Cosmological Research Articles

Сотворил ли Бог окаменелости? К истории одной идеи

The subject of the paper is prochronism, e.g. the teaching which says that the world was created with the appearance of old age. It is shown that the sources of prochronism could be traced to the medieval doctrine of double truth and philosophy of Descartes, who suggested that cosmological theories on the origin of the Universe are purely conditional, while in fact the world was instantly created complete and mature. The idea of apparent, but non-existent past gained much credence during the first half of the 19th century, when paleontological and geological discoveries raised a question on how to square the age of the Earth and the life on it with the six days of Genesis. The hypothesis of prochronism was most fully developed in «Omphalos: an attempt to untie the geological knot» (1857), the book by the English naturalist P. Gosse. During the Darwinian time the interest in this doctrine was shown not only by Christian thinkers, but also by secular philosophers and science fiction writers. Elements of prochronism were also present in the writings of Scriptural geologists in the 19th century and their successors, the young earth creationists in the 20th century. The main objections against prochronism are critically considered. According to the most popular of them, if God had made the world appear older that it is, He thus would have deceived people. But from the point of view of prochronism, the creation of traces of never existed past was necessitated by the logic of causality, which required God to actualize all the consequences of historical epochs skipped by Him. The link between prochronism and the problem of pre-human sufferings is outlined. The conclusion is made that this doctrine, despite being counter-intuitive and rather notorious, is intellectually consistent and immune to the criticism.

The Effective Fluid Approach for Modified Gravity and Its Applications

In this review, we briefly summarize the so-called effective fluid approach, which is a compact framework that can be used to describe a plethora of different modified gravity models as general relativity (GR) and a dark energy (DE) fluid. This approach, which is complementary to the cosmological effective field theory, has several benefits, as it allows for the easier inclusion of most modified gravity models into the state-of-the-art Boltzmann codes that are typically hard-coded for GR and DE. Furthermore, it can also provide theoretical insights into their behavior since in linear perturbation theory it is easy to derive physically motivated quantities such as the DE anisotropic stress or the DE sound speed. We also present some explicit applications of the effective fluid approach with f(R), Horndeski and scalar–vector–tensor models, namely, how this approach can be used to easily solve the perturbation equations and incorporate the aforementioned modified gravity models into Boltzmann codes so as to obtain cosmological constraints using Monte Carlo analyses.

Universe before Big Bang

The ghost condensation of the early universe in a pre-big bang phase has been presented in this paper through duration of a non-singular bounce. The undergoing universe contracts and passes smoothly in an expanding universe via a post-big bang phase. Initially developing and then taming any ghost like instabilities, the Null Energy Condition (NEC) is explicitly violated through the curvature mechanism of an adiabatic perturbed metric. The vacuum state of the ongoing phase is stabilized via a Lagrangian that in essence stabilizes the vacuum state under the higher order derivatives. The violation of the NEC regards a catastrophic vacuum instability, which re-emerges with a correction valid at small energies and momenta, below the UV-cut-off scale that, could potentially be problematic if one tries to construct a UV-completed theory of this Ekpyrotic model. The scale-invariant curvature perturbation, that arises and is sourced out of the scale-invariant entropy perturbations sourced by 2-Ekpyrotic scalar fields, that, in contrast, becomes constant on the super-horizon limits, due to the non-singular nature of the background geometry. Apart, from the ghost condensates, this theory addresses the new Ekpyrotic theory which in order becomes a distinguishable alternative to inflation theory for the birth of the universe. As per the recent WMAP data, the Ekpyrotic model has a spectral red tilt that shows the bounced scalar potential falling through a negative phase shift during the matter-fluid fluctuations in the hot big bang phase.

Tachyonic cosmology with cubic contractions of the Riemann tensor

A new cosmological theory is proposed in the theoretical framework of modified gravity theories which is based on a tachyonic field non-minimally coupled with a specific topological invariant constructed with third order contractions of the Riemann tensor. After proposing the action of the cosmological model, the modified Friedmann relations and the Klein–Gordon equations are obtained, describing the corresponding geometrical corrections to the Einstein–Hilbert action. The physical features of the cosmological system are investigated by adopting the dynamical system analysis in the case of an exponential function for the geometrical coupling term. The investigation revealed that the cosmological system can explain the current accelerated expansion of the Universe and the matter dominated epoch, showing a high compatibility to the recent history of our Universe for various values of the coupling coefficients.

Singularities for Focal Sets of Timelike Sabban Curves in de Sitter 3-Space

In the theory of cosmology, de Sitter space is the symmetrical model of accelerated expansions of the universe. It is derived from the solution of the Einstein field equation, which has a positive cosmological constant. In this paper, we define the evolutes and focal surfaces of timelike Sabban curves in de Sitter space. We find that de Sitter focal surfaces can be regarded as caustics and de Sitter evolutes corresponding to the locus of the polar vectors of osculating de Sitter subspaces. By using singularity theory, we classify the singularities of the de Sitter focal surfaces and de Sitter evolutes and show that there is a close relationship between a new geometric invariant and the types of singularities. Moreover, the Legendrian dual relationships between the hyperbolic tangent indicatrix of timelike Sabban curves and the focal surfaces are given. Finally, we provide an example to illustrate our main results.

Some existence results for a class of Euclidean bosonic equations

We deal with a class of non-linear bosonic equation on Euclidean space(P)Δe−cΔu−u+g(x,u)=0,x∈RN. These equations emerge in the study of nonlocal cosmology and string theory, and they depend on operators of the form exp⁡(−cΔ), in which Δ is the Euclidean Laplace operator. By using variational method we study the existence of ground state solution and the existence of infinitely many solutions of (P).

Redshift drift cosmography with ELT and SKAO measurements

ABSTRACT Mapping the expansion history of the universe is a compelling task of physical cosmology, especially in the context of the observational evidence for the recent acceleration of the universe, which demonstrates that canonical theories of cosmology and particle physics are incomplete and that there is new physics still to be discovered. Cosmography is a phenomenological approach to cosmology, where (with some caveats) physical quantities are expanded as a Taylor series in the cosmological redshift z, or analogous parameters such as the rescaled redshift y = z/(1 + z) or the logarithmic redshift x = ln (1 + z). Moreover, the redshift drift of objects following cosmological expansion provides a model-independent observable, detectable by facilities currently under construction, viz. the Extremely Large Telescope and the Square Kilometre Array Observatory (at least in its full configuration). Here, we use simulated redshift drift measurements from the two facilities to carry out an assessment of the cosmological impact and model discriminating power of redshift drift cosmography. We find that the combination of measurements from the two facilities can provide a stringent test of the Λ cold dark matter paradigm, and that overall the logarithmic-based expansions of the spectroscopic velocity drift are the most reliable ones, performing better than analogous expansions in the redshift or the rescaled redshift: the former nominally gives the smaller error bars for the cosmographic coefficients but is vulnerable to biases in the higher order terms (in other words, it is only reliable at low redshifts), while the latter always performs poorly.

Compatibility of Einstein-Gauss-Bonnet inflation theory with non-minimal derivative coupling in the constant-roll

Inflation is a theory in cosmology that explains that the early universe experienceda very fast expansion in a very short time and is able to explain some cosmological problemsand the presence of gravitational waves generated during the inflation period. Based on theevent GW170817, it was found that c2t = 1, which indicates that the speed of gravitationalwaves is nearly equal to the speed of light. This contradicts several modified theories of gravity,one of which is the Einstein-Gauss-Bonnet theory. This paper examines the compatibility ofEinstein-Gauss-Bonnet inflation theory with the GW170817 phenomenon, with the addition ofthe Non-minimal derivative coupling term and the constant-roll approach and its characteristics.The formulation of observational quantities is carried out using Horndeski theory and EffectiveField Theory with ADM formalism and the calculations are done numerically. The constantvalues are selected in such a way that the spectral index values and tensor-scalar ratios are closeto the 2018 Planck data. The results found that this theory is compatible with GW170817 withthe influence of Gauss-Bonnet term and constant-roll parameter β most dominant.

Anomalies in physical cosmology

The ΛCDM cosmology passes demanding tests that establish it as a good approximation to reality. The theory is incomplete, of course, and open issues are being examined in active research programs. I offer a review of less widely discussed anomalies that might also point to hints to a still better cosmological theory if more closely examined.

Noether currents in theories with higher derivatives and theories with differential field transformation in action (DFTA)

The article is devoted to the investigation of the Noether currents and integrals of motion in the special subclass of theories with higher field derivatives -- theories under differential field transformations in action (DFTA). Under fairly general assertions, we derive a simple representation for the integrals as sums of "old" integrals of motion, terms, that vanishes on the "old" equations of motion and surface integrals. We show that for some cosmological theories of that kind with high order derivatives the last contribution can violate gauge invariance, specifically, diffeomorphisms. Then we investigate ambiguity of the Noether procedure for higher derivative theories and fix it in the way the problem resolves in quite general setting. The obtained results are discussed for the several extensions of the General Relativity, which are obtained by DFTA, in particular, for mimetic, disformal and Regge-Teitelboim theories of gravity.

New observables of the cosmic microwave background

We introduce new observables of the cosmic microwave background radiation, which can be measured through the detection of high order modes excited within an antenna feed system, coherently combined with those currently detected by space observatories. The use of such observables could potentially further constrain the validity of cosmological theories.

An Illustrated History of the Maṇḍala: From Its Genesis to the Kālacakratantra

An Illustrated History of the Maṇḍala: From Its Genesis to the Kālacakratantra

Updating non-standard neutrinos properties with Planck-CMB data and full-shape analysis of BOSS and eBOSS galaxies

Using the latest observational data from Planck-CMB and its combination with the pre-reconstructed full-shape (FS) galaxy power spectrum measurements from the BOSS DR12 sample and eBOSS LRG DR16 sample, we report the observational constraints on the cosmic neutrino properties given by the extended ΛCDM scenario: ΛCDM + N eff + ∑ mν + c 2 eff + c 2 vis + ξν , and its particular case ΛCDM + c 2 eff + c 2 vis + ξν , where N eff, ∑ mν , c 2 eff, c 2 vis, ξν are the effective number of species, the total neutrino mass, the sound speed in the neutrinos rest frame, the viscosity parameter and the degeneracy parameter quantifying a cosmological leptonic asymmetry, respectively. We observe that the combination of FS power spectrum measurements with the CMB data significantly improves the parametric space of the models compared to the CMB data alone case. We find no evidence for neutrinos properties other than the ones predicted by the standard cosmological theory. Our most robust observational constraints are given by CMB + BOSS analysis. For the generalized extended ΛCDM scenario, we find c 2 eff = 0.3304+0.0064 -0.0075, c 2 vis = 0.301+0.037 -0.033, ξν < 0.05, N eff = 2.90 ± 0.15 at 68% CL, with ∑ mν < 0.116 eV at 95% CL. These are the strongest limits ever reported for these extended ΛCDM scenarios.

Asymmetry in Galaxy Spin Directions—Analysis of Data from DES and Comparison to Four Other Sky Surveys

The paper shows an analysis of the large-scale distribution of galaxy spin directions of 739,286 galaxies imaged by DES. The distribution of the spin directions of the galaxies exhibits a large-scale dipole axis. Comparison of the location of the dipole axis to a similar analysis with data from SDSS, Pan-STARRS, and DESI Legacy Survey shows that all sky surveys exhibit dipole axes within 52° or less from each other, well within 1σ error, while non-random distribution is unexpected, the findings are consistent across all sky surveys, regardless of the telescope or whether the data were annotated manually or automatically. Possible errors that can lead to the observation are discussed. The paper also discusses previous studies showing opposite conclusions and analyzes the decisions that led to these results. Although the observation is provocative, and further research will be required, the existing evidence justifies considering the contention that galaxy spin directions as observed from Earth are not necessarily randomly distributed. Possible explanations can be related to mature cosmological theories, but also to the internal structure of galaxies.

Cosmological Perturbations in Bouncing Cosmologies and the Case of the Pre-Big Bang Scenario

Pre-Big Bang cosmology inspired generations of cosmologists in attempts to cure the initial Big Bang singularity using a fundamental length scale as proposed by string theory. The existence of a phase of collapse/inflation with increasing curvature followed by a cosmic bounce has been proposed as an alternative to standard inflation in the solution of the horizon and curvature problems. However, the generation of a nearly scale-invariant spectrum of perturbations is not an automatic prediction of such scenarios. In this paper, I review some general statements about the evolution of perturbations in bouncing cosmologies and some historically significant attempts to reconcile the predicted spectra with the observations. Bouncing cosmologies and, in particular, the pre-Big Bang scenario stand as viable, although more complicated, alternatives to inflation that may still help solve current theoretical and observational tensions.

Bayesian control variates for optimal covariance estimation with pairs of simulations and surrogates

ABSTRACT Predictions of the mean and covariance matrix of summary statistics are critical for confronting cosmological theories with observations, not least for likelihood approximations and parameter inference. Accurate estimates require running costly N-body and hydrodynamics simulations. Approximate solvers, or surrogates, greatly reduce the computational cost but introduce biases, especially in the non-linear regime of structure growth. We propose ‘CARPool Bayes’ to solve the inference problem for both the means and covariances using a combination of simulations and surrogates. Our approach allows incorporating prior information for the mean and covariance. We derive closed-form solutions for maximum a posteriori covariance estimates that are efficient Bayesian shrinkage estimators, guarantee positive semidefiniteness, and can optionally leverage analytical covariance approximations. We discuss choices of the prior and propose a procedure for obtaining optimal prior hyperparameter values with a small set of test simulations. We test our method by estimating the covariances of clustering statistics of gadget-iiiN-body simulations at redshift z = 0.5 using surrogates from a 100–1000× faster particle-mesh code. Taking the sample covariance from 15 000 simulations as the truth, and using an empirical Bayes prior with diagonal blocks, our estimator produces nearly identical Fisher matrix contours for ΛCDM parameters using only 15 simulations of the non-linear dark matter power spectrum. In this case, the number of simulations is so small that the sample covariance is degenerate. We show cases where even with a naïve prior our method improves the estimate. Our framework is applicable to a wide range of cosmological problems where fast surrogates are available.

Newtonian Cosmology and Relativistic Theory

This paper refutes the erroneous statements that arose in theoretical cosmology almost 90 years ago. The method accepted in the literature for deriving the local properties of the Friedmann cosmological model, using only Newton theory, without resorting to Einstein theory, is considered. We showed that the usual method of such inference is not sufficient to obtain the correct result, and leads to errors. Requirements are formulated that are sufficient for the Newtonian model to really be an approximation to the relativistic theory.

Cosmological-static metric correspondence and Kruskal type solutions from symmetry transformations

We develop a formalism which provides a new view for the transformation of spherically symmetric metrics, regarding cosmological and Kruskal type metrics. Our analysis begins with some general relevant dynamical metrics in cosmology, and prove that they all can be transformed to a unique static form. We extend the formalism to obtain generalized Kruskal type coordinates in cosmology and black hole theory. This extended formalism provides a novel mechanism to obtain suitable coordinate charts associated with spherically symmetric metrics. In particular, we obtain explicitly new Kruskal type coordinates for extremal Reissner-Nordström and Schwarzschild-de-Sitter metrics, as well for an extension of the de-Sitter metric.

Hyperelliptic Functions and Motion in General Relativity

Analysis of black hole spacetimes requires study of the motion of particles and light in these spacetimes. Here exact solutions of the geodesic equations are the means of choice. Numerous interesting black hole spacetimes have been analyzed in terms of elliptic functions. However, the presence of a cosmological constant, higher dimensions or alternative gravity theories often necessitate an analysis in terms of hyperelliptic functions. Here we review the method and current status for solving the geodesic equations for the general hyperelliptic case, illustrating it with a set of examples of genus g=2: higher dimensional Schwarzschild black holes, rotating dyonic U(1)2 black holes, and black rings.

KOSMOLOGI DALAM PANDANGAN IMAM KHOMEINI

The harmony between humans and the universe is getting less due to overexploitation. To overcome this, the proper guidance on treating the universe properly is highly needed. Therefore, Alquran has invited humans to take care of and be concerned about natural sustainability. This study focuses on the cosmology of Imam Khomeini regarding the universe since he is one of the most significant figures in the Iran revolution, known as a statesman, Sufi, philosopher, and Theologian. This study employs a qualitative approach using a literature review of Imam Khomeini’s publications. Anchored in Tajalli and Wahdatul would proposed by Ibnu ‘Arabi and other cosmology theories from philosophers and theologians, the cosmology of Khomeini was analyzed critically. The study reveals that the universe is the name of Allah, the name is the sign, and all creatures in the world are the sign of Allah. This leads to the perspective that the universe is Tajalli. From this point of view, humans should treat the universe more appropriately since it is a medium to make them get closer to their god.