Cosmology (Physics)

Cosmological Measurements with Forthcoming Radio Continuum Surveys

by Alvise Raccanelli

Co-authored with Gong-Bo Zhao, David Bacon, Matt Jarvis, Will Percival, Ray Norris, Huub Rottgering, Filipe Abdalla, Catherine Cress, Jean-Claude Kubwimana, Sam Lindsay, Bob Nichol, Mario Santos, Dominik Schwarz.
Submitted to MNRAS, 2011

We present forecasts for constraints on cosmological models which can be obtained by forthcoming radio continuum... more We present forecasts for constraints on cosmological models which can be obtained by forthcoming radio continuum surveys: the wide surveys with the LOw Frequency ARray (LOFAR), Australian Square Kilometre Array Pathfinder (ASKAP) and the Westerbork Observations of the Deep APERTIF Northern sky (WODAN). We use simulated catalogues appropriate to the planned surveys to predict measurements obtained with the source auto-correlation, the cross-correlation between radio sources and CMB maps (the Integrated Sachs-Wolfe effect), the cross-correlation of radio sources with foreground objects due to cosmic magnification, and a joint analysis together with the CMB power spectrum and supernovae. We show that near future radio surveys will bring complementary measurements to other experiments, probing different cosmological volumes, and having different systematics. Our results show that the unprecedented sky coverage of these surveys combined should provide the most significant measurement yet of the Integrated Sachs-Wolfe effect. In addition, we show that using the ISW effect will significantly tighten constraints on modified gravity parameters, while the best measurements of dark energy models will come from galaxy auto-correlation function analyses. Using the combination of EMU and WODAN to provide a full sky survey, it will be possible to measure the dark energy parameters with an uncertainty of \{$\sigma (w_0) = 0.05$, $\sigma (w_a) = 0.12$\} and the modified gravity parameters \{$\sigma (\eta_0) = 0.10$, $\sigma (\mu_0) = 0.05$\}, assuming Planck CMB+SN(current data) priors. Finally, we show that radio surveys would detect a primordial non-Gaussianity of $f_{\rm NL}$ = 8 at 1-$\sigma$ and we briefly discuss other promising probes.

Beyond the plane-parallel and Newtonian approach: Wide-angle redshift distortions and convergence in general relativity

by Alvise Raccanelli

Co-authored with Daniele Bertacca, Roy Maartens, Chris Clarkson

We extend previous analyses of wide-angle correlations in the galaxy power spectrum in redshift space to include the... more We extend previous analyses of wide-angle correlations in the galaxy power spectrum in redshift space to include the general relativistic effects. These general relativistic corrections to the standard approach become important on large scales and at high redshifts - and they lead to new terms in the wide-angle correlations. We show these can lead to corrections of nearly 10% over the usual Newtonian approximation.

Misyurov D.A. Dialectical formulas based on the binary notation as the development formulas // Credo New. 2012. №2

by Dmitry Misyurov

The article suggests dialectical formulas based on the binary notation as the development formulas: formula with... more The article suggests dialectical formulas based on the binary notation as the development formulas: formula with dominant and the non-dominant elements; universal formula; formula with symbolic weight of elements; tautological formula. For example, it suggests an opportunity to use the dialectical formulas for modeling and artificial intelligence creation, etc.

The arawakan Flute Cults

by Robin Wright

Disordered locality as an explanation for the dark energy

by Chanda Prescod-Weinstein

Using Dark Matter Haloes to Learn about Cosmic Acceleration: A New Proposal for a Universal Mass Function

by Chanda Prescod-Weinstein

Motion of the Local Group as a cosmological probe

by Maciej Bilicki

Doctoral thesis written under the supervision of prof. Michal Chodorowski, defended on March 30, 2012, at the Nicolaus Copernicus Astronomical Center of the Polish Academy of Sciences.

In this thesis, we use the motion of the Local Group of galaxies (LG) through the Universe to measure the cosmological... more In this thesis, we use the motion of the Local Group of galaxies (LG) through the Universe to measure the cosmological parameter of non-relativistic matter density, Omega_m. For that purpose, we compare the peculiar velocity of the LG with its gravitational acceleration. The former is known from the dipole of the cosmic microwave background radiation and the latter is estimated here from the clustering dipole of galaxies in the Two Micron All Sky Survey (2MASS) Extended Source Catalog. We start by presenting the general framework of perturbation theory of gravitational instability in the expanding Universe and how it applies to the peculiar motion of the LG. Next, we study a particular effect for the dipole measurement, related to the fact that a nearby Local Void is partially hidden behind our Galaxy. We then describe in detail how we handled the 2MASS extragalactic data for the purpose of our analysis. Finally, we present two methods to estimate the density Omega_m, combined with the linear biasing b into the parameter beta = (Omega_m)^{0.55} / b, from the comparison of the LG velocity and acceleration. The first approach is to study the growth of the 2MASS clustering dipole with increased depth of the sample and compare it with theoretical expectations. The second is to apply the maximum-likelihood method in order to improve the precision of the measurement. With both these methods we find beta=0.4 and Omega_m=0.2, which is consistent with various independent estimates. We also briefly mention some future prospects in the field.

A conjecture on the origin of dark energy

by Shan Gao

Chinese Physics Letters 22, 783-784 (2005).

A conjecture on the origin of the dark energy in our universe is proposed. The analysis indicates that the dark energy... more A conjecture on the origin of the dark energy in our universe is proposed. The analysis indicates that the dark energy may originate from the quantum fluctuations of space–time limited in our universe. Applying both the uncertainty principle and the holographic principle, the author finds that the density of such quantum fluctuation energy is ρ V = 3c 4/32GL H 2 , where L H is the size of the event horizon of our universe and G is the gravitational constant. Using this dark energy model which contains no adjustable parameters, we obtain the current fraction ΩΛ≡ρ V /ρ c ≈π/4 and the corresponding equation of state w(z)≈−1+(1−π/4)z with ρ c being the critical energy density. These theoretical results are perfectly consistent with the recent cosmological observations. The striking coincidence implies that the quantum fluctuation energy of space–time may be the only source of dark energy. In addition, the analysis shows that the vacuum fluctuation energy does exist, but it comes from space–time rather than matter. This may have some deep implications for discrete space–time and quantum gravity.

The 6dF Galaxy Survey: Baryon Acoustic Oscillations and the Local Hubble Constant

by Florian Beutler

The WiggleZ Dark Energy Survey: mapping the distance-redshift relation with baryon acoustic oscillations

by Florian Beutler

Narrative Cosmology Article

by Kent Forbes

The Source Density and Observability of Pair-Instability Supernovae from the First Stars

by Jacob Hummel

Bumps on the Road to Here (from Eternity)

by Eric Winsberg

In his recent book, _From Eternity to Here_, and in other more technical papers, Sean Carroll (partly in collaboration... more In his recent book, _From Eternity to Here_, and in other more technical papers, Sean Carroll (partly in collaboration with Jennifer Chen) has put forward an intriguing new way to think about the origin of the Universe. His approach, in a nutshell, is to raise certain worries about a standard Boltzmannian picture of statistical mechanics, and to present certain commitments that he thinks we ought to hold—commitments that the standard picture doesn’t share. He then proposes a cosmological model—one that purports to give us insight into what sort of process brought about the “initial state” of the universe—that can uniquely accommodate those commitments. The conclusion of Carroll’s argument is that statistical mechanical reasoning provides grounds for provisionally accepting that cosmological model. My goal in this paper is to reconstruct and critically assess this proposal. I argue that “statistical cosmology” requires a careful balance of philosophical intuitions and commitments against technical, scientific considerations; how much stock we ought to place in these intuitions and commitments should depend on where they lead us—those that lead us astray scientifically might well be in need of philosophical re examination.

An Astrophysical Peek into Einstein’s Static Universe: No Dark Energy

by Abhas Mitra

A. Mitra, "An Astrophysical Peek into Einstein’s Static Universe: No Dark Energy," International Journal of Astronomy and Astrophysics, Vol. 1 No. 4, pp. 183-199.

It is shown that in order that the fluid pressure and acceleration are uniform and finite in Einstein’s Static... more It is shown that in order that the fluid pressure and acceleration are uniform and finite in Einstein’s Static Universe (ESU), , the cosmological constant, is zero.  being a fundamental constant, should be the same everywhere including the Friedman model. Independent proofs show that it must be so. Accordingly, the supposed acceleration of the universe and the attendant concept of a “Dark Energy” (DE) could be an illusion; an artifact of explaining cosmological observations in terms of an oversimplified model which is fundamentally inappropriate. Indeed observations show that the actual universe is lumpy and inhomogeneous at the largest scales. Further in order that there is no preferred centre, such an inhomogeneity might be ex- pressed in terms of infinite hierarchial fractals. Also, the recent finding that the Friedman model intrinsically corresponds to zero pressure (and hence zero temperature) in accordance with the fact that an ideal Hubble flow implies no collision, no randomness (Mitra, Astrophys. Sp. Sc., 333,351, 2011) too shows that the Friedman model cannot represent the real universe having pressure, temperature and radiation. Dark Energy might also be an artifact of the neglect of dust absorption of distant Type 1a supernovae coupled with likely evolution of supernovae luminosities or imprecise calibration of cosmic distance ladders or other systematic errors (White, Rep. Prog. Phys., 70, 883, 2007). In reality, observations may not rule out an inhomogeneous static universe (Ellis, Gen. Rel. Grav. 9, 87, 1978), if the fundamental “constant”s are indeed constant.

Origin of the Universe and Unbelief

by Taner Edis

Entry in Tom Flynn, ed., The New Encyclopedia of Unbelief (Amherst: Prometheus, 2007)

gigantic radio telescope

by Vratik upadhyay

creation of cosmology

by Vratik upadhyay

A Comparison of the LVDP and ΛCDM Cosmological Models

by Ozgur Akarsu

Ozgur Akarsu, Tekin Dereli; International Journal of Theoretical Physics (2012) doi:10.1007/s10773-012-1200-0 arXiv:1202.0495v1 [gr-qc]

We compare the cosmological kinematics obtained via our law of linearly varying deceleration parameter (LVDP) with the... more We compare the cosmological kinematics obtained via our law of linearly varying deceleration parameter (LVDP) with the kinematics obtained in the ΛCDM model. We show that the LVDP model is almost indistinguishable from the ΛCDM model up to the near future of our universe as far as the current observations are concerned, though their predictions differ tremendously into the far future.

A Four-Dimensional ΛCDM-Type Cosmological Model Induced from Higher Dimensions Using a Kinematical Constraint

by Ozgur Akarsu

Ö. Akarsu, T. Dereli (2012) arXiv:1201.4545v1 [gr-qc]

A class of cosmological solutions of higher dimensional Einstein field equations with the energy- momentum tensor of a... more A class of cosmological solutions of higher dimensional Einstein field equations with the energy- momentum tensor of a homogeneous, isotropic fluid as the source are considered with an anisotropic metric that includes the direct sum of a 3-dimensional (physical, flat) external space metric and an n-dimensional (compact, flat) internal space metric. A simple kinematical constraint is postulated that correlates the expansion rates of the external and internal spaces in terms of a real parameter λ. A specific solution for which both the external and internal spaces expand at different rates is given analytically for n = 3. Assuming that the internal dimensions were at Planck length scales at the beginning t = 0, the external space starts with a Big Bang and the external and internal spaces both reach the same size after 10^{−176} Gyr. Then during the lifetime of the observed universe (13.7 Gyr), the external dimensions would expand 10^{59} times while the internal dimensions expand only 1.49 times. The effective four dimensional universe would exhibit a behavior consistent with our current understanding of the observed universe. It would start in a stiff fluid dominated phase and evolve through radiation dominated and pressureless matter dominated phases, eventually going into a de Sitter phase at late times.

Cosmography with galaxy clusters: shedding light on dark energy

by Marcelle Soares-Santos