Cosmological Predictions Research Articles

Nonstandard optics from quantum space-time

We study light propagation in the picture of semiclassical space-time that emerges in canonical quantum gravity in the loop representation. In such a picture, where space-time exhibits a polymerlike structure at microscales, it is natural to expect departures from the perfect nondispersiveness of an ordinary vacuum. We evaluate these departures, computing the modifications to Maxwell's equations due to quantum gravity and showing that under certain circumstances nonvanishing corrections appear that depend on the helicity of propagating waves. These effects could lead to observable cosmological predictions of the discrete nature of quantum space-time. In particular, recent observations of nondispersiveness in the spectra of gamma-ray bursts at various energies could be used to constrain the type of semiclassical state that describes the universe.

Operator ordering and consistency of the wave function of the Universe

We demonstrate in the context of the minisuperspace model consisting of a closed Friedmann-Robertson-Walker universe coupled to a scalar field that Vilenkin's tunneling wave function can only be consistently defined for particular choices of operator ordering in the Wheeler-DeWitt equation. The requirement of regularity of the wave function has the particular consequence that the probability amplitude, which has been used previously in the literature in discussions of issues such as the prediction of inflation, is likewise ill defined for certain choices of operator ordering with Vilenkin's boundary condition. By contrast, the Hartle-Hawking no-boundary wave function can be consistently defined within these models, independently of operator ordering. The significance of this result is discussed within the context of the debate about the predictions of semiclassical quantum cosmology. In particular, it is argued that inflation cannot be confidently regarded as a ``prediction'' of the tunneling wave function, for reasons similar to those previously invoked in the case of the no-boundary wave function. A synthesis of the no-boundary and tunneling approaches is argued for.

The supersymmetric flavour and CP problems from a cosmological perspective

The supersymmetric flavour and CP problems can be avoided if the first two generations of sfermions are heavier than a few TeV and approximately degenerate in mass. However using flavour and CP-violating constraints on the third sfermion generation, together with the decoupling of the first two generations, can dramatically affect cosmological predictions such as the relic abundance of stable particles. In particular, we show that if the lightest supersymmetric particle is essentially bino-like then requiring that all flavour changing neutral current and CP-violating processes are adequately suppressed, imposes severe limits on the bino mass, where typically m B ̃ ≳ (200–300) GeV. This leads to difficulties for models implementing the scenario of heavy sfermion masses.

The Hubble Diagram of Type Ia Supernovae in Non–Uniform Pressure Universes

We use the redshift-magnitude relation, as derived by Dbrowski, for the two exact non-uniform pressure spherically symmetric Stephani universes with the observer positioned at the center of symmetry in order to test the agreement of these models with recent observations of high-redshift Type Ia supernovae (SN Ia's). By a particular choice of model parameters, we show that these models can give an excellent fit to the observed redshifts and (corrected) B-band apparent magnitudes of the data, but for an age of the universe that is typically about 2 Gyr?and may be more than 3 Gyr?greater than in the corresponding Friedmann model, for which nonnegative values of the deceleration parameter appear to be favored by the data. We show that this age increase is obtained for a wide range of the non-uniform pressure parameters of the Stephani models. We claim that this paper is the first attempt to compare inhomogeneous models of the universe with real astronomical data. Several recent calibrations of the Hubble parameter from the Hubble diagram of SN Ia's and other distance indicators indicate a value of H0 65 and a Hubble time of ~15 Gyr. Based on this value for H0 and assuming ? ? 0, the data would imply a Friedmann age of at most 13 Gyr and in fact a best-fit (for q0 = 0.5) age of only 10 Gyr. Our Stephani models, on the other hand, can give a good fit to the data with an age of up to 15 Gyr. The Stephani models considered here could, therefore, significantly alleviate the conflict between recent cosmological and astrophysical age predictions. The choice of model parameters is quite robust: in order to obtain a good fit to the current data, one requires only that the non-uniform pressure parameter a in one of the models be negative and satisfy |a| 3 km2 s-2 Mpc-1. This limit gives a value for the acceleration scalar of order | |0.66?10 -->?10r Mpc-1, where r is the radial coordinate in the model. Thus, although the pressure is not zero at the center of symmetry, r = 0, the effect of acceleration is nondetectable at the center, since the acceleration scalar vanishes there. However, the effect of the nonuniform pressure on the redshift-magnitude relation is clearly seen, since neighboring galaxies are not situated at the center, and they necessarily experience acceleration. By allowing slightly larger negative values of a one may fine-tune the model to give an even better fit to the data.

Cosmological implications of a large complete quasar sample.

Objective and reproducible determinations of the probabilistic significance levels of the deviations between theoretical cosmological prediction and direct model-independent observation are made for the Large Bright Quasar Sample [Foltz, C., Chaffee, F. H., Hewett, P. C., MacAlpine, G. M., Turnshek, D. A., et al. (1987) Astron. J. 94, 1423-1460]. The Expanding Universe model as represented by the Friedman-Lemaitre cosmology with parameters qo = 0, Lambda = 0 denoted as C1 and chronometric cosmology (no relevant adjustable parameters) denoted as C2 are the cosmologies considered. The mean and the dispersion of the apparent magnitudes and the slope of the apparent magnitude-redshift relation are the directly observed statistics predicted. The C1 predictions of these cosmology-independent quantities are deviant by as much as 11sigma from direct observation; none of the C2 predictions deviate by >2sigma. The C1 deviations may be reconciled with theory by the hypothesis of quasar "evolution," which, however, appears incapable of being substantiated through direct observation. The excellent quantitative agreement of the C1 deviations with those predicted by C2 without adjustable parameters for the results of analysis predicated on C1 indicates that the evolution hypothesis may well be a theoretical artifact.

Fundamental Discreteness Limitations of CosmologicalN‐Body Clustering Simulations

Fundamental physical considerations and past tests suggest that there may be a problem with discreteness error in N-body methods widely used in cosmological clustering studies. This could cause problems with accuracy when coupled to hydrodynamics codes. We therefore investigate some of the effects that discreteness and two-body scattering may have on N-body simulations with realistic cosmological initial conditions. We use an identical subset of particles from the initial conditions for a 1283 particle-mesh (PM) calculation as the initial conditions for a variety of particle-particle-particle mesh (P3M) and tree code runs. The force softening length and particle number in the P3M and tree code runs are varied, and results are compared with those of the PM run. In particular, we investigate the effect of mass resolution (or equivalently the mean interparticle separation) since most high-resolution codes only have high resolution in gravitational force, not in mass. We show the evolution of a wide variety of statistical measures. The phase-insensitive two-point statistics, P(k) and ξ(R), are affected by the number of particles when the force resolution is held constant and differ in different N-body codes with similar parameters and the same initial conditions. Phase-sensitive statistics show greater differences. Results converge at the mean interparticle separation scale of the lowest mass-resolution code. As more particles are added but the absolute scale of the force resolution is held constant, the P3M and the tree runs agree more and more strongly with each other and with the PM run that had the same initial conditions, suggesting that the time integration is converging. However, they do not particularly converge to a PM run that continued the power-law fluctuations to small scales. This suggests high particle density is necessary for correct time evolution, since many different results cannot all be correct. Our results showing the effect of the presence or absence of small-scale initial power suggest that leaving it out is a considerable source of error on comoving scales of the missing wavelengths, which can be resolved by putting in a high particle density. Since the codes never agree well on scales below the mean comoving interparticle separation, we find little justification to use results on these scales to make quantitative predictions in cosmology. The range of values found for some quantities spans 50%, but others, such as the amount of mass in high-density regions, can be off by a factor of 3 or more. Our results have strong implications for applications such as the density of galaxy halos, early generation objects such as QSO absorber clouds, etc.

Non-universality effects and dark matter in gravity mediated SUSY breaking

Dark matter detection rates for supergravity models with R parity where supersymmetry is broken at a scale ≳ M G are discussed. Non-universal soft breaking masses in both the Higgs and squark sectors are considered, and it is seen that these can effect rates by a factor of 10 – 100 when m χ ∼ 1 0 ≳ 65 GeV ( χ 1 0 = lightest neutralino) but otherwise make relatively small corrections. The b → s + γ branching ratio is seen to correlate with detector event rates, large (small) branching ratios corresponding to small (large) event rates. Effects of precision determinations of cosmological parameters or event rate predictions by future satellite experiments are discussed for the ΛCDM and the ΦCDM models.

Quantum pasts and the utility of history

From data in the present we can predict the future and retrodict the past. These predictions and retrodictions are for histories – most simply time sequences of events. Quantum mechanics gives probabilities for individual histories in a decoherent set of alternative histories. This paper discusses several issues connected with the distinction between prediction and retrodiction in quantum cosmology: the difference between classical and quantum retrodiction, the permanence of the past, why we predict the future but remember the past, the nature and utility of reconstructing the past(s), and information theoretic measures of the utility of history.

Cosmological Model Predictions for Weak Lensing: Linear and Nonlinear Regimes

Weak lensing by large scale structure induces correlated ellipticities in the images of distant galaxies. The two-point correlation is determined by the matter power spectrum along the line of sight. We use the fully nonlinear evolution of the power spectrum to compute the predicted ellipticity correlation. We present results for different measures of the second moment for angular scales \theta \simeq 1'-3 degrees and for alternative normalizations of the power spectrum, in order to explore the best strategy for constraining the cosmological parameters. Normalizing to observed cluster abundance the rms amplitude of ellipticity within a 15' radius is \simeq 0.01 z_s^{0.6}, almost independent of the cosmological model, with z_s being the median redshift of background galaxies. Nonlinear effects in the evolution of the power spectrum significantly enhance the ellipticity for \theta < 10' -- on 1' the rms ellipticity is \simeq 0.05, which is nearly twice the linear prediction. This enhancement means that the signal to noise for the ellipticity is only weakly increasing with angle for 2'< \theta < 2 degrees, unlike the expectation from linear theory that it is strongly peaked on degree scales. The scaling with cosmological parameters also changes due to nonlinear effects. By measuring the correlations on small (nonlinear) and large (linear) angular scales, different cosmological parameters can be independently constrained to obtain a model independent estimate of both power spectrum amplitude and matter density \Omega_m. Nonlinear effects also modify the probability distribution of the ellipticity. Using second order perturbation theory we find that over most of the range of interest there are significant deviations from a normal distribution.

Regularization scheme dependence of predictions in inflationary cosmology.

We show that there exists a large class of regularization schemes for probabilistic predictions in the theory of a self-reproducing inflationary univere, all of which eliminate the apparent dependence on the time reparametrization. However, all these schemes lead to different answers for relative probabilities of finding various types of post-inflationary universes. Besides, all these schemes fail to be reparametrization invariant beyond the range of the inflaton field close to end of inflation boundary. Therefore, we argue that at the current level of understanding, the simple regularization schemes associated with cutoffs at equal time hypersurfaces are as good as the recently proposed more complicated procedures which try to fix the time-reparametrization dependence.

On the Measurement of the Hubble Constant in a Local Low-Density Universe

Astrophysical observations indicate that the ``Local Universe" has a relatively lower matter density ($\Omega_0$) than the predictions of the standard inflation cosmology and the large-scale motions of galaxies which provide a mean mass density to be very close to unity. In such a local underdense region the Hubble expansion may not be representative of the global behaviour. Utilizing an underdense sphere embedded in a flat universe as the model of our ``Local Universe", we show that the local Hubble constant would be 1.2 -- 1.4 times larger than the global value on scale of $\sim80$ Mpc, depending on the variation of $\Omega_0$. This may account for the recent measurements of the unpleasantly large Hubble constant of $\sim$80 km/s/Mpc using the Cepheid variables in the Virgo cluster and the relative distance between Virgo and Coma cluster and removes the resulted apparent paradox of the age of our universe.

Stationarity of inflation and predictions of quantum cosmology.

We describe several different regimes which are possible in inflationary cosmology. The simplest one is inflation without self-reproduction of the universe. In this scenario the universe is not stationary. The second regime, which exists in a broad class of inflationary models, is eternal inflation with the self-reproduction of inflationary domains. In this regime local properties of domains with a given density and given values of fields do not depend on the time when these domains were produced. The probability distribution to find a domain with given properties in a self-reproducing universe may or may not be stationary, depending on the choice of an inflationary model. We give examples of models where each of these possibilities can be realized, and discuss some implications of our results for quantum cosmology. In particular, we propose a new mechanism which may help solving the cosmological constant problem.

Dirac's cosmology with varying cosmological constant

The phenomenological approach to investigating the decay of the vacuum energy density is generalized in the spirit of Dirac's large number hypothesis. Different arguments are outlined to justify an universal dependence of the type λ=ΒH2 (Β is a pure number andH is the Hubble parameter). Such time-varying A does change the predictions of the earlier Dirac's cosmology. The deceleration parameter (q0=(2−Β)/(1+Β)) and the age parameter (H0t0=(1+Β)/3) are now compatible with the observations. The model also allows a “power-law” inflationary phase and a rate of matter creation smaller than the one present in the steady state universe.

Statistically efficient parallel testing of the Friedmann and chronometric flux-redshift predictions in the radio band

view Abstract Citations (6) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Statistically Efficient Parallel Testing of the Friedmann and Chronometric Flux-Redshift Predictions in the Radio Band Segal, I. E. ; Nicoll, J. F. ; Blackman, E. Abstract The flux-redshift predictions of Friedmann and chronometric cosmology are subjected to statistically efficient parallel tests on the basis of the 3C catalog of radio sources, as updated by Spinrad et al. (1985). Sub-samples limited in flux, redshift, and spectral index are treated to this end. Luminosity functions are estimated by an optimal nonparametric procedure that does not postulate spatial homogeneity or require completeness in redshift. Directly observed quantities are compared with the predictions of the respective cosmologies, and objective statistical significance levels are determined. Within the frame of the Friedmann cosmology, the disperson in log flux invariably exceeds the observed value, and the same is true of the correlation of log luminosity with redshift. Over the full redshift range of the sample, extending to z ~ 2.5, the deviations are significant at the ~4 σ, level. On the parallel basis the chronometric predictions are highly consistent with the observations, without evolution or any adjustable cosmological parameter such as q_0_. Moreover, the chronometric cosmology predicts quite accurately the deviations of the Friedmann predictions from direct observation, while the Friedmann cosmology is unable to explain the excellent fit of the chronometric predictions. Publication: The Astrophysical Journal Pub Date: July 1994 DOI: 10.1086/174382 Bibcode: 1994ApJ...430...63S Keywords: Computational Astrophysics; Cosmology; Galactic Evolution; Prediction Analysis Techniques; Radio Sources (Astronomy); Red Shift; Statistical Tests; Astronomical Catalogs; Chronology; Luminosity; Astrophysics; COSMOLOGY: THEORY; GALAXIES: DISTANCES AND REDSHIFTS; GALAXIES: EVOLUTION; RADIO CONTINUUM: GALAXIES full text sources ADS |

Optical galaxies within Formula - IV. The peculiar velocity field

The density field of optically selected galaxies within |$8000\,\ {\rm km} \ {\rm s}^{-1}$| is used to predict the peculiar velocities of |$D_{\rm n}-\sigma$| and IRTF galaxies employing linear gravitational instability theory. To obtain acceptable fits to the observed peculiar velocities in the CMB frame, it is necessary to fit two parameters: |$\beta_{\rm o} \equiv \Omega^{0.6} b_{\rm o}^{-1}$| (where |$b_{\rm o}$| is a biasing parameter for optical galaxies), which scales the predictions of the optical density field within |$8000\,\ {\rm km} \ {\rm s}^{-1}$|⁠; and a residual bulk motion due to sources outside the volume. The fits yield |$\beta_{\rm o}=0.50 \pm 0.06$ (1 $\sigma$| random errors) for both the IRTF and the |$D_{\rm n}-\sigma$| samples, and a residual bulk motion of |$405 \pm 45\,\ {\rm km} \ {\rm s}^{-1}$| towards |$l=292^{\circ}, b=7^{\circ}$| for the IRTF field galaxies. There is no evidence for a mass concentration in the zone of avoidance within |$8000 \ {\rm km} \ {\rm s}^{-1}$| whose effect on the Local Group is more than |$100 \ {\rm km} \ {\rm s}^{-1}$|⁠, so the residual bulk motion must be due primarily to sources beyond |$8000 \ {\rm km} \ {\rm s}^{-1}$|⁠. The result for |$\beta_{\rm o}$| corresponds to |$\Omega=0.32\pm 0.06$| if mass traces light |$(b_{\rm o}=1)$|⁠, or to |$b_{\rm o}=2.0\pm 0.24$| if |$\Omega=1$|⁠. If biasing is independent of scale, then taken together these results are inconsistent with the predictions of the standard cold dark matter cosmology for any choice of the biasing parameter, but are compatible with cosmological models that fit the galaxy number counts on large scales.

The redshift-distance relation.

Key predictions of the Hubble law are inconsistent with direct observations on equitable complete samples of extragalactic sources in the optical, infrared, and x-ray wave bands-e.g., the predicted dispersion in apparent magnitude is persistently greatly in excess of its observed value, precluding an explanation via hypothetical perturbations or irregularities. In contrast, the predictions of the Lundmark (homogeneous quadratic) law are consistent with the observations. The Lundmark law moreover predicts the deviations between Hubble law predictions and observation with statistical consistency, while the Hubble law provides no explanation for the close fit of the Lundmark law. The flux-redshift law F [symbol, see text] (1 + z)/z appears consistent with observations on equitable complete samples in the entire observed redshift range, when due account is taken of flux limits by an optimal statistical method. Under the theoretical assumption that space is a fixed sphere, as in the Einstein universe, this law implies the redshift-distance relation z = tan2(r/2R), where R is the radius of the spherical space. This relation coincides with the prediction of chronometric cosmology, which estimates R as 160 +/- 40 Mpc (1 parsec = 3.09 x 10(16) m) from the proper motion to redshift relation of superluminal sources. Tangential aspects, including statistical methodology, fundamental physical theory, bright cluster galaxy samples, and proposed luminosity evolution, are briefly considered.

Detection and selection effects in observations of faint galaxies

Cosmological predictions of number count and redshift distribution of faint galaxies are made by incorporating detection and selection effects in the theoretical framework. It is shown that the detection rate for galaxies at given apparent magnitude strongly depends on the detection criterion and magnitude measurement algorithm, and that a large number of faint galaxies with high redshift could remain undetected in recent galaxy surveys

Is beryllium in metal-poor stars of galactic or cosmological origin?

Standard Big Bang nucleosynthesis predicts a very small primordial abundance of beryllium. Observations of nine very metal-poor stars indicate a beryllium abundance roughly proportional to the oxygen abundance, a trend that can be explained in terms of galactic chemical evolution. Combining this rate of beryllium production with recent observations of boron and lithium in similar stars yields an upper limit to the primordial beryllium abundance several orders of magnitude greater than the cosmological prediction, a result that can be explained by cosmicray activity in the early Galaxy.

The dark matter problem and quantum gravity

We explicitly solve the one-loop renormalization group equations for a particular higher derivative quantum gravity and obtain the induced r-dependence of Newton's constant due to quantum fluctuations of the geometry. We then show how, by considering these effects, it may be possible to (a) reconcile nucleosynthesis bounds on the density parameter of the Universe with the predictions of inflationary cosmology, and (b) reproduce the inferred variation of the density parameter with distance. Our calculation can be interpreted as a computation of the contribution of gravitons to the (local) energy density of the Universe.

Particle physics after a year of LEP

The Z° boson has changed in the last year from being an exotic rarity to being the tool for a wide range of research. CERN's large electron-positron collider, LEP, produces enough Z° particles to allow many predictions of particle physics theory and cosmology to be tested.