Cosmological Corrections Research Articles

Light deflection by rotating regular black holes with a cosmological constant

Using the Gauss-Bonnet theorem, we compute and examine the deflection angle of light rays by rotating regular black holes with a cosmological constant. By the help of optical geometries, we first deal with the Hayward black holes with cosmological contributions. Then, we reconsider the study of the Bardeen solutions. We inspect the cosmological constant effect on the deflection angle of light rays. Concretely, we find extra cosmological correction terms generalizing certain obtained findings. Using graphical analysis, we provide a comparative discussion with respect to the Kerr solutions. The results confirm that the non-linear electrodynamic charges affect the space-time geometry by decreasing the deflection angle of light rays by such cosmological black holes.

Getting the Cosmology Right

Getting the Cosmology Right

Gauss\u2013Bonnet term corrections in scalar field cosmology

The influence of non-minimal coupling of a scalar field and the Gauss–Bonnet term on the inflationary stage of evolution of the universe is investigated in this paper. The main cosmological effects of such a coupling were considered. The deviations between Einstein–Gauss–Bonnet inflation and standard one based on Einstein gravity were determined. The corrections of a weak GB coupling preserving the type of the scalar field potential to standard inflationary models is considered as well.

Characteristic for long GRBs with high energy component presence, which not required cosmological corrections

Several thousands of gamma-ray bursts were observed by various experiments. During several GRBs very high-energy photons were detected both in space and ground-based experiments (up to some tens of GeV and up to some TeV, respectively). Usually 2 classes of bursts are considered: short and long GRBs separated by t90~2s. Because of several hundreds of GRBs located at high redshift, its sources’ origins nature concluding as cosmological. Therefore correction to cosmological dilation of GRBs t90 should be considered during any analysis of bursts duration. Firstly very high-energy component was observed during GRB 970417a: 18 photons with energy ~650 GeV were registered by Milagrito within t90 interval of this burst. Now several tens of GRBs reveal activity in energy bands up to some tens of GeV and up to some TeV accordingly data of space and ground-based experiments correspondingly. Unfortunately redshift is unknown approximately for half of GRBs with high energy component presence. Here we introduce new parameter Rt is ratio of maximum energy photon arrival time to burst duration and it not required cosmological correction. At least 2 groups of long GRBs could be separated using parameter Rt: for 25% events highest energy gammas detected within t 90 interval, but for other 75% of bursts it registered more than 10 sec. later than one. Moreover, preliminary results of analysis allow concluding 2 subtypes of second group GRBs. For one μ-quantum with maximum energy arrived within t90. For other such photon was registered later than t90. Therefore, the results of preliminary analyses allow conclude long GRBs population inhomogeneity.

Positivity in the effective field theory of cosmological perturbations

Requiring the existence of a unitary, causal and local UV-completion places a set of positivity bounds on the corresponding effective field theories (EFTs). We discuss the obstructions and possibility in applying the positivity bound to cosmology, in particular the EFT of cosmological perturbations. Taking a c_T=1 beyond-Horndeski EFT as an illustrative example, we derive such bounds, which incorporate the cosmological correction of order H^2/Lambda ^2, Lambda being the cutoff scale. The derived bounds are applied to slow-roll inflation with beyond Horndeski operators. It is found that the cosmological positivity bounds may be either stronger or weaker than their flat space counterpart.

Forecasts on the speed of gravitational waves at high z

The observation of GW170817 binary neutron star (BNS) merger event has imposed strong bounds on the speed of gravitational waves (GWs) locally, inferring that the speed of GWs propagation is equal to the speed of light. Current GW detectors in operation will not be able to observe BNS merger to long cosmological distance, where possible cosmological corrections on the cosmic expansion history are expected to play an important role, specially for investigating possible deviations from general relativity. Future GW detectors designer projects will be able to detect many coalescences of BNS at high z, such as the third generation of the ground GW detector called Einstein Telescope (ET) and the space-based detector deci-hertz interferometer gravitational wave observatory (DECIGO). In this paper, we relax the condition cT/c = 1 to investigate modified GW propagation where the speed of GWs propagation is not necessarily equal to the speed of light. Also, we consider the possibility for the running of the Planck mass corrections on modified GW propagation. We parametrize both corrections in terms of an effective GW luminosity distance and we perform a forecast analysis using standard siren events from BNS mergers, within the sensitivity predicted for the ET and DECIGO. We find at high z very strong forecast bounds on the running of the Planck mass, namely \U0001d4aa(10−1) and \U0001d4aa(10−2) from ET and DECIGO, respectively. Possible anomalies on GW propagation are bound to |cT/c − 1| ⩽ 10−2 (10−2) from ET (DECIGO), respectively. We finally discuss the consequences of our results on modified gravity phenomenology.

The luminosity–volume test for cosmological fast radio bursts

We have applied the luminosity–volume test, also known as ⟨V/Vmax⟩, to fast radio bursts (FRBs). We compare the 23 FRBs, recently discovered by ASKAP, with 20 of the FRBs found by Parkes. These samples have different flux limits and correspond to different explored volumes. We put constrains on their redshifts with probability distributions (PDFs) and applied the appropriate cosmological corrections to the spectrum and rate in order to compute the ⟨V/Vmax⟩ for the ASKAP and Parkes samples. For a radio spectrum of FRBs ℱν ∝ ν−1.6, we found ⟨V/Vmax⟩ = 0.68 ± 0.05 for the ASKAP sample, that includes FRBs up to z = 0.72+0.42−0.26, and 0.54 ± 0.04 for Parkes, that extends up to z = 2.1+0.47−0.38. The ASKAP value suggests that the population of FRB progenitors evolves faster than the star formation rate, while the Parkes value is consistent with it. Even a delayed (as a power law or Gaussian) star formation rate cannot reproduce the ⟨V/Vmax⟩ of both samples. If FRBs do not evolve in luminosity, the ⟨V/Vmax⟩ values of ASKAP and Parkes sample are consistent with a population of progenitors whose density strongly evolves with redshift as ∼z2.8 up to z ∼ 0.7.

The sources of long GRBs: population inhomogeneity or possibility its using as standard candles

Large articles amount refers to GRBs (at least long ones) as standard candles and then concludes various cosmological consequences. But firstly long GRBs sources population homogeneity should be proved. Redshift distribution analysis should represent GRBs population homogeneity if its shape similar to one of objects with real uniform distribution in our Metagalaxy, such as SN1a (subsets of 42 and 53 ones used for its Ω and Λ definition). There are one maximum in each subset redshifts distributions. Typically considered short and long GRBs classes separated by t90=2s. Moreover, registered event duration strongly depends on detector energy band and method used for temporal profile analysis and the same events could have different duration on various detectors data. GRBs mostly located at high redshifts and cosmological correction should be used in duration investigation. Redshift distribution for registered by Swift/BAT GRBs with t90>1s (corrected to z) was analyzed with short GRBs exclusion. But its redshift distribution is sufficiently differs from ones for SN1a: bursts deficit occur at z∼2, possibly caused by long GRBs population inhomogeneity. So, preliminary analyses results allow conclude long GRBs population inhomogeneity. Thus using GRBs as “standard candles” previously required events advanced classification completion and consideration only certain GRBs subsets.

Cosmological perturbations with inverse-volume corrections in loop quantum cosmology

Although the cosmological perturbations with inverse-volume corrections from loop quantum cosmology have been studied using the anomaly-free algebra approach in much of the literature, there still remains an important issue that some counterterms in the perturbed constraints cannot be uniquely fixed on the spatially flat Friedmann-Robterson-Walker background, which causes ambiguities in the perturbation equations. In this paper, we show that this problem can be overcome by extending the anomaly-free algebra to the spatially closed Friedmann-Robterson-Walker background. We find that a consistent deformed algebra can be obtained in the spatially closed case, and each counter term can be uniquely fixed in terms of the inverse-volume correction functions; then, by taking the large $r_o$ limit, we recover the anomaly-free Hamiltonian on the spatially flat background. Using this Hamiltonian we obtain the gauge invariant cosmological perturbations for scalar, vector and tensor modes in the spatially flat case. Moreover, we also derive the quantum-corrected Mukhanov equations, from which the scalar and tensor spectral indices with inverse-volume corrections are given. Some key cosmological perturbation equations obtained in this paper are different from those in previous literature.

The maximum angular-diameter distance in cosmology

Unlike other observational signatures in cosmology, the angular-diameter distance d_A(z) uniquely reaches a maximum (at z_max) and then shrinks to zero towards the big bang. The location of this turning point depends sensitively on the model, but has been difficult to measure. In this paper, we estimate and use z_max inferred from quasar cores: (1) by employing a sample of 140 objects yielding a much reduced dispersion due to pre-constrained limits on their spectral index and luminosity, (2) by reconstructing d_A(z) using Gaussian processes, and (3) comparing the predictions of seven different cosmologies and showing that the measured value of z_max can effectively discriminate between them. We find that z_max=1.70 +\- 0.20---an important new probe of the Universe's geometry. The most strongly favoured model is R_h=ct, followed by Planck LCDM. Several others, including Milne, Einstein-de Sitter and Static tired light are strongly rejected. According to these results, the R_h=ct universe, which predicts z_max=1.718, has a ~92.8% probability of being the correct cosmology. For consistency, we also carry out model selection based on d_A(z) itself. This test confirms that R_h=ct and Planck LCDM are among the few models that account for angular-size data better than those that are disfavoured by z_max. The d_A(z) comparison, however, is less discerning than that with z_max, due to the additional free parameter, H_0. We find that H_0=63.4 +\- 1.2 km/s/Mpc for R_h=ct, and 69.9 +\- 1.5 km/s/Mpc for LCDM. Both are consistent with previously measured values in each model, though they differ from each other by over 4 sigma. In contrast, model selection based on z_max is independent of H_0.

Cosmological tests with strong gravitational lenses using Gaussian processes

Strong gravitational lenses provide source/lens distance ratios {mathcal {D}}_{mathrm{obs}} useful in cosmological tests. Previously, a catalog of 69 such systems was used in a one-on-one comparison between the standard model, varLambda CDM, and the R_{mathrm{h}}=ct universe, which has thus far been favored by the application of model selection tools to many other kinds of data. But in that work, the use of model parametric fits to the observations could not easily distinguish between these two cosmologies, in part due to the limited measurement precision. Here, we instead use recently developed methods based on Gaussian Processes (GP), in which {mathcal {D}}_{mathrm{obs}} may be reconstructed directly from the data without assuming any parametric form. This approach not only smooths out the reconstructed function representing the data, but also reduces the size of the 1sigma confidence regions, thereby providing greater power to discern between different models. With the current sample size, we show that analyzing strong lenses with a GP approach can definitely improve the model comparisons, producing probability differences in the range sim 10–30%. These results are still marginal, however, given the relatively small sample. Nonetheless, we conclude that the probability of R_{mathrm{h}}=ct being the correct cosmology is somewhat higher than that of varLambda CDM, with a degree of significance that grows with the number of sources in the subsamples we consider. Future surveys will significantly grow the catalog of strong lenses and will therefore benefit considerably from the GP method we describe here. In addition, we point out that if the R_{mathrm{h}}=ct universe is eventually shown to be the correct cosmology, the lack of free parameters in the study of strong lenses should provide a remarkably powerful tool for uncovering the mass structure in lensing galaxies.

Reconstruction of the HII galaxy Hubble diagram using Gaussian processes

The Hubble diagram constructed using HII galaxies (HIIGx) and Giant extragalactic HII regions (GEHR) as standard candles already extends beyond the current reach of Type Ia SNe. A sample of 156 HIIGx and GEHR sources has been used previously to compare the predictions of ΛCDM and Rh = ct, the results of which suggested that the HIIGx and GEHR sources strongly favour the latter over the former. But this analysis was based on the application of parametric fits to the data and the use of information criteria, which disfavour the less parsimonious models. In this paper, we advance the use of HII sources as standard candles by utilizing Gaussian processes (GP) to reconstruct the distance modulus representing these data without the need to pre-assume any particular model, none of which may in the end actually be the correct cosmology. In addition, this approach tightly constrains the 1σ confidence region of the reconstructed function, thus providing a better tool with which to differentiate between competing cosmologies. With this approach, we show that the Planck concordance model is in tension with the HII data at more than 2.5σ, while Rh = ct agrees with the GP reconstruction very well, particularly at redshifts ≳ 10−3.

Empire and the Johannine Epistles

In what ways are the Johannine Epistles a response to empire ideology and propaganda? These Epistles proclaim a more complete and correct cosmology, a greater Savior and soteriology, a better pedagogy, a truer doctrine, a sounder koinōnia, and a more nurturing paterfamilias; moreover, they do so while indicting schismatics, who, in the view of the elder, represent the face of the empire. Although the resurrection and ascension of Jesus Christ drive the elder’s witness and ministry, he must still shape his message to counter the encroachment of empire in the church and on the mission field.

MAPPING THE REAL-SPACE DISTRIBUTIONS OF GALAXIES IN SDSS DR7. I. TWO-POINT CORRELATION FUNCTIONS

ABSTRACT Using a method to correct redshift-space distortion (RSD) for individual galaxies, we mapped the real-space distributions of galaxies in the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7). We use an ensemble of mock catalogs to demonstrate the reliability of our method. Here, in the first paper in a series, we focus mainly on the two-point correlation function (2PCF) of galaxies. Overall the 2PCF measured in the reconstructed real space for galaxies brighter than agrees with the direct measurement to an accuracy better than the measurement error due to cosmic variance, if the reconstruction uses the correct cosmology. Applying the method to the SDSS DR7, we construct a real-space version of the main galaxy catalog, which contains 396,068 galaxies in the North Galactic Cap with redshifts in the range 0.01 ≤ z ≤ 0.12. The Sloan Great Wall, the largest known structure in the nearby universe, is not as dominant an overdense structure as it appears to be in redshift space. We measure the 2PCFs in reconstructed real space for galaxies of different luminosities and colors. All of them show clear deviations from single power-law forms, and reveal clear transitions from one-halo to two-halo terms. A comparison with the corresponding 2PCFs in redshift space nicely demonstrates how RSDs boost the clustering power on large scales (by about 40%–50% at scales ) and suppress it on small scales (by about 70%–80% on a scale of ).

Emergence of a low spin phase in group field theory condensates

Recent results have shown how quantum cosmology models can be derived from the effective dynamics of condensate states in group field theory (GFT), where ‘cosmology is the hydrodynamics of quantum gravity’: the classical Friedmann dynamics for homogeneous, isotropic universes, as well as loop quantum cosmology (LQC) corrections to general relativity have been shown to emerge from fundamental quantum gravity. We take one further step towards strengthening the link with LQC and show, in a class of GFT models for gravity coupled to a free massless scalar field and for generic initial conditions, that GFT condensates dynamically reach a low spin phase of many quanta of geometry, in which all but an exponentially small number of quanta are characterised by a single spin j0 (i.e. by a constant volume per quantum). As the low spin regime is reached, GFT condensates expand to exponentially large volumes, and the dynamics of the total volume follows precisely the classical Friedmann equations. This behaviour follows from a single requirement on the couplings in the GFT model under study. We present one particular simple case in which the dominant spin is the lowest one: or, if this is excluded, . The type of quantum state usually assumed in the derivation of LQC is hence derived from the quantum dynamics of GFT. These results confirm and extend recent results by Oriti, Sindoni and Wilson-Ewing in the same setting.

On the Effect of the Cosmological Expansion on the Gravitational Lensing by a Point Mass

We analyze the effect of the cosmological expansion on the deflection of light caused by a point mass, adopting the McVittie metric as the geometrical description of a pointlike lens embedded in an expanding universe. In the case of a generic, non-constant Hubble parameter $H$ we derive and approximately solve the null geodesic equations, finding an expression for the bending angle $\delta$, which we expand in powers of the mass-to-closest approach distance ratio and of the impact parameter-to-lens distance ratio. It turns out that the leading order of the aforementioned expansion is the same as the one calculated for the Schawarzschild metric and that cosmological corrections contribute to $\delta$ only at sub-dominant orders. We explicitly calculate these cosmological corrections for the case of $H$ constant and find that they provide a correction of order $10^{-11}$ on the lens mass estimate.

Spectroscopy of Kerr Black Holes with Earth- and Space-Based Interferometers.

We estimate the potential of present and future interferometric gravitational-wave detectors to test the Kerr nature of black holes through "gravitational spectroscopy," i.e., the measurement of multiple quasinormal mode frequencies from the remnant of a black hole merger. Using population synthesis models of the formation and evolution of stellar-mass black hole binaries, we find that Voyager-class interferometers will be necessary to perform these tests. Gravitational spectroscopy in the local Universe may become routine with the Einstein Telescope, but a 40-km facility like Cosmic Explorer is necessary to go beyond z∼3. In contrast, detectors like eLISA (evolved Laser Interferometer Space Antenna) should carry out a few-or even hundreds-of these tests every year, depending on uncertainties in massive black hole formation models. Many space-based spectroscopical measurements will occur at high redshift, testing the strong gravity dynamics of Kerr black holes in domains where cosmological corrections to general relativity (if they occur in nature) must be significant.

Inflationary spectra with inverse-volume corrections in loop quantum cosmology and their observational constraints from Planck 2015 data

We first derive the primordial power spectra, spectral indices and runnings of both scalar and tensor perturbations of a flat inflationary universe to the second-order approximations of the slow-roll parameters, in the framework of loop quantum cosmology with the inverse-volume quantum corrections. This represents an extension of our previous work in which the parameter σ was assumed to be an integer, where σ characterizes the quantum corrections and in general can take any of values from the range σ ∊ (0, 6]. Restricting to the first-order approximations of the slow-roll parameters, we find corrections to the results obtained previously in the literature, and point out the causes for such errors. To our best knowledge, these represent the most accurate calculations of scalar and tensor perturbations given so far in the literature. Then, fitting the perturbations to the recently released data by Planck (2015), we obtain the most severe constraints for various values of σ. Using these constraints as our referring point, we discuss whether these quantum gravitational corrections can lead to measurable signatures in the future cosmological observations. We show that, depending on the value of σ, the scale-dependent contributions to the relativistic inflationary spectra due to the inverse-volume corrections could be well within the range of the detectability of the forthcoming generations of experiments, such as the Stage IV experiments.

Constancy of the cluster gas mass fraction in the R h = ct Universe

The ratio of baryonic to dark matter densities is assumed to have remained constant throughout the formation of structure. With this, simulations show that the fraction f gas ( z ) of baryonic mass to total mass in galaxy clusters should be nearly constant with redshift z . However, the measurement of these quantities depends on the angular distance to the source, which evolves with z according to the assumed background cosmology. An accurate determination of f gas ( z ) for a large sample of hot ( kT e >5 keV), dynamically relaxed clusters could therefore be used as a probe of the cosmological expansion up to z <2. The fraction f gas ( z ) would remain constant only when the correct cosmology is used to fit the data. In this paper, we compare the predicted gas mass fractions for both Λ cold dark matter ( Λ CDM) and the R h = ct Universe and test them against the three largest cluster samples (LaRoque et al. 2006 Astrophys. J. 652, 917–936 ( doi:10.1086/508139 ); Allen et al. 2008 Mon. Not. R. Astron. Soc. 383, 879–896 ( doi:10.1111/j.1365-2966.2007.12610.x ); Ettori et al. 2009 Astron. Astrophys. 501, 61–73 ( doi:10.1051/0004-6361/200810878 )). We show that R h = ct is consistent with a constant f gas in the redshift range z ≲ 2 , as was previously shown for the reference Λ CDM model (with parameter values H 0 =70 km s −1 Mpc −1 , Ω m =0.3 and w Λ =−1). Unlike Λ CDM, however, the R h = ct Universe has no free parameters to optimize in fitting the data. Model selection tools, such as the Akaike information criterion and the Bayes information criterion (BIC), therefore tend to favour R h = ct over Λ CDM. For example, the BIC favours R h = ct with a likelihood of approximately 95% versus approximately 5% for Λ CDM.

Identifying cosmological perturbations in group field theory condensates

AbstractOne proposal for deriving effective cosmological models from theories of quantum gravity is to view the former as a mean-field (hydrodynamic) description of the latter, which describes a universe formed by a ‘condensate’ of quanta of geometry. This idea has been successfully applied within the setting of group field theory (GFT), a quantum field theory of ‘atoms of space’ which can form such a condensate. We further clarify the interpretation of this mean-field approximation, and show how it can be used to obtain a semiclassical description of the GFT, in which the mean field encodes a classical statistical distribution of geometric data. In this sense, GFT condensates are quantum homogeneous geometries that also contain statistical information about cosmological inhomogeneities. We show in the isotropic case how this information can be extracted from geometric GFT observables and mapped to quantities of observational interest. Basic uncertainty relations of (non-commutative) Fourier transforms imply that this statistical description can only be compatible with the observed near-homogeneity of the Universe if the typical length scale associated to the distribution is much larger than the fundamental ‘Planck’ scale. As an example of effective cosmological equations derived from the GFT dynamics, we then use a simple approximation in one class of GFT models to derive the ‘improved dynamics’ prescription of holonomy corrections in loop quantum cosmology.