Journal articles on the topic 'Cosmology: large-scale structure of Universe'
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1
Bahcall, N. A. "Large Scale Structure of the Universe." Symposium - International Astronomical Union 179 (1998): 317–28. http://dx.doi.org/10.1017/s0074180900128906.
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How is the universe organized on large scales? How did this structure evolve from the unknown initial conditions of a rather smooth early universe to the present time? The answers to these questions will shed light on the cosmology we live in, the amount, composition and distribution of matter in the universe, the initial spectrum of density fluctuations that gave rise to this structure, and the formation and evolution of galaxies, lusters of galaxies, and larger scale structures.To address these fundamental questions, large and accurate sky surveys are needed—in various wavelengths and to various depths. In this presentation I review current observational studies of large scale structure, present the constraints these observations place on cosmological models and on the amount of dark matter in the universe, and highlight some of the main unsolved problems in the field of large-scale structure that could be solved over the next decade with the aid of current and future surveys. I briefly discuss some of these surveys, including the Sloan Digital Sky Survey that will provide a complete imaging and spectroscopic survey of the high-latitude northern sky, with redshifts for the brightest ∼ 106 galaxies, 105 quasars, and 103.5 rich clusters of galaxies. The potentialities of the SDSS survey, as well as of cross-wavelength surveys, for resolving some of the unsolved problems in large-scale structure and cosmology are discussed.
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PANCHAPAKESAN, N., and SHIV K. SETHI. "INFLATIONARY COSMOLOGY AND LARGE SCALE STRUCTURE OF THE UNIVERSE." International Journal of Modern Physics A 07, no. 16 (June 30, 1992): 3769–80. http://dx.doi.org/10.1142/s0217751x92001678.
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Scale-invariant (flat) fluctuation spectra are the most generic outcomes of inflation. However, current observations of large scale structure require more fluctuation power on large scales than flat spectra give. One such observation concerns the existence of large cosmological bubbles on the scales ~ (20–50) Mpc in the galaxy distribution. We attempt an explanation of these structures based on an inflationary model containing two scalar fields. One of these fields undergoes a first order phase transition, owing to the evolution of the other. We study the distribution of bubbles formed during the phase trnasition and show that for a wide range of choice of the free parameters in our model, a few bubbles can survive and grow to become the bubble structures observed at present.
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Suto, Yasushi. "Simulations of Large-Scale Structure in the New Millennium." Symposium - International Astronomical Union 216 (2005): 105–19. http://dx.doi.org/10.1017/s0074180900196548.
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Simulations of large-scale structure in the universe have played a vital role in observational cosmology since the 1980's in particular. Their important role will definitely continue to be true in the 21st century; indeed the requirements for simulations in the precision cosmology era will become more progressively demanding as they are supposed to fill the missing link in an accurate and reliable manner between the “initial” condition at z=1000 revealed by WMAP and the galaxy/quasar distribution at z=0 − 6 surveyed by 2dF and SDSS. In this review, I will summarize what we have learned so far from the previous cosmological simulations, and discuss several remaining problems for the new millennium.
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ELLIS, GEORGE F. R. "COSMOLOGY AND LOCAL PHYSICS." International Journal of Modern Physics A 17, no. 20 (August 10, 2002): 2667–71. http://dx.doi.org/10.1142/s0217751x02011588.
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This article considers the two-way relationship between local physics and the large scale structure of the universe - in particular considering Olber's paradox, Mach's principle, and the various arrows of time. Thus the focus is various ways in which local physics is influenced by the universe itself.
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Futamase, Toshifumi. "Gravitational lensing in cosmology." International Journal of Modern Physics D 24, no. 05 (March 18, 2015): 1530011. http://dx.doi.org/10.1142/s0218271815300116.
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Gravitational lensing is a unique and direct probe of mass in the universe. It depends only on the law of gravity and does not depend on the dynamical state nor the composition of matter. Thus, it is used to study the distribution of the dark matter in the lensing object. Combined with the traditional observations such as optical and X-ray, it gives us useful informations of the structure formation in the universe. The lensing observables depend also on the global geometry as well as large scale structure of the universe. Therefore it is possible to withdraw useful constraints on the cosmological parameters once the distribution of lensing mass is accurately known. Since the first discovery of the lensing event by a galaxy in 1979, various kinds of lensing phenomena caused by star, galaxy, cluster of galaxies and large scale structure have been observed and are used to study mass distribution in various scales and cosmology. Thus, the gravitational lensing is now regarded as an indispensable research field in the observational cosmology. In this paper, we give an instructive introduction to gravitational lensing and its applications to cosmology.
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Ruffini, R., D. J. Song, and S. Taraglio. "The Neutrino Mass and the Cellular Large Scale Structure of the Universe." Symposium - International Astronomical Union 124 (1987): 719–22. http://dx.doi.org/10.1017/s0074180900159820.
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We show how within the theoretical framework of a Gamow cosmology with massive neutrinos, the observed correlation functions between galaxies and between clusters of galaxies, naturally lead to a “cellular” structure of the Universe. From the size of “elementary cells” we derive constraints on the value of the masses and chemical potentials of the cosmological “inos”. We outline a procedure to estimate the “effective” average mass density of the Universe. We predict also the angular size of the inhomogeneities to be expected in the cosmological black body radiation as remnants of this cellular structure. A possible relation of our model to a fractal structure is indicated.
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Okamura, Sadanori, Elaine Sadler, Francesco Bertola, Mark Birkinshaw, Françoise Combes, Roger L. Davies, Thanu Padmanabhan, and Rachel L. Webster. "DIVISION VIII: GALAXIES AND THE UNIVERSE." Proceedings of the International Astronomical Union 4, T27A (December 2008): 283–85. http://dx.doi.org/10.1017/s1743921308025702.
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Division VIII provides a focus for astronomers studying a wide range of problems related to galaxies and cosmology. Objects of the study include individual galaxies, groups and clusters of galaxies, large scale structure, comic microwave background radiation and the universe itself. Approaches are diverse from observational one to theoretical one including computer simulations.
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Masaki, Shogo, Takahiro Nishimichi, and Masahiro Takada. "Anisotropic separate universe simulations." Monthly Notices of the Royal Astronomical Society 496, no. 1 (June 5, 2020): 483–96. http://dx.doi.org/10.1093/mnras/staa1579.
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ABSTRACT The long-wavelength coherent overdensity and tidal force, which are not direct observables for a finite-volume survey, affect time evolution of cosmic structure formation and therefore clustering observables through the mode coupling. In this paper, we develop an ‘anisotropic’ separate universe (SU) simulation technique to simulate large-scale structure formation taking into account the effect of large-scale tidal force into the anisotropic expansion of local background. We modify the treepmN-body simulation code to implement the anisotropic SU simulations, and then study the ‘response’ function of matter power spectrum that describes how the matter power spectrum responds to the large-scale tidal effect as a function of wavenumber and redshift for a given global cosmology. We test and validate the SU simulation results from the comparison with the perturbation theory predictions and the results from high-resolution particle-mesh simulations. We find that the response function displays characteristic scale dependencies over the range of scales down to non-linear scales, up to k ≃ 6 h Mpc−1.
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Silk, Joseph. "Origin and evolution of the large-scale structure of the universe." Canadian Journal of Physics 68, no. 9 (September 1, 1990): 799–807. http://dx.doi.org/10.1139/p90-117.
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Ever since the epoch of the spontaneous breaking of grand unification symmetry between the nuclear and electromagnetic interactions, the universe has expanded under the imprint of a spectrum of density fluctuations that is generally considered to have originated in this phase transition. I will discuss various possibilities for the form of the primordial fluctuation spectrum, spanning the range of adiabatic fluctuations, isocurvature fluctuations, and cosmic strings. Growth of the seed fluctuations by gravitational instability generates the formation of large-scale structures, from the scale of galaxies to that of clusters and superclusters of galaxies. There are three areas of confrontation with observational cosmology that will be reviewed. The large-scale distribution of the galaxies, including the apparent voids, sheets and filaments, and the coherent peculiar velocity field on scales of several tens of megaparsecs, probe the primordial fluctuation spectrum on scales that are only mildly nonlinear. Even larger scales are probed by study of the anisotropy of the cosmic microwave background radiation, which provides a direct glimpse of the primordial fluctuations that existed about 106 years or so after the initial big bang singularity. Galaxy formation is the process by which the building blocks of the universe have formed, involving a complex interaction between hydrodynamical and dynamical processes in a collapsing gas cloud. Both by detection of forming galaxies in the most remote regions of the universe and by study of the fundamental morphological characteristics of galaxies, which provide a fossilized memory of their past, can one relate the origin of galaxies to the same primordial fluctuation spectrum that gave rise' to the large-scale structure of the universe.
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Smoot, G. F. "Of Cosmic Background Anisotropies." Symposium - International Astronomical Union 168 (1996): 31–44. http://dx.doi.org/10.1017/s007418090010991x.
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Observations of the Cosmic Microwave Background (CMB) Radiation have put the standard model of cosmology, the Big Bang, on firm footing and provide tests of various ideas of large scale structure formation. CMB observations now let us test the role of gravity and General Relativity in cosmology including the geometry, topology, and dynamics of the Universe. Foreground galactic emissions, dust thermal emission and emission from energetic electrons, provide a serious limit to observations. Nevertheless, observations may determine if the evolution of the Universe can be understood from fundamental physical principles.
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CLIFTON, TIMOTHY. "BACK-REACTION IN RELATIVISTIC COSMOLOGY." International Journal of Modern Physics D 22, no. 03 (March 2013): 1330004. http://dx.doi.org/10.1142/s0218271813300048.
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We introduce the concept of back-reaction in relativistic cosmological modeling. Roughly speaking, this can be thought of as the difference between the large-scale behavior of an inhomogeneous cosmological solution of Einstein's equations, and a homogeneous and isotropic solution that is a best-fit to either the average of observables or dynamics in the inhomogeneous solution. This is sometimes paraphrased as "the effect that structure has of the large-scale evolution of the universe." Various different approaches have been taken in the literature in order to try and understand back-reaction in cosmology. We provide a brief and critical summary of some of them, highlighting recent progress that has been made in each case.
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CIARCELLUTI, PAOLO. "COSMOLOGY WITH MIRROR DARK MATTER." International Journal of Modern Physics D 19, no. 14 (December 2010): 2151–230. http://dx.doi.org/10.1142/s0218271810018438.
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Mirror matter is a stable self-collisional dark matter candidate. If parity is a conserved unbroken symmetry of nature, there could exist a parallel hidden (mirror) sector of the universe composed of particles with the same masses and obeying the same physical laws as our (visible) sector, except for the opposite-handedness of weak interactions. The two sectors interact predominantly via gravity, therefore mirror matter is naturally "dark". Here I review the cosmological signatures of mirror dark matter, concerning thermodynamics of the early universe, big bang nucleosynthesis, primordial structure formation and evolution, cosmic microwave background and large scale structure power spectra. Besides gravity, the effects on primordial nucleosynthesis of the kinetic mixing between photons and mirror photons are considered. Summarizing the present status of research and comparing theoretical results with observations/experiments, it emerges that mirror matter is not just a viable, but a promising dark matter candidate.
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Peña, G. A., and G. N. Candlish. "The large-scale structure from non-Gaussian primordial perturbations." Monthly Notices of the Royal Astronomical Society 511, no. 2 (January 29, 2022): 2259–73. http://dx.doi.org/10.1093/mnras/stac206.
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ABSTRACT The late-time effect of primordial non-Gaussianity offers a window into the physics of inflation and the very early Universe. In this work, we study the consequences of a particular class of primordial non-Gaussianity that is fully characterized by initial density fluctuations drawn from a non-Gaussian probability density function, rather than by construction of a particular form for the primordial bispectrum. We numerically generate multiple realizations of cosmological structure and use the late-time matter power spectrum, bispectrum, and trispectrum to determine the effect of these modified initial conditions. We show that the initial non-Gaussianity has only a small imprint on the first three polyspectra, when compared to a standard Gaussian cosmology. Furthermore, some of our models present an interesting scale-dependent deviation from the Gaussian case in the bispectrum and trispectrum, although the signal is at most at the per cent level. The majority of our models are consistent with cosmic microwave background constraints on the trispectrum, while the others are only marginally excluded. Finally, we discuss further possible extensions of our study.
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Bahcall, Neta A. "Dark matter universe." Proceedings of the National Academy of Sciences 112, no. 40 (September 28, 2015): 12243–45. http://dx.doi.org/10.1073/pnas.1516944112.
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Most of the mass in the universe is in the form of dark matter—a new type of nonbaryonic particle not yet detected in the laboratory or in other detection experiments. The evidence for the existence of dark matter through its gravitational impact is clear in astronomical observations—from the early observations of the large motions of galaxies in clusters and the motions of stars and gas in galaxies, to observations of the large-scale structure in the universe, gravitational lensing, and the cosmic microwave background. The extensive data consistently show the dominance of dark matter and quantify its amount and distribution, assuming general relativity is valid. The data inform us that the dark matter is nonbaryonic, is “cold” (i.e., moves nonrelativistically in the early universe), and interacts only weakly with matter other than by gravity. The current Lambda cold dark matter cosmology—a simple (but strange) flat cold dark matter model dominated by a cosmological constant Lambda, with only six basic parameters (including the density of matter and of baryons, the initial mass fluctuations amplitude and its scale dependence, and the age of the universe and of the first stars)—fits remarkably well all the accumulated data. However, what is the dark matter? This is one of the most fundamental open questions in cosmology and particle physics. Its existence requires an extension of our current understanding of particle physics or otherwise point to a modification of gravity on cosmological scales. The exploration and ultimate detection of dark matter are led by experiments for direct and indirect detection of this yet mysterious particle.
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Canizares, Claude R. "Gravitational Lenses as Tools in Observational Cosmology." Symposium - International Astronomical Union 124 (1987): 729–46. http://dx.doi.org/10.1017/s0074180900159844.
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The study of gravitational lenses is intimately tied to observational cosmology. When we observe a gravitationally lensed quasar, we are viewing a single object along two or more neighboring paths (null geodesics) of cosmological dimensions (Figure 1). What we see depends on bulk properties of the universe, such as Ho and qo, on the large scale structure and inhomogeneities along the paths, and on the small scale structure in and around the primary deflector. Furthermore, the deflection of light depends on the gravitational field along the line of sight, so it is sensitive to all forms of matter: luminous or dark, baryonic or exotic. Thus the images of gravitationally lensed quasars contain an imprint of the universe that is virtually inaccessible by any other means. The hope of decoding this imprint has stimulated observers and theorists to expend many thousands of hours of telescope time, computer time and cogitation on the elucidation of gravitational lens properties.
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Impey, Chris. "What We Don’t Know About the Universe." International Astronomical Union Colloquium 171 (1999): 393–400. http://dx.doi.org/10.1017/s0252921100054610.
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AbstractDespite progress on many fronts in cosmology, outstanding questions remain. What is the nature of the dark matter? Is the inflationary big bang model viable? Must we accept a non-zero cosmological constant? Do we know the true population of galaxies? What is the range of star formation histories in the universe? Can gravity alone explain the large scale structure we observe? Studies of the low surface brightness universe may provide the answers to many of these questions.
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Peña, G. A., and G. N. Candlish. "The Effect of Non-Gaussian Primordial Perturbations on Large-Scale Structure." Proceedings of the International Astronomical Union 16, S362 (June 2020): 26–32. http://dx.doi.org/10.1017/s1743921322001788.
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AbstractThe late-time effect of primordial non-Gaussianity offers a window into the physics of inflation and the very early Universe. In this work we study the consequences of a particular class of primordial non-Gaussianity that is fully characterized by initial density fluctuations drawn from a non-Gaussian probability density function, rather than by construction of a particular form for the primordial bispectrum. We numerically generate multiple realisations of cosmological structure and use the late-time matter polyspectra to determine the effect of these modified initial conditions. In this non-Gaussianity has only a small imprint on the first polyspectra, when compared to a standard Gaussian cosmology. Furthermore, some of our models present an interesting scale-dependent deviation from the Gaussian case in the bispectrum and trispectrum, although the signal is at most at the percent level.
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Pfeifer, Simon, Ian G. McCarthy, Sam G. Stafford, Shaun T. Brown, Andreea S. Font, Juliana Kwan, Jaime Salcido, and Joop Schaye. "The BAHAMAS project: effects of dynamical dark energy on large-scale structure." Monthly Notices of the Royal Astronomical Society 498, no. 2 (August 6, 2020): 1576–92. http://dx.doi.org/10.1093/mnras/staa2240.
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ABSTRACT In this work, we consider the impact of spatially uniform but time-varying dark energy (or ‘dynamical dark energy’, DDE) on large-scale structure in a spatially flat universe, using large cosmological hydrodynamical simulations that form part of the BAHAMAS project. As DDE changes the expansion history of the universe, it impacts the growth of structure. We explore variations in DDE that are constrained to be consistent with the cosmic microwave background. We find that DDE can affect the clustering of matter and haloes at the $\sim 10{{\ \rm per\ cent}}$ level (suppressing it for so-called freezing models, while enhancing it for thawing models), which should be distinguishable with upcoming large-scale structure surveys. DDE cosmologies can also enhance or suppress the halo mass function (with respect to Lambda cold dark matter) over a wide range of halo masses. The internal properties of haloes are minimally affected by changes in DDE, however. Finally, we show that the impact of baryons and associated feedback processes is largely independent of the change in cosmology and that these processes can be modelled separately to typically better than a few per cent accuracy.
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Mughal, Muhammad Zahid, Iftikhar Ahmad, and Juan Luis García Guirao. "Relativistic Cosmology with an Introduction to Inflation." Universe 7, no. 8 (July 30, 2021): 276. http://dx.doi.org/10.3390/universe7080276.
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In this review article, the study of the development of relativistic cosmology and the introduction of inflation in it as an exponentially expanding early phase of the universe is carried out. We study the properties of the standard cosmological model developed in the framework of relativistic cosmology and the geometric structure of spacetime connected coherently with it. The geometric properties of space and spacetime ingrained into the standard model of cosmology are investigated in addition. The big bang model of the beginning of the universe is based on the standard model which succumbed to failure in explaining the flatness and the large-scale homogeneity of the universe as demonstrated by observational evidence. These cosmological problems were resolved by introducing a brief acceleratedly expanding phase in the very early universe known as inflation. The cosmic inflation by setting the initial conditions of the standard big bang model resolves these problems of the theory. We discuss how the inflationary paradigm solves these problems by proposing the fast expansion period in the early universe. Further inflation and dark energy in fR modified gravity are also reviewed.
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Tartaglia, Angelo. "The strained state cosmology." International Journal of Modern Physics A 31, no. 02n03 (January 20, 2016): 1641015. http://dx.doi.org/10.1142/s0217751x16410153.
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Starting from some relevant facts concerning the behavior of the universe over large scale and time span, the analogy between the geometric approach of General Relativity and the classical description of an elastic strained material continuum is discussed. Extending the elastic deformation approach to four dimensions it is shown that the accelerated expansion of the universe is recovered. The strain field of space-time reproduces properties similar to the ones ascribed to the dark energy currently called in to explain the accelerated expansion. The strain field in the primordial universe behaves as radiation, but asymptotically it reproduces the cosmological constant. Subjecting the theory to a number of cosmological tests confirms the soundness of the approach and gives an optimal value for the one parameter of the model, i.e. the bulk modulus of the space-time continuum. Finally various aspects of the Strained State Cosmology (SSC) are discussed and contrasted with some non-linear massive gravity theories. The possible role of structure topological defects is also mentioned. The conclusion is that SSC is at least as good as the [Formula: see text]CDM standard cosmology, giving a more intuitive interpretation of the physical nature of the phenomena.
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Giovanelli, Riccardo. "ALFALFA: HI Cosmology in the Local Universe." Proceedings of the International Astronomical Union 3, S244 (June 2007): 73–82. http://dx.doi.org/10.1017/s1743921307013853.
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AbstractFor the last 25 years, the 21 cm line has been used productively to investigate the large–scale structure of the Universe, its peculiar velocity field and the measurement of cosmic parameters. In February 2005 a blind HI survey that will cover 7074 square degrees of the high latitude sky was started at Arecibo, using the 7-beam feed L-band feed array (ALFA). Known as the Arecibo Legacy Fast ALFA (ALFALFA) Survey, the program is producing a census of HI-bearing objects over a cosmologically significant volume of the local Universe. With respect to previous blind HI surveys, ALFALFA offers an improvement of about one order of magnitude in sensitivity, 4 times the angular resolution, 3 times the spectral resolution, and 1.6 times the total bandwidth of HIPASS. ALFALFA can detect 7×104D2M⊙of HI, whereDis the source distance in Mpc. As of mid 2007, 44% of the survey observations and 15% of the source extraction are completed. We discuss the status of the survey and present a few preliminary results, in particular with reference to the proposed “dark galaxy” VirgoHI21.
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Dumin, Yurii V. "Nonlocal Quantum Effects in Cosmology." Advances in High Energy Physics 2014 (2014): 1–8. http://dx.doi.org/10.1155/2014/241831.
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Since it is commonly believed that the observed large-scale structure of the universe is an imprint of quantum fluctuations existing at the very early stage of its evolution, it is reasonable to pose the question: do the effects of quantum nonlocality, which are well established now by the laboratory studies, manifest themselves also in the early universe? We try to answer this question by utilizing the results of a few experiments, namely, with the superconducting multi-Josephson-junction loops and the ultracold gases in periodic potentials. Employing a close analogy between the above-mentioned setups and the simplest one-dimensional Friedmann-Robertson-Walker cosmological model, we show that the specific nonlocal correlations revealed in the laboratory studies might be of considerable importance also in treating the strongly nonequilibrium phase transitions of Higgs fields in the early universe. Particularly, they should substantially reduce the number of topological defects (e.g., domain walls) expected due to independent establishment of the new phases in the remote spatial regions. This gives us a hint on resolving a long-standing problem of the excessive concentration of topological defects, inconsistent with observational constraints. The same effect may be also relevant to the recent problem of the anomalous behavior of cosmic microwave background fluctuations at large angular scales.
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Yee, H. K. C., M. J. Sawicki, R. G. Carlberg, H. Lin, S. L. Morris, D. R. Patton, G. D. Wirth, et al. "The CNOC2 Field Galaxy Redshipt Survey." Highlights of Astronomy 11, no. 1 (1998): 460–63. http://dx.doi.org/10.1017/s153929960002178x.
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Fundamental to our understanding of the universe is the evolution of structures, from galaxies to clusters of galaxies to large-scale sheets and filaments of galaxies and voids. The investigation of the evolution of large-scale structure not only provides us with the key test of theories of structure formation, but also allows us to measure fundamental cosmological parameters. The CNOC2 (Canadian Network for Observational Cosmology) Field Galaxy Redshift Survey is the first large redshift survey of faint galaxies carried out with the explicit goal of investigating the evolution of large scale structure. This survey also provides the largest redshift and photometric data set currently available for the study of galaxy population and evolution at the moderate redshift range between 0.1 and 0.6. In this paper we describe the scope and technique of the survey, its status, and some preliminary results.
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Ijjas, Anna. "Numerical Relativity as a New Tool for Fundamental Cosmology." Physics 4, no. 1 (March 4, 2022): 301–14. http://dx.doi.org/10.3390/physics4010021.
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Advances in our understanding of the origin, evolution, and structure of the universe have long been driven by cosmological perturbation theory, model building, and effective field theory. In this review, numerical relativity is introduced as a powerful new complementary tool for fundamental cosmology. To illustrate its power, applications of numerical relativity are discussed to studying the robustness of slow contraction and inflation in homogenizing, isotropizing, and flattening the universe beginning from generic unsmooth initial conditions. In particular, it is described how recent numerical relativity studies of slow contraction have revealed a novel, non-linear smoothing mechanism based on ultralocality that challenges the conventional view on what is required to explain the large-scale homogeneity and isotropy of the observable universe.
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CIARCELLUTI, PAOLO. "COSMOLOGY WITH MIRROR DARK MATTER II: COSMIC MICROWAVE BACKGROUND AND LARGE SCALE STRUCTURE." International Journal of Modern Physics D 14, no. 02 (February 2005): 223–56. http://dx.doi.org/10.1142/s0218271805006225.
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This is the second paper of a series devoted to the study of the cosmological implications of the existence of mirror dark matter. The parallel hidden mirror world has the same microphysics as the observable one and couples the latter only gravitationally. The primordial nucleosynthesis bounds demand that the mirror sector should have a smaller temperature T′ than the ordinary one T, and by this reason its evolution can be substantially deviated from the standard cosmology. In this paper we take scalar adiabatic perturbations as the input in a flat Universe, and compute the power spectra for ordinary and mirror CMB and LSS, changing the cosmological parameters, and always comparing with the CDM case. We find differences in both the CMB and LSS power spectra, and we demonstrate that the LSS spectrum is particularly sensitive to the mirror parameters, due to the presence of both the oscillatory features of mirror baryons and the collisional mirror Silk damping. For x<0.3 the mirror baryon–photon decoupling happens before the matter–radiation equality, so that CMB and LSS power spectra in linear regime are equivalent for mirror and CDM cases. For higher x-values the LSS spectra strongly depend on the amount of mirror baryons. Finally, qualitatively comparing with the present observational limits on the CMB and LSS spectra, we show that for x<0.3 the entire dark matter could be made of mirror baryons, while in the case x≳0.3 the pattern of the LSS power spectrum excludes the possibility of dark matter consisting entirely of mirror baryons, but they could present as admixture (up to ~50%) to the conventional CDM.
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Lesgourgues, Julien, and Sergio Pastor. "Neutrino Mass from Cosmology." Advances in High Energy Physics 2012 (2012): 1–34. http://dx.doi.org/10.1155/2012/608515.
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Neutrinos can play an important role in the evolution of the universe, modifying some of the cosmological observables. In this contribution we summarize the main aspects of cosmological relic neutrinos, and we describe how the precision of present cosmological data can be used to learn about neutrino properties, in particular their mass, providing complementary information to beta decay and neutrinoless double-beta decay experiments. We show how the analysis of current cosmological observations, such as the anisotropies of the cosmic microwave background or the distribution of large-scale structure, provides an upper bound on the sum of neutrino masses of order 1 eV or less, with very good perspectives from future cosmological measurements which are expected to be sensitive to neutrino masses well into the sub-eV range.
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Nikonov, Maxim, Mikhail Chekal, Stanislav Shirokov, Andrey Baryshev, and Vladimir Gorokhov. "The Line-of-Sight Analysis of Spatial Distribution of Galaxies in the COSMOS2015 Catalogue." Universe 6, no. 11 (November 20, 2020): 215. http://dx.doi.org/10.3390/universe6110215.
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New observations of high-redshift objects are crucial for the improvement of the standard ΛCDM cosmological model and our understanding of the Universe. One of the main directions of modern observational cosmology is the analysis of the large-scale structure of Universe, in particular, in deep fields. We study the large-scale structure of the Universe along the line of sight using the latest version of the COSMOS2015 catalogue, which contains 518,404 high quality photometric redshifts of galaxies selected in the optical range of the COSMOS field (2×2 deg2), with depth up to the redshift z∼6. We analyze large-scale fluctuations in the number of galaxies along the line of sight and provide an estimate of the average linear sizes of the self-correlating fluctuations (structures) in independent redshift bins of Δz=0.1 along with the estimate of the standard deviation from homogeneity (the observed cosmic variance). We suggest a new method of the line-of-sight analysis based on previous works and formulate further prospects of method development. For the case of the theoretical form of approximation of homogeneity in the ΛCDM framework, the average standard deviation of detected structures from homogeneity is σmeanΛCDM=0.09±0.02, and the average characteristic size of structures is RmeanΛCDM=790±150 Mpc. For the case of the empirical approximation of homogeneity, the average standard deviation of detected structures from homogeneity is σmeanempiric=0.08±0.01, and the average characteristic size of structures is Rmeanempiric=640±140 Mpc.
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Biagetti, Matteo. "The Hunt for Primordial Interactions in the Large-Scale Structures of the Universe." Galaxies 7, no. 3 (August 8, 2019): 71. http://dx.doi.org/10.3390/galaxies7030071.
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The understanding of the primordial mechanism that seeded the cosmic structures we observe today in the sky is one of the major goals in cosmology. The leading paradigm for such a mechanism is provided by the inflationary scenario, a period of violent accelerated expansion in the very early stages of evolution of the universe. While our current knowledge of the physics of inflation is limited to phenomenological models which fit observations, an exquisite understanding of the particle content and interactions taking place during inflation would provide breakthroughs in our understanding of fundamental physics at high energies. In this review, we summarize recent theoretical progress in the modeling of the imprint of primordial interactions in the large-scale structures of the universe. We focus specifically on the effects of such interactions on the statistical distribution of dark-matter halos, providing a consistent treatment of the steps required to connect the correlations generated among fields during inflation all the way to the late-time correlations of halos.
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Peacock, John A. "The cosmic web: a selective history and outlook." Proceedings of the International Astronomical Union 11, S308 (June 2014): 125–42. http://dx.doi.org/10.1017/s1743921316009741.
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AbstractIn the Century since Slipher's first observations, roughly three million galaxy redshifts have been measured. The resulting maps of large-scale structure have taught us much of central importance in cosmology, ranging from the matter content of the universe to the study of the primordial density fluctuations. This talk aims to review some of the key observational and theoretical milestones on this journey, and to speculate about what the future may bring.
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Fasano, A., M. Aguiar, A. Benoit, A. Bideaud, O. Bourrion, M. Calvo, A. Catalano, et al. "KISS: a spectrometric imager for millimetre cosmology." EPJ Web of Conferences 228 (2020): 00010. http://dx.doi.org/10.1051/epjconf/202022800010.
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Clusters of galaxies are used to map the large-scale structures in the universe and as probe of universe evolution. They can be observed through the Sunyaev-Zel’dovich (SZ) effect. In this respect the spectro-imaging at low resolution frequency is an important tool, today, for the study of cluster of galaxies. We have developed KISS (KIDs Interferometer Spectrum Survey), a spectrometric imager dedicated to the secondary anisotropies of the Cosmic Microwave Background (CMB). The multi-frequency approach permits to improve the component separation with respect to predecessor experiments. In this paper, firstly, we provide a description of the scientific context and the state of the art of SZ observations. Secondly, we describe the KISS instrument. Finally, we show preliminary results of the ongoing commissioning campaign.
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Dupuy, Alexandra, Hélène M. Courtois, Noam I. Libeskind, and Daniel Guinet. "Segmenting the Universe into dynamically coherent basins." Monthly Notices of the Royal Astronomical Society 493, no. 3 (February 24, 2020): 3513–20. http://dx.doi.org/10.1093/mnras/staa536.
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ABSTRACT This paper explores in depth a watershed concept to partition the Universe, introduced in a previous Letter and applied to the Cosmicflows-3 observational data set. We present a series of tests conducted with cosmological dark matter simulations. In particular, we are interested in quantifying the evolution with redshift of large-scale structures when defined as segmented basins of attraction. This new dynamical definition in the field of measuring standard rulers demonstrates robustness since all basins show a density contrast δ above 1 (mean Universe density) independently of the simulation spatial resolution or the redshift. Another major finding is that density profiles of the basins show universality in slope. Consequently, there is a unique definition of what is a gravitational watershed at a large scale, which can be further used as a probe for cosmology studies.
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Porto, Rafael A. "Gravitational waves and the (quantum) nature of the primordial seed." International Journal of Modern Physics D 23, no. 12 (October 2014): 1441005. http://dx.doi.org/10.1142/s0218271814410053.
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At first glance, the (indirect) measurement of primordial tensor modes by the BICEP2 Collaboration supports an inflationary paradigm for early universe cosmology together with quantum vacuum fluctuations (aka gravitons) as the origin of the spectrum. In this paper, we argue the observed signal may instead be a signature of semiclassical sources of perturbations during inflation. In this scenario, despite a large tensor-to-scalar ratio r ≃ 0.2, it may be possible to write an effective field theory (EFT) of a rolling scalar field without super-Planckian excursions. If the results from BICEP2 withstand further scrutiny, measurements of primordial non-Gaussianity with large scale structure surveys, and direct detection of gravitational waves (GWs) with the new generation of observatories, will be of paramount importance to elucidate the (quantum) origin of structure in the universe.
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Baryshev, Yurij V., Francesco Sylos Labini, Marco Montuori, Luciano Pietronero, and Pekka Teerikorpi. "On the Fractal Structure of Galaxy Distribution and its Implications for Cosmology." Fractals 06, no. 03 (September 1998): 231–43. http://dx.doi.org/10.1142/s0218348x98000286.
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Two fundamental empirical laws have been established in the analysis of galaxy space distribution. First, recent analyses have revealed that the three-dimensional distribution of galaxies and clusters is characterized by large-scale structures and huge voids: such a distribution shows fractal correlations up to the limits of the available samples. This has confirmed the earlier de Vaucouleurs power-law density — distance relation, now corresponding to a fractal structure with dimension D ≈ 2, at least, in the range of scales ~1 ÷ 200 Mpc (H0=55 km/sec/Mpc). An eventual cut-off towards homogenization has not been yet identified. Second, since Huble's discovery, the linear redshift-distance law has been well established within 200 Mpc and also much deeper. The co-existence of these laws within the same scales is a challenge for the standard cosmology, where the linear Hubble law is a strict consequence of homogeneity of the expanding universe. This puzzle is now sufficiently strong to raise doubts for the standard cosmology.
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Chu, Yaoquan, and LiZhi Fang. "Spatial Distribution of Quasars." Symposium - International Astronomical Union 124 (1987): 627–38. http://dx.doi.org/10.1017/s0074180900159650.
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The distribution of quasars has become one of the most interesting problems in observational cosmology. This is due mainly to the development of theory of the formation of large scale structure in the universe. In recent years, several scenarios of clustering have been proposed. In the adiabatic case, the clustering process is from larger scales to smaller ones, i.e., the first systems to form out would be on the scale of superclusters, then these systems fragment to form smaller scale systems such as galaxies. In the isothermal case, the clustering is from smaller scales to larger ones, namely, galaxies condense out at first and larger scale systems, such as clusters and superclusters, then form later via hierachical build-up processes. In the universe contain two components, the scenario of clustering might be different from both standard adiabatic and isothermal cases(1). According to this new scenario, there should be two kinds of small scale objects, one is formed due to fragment of larger scale systems, another is formed before large scale systems form.
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Puget, J. L., N. Aghanim, R. Gispert, F. R. Bouchet, and E. Hivon. "Planning Future Space Measurements of the CMB." Symposium - International Astronomical Union 168 (1996): 447–52. http://dx.doi.org/10.1017/s0074180900110344.
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A central problem in cosmology is the building and testing of a full and detailed theory for the formation of (large-scale) structures in the Universe. It is widely believed that the observed structures today grew by gravitational instability out of very small density perturbations. Such perturbations should have left imprints as small temperature anisotropies in the cosmic microwave background (CMB) radiation.
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PIETRONERO, LUCIANO, MAURIZIO BOTTACCIO, MARCO MONTUORI, and FRANCESCO SYLOS LABINI. "SCALING IN COSMIC STRUCTURES." Fractals 11, supp01 (February 2003): 271–79. http://dx.doi.org/10.1142/s0218348x03001938.
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The study of the properties of cosmic structures in the universe is one of the most fascinating subject of the modern cosmology research. Far from being predicted, the large scale structure of the matter distribution is a very recent discovery, which continuosly exhibits new features and issues. We have faced such topic along two directions; from one side we have studied the correlation properties of the cosmic structures, that we have found substantially different from the commonly accepted ones. From the other side, we have studied the statistical properties of the very simplified system, in the attempt to capture the essential ingredients of the formation of the observed strucures.
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Vazza, F. "How complex is the cosmic web?" Monthly Notices of the Royal Astronomical Society 491, no. 4 (November 27, 2019): 5447–63. http://dx.doi.org/10.1093/mnras/stz3317.
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ABSTRACT The growth of large-scale cosmic structure is a beautiful exemplification of how complexity can emerge in our Universe, starting from simple initial conditions and simple physical laws. Using enzo cosmological numerical simulations, I applied tools from Information Theory (namely, ‘statistical complexity’) to quantify the amount of complexity in the simulated cosmic volume, as a function of cosmic epoch and environment. This analysis can quantify how much difficult to predict, at least in a statistical sense, is the evolution of the thermal, kinetic, and magnetic energy of the dominant component of ordinary matter in the Universe (the intragalactic medium plasma). The most complex environment in the simulated cosmic web is generally found to be the periphery of large-scale structures (e.g. galaxy clusters and filaments), where the complexity is on average ∼10–102 times larger than in more rarefied regions, even if the latter dominate the volume-integrated complexity of the simulated Universe. If the energy evolution of gas in the cosmic web is measured on a ≈100 ${\rm kpc}\, h^{-1}$ resolution and over a ≈200 $\rm Myr$ time-scale, its total complexity is in the range of $\sim 10^{16}\!-\!10^{17} \rm \,bits$, with little dependence on the assumed gas physics, cosmology, or cosmic variance.
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Padmanabhan, Hamsa. "Neutral hydrogen in the post-reionization universe." Proceedings of the International Astronomical Union 12, S333 (October 2017): 216–21. http://dx.doi.org/10.1017/s1743921317010821.
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AbstractThe evolution of neutral hydrogen (HI) across redshifts is a powerful probe of cosmology, large scale structure in the universe and the intergalactic medium. Using a data-driven halo model to describe the distribution of HI in the post-reionization universe (z ∼ 5 to 0), we obtain the best-fitting parameters from a rich sample of observational data: low redshift 21-cm emission line studies, intermediate redshift intensity mapping experiments, and higher redshift Damped Lyman Alpha (DLA) observations. Our model describes the abundance and clustering of neutral hydrogen across redshifts 0 - 5, and is useful for investigating different aspects of galaxy evolution and for comparison with hydrodynamical simulations. The framework can be applied for forecasting future observations with neutral hydrogen, and extended to the case of intensity mapping with molecular and other line transitions at intermediate redshifts.
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Munshi, Dipak, and Patrick Valageas. "Cosmology with weak lensing surveys." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 363, no. 1837 (October 25, 2005): 2675–91. http://dx.doi.org/10.1098/rsta.2005.1672.
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Weak gravitational lensing is responsible for the shearing and magnification of the images of high-redshift sources due to the presence of intervening mass. Since the lensing effects arise from deflections of the light rays due to fluctuations of the gravitational potential, they can be directly related to the underlying density field of the large-scale structures. Weak gravitational surveys are complementary to both galaxy surveys and cosmic microwave background observations as they probe unbiased nonlinear matter power spectra at medium redshift. Ongoing CMBR experiments such as WMAP and a future Planck satellite mission will measure the standard cosmological parameters with unprecedented accuracy. The focus of attention will then shift to understanding the nature of dark matter and vacuum energy: several recent studies suggest that lensing is the best method for constraining the dark energy equation of state. During the next 5 year period, ongoing and future weak lensing surveys such as the Joint Dark Energy Mission (JDEM; e.g. SNAP) or the Large-aperture Synoptic Survey Telescope will play a major role in advancing our understanding of the universe in this direction. In this review article, we describe various aspects of probing the matter power spectrum and the bispectrum and other related statistics with weak lensing surveys. This can be used to probe the background dynamics of the universe as well as the nature of dark matter and dark energy.
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Audouze, J., G. Setti, J. Gunn, S. Hayakawa, M. S. Longair, I. Novikov, G. A. Tammann, V. Trimble, and G. de Vaucouleurs. "47. Cosmology." Transactions of the International Astronomical Union 19, no. 1 (1985): 655–50. http://dx.doi.org/10.1017/s0251107x00006726.
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The preparation of a report dealing with such a large domain is almost an impossible task. Because so many different questions, problems and expertises are assembled under the word “Cosmology”, my approach has been the following: first to divide this field in a somewhat arbitrary fashion into the following sections: very early universe – elementary particle and cosmology – early nucleosynthesiscosmological parameters (Hubble constant, deceleration parameter, cosmological constant) – large scale structures, intergalactic gas, missing mass – clusters of galaxies and intercluster gas – anisotropy of the black body radiation – formation of galaxies – quasars and their evolution – cosmological evolution of radiosources. I have then asked to the most knowledgeable specialists to review briefly each of these most important questions on which many excitinq and very new results have been obtained not only by the astrophysicists themselves but also by particle physicists, nuclear physicists, theoretical physicists, … This is why the reader will read in section 1 the report on primordial nucleosynthesis written by G. Steigman, in section 2 Anisotropy of the black body radiation by D.T. Wilkinson and E. Meichiorri, in section 3 Clusters of galaxies by 3. Einasto, in section 4 Galaxy formation by B.J.T. Jones, in section 5 Quasars and their evolution by M. Schmidt and in section 6 the Cosmological evolution of radio sources by R.A. Windhorst. Let me thank these colleagues for their excellent work in writing these various reviews.
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Ahmedov, Bobomurat J., Roustam M. Zalaletdinov, Zafar Ya Turakulov, Salakhutdin N. Nuritdinov, and Karomat T. Mirtadjieva. "Relativistic astrophysics and cosmology in Uzbekistan." Proceedings of the International Astronomical Union 2, SPS5 (August 2006): 159–66. http://dx.doi.org/10.1017/s174392130700693x.
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AbstractThe theoretical results obtained in Uzbekistan in the field of relativistic astrophysics and cosmology are presented. In particular electrostatic plasma modes along the open field lines of a rotating neutron star and Goldreich-Julian charge density in general relativity are analyzed for the rotating and oscillating magnetized neutron stars. The impact that stellar oscillations of different type (radial, toroidal and spheroidal ones) have on electric and magnetic fields external to a relativistic magnetized star has been investigated. A study of the dynamical evolution and the number of stellar encounters in globular clusters with a central black hole is presented. Perturbation features and instabilities of the large-scale oscillations on the background of the non-linearly pulsating isotropic and isotropic Ω-models are studied. The non-stationary dispersion equation of the sectorial perturbations for the general case and the results of certain oscillation mode analysis are given. The model composed as the linear superposition of two other models was constructed and the stability of this model is studied. In a cosmological setting the theory of macroscopic gravity as a large-distance scale generalization of general relativity has been developed. Exact cosmological solutions to the equations of macroscopic gravity for a flat spatially homogeneous, isotropic space-time are found. The gravitational correlation terms in the averaged Einstein equations have the form of spatial curvature, dark matter and dark energy (cosmological constant) with particular equations of state for each correlation regime. Interpretation of these cosmological models to explain the observed large-scale structure of the accelerating Universe with a significant amount of the nonluminous (dark) matter is discussed.
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Vazquez Gonzalez, J. Alberto, Luis E. Padilla, and Tonatiuh Matos. "Inflationary cosmology: from theory to observations." Revista Mexicana de Física E 17, no. 1 Jan-Jun (January 28, 2020): 73. http://dx.doi.org/10.31349/revmexfise.17.73.
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The main aim of this paper is to provide a qualitative introduction to the cosmological inflation theory and its relationship with current cosmological observations. The inflationary model solves many of the fundamental problemsthat challenge the Standard Big Bang cosmology such as the Flatness, Horizon and the magnetic Monopole problems. Additionally it provides an explanation for the initial conditions observed throughout the Large-Scale Structure of the Universe, such as galaxies. In this review we describe general solutions to the problems in the Big Bang cosmology carry out by a single scalar eld. Then, with the use of current surveys, we show the constraints imposed on the inflationary parameters (ns; r) which allow us to make the connection between theoretical and observational cosmology. In this way, with the latest results, it is possible to select or at least to constrain the right inflationary model, parameterized by a single scalar eld potential V (\phi).
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Bean, Rachel, Pedro G. Ferreira, and Andy Taylor. "A new golden age: testing general relativity with cosmology." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 369, no. 1957 (December 28, 2011): 4941–46. http://dx.doi.org/10.1098/rsta.2011.0366.
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Gravity drives the evolution of the Universe and is at the heart of its complexity. Einstein's field equations can be used to work out the detailed dynamics of space and time and to calculate the emergence of large-scale structure in the distribution of galaxies and radiation. Over the past few years, it has become clear that cosmological observations can be used not only to constrain different world models within the context of Einstein gravity but also to constrain the theory of gravity itself. In this article, we look at different aspects of this new field in which cosmology is used to test theories of gravity with a wide range of observations.
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Huterer, Dragan. "Mapping the universe with dark energy survey." International Journal of Modern Physics A 33, no. 34 (December 10, 2018): 1845015. http://dx.doi.org/10.1142/s0217751x1845015x.
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First, I summarize the current status of dark energy, including methods to use data to separate between general-relativity and modified-gravity scenarios for the accelerating universe. Then, I discuss recent results from the Dark Energy Survey, currently the world’s leading experiment mapping large-scale structure in the universe. Year-1 DES analysis performed in 2017 included the combination of galaxy clustering, cosmic shear, and their cross-correlation to impose constraints on key cosmological parameters, while upcoming Year-3 and -5 analyses will dramatically improve those constraints. I discuss some of the challenges in this complex analysis, its results, and the more general path forward toward better understanding of dark matter and dark energy in the universe. I also comment on the foremost tension in the field of cosmology today: between local measurements of the Hubble constant from type Ia supernovae, and global measurements from the cosmic microwave background anisotropies.
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Hong, Sungryong, Donghui Jeong, Ho Seong Hwang, Juhan Kim, Sungwook E. Hong, Changbom Park, Arjun Dey, Milos Milosavljevic, Karl Gebhardt, and Kyoung-Soo Lee. "Constraining cosmology with big data statistics of cosmological graphs." Monthly Notices of the Royal Astronomical Society 493, no. 4 (February 27, 2020): 5972–86. http://dx.doi.org/10.1093/mnras/staa566.
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ABSTRACT By utilizing large-scale graph analytic tools implemented in the modern big data platform, apache spark, we investigate the topological structure of gravitational clustering in five different universes produced by cosmological N-body simulations with varying parameters: (1) a WMAP 5-yr compatible ΛCDM cosmology, (2) two different dark energy equation of state variants, and (3) two different cosmic matter density variants. For the big data calculations, we use a custom build of standalone Spark/Hadoop cluster at Korea Institute for Advanced Study and Dataproc Compute Engine in Google Cloud Platform with sample sizes ranging from 7 to 200 million. We find that among the many possible graph-topological measures, three simple ones: (1) the average of number of neighbours (the so-called average vertex degree) α, (2) closed-to-connected triple fraction (the so-called transitivity) $\tau _\Delta$, and (3) the cumulative number density ns ≥ 5 of subgraphs with connected component size s ≥ 5, can effectively discriminate among the five model universes. Since these graph-topological measures are directly related with the usual n-points correlation functions of the cosmic density field, graph-topological statistics powered by big data computational infrastructure opens a new, intuitive, and computationally efficient window into the dark Universe.
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Collins, C. A. "Galaxy Clustering in the Southern Hemisphere." International Astronomical Union Colloquium 148 (1995): 510–21. http://dx.doi.org/10.1017/s0252921100022454.
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AbstractIn this paper some of the major results from the COSMOS and APM digitised galaxy surveys are presented. The main motivation behind these catalogues was to study large-scale structure in the universe. We begin by outlining the importance of such studies to cosmology and discussing the early results from the visually compiled galaxy catalogues. The impact of the digitised catalogues is demonstrated by focussing on three key areas of research; the galaxy-galaxy two-point angular correlation function, the cluster-cluster spatial correlation function, and galaxy number counts.
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Mohayaee, Roya, Mohamed Rameez, and Subir Sarkar. "Do supernovae indicate an accelerating universe?" European Physical Journal Special Topics 230, no. 9 (June 23, 2021): 2067–76. http://dx.doi.org/10.1140/epjs/s11734-021-00199-6.
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AbstractIn the late 1990’s, observations of two directionally-skewed samples of, in total, 93 Type Ia supernovae were analysed in the framework of the Friedmann–Lemaître–Robertson–Walker (FLRW) cosmology. Assuming these to be ‘standard(isable) candles’ it was inferred that the Hubble expansion rate is accelerating as if driven by a positive Cosmological Constant $$\varLambda $$ Λ in Einstein’s theory of gravity. This is still the only direct evidence for the ‘dark energy’ that is the dominant component of today’s standard $$\varLambda $$ Λ CDM cosmological model. Other data such as baryon acoustic oscillations (BAO) in the large-scale distribution of galaxies, temperature fluctuations in the cosmic microwave background (CMB), measurement of stellar ages, the rate of growth of structure, etc are all ‘concordant’ with this model but do not provide independent evidence for accelerated expansion. The recent discussions about whether the inferred acceleration is real rests on analysis of a larger sample of 740 SNe Ia which shows that these are not quite standard candles, and more importantly highlights the ‘corrections’ that are applied to analyse the data in the FLRW framework. The latter holds in the reference frame in which the CMB is isotropic, whereas observations are carried out in our heliocentric frame in which the CMB has a large dipole anisotropy. This is assumed to be of kinematic origin i.e. due to our non-Hubble motion driven by local inhomogeneity in the matter distribution which has grown under gravity from primordial density perturbations traced by the CMB fluctuations. The $$\varLambda $$ Λ CDM model predicts how this peculiar velocity should fall off as the averaging scale is raised and the universe becomes sensibly homogeneous. However observations of the local ‘bulk flow’ are inconsistent with this expectation and convergence to the CMB frame is not seen. Moreover, the kinematic interpretation implies a corresponding dipole in the sky distribution of high redshift quasars, which is rejected by observations at $$4.9\sigma $$ 4.9 σ . Hence the peculiar velocity corrections employed in supernova cosmology are inconsistent and discontinuous within the data. The acceleration of the Hubble expansion rate is in fact anisotropic at $$3.9\sigma $$ 3.9 σ and aligned with the bulk flow. Thus dark energy could be an artefact of analysing data assuming that we are idealised observers in an FLRW universe, when in fact the real universe is inhomogeneous and anisotropic out to distances large enough to impact on cosmological analyses.
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Lee, Khee-Gan. "Lyα Forest Tomography of the z > 2 Cosmic Web." Proceedings of the International Astronomical Union 11, S308 (June 2014): 360–63. http://dx.doi.org/10.1017/s1743921316010164.
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AbstractThe hydrogen Lyα forest is an important probe of the z > 2 Universe that is otherwise challenging to observe with galaxy redshift surveys, but this technique has traditionally been limited to 1D studies in front of bright quasars. However, by pushing to faint magnitudes (g > 23) with 8-10m large telescopes it becomes possible to exploit the high area density of high-redshift star-forming galaxies to create 3D tomographic maps of large-scale structure in the foreground. I describe the first pilot observations using this technique, as well discuss future surveys and the resulting science possibilities for galaxy evolution and cosmology.
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Frontiere, Nicholas, J. D. Emberson, Michael Buehlmann, Joseph Adamo, Salman Habib, Katrin Heitmann, and Claude-André Faucher-Giguère. "Simulating Hydrodynamics in Cosmology with CRK-HACC." Astrophysical Journal Supplement Series 264, no. 2 (January 24, 2023): 34. http://dx.doi.org/10.3847/1538-4365/aca58d.
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Abstract We introduce CRK-HACC, an extension of the Hardware/Hybrid Accelerated Cosmology Code (HACC), to resolve gas hydrodynamics in large-scale structure formation simulations of the universe. The new framework couples the HACC gravitational N-body solver with a modern smoothed-particle hydrodynamics (SPH) approach called conservative reproducing kernel SPH (CRKSPH). CRKSPH utilizes smoothing functions that exactly interpolate linear fields while manifestly preserving conservation laws (momentum, mass, and energy). The CRKSPH method has been incorporated to accurately model baryonic effects in cosmology simulations—an important addition targeting the generation of precise synthetic sky predictions for upcoming observational surveys. CRK-HACC inherits the codesign strategies of the HACC solver and is built to run on modern GPU-accelerated supercomputers. In this work, we summarize the primary solver components and present a number of standard validation tests to demonstrate code accuracy, including idealized hydrodynamic and cosmological setups, as well as self-similarity measurements.
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Fosalba, Pablo, and Enrique Gaztañaga. "Explaining cosmological anisotropy: evidence for causal horizons from CMB data." Monthly Notices of the Royal Astronomical Society 504, no. 4 (April 30, 2021): 5840–62. http://dx.doi.org/10.1093/mnras/stab1193.
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ABSTRACT The origin of power asymmetry and other measures of statistical anisotropy on the largest scales of the universe, as manifested in cosmic microwave background (CMB) and large-scale structure data, is a long-standing open question in cosmology. In this paper, we analyse the Planck Legacy temperature anisotropy data and find strong evidence for a violation of the Cosmological principle of isotropy, with a probability of being a statistical fluctuation of the order of ∼10−9. The detected anisotropy is related to large-scale directional ΛCDM cosmological parameter variations across the CMB sky, which are sourced by three distinct patches in the maps with circularly averaged sizes between 40° and 70° in radius. We discuss the robustness of our findings to different foreground separation methods and analysis choices, and find consistent results from WMAP data when limiting the analysis to the same scales. We argue that these well-defined regions within the cosmological parameter maps may reflect finite and casually disjoint horizons across the observable universe. In particular, we show that the observed relation between horizon size and mean dark energy density within a given horizon is in good agreement with expectations from a recently proposed model of the universe that explains cosmic acceleration and cosmological parameter tensions between the high- and low-redshift universe from the existence of casual horizons within our universe.