturbations, gravitational lensing, and the vector and tensor perturbations induced by magnetic fields; the Faraday rotation signal peaks on significantly smaller angular scales than any of these, with a power spectrum amplitude which can be comparable to that from gravitational lensing. Prospects for detection are briefly discussed.
ABSTRACT The recent compilation of quasar (QSO) X-ray and ultraviolet (UV) flux measurements include QSOs that appear to not be standardizable via the X-ray luminosity and UV luminosity (LX–LUV) relation and so should not be used to constrain cosmological model parameters. Here, we show that the largest of seven sub-samples in this compilation, the SDSS-4XMM QSOs that contribute about 2/3 of the total QSOs, have LX–LUV relations that depend on the cosmological model assumed and also on redshift, and is the main cause of the similar problem discovered earlier for the full QSO compilation. The second and third biggest sub-samples, the SDSS-Chandra and XXL QSOs that together contribute about 30 per cent of the total QSOs, appear standardizable, but provide only weak constraints on cosmological parameters that are not inconsistent with the standard spatially flat ΛCDM model or with constraints from better-established cosmological probes.
To determine whether or not H II starburst galaxies (H IIG) are standardizable candles, we study the correlation between the H$β$ luminosity ($L$) and the velocity dispersion ($σ$) of the ionized gas from H IIG measurements by simultaneously constraining the $L-σ$ relation parameters and the cosmological model parameters. We investigate six flat and nonflat relativistic dark energy cosmological models, spatially flat and nonflat, and with cosmological constant or dynamical dark energy. We find that low-redshift and high-redshift H IIG data subsets are standardizable but obey different $L-σ$ relations. Current H IIG data are too sparse and too non-uniformly distributed in redshift to allow for a determination of whether what we have found is just a consequence of H IIG evolution. Until this issue is better understood, H IIG data cosmological constraints must be treated with caution.
We use all available baryon acoustic oscillation distance measurements and Hubble parameter data to constrain the cosmological constant $\Lambda$, dynamical dark energy, and spatial curvature in simple cosmological models. We find that the consensus spatially flat $\Lambda$CDM model provides a reasonable fit to the data, but depending on the Hubble constant prior and cosmological model, it can be a little more than 1$\sigma$ away from the best-fit model, which can favor mild dark energy dynamics or non-flat spatial hypersurfaces.
We use 78 reverberation-measured Mg II time-lag quasars (QSOs) in the redshift range $0.0033 \leq z \leq 1.89$ to constrain cosmological parameters in six different cosmological models. The basis of our method is the use of the radius-luminosity or $R-L$ relation to standardize these 78 Mg II QSOs. In each cosmological model we simultaneously determine $R-L$ relation and cosmological model parameters, thus avoiding the circularity problem. We find that the $R-L$ relation parameter values are independent of the cosmological model used in the analysis thus establishing that current Mg II QSOs are standardizable candles. Cosmological constraints obtained using these QSOs are significantly weaker than, but consistent with, those obtained from a joint analysis of baryon acoustic oscillation (BAO) observations and Hubble parameter [$H(z)$] measurements. So, we also analyse these QSOs in conjunction with the BAO + $H(z)$ data and find cosmological constraints consistent with the standard spatially-flat $\Lambda$CDM model as well as with mild dark energy dynamics and a little spatial curvature. A larger sample of higher-quality reverberation-measured QSOs should have a smaller intrinsic dispersion and so should provide tighter constraints on cosmological parameters.
We use the Simon, Verde, & Jimenez (2005) determination of the redshift dependence of the Hubble parameter to constrain cosmological parameters in three dark energy cosmological models. We consider the standard $\Lambda$CDM model, the XCDM parameterization of the dark energy equation of state, and a slowly rolling dark energy scalar field with an inverse power-law potential. The constraints are restrictive, consistent with those derived from Type Ia supernova redshift-magnitude data, and complement those from galaxy cluster gas mass fraction versus redshift data.
We study eight different gamma-ray burst (GRB) data sets to examine whether current GRB measurements -- that probe a largely unexplored part of cosmological redshift ($z$) space -- can be used to reliably constrain cosmological model parameters. We use three Amati-correlation samples and five Combo-correlation samples to simultaneously derive correlation and cosmological model parameter constraints. The intrinsic dispersion of each GRB data set is taken as a goodness measurement. We examine the consistency between the cosmological bounds from GRBs with those determined from better-established cosmological probes, such as baryonic acoustic oscillation (BAO) and Hubble parameter $H(z)$ measurements. We use the Markov chain Monte Carlo method implemented in \textsc{MontePython} to find best-fit correlation and cosmological parameters, in six different cosmological models, for the eight GRB samples, alone or in conjunction with BAO and $H(z)$ data. For the Amati correlation case, we compile a data set of 118 bursts, the A118 sample, which is the largest -- about half of the total Amati-correlation GRBs -- current collection of GRBs suitable for constraining cosmological parameters. This updated GRB compilation has the smallest intrinsic dispersion of the three Amati-correlation GRB data sets we examined. We are unable to define a collection of reliable bursts for current Combo-correlation GRB data. Cosmological constraints determined from the A118 sample are consistent with -- but significantly weaker than -- those from BAO and $H(z)$ data. They also are consistent with the spatially-flat $\Lambda$CDM model as well as with dynamical dark energy models and non-spatially-flat models. Since GRBs probe a largely unexplored region of $z$, it is well worth acquiring more and better-quality burst data which will give a more definitive answer to the question of the title.
