Cosmological Applications Research Articles

Radio Plateaus in Gamma-Ray Burst Afterglows and Their Application in Cosmology

The plateau phase in radio afterglows has been observed in very few gamma-ray bursts (GRBs), and in this paper, 27 radio light curves with plateau phases were acquired from the published literature. We obtain the related parameters of the radio plateau, such as temporal indexes during the plateau phase (α 1 and α 2), break time (T b,z), and the corresponding radio flux (F b). The two-parameter Dainotti relation between the break time of the plateau and the corresponding break luminosity (L b,z) in the radio band is . Including the isotropic energy E γ,iso and peak energy E p,i, the three-parameter correlations for the radio plateaus are written as and , respectively. The correlations are less consistent with those of the X-ray and optical plateaus, implying that radio plateaus may have a different physical mechanism. The typical frequencies crossing the observational band may be a reasonable hypothesis that causes the breaks of the radio afterglows. We calibrate the GRB empirical luminosity correlations as a standard candle for constraining cosmological parameters and find that our samples can constrain the flat ΛCDM model well but are not sensitive to the nonflat ΛCDM model. By combining GRBs with other probes, such as supernovae and the CMB, the constraints on the cosmological parameters are Ωm = 0.297 ± 0.006 for the flat ΛCDM model and Ωm = 0.283 ± 0.008, ΩΛ = 0.711 ± 0.006 for the nonflat ΛCDM model.

Dark Energy or Modified Gravity?

Abstract We consider some of the epistemic benefits of exploring “theory space” in the context of modifications of general relativity with intended applications in cosmology. We show how studying modifications of general relativity can help in assessing the robustness of empirical inferences, particularly in inaccessible regimes. We also discuss challenges to sharply distinguishing apparently distinct directions in theory space.

Trans-Planckian censorship constraints on properties and cosmological applications of axion-like fields

We use the Trans-Planckian Censorship Conjecture (TCC) to constrain the decay constants f characterizing a set of N identical axion-like fields with cosine potentials, improving upon the precision of other Swampland conjectures and existing string-theoretic arguments. We find that consistency with the TCC requires any such set of axion-like fields to satisfy fN≲0.6Mpl, where Mpl is the reduced Planck mass. We show that this bound makes models of axion-driven inflation incapable of simultaneously producing the required number of e-foldings and the observed scalar spectral tilt. In contrast, we find that models of axion quintessence can be simultaneously compatible with the TCC and observational data, provided that the axions' initial field values are set near the maxima of their potentials to within roughly ±π5f.

Cosmology in the Lorentz gauge theory

This proceeding is an introduction to cosmological applications of the Lorentz gauge theory. It provides the ingredients for a unique, though yet tentative [Formula: see text]CDM theory of cosmology. Emergence of spacetime is described by the spontaneous symmetry breaking called here the khronogenesis. Space is then associated with the field strength of the antiself-dual gauge potential, and gravity is associated with the self-dual field strength. In the cosmological setting, khronogenesis seems to predict inflation. It is shown that the Lorentz gauge theory allows the consistent description of spin currents which could have important roles in cosmological phenomenology.

Fock Quantization of a Klein–Gordon Field in the Interior Geometry of a Nonrotating Black Hole

We study the canonical quantization of a scalar field in Kantowski–Sachs spacetime. For simplicity, we consider compactified spatial sections, since this does not affect the ultraviolet behavior. A time-dependent canonical transformation is performed prior to quantization. As in previously studied cases, the purpose of this canonical transformation is to identify and extract the background contribution to the field evolution which is obstructing a unitary implementation of the field dynamics at the quantum level. This splitting of the time dependence into a background piece and the part to be seen as true quantum evolution is, to a large extent, determined by the unitarity requirement itself. The quantization is performed in the usual setup of Fock representations, demanding the preservation of the spatial symmetries. Under the joint requirements of quantum unitary dynamics and compatibility with those classical symmetries, the quantization is shown to be unique, in the sense that any two representations with these properties are unitarily equivalent. This confirms the validity of our conditions as criteria to discriminate among possibly inequivalent quantum descriptions. The interest of this analysis goes beyond cosmological applications since the interior of a nonrotating black hole has a geometry of the Kantowski–Sachs type.

The cosmological simulation code OpenGadget3 – implementation of meshless finite mass

ABSTRACT Subsonic turbulence plays a major role in determining properties of the intracluster medium (ICM). We introduce a new meshless finite mass (MFM) implementation in OpenGadget3 and apply it to this specific problem. To this end, we present a set of test cases to validate our implementation of the MFM framework in our code. These include but are not limited to: the soundwave and Kepler disc as smooth situations to probe the stability, a Rayleigh–Taylor and Kelvin–Helmholtz instability as popular mixing instabilities, a blob test as more complex example including both mixing and shocks, shock tubes with various Mach numbers, a Sedov blast wave, different tests including self-gravity such as gravitational freefall, a hydrostatic sphere, the Zeldovich-pancake, and a 1015 M⊙ galaxy cluster as cosmological application. Advantages over smoothed particle hydrodynamics (SPH) include increased mixing and a better convergence behaviour. We demonstrate that the MFM-solver is robust, also in a cosmological context. We show evidence that the solver preforms extraordinarily well when applied to decaying subsonic turbulence, a problem very difficult to handle for many methods. MFM captures the expected velocity power spectrum with high accuracy and shows a good convergence behaviour. Using MFM or SPH within OpenGadget3 leads to a comparable decay in turbulent energy due to numerical dissipation. When studying the energy decay for different initial turbulent energy fractions, we find that MFM performs well down to Mach numbers $\mathcal {M}\approx 0.01$. Finally, we show how important the slope limiter and the energy-entropy switch are to control the behaviour and the evolution of the fluids.

Parametrization of Hubble parameter in f̂(𝒯 ,𝒯G) gravity model with tachyon field

We look into the cosmological uses of the new modified gravitational theory [Formula: see text], which is based on the torsion invariant [Formula: see text] and the teleparallel equivalent of the Gauss–Bonnet term [Formula: see text]. The corresponding cosmology of [Formula: see text] gravity is very intriguing because it varies from both [Formula: see text] theories and the [Formula: see text] class of curvature-modified gravity. In this paper, we have investigated the applicability of an alternative gravitational theory called [Formula: see text] by applying the energy conditions. Here, we assumed the form of [Formula: see text], where [Formula: see text] and [Formula: see text] are arbitrary constants. We have examined the cosmological applications of [Formula: see text] gravity. Here, we consider two particular expressions of the time-dependent Hubble parameter. Both the model parameters are constrained jointly by the Observation Hubble dataset (OHD), the Pantheon dataset and the BAO data to constrain the model parameters using the Markov Chain Monte Carlo (MCMC) minimization technique. We determine the present values of Hubble constant for model [Formula: see text]: [Formula: see text], [Formula: see text] and [Formula: see text]; and model [Formula: see text]: [Formula: see text], [Formula: see text] and [Formula: see text] for the OHD+BAO+Pantheon dataset. Using the most recent estimated values of Hubble parameter, we properly analyzed the energy conditions and looked at the final behavior of our model. Additionally, we have explored the [Formula: see text] plane and also we have extracted the scalar field as well as potential of [Formula: see text] gravity and its relationship to the tachyon field. In addition, we find that, depending on the model parameters, the dark energy (DE) equation-of-state (EoS) parameter may be quintessence or phantom-like, or it may undergo phantom-divide crossing. Finally, we find that all the essential features of the model are satisfied successfully.

Parity violating scalar-tensor model in teleparallel gravity and its cosmological application

The parity violating model based on teleparallel gravity is a competitive scheme for parity violating gravity, which has been preliminary studied in the literature. To further investigate the parity violating model in teleparallel gravity, in this paper, we construct all independent parity-odd terms that are quadratic in torsion tensor and coupled to a scalar field in a way without higher-order derivatives. Using these parity-odd terms, we formulate a general parity violating scalar-tensor model in teleparallel gravity and obtain its equations of motion. To explore potentially viable models within the general model, we investigate the cosmological application of a submodel of the general model in which terms above the second power of torsion are eliminated. We focus on analyzing cosmological perturbations and identify the conditions that preserve the parity violating signal of gravitational waves at linear order while avoiding the ghost instability.

Cosmological application of the lens-redshift probability distribution with improved galaxy-scale gravitational lensing sample

Cosmological application of the lens-redshift probability distribution with improved galaxy-scale gravitational lensing sample

Tensor gauge boson dark matter extension of the electroweak sector

The existence of dark matter is explained by a new, massive, neutral, non-symmetric, rank-2 tensor gauge boson (hbox {Z}_{{upmu upnu }}-boson). The hbox {Z}_{{upmu upnu }}-boson can be predicted by the tensor gauge boson extension of the Electro Weak (EW) theory, proposed by Savvidy (Phys Lett B 625:341, 2005). The non-symmetric rank-2 tensor hbox {Z}_{{upmu upnu }} can be decomposed into a symmetric (hbox {Z}_{{(upmu upnu )}}) and anti-symmetric (hbox {Z}_{{[upmu upnu ]}}) part. Based on the non-Lagrangian formulation for the free sector of the hbox {R}_{textrm{2}}-theory proposed recently by Criado et al. (Phys Rev D 102:125031, arXiv:2010.02224, 2020), our massive anti-symmetric tensor field hbox {Z}_{{[upmu upnu ]}} corresponds to the massive symmetric spinor field hbox {Z}_{{upalpha upbeta upgamma updelta }} in the (2,0) irrep. For the massive hbox {Z}_{{upalpha upbeta upgamma updelta }} with the hbox {Z}_{textrm{2}}-symmetric Higgs portal couplings to a Standard Model (SM) particle, we compute the self-annihilation cross-section of the hbox {Z}_{{upalpha upbeta upgamma updelta }} dark matter and calculate its relic abundance. We also study the SM-SM particle scattering due to the exchange of the massive-hbox {Z}_{{(upmu upnu )}} symmetric field at a high energy scale. This proposition may have far reaching applications in astrophysics and cosmology.

Cosmological application of the Maxwell gravity

In this study, we consider a cosmological model for the Maxwell gravity which is constructed by gauging the semi-simple extended Poincaré algebra. Inspired by the Einstein–Yang–Mills theory, we describe the Maxwell gauge field in terms of two additional time-dependent scalar fields. Within the context of a homogeneous and isotropic Friedmann–Lemaître–Robertson–Walker universe, we derive the Friedmann equations together with new contributions. Additionally, we examine the modified Friedmann equation to demonstrate how diverse cosmological scenarios can be achieved within this framework. Moreover, we investigate the gauge theory of gravity based on the Maxwell algebra and show that this model leads to the (anti)-de Sitter universe as well as a non-accelerated universe model.

Data-driven templates with dictionary learning and sparse representations for photometric redshift estimation

The quality of photometric redshift estimates is fundamental for cosmological applications, as the constraints on the cosmological parameters obtained by the photometric surveys strongly rely on their precision and accuracy. In order to obtain reliable redshift estimates, a large number of studies have proposed different algorithms based on SED template fitting and machine learning methodologies. While template fitting strategies do not need spectroscopic data for training, they also provide consistent estimates in most scenarios. On the other hand, machine learning-based approaches succeed at building a mapping function between the input space (composed by magnitudes and other physical parameters) and the target photometric redshift space. These empirical methods lead to more accurate results as long as the spectroscopic ground truth properly represents the actual galaxy population distribution. Thus, combining template fitting and machine learning techniques would allow to leverage the advantages of both methodologies yielding hybrid methods. The goal is to provide a good estimation accuracy while maximizing the photometric range coverage. This is particularly important in the high-z regime, where the spectroscopic training sample is rarely available. We propose in this article a new method to derive data-driven templates from simulated spectra using dictionary learning. As these representations are obtained directly from the data, they allow to capture the physical properties of the galaxies better than theoretical templates. Inspired by hybrid algorithms, the dictionary is built hierarchically and the features of the different types of galaxies are separated. Once the dictionary has been created, the data-driven templates are artificially redshifted and the observed spectra are sparsely decomposed on this dictionary. The value providing the minimum reconstruction error is selected as the photometric redshift estimate. This new technique, astride template fitting and machine learning, builds representations for the galaxy spectra through unsupervised learning and computes the photometric redshifts by χ2 minimization. The performance of the algorithm has been evaluated on realistic galaxy photometric simulations as well as on real data from the Canada–France–Hawaii Telescope Lensing Survey.

Principal component analysis of galaxy clustering in hyperspace of galaxy properties

ABSTRACT Ongoing and upcoming galaxy surveys are providing precision measurements of galaxy clustering. However, a major obstacle in its cosmological application is the stochasticity in the galaxy bias. We explore whether the principal component analysis (PCA) of galaxy correlation matrix in hyperspace of galaxy properties (e.g. magnitude and colour) can reveal further information on mitigating this issue. Based on the hydrodynamic simulation TNG300-1, we analyse the cross-power spectrum matrix of galaxies in the magnitude and colour space of multiple photometric bands. (1) We find that the first principal component $E_i^{(1)}$ is an excellent proxy of the galaxy deterministic bias bD, in that $E_i^{(1)}=\sqrt{P_{mm}/\lambda ^{(1)}}b_{D,i}$. Here, i denotes the i-th galaxy sub-sample. λ(1) is the largest eigenvalue, and Pmm is the matter power spectrum. We verify that this relation holds for all the galaxy samples investigated, down to k ∼ 2h Mpc−1. Since $E_i^{(1)}$ is a direct observable, we can utilize it to design a linear weighting scheme to suppress the stochasticity in the galaxy–matter relation. For an LSST-like magnitude limit galaxy sample, the stochasticity $\mathcal {S}\equiv 1-r^2$ can be suppressed by a factor of $\gtrsim 2$ at k = 1h Mpc−1. This reduces the stochasticity-induced systematic error in the matter power spectrum reconstruction combining galaxy clustering and galaxy-galaxy lensing from $\sim 12~{{\ \rm per\ cent}}$ to $\sim 5~{{\ \rm per\ cent}}$ at k = 1h Mpc−1. (2) We also find that $\mathcal {S}$ increases monotonically with fλ and $f_{\lambda ^2}$. $f_{\lambda ,\lambda ^2}$ quantify the fractional contribution of other eigenmodes to the galaxy clustering and are direct observables. Therefore, the two provide extra information on mitigating galaxy stochasticity.

Forecast of cross-correlation of Chinese Survey Space Telescope cosmic shear tomography with Ali CMB Polarization Telescope cosmic microwave background lensing

ABSTRACT We present a forecast study on the cross-correlation between cosmic shear tomography from the Chinese Survey Space Telescope (CSST) and cosmic microwave background (CMB) lensing from Ali CMB Polarization Telescope (AliCPT-1) in Tibet. The correlated galaxy and CMB lensing signals were generated from Gaussian realizations based on inputted auto and cross-spectra. To account for the error budget, we considered the CMB lensing reconstruction noise based on the AliCPT-1 lensing reconstruction pipeline; shape noise of the galaxy lensing measurement; CSST photo-z error; photo-z bias; intrinsic alignment (IA) effect; and multiplicative bias. The AliCPT-1 CMB lensing mock data were generated according to two experimental stages, namely the ‘4 modules*yr’ and ‘48 modules*yr’ cases. We estimate the cross-spectra in four tomographic bins according to the CSST photo-z distribution in the range of z ∈ [0, 4). After reconstructing the pseudo-cross-spectra from the realizations, we calculate the signal-to-noise ratio (SNR). By combining the four photo-z bins, the total cross-correlation SNR ≈ 15 (AliCPT-1 ‘4 modules*yr’) and SNR ≈ 22 (AliCPT-1 ‘48 modules*yr’). Finally, we study the cosmological application of this cross-correlation signal. Excluding IA in the template fitting would lead to roughly a 0.6σ increment in σ8 due to the negative IA contribution to the galaxy lensing data. For AliCPT-1 first and second stages, the cross-correlation of CSST cosmic shear with CMB lensing gives errors on the clustering amplitude $\sigma _{\sigma _8}=^{+0.043}_{-0.038}$ or $\sigma _{S_8}=\pm 0.031$ and $\sigma _{\sigma _8}=^{+0.030}_{-0.027}$ or $\sigma _{S_8}=\pm 0.018$, respectively.

The foreground transfer function for H i intensity mapping signal reconstruction: MeerKLASS and precision cosmology applications

ABSTRACT Blind cleaning methods are currently the preferred strategy for handling foreground contamination in single-dish H i intensity mapping surveys. Despite the increasing sophistication of blind techniques, some signal loss will be inevitable across all scales. Constructing a corrective transfer function using mock signal injection into the contaminated data has been a practice relied on for H i intensity mapping experiments. However, assessing whether this approach is viable for future intensity mapping surveys, where precision cosmology is the aim, remains unexplored. In this work, using simulations, we validate for the first time the use of a foreground transfer function to reconstruct power spectra of foreground-cleaned low-redshift intensity maps and look to expose any limitations. We reveal that even when aggressive foreground cleaning is required, which causes ${\gt }\, 50~{{\ \rm per\ cent}}$ negative bias on the largest scales, the power spectrum can be reconstructed using a transfer function to within sub-per cent accuracy. We specifically outline the recipe for constructing an unbiased transfer function, highlighting the pitfalls if one deviates from this recipe, and also correctly identify how a transfer function should be applied in an autocorrelation power spectrum. We validate a method that utilizes the transfer function variance for error estimation in foreground-cleaned power spectra. Finally, we demonstrate how incorrect fiducial parameter assumptions (up to ${\pm }100~{{\ \rm per\ cent}}$ bias) in the generation of mocks, used in the construction of the transfer function, do not significantly bias signal reconstruction or parameter inference (inducing ${\lt }\, 5~{{\ \rm per\ cent}}$ bias in recovered values).

Legendre scalarization in gravity and cosmology

We propose a new formulation of f(R) gravity, dubbed scalarized f(R) gravity, in which the Legendre transform is included as a dynamical term. This leads to a theory with second-order field equations that describes general relativity with a self-interacting scalar field, without requiring the introduction of conformal frames. We demonstrate that the quadratic version of scalarized f(R) gravity reduces to general relativity with a massive scalar field, and we explore its implications for Friedmann cosmology. Our findings suggest that scalarized f(R) gravity may lead to simplified descriptions of cosmological applications, while the proposed formulation could offer a new perspective on the relationship between f(R) gravity and scalar–tensor theories.

Kasner cosmology in bumblebee gravity

Kasner cosmology is a vacuum and anisotropically expanding spacetime in the general relativity context. In this work, such a cosmological model is studied in another context, the bumblebee model, where the Lorentz symmetry is spontaneously broken. By using the bumblebee context it is possible to justify the anisotropic feature of the Kasner cosmology. Thus, the origin of the anisotropy in this cosmological model could be in the Lorentz symmetry breaking. Lastly, an application in the pre-inflationary cosmology is suggested.

The dynamics of domain wall strings

We study the dynamics of domain wall solitons in (2+1)d field theories. These objects are extended along one of the spatial directions, so they also behave as strings; hence the name of domain wall strings. We show analytically and numerically that the amount of radiation from the propagation of wiggles on these objects is negligible except for regions of high curvature. Therefore, at low curvatures, the domain wall strings behave exactly as the Nambu-Goto action predicts. We show this explicitly with the use of several different numerical experiments of the evolution of these objects in a lattice. We then explore their dynamics in the presence of internal mode excitations. We do this again by performing field theory simulations and identify an effective action that captures the relevant interactions between the different degrees of freedom living on the string. We uncover a new parametric resonance instability that transfers energy from the internal mode to the position of the domain wall. We show that this instability accelerates the radiation of the internal mode energy. We also explore the possibility of exciting the internal mode of the soliton with the collision of wiggles on the domain wall. Our numerical experiments indicate that this does not happen unless the wiggles have already a wavelength of the order of the string thickness. Finally, we comment on the possible relevance of our findings to cosmological networks of defects. We argue that our results cast some doubts on the significance of the internal modes in cosmological applications beyond a brief transient period right after their formation. This, however, should be further investigated using cosmological simulations of our model.

The XXL Survey

Context.X-ray observations of galaxy clusters are impacted by the presence of active galactic nuclei (AGNs) in a manner that is challenging to quantify, leading to biases in the detection and measurement of cluster properties for both astrophysics and cosmological applications.Aims.We detect and characterise clusters contaminated by central AGNs within the XXL survey footprint and provide a systematic assessment of the cosmological impact of such systems in X-ray cluster samples.Methods.We introduce a new automated class for AGN-contaminated (AC) clusters in the XXL source detection pipeline. The majority of these systems are otherwise missed by current X-ray cluster-detection methods. The AC selection is also effective in distinguishing AGN and cool-core presence using supplementary optical and infrared information.Results.We present 33 AC objects, including 25 clusters in the redshift range, 0.14 ≤ z ≤ 1.03, and eight other sources with significantly peaked central profiles based on X-ray observations. Six of these are new confirmed clusters. We computed the missed fraction of the XXL survey, which is defined as the fraction of genuine clusters that are undetected due to their centrally peaked X-ray profiles. We report seven undetected AC clusters abovez > 0.6, in the range where X-ray cluster detection efficiency drops significantly. The missed fraction is estimated to be at the level of 5% for the 50 square-degree XXL area. The impact on cosmological estimates from missed clusters is negligible for XXL, but it produces a tension of ∼3σwith the fiducial cosmology when considering larger survey areas.Conclusions.This work demonstrates the first systematic attempt to quantify the percentage of missed clusters in X-ray surveys as a result of central AGN contamination. Looking towards surveys such as eROSITA and Athena, larger areas and increased sensitivity will significantly enhance cluster detection, and therefore robust methods for characterising AGN contamination will be crucial for precise cluster cosmology, particularly in the redshiftz > 1 regime.

Anisotropic Universe in [formula omitted] gravity, a novel study

f(Q,T) theory of gravity is very recently proposed to incorporate within the action Lagrangian, the trace T of the energy–momentum tensor along with the non-metricity scalar Q. The cosmological application of this theory in a spatially flat isotropic and homogeneous Universe is well-studied. However, our Universe is not isotropic since the Planck era and therefore to study a complete evolution of the Universe we must investigate the f(Q,T) theory in a model with a small anisotropy. This motivated us to presume a locally rotationally symmetric (LRS) Bianchi-I spacetime and derive the motion equations. We analyse the model candidate f(Q,T)=αQn+1+βT, and to constrain the parameter n, we employ the statistical Markov chain Monte Carlo (MCMC) method with the Bayesian approach using two independent observational datasets, namely, the Hubble datasets, and Type Ia supernovae (SNe Ia) datasets.