Fingerprinting dark energy

Dark energy perturbations are normally either neglected or else included in a purely numerical way, obscuring their dependence on underlying parameters like the equation of state or the sound speed. However, while many different explanations for the dark energy can have the same equation of state, they usually differ in their perturbations so that these provide a fingerprint for distinguishing between different models with the same equation of state. In this paper we derive simple yet accurate approximations that are able to characterize a specific class of models (encompassing most scalar-field models) which is often generically called "dark energy". We then use the approximate solutions to look at the impact of the dark energy perturbations on the dark matter power spectrum and on the integrated Sachs-Wolfe effect in the cosmic microwave background radiation.Comment: 11 pages, 5 figures, minor changes to match published versio

Cosmological redshift distortion: deceleration, bias and density parameters from future redshift surveys of galaxies

The observed two-point correlation functions of galaxies in redshift space become anisotropic due to the geometry of the universe as well as due to the presence of the peculiar velocity field. On the basis of linear perturbation theory, we expand the induced anisotropies of the correlation functions with respect to the redshift $z$, and obtain analytic formulae to infer the deceleration parameter $q_0$, the density parameter $\Omega_0$ and the derivative of the bias parameter $d\ln b/dz$ at $z=0$ in terms of the observable statistical quantities. The present method does not require any assumption of the shape and amplitude of the underlying fluctuation spectrum, and thus can be applied to future redshift surveys of galaxies including the Sloan Digital Sky Survey. We also evaluate quantitatively the systematic error in estimating the value of $\beta_0 \equiv \Omega_0^{0.6}/b$ from a galaxy redshift survey on the basis of a conventional estimator for $\beta_0$ which neglects both the geometrical distortion effect and the time evolution of the parameter $\beta(z)$. If the magnitude limit of the survey is as faint as 18.5 (in B-band) as in the case of the Sloan Digital Sky Survey, the systematic error ranges between -20% and 10% depending on the cosmological parameters. Although such systematic errors are smaller than the statistical errors in the current surveys, they will dominate the expected statistical error for future surveys.Comment: 9 pages, 5 figs, aastex, ApJ in press, replaced version includes minor correction

The X-ray Cluster Dipole

We estimate the dipole of the whole sky X-ray flux-limited sample of Abell/ACO clusters (XBACs) and compare it to the optical Abell/ACO cluster dipole. The X-ray cluster dipole is well aligned ($\le 25^{\circ}$) with the CMB dipole, while it follows closely the radial profile of its optical cluster counterpart although its amplitude is $\sim 10 - 30$ per cent lower. In view of the fact that the the XBACs sample is not affected by the volume incompleteness and the projection effects that are known to exist at some level in the optical parent Abell/ACO cluster catalogue, our present results confirm the previous optical cluster dipole analysis that there are significant contributions to the Local Group motion from large distances ($\sim 160h^{-1}$Mpc). In order to assess the expected contribution to the X-ray cluster dipole from a purely X-ray selected sample we compare the dipoles of the XBACs and the Brightest Cluster Sample (Ebeling et al. 1997a) in their overlap region. The resulting dipoles are in mutual good aggreement with an indication that the XBACs sample slightly underestimates the full X-ray dipole (by $\le 5$ per cent) while the Virgo cluster contributes about 10 - 15 per cent to the overall X-ray cluster dipole. Using linear perturbation theory to relate the X-ray cluster dipole to the Local group peculiar velocity we estimate the density parameter to be $\beta_{c_{x}} \simeq 0.24 \pm 0.05$.Comment: 16 pages, latex, + 4 ps figures, submitted to Ap

Spherical Collapse and the Halo Model in Braneworld Gravity

We present a detailed study of the collapse of a spherical perturbation in DGP braneworld gravity for the purpose of modeling simulation results for the halo mass function, bias and matter power spectrum. The presence of evolving modifications to the gravitational force in form of the scalar brane-bending mode lead to qualitative differences to the collapse in ordinary gravity. In particular, differences in the energetics of the collapse necessitate a new, generalized method for defining the virial radius which does not rely on strict energy conservation. These differences and techniques apply to smooth dark energy models with w unequal -1 as well. We also discuss the impact of the exterior of the perturbation on collapse quantities due to the lack of a Birkhoff theorem in DGP. The resulting predictions for the mass function, halo bias and power spectrum are in good overall agreement with DGP N-body simulations on both the self-accelerating and normal branch. In particular, the impact of the Vainshtein mechanism as measured in the full simulations is matched well. The model and techniques introduced here can serve as practical tools for placing consistent constraints on braneworld models using observations of large scale structure.Comment: 20 pages, 16 figures; v2: minor addition to appendix; matches published version; v3: typos in Eqs. (20), (23) correcte

A seeded ambient temperature ferrit process for the treatment of AMD waters: Magnetite formation in the presence and absence of calcium ions under steady state operation

An ambient temperature ferrite process has been developed for the removal of iron and non-ferrous metals from AMD waters. The process involves the controlled formation of magnetite (Fe3 O4 ) that has the capacity to substitute divalent and trivalent cations as part of the lattice, thus forming a stable easy-to-separate ferrite. This paper reports on continuous operations of the process in the absence and presence of Ca2+, which is well known to impede ferrite formation. In the first instance, the process involves the precipitation of hydroxy-metals at pH 10.5 and their subsequent adsorption onto magnetite seed in a contact stabilisation reactor. Second, liquid-solid separation is effected and the solid fraction is subsequently treated in an oxidising reactor in which a fraction of the ferrous species is oxidised to an intermediate ferric precipitate. Finally, both ferrous and ferric species undergo crystalchemical processing and are incorporated into stable magnetite. Results indicate that Ca2+ interference can be overcome by maintaining a high ratio of precipitated ferrous species to dissolved Ca2+. It was found that in order to attain the required high Fe2+:Ca2+ ratio, the solid ferrous-hydroxy species concentration in the oxidation reactor should be maintained at above 1 200 mg Fe/l. Ferrous to calcium ratios greater than 3 were found to favour magnetite formation. In the absence of Ca2+, a solid ferroushydroxy species concentration of approximately 500 mg/l was sufficient for magnetite formation. Operating the process at ferroushydroxy concentrations of lower than 1 200 and 500 mg/l in the presence and absence of calcium respectively enhanced the formation of other iron oxides, primarily goethite. In all experiments the iron concentration in the effluent was less than 1 mg/l, the sludge volume index (SVI) extremely low (< 4 ml/g) and the percentage of ferrous-hydroxy species in the sludge can be reduced to about 1%. These features, together with the potential to incorporate heavy metals into a stable compound, make the process very promising for AMD treatment

Stimulus-dependent dynamics of p53 in single cells

Many biological networks respond to various inputs through a common signaling molecule that triggers distinct cellular outcomes. One potential mechanism for achieving specific input-output relationships is to trigger distinct dynamical patterns in response to different stimuli. Here we focused on the dynamics of p53, a tumor suppressor activated in response to cellular stress. We quantified the dynamics of p53 in individual cells in response to UV and observed a single pulse that increases in amplitude and duration in proportion to the UV dose. This graded response contrasts with the previously described series of fixed pulses in response to γ-radiation. We further found that while γ-triggered p53 pulses are excitable, the p53 response to UV is not excitable and depends on continuous signaling from the input-sensing kinases. Using mathematical modeling and experiments, we identified feedback loops that contribute to specific features of the stimulus-dependent dynamics of p53, including excitability and input-duration dependency. Our study shows that different stresses elicit different temporal profiles of p53, suggesting that modulation of p53 dynamics might be used to achieve specificity in this network

Dipole anisotropies of IRAS galaxies and the contribution of a large-scale local void

Recent observations of dipole anisotropies show that the velocity of the Local Group (\Vec v_{\rm G}) induced by the clustering of IRAS galax ies has an amplitude and direction similar to those of the velocity of Cosmic Microwave Background dipole anisotropy (\Vec v_{\rm CMB}), but the difference | \Vec v_{\rm G} - \Vec v_{\rm CMB} | is still $\sim 170$ km/s, which is about 28% of |\Vec v_{\rm CMB} |. Here we consider the possibility that the origin of this difference comes from a hypothetical large-scale local void, with which we can account for the accelerating behavior of type Ia supernovae due to the spatial inhomogeneity of the Hubble constant without dark energies and derive the constraint to the model parameters of the local void. It is found as a result that the distance between the Local Group and the center of the void must be $(10 -- 20) h^{-1}$ Mpc, whose accurate value depends on the background model parameters.Comment: 13 pages, 1 figure, to be published in ApJ 584, No.2 (2003

Non-linear Evolution of f(R) Cosmologies III: Halo Statistics

The statistical properties of dark matter halos, the building blocks of cosmological observables associated with structure in the universe, offer many opportunities to test models for cosmic acceleration, especially those that seek to modify gravitational forces. We study the abundance, bias and profiles of halos in cosmological simulations for one such model: the modified action f(R) theory. In the large field regime that is accessible to current observations, enhanced gravitational forces raise the abundance of rare massive halos and decrease their bias but leave their (lensing) mass profiles largely unchanged. This regime is well described by scaling relations based on a modification of spherical collapse calculations. In the small field regime, enhanced forces are suppressed inside halos and the effects on halo properties are substantially reduced for the most massive halos. Nonetheless, the scaling relations still retain limited applicability for the purpose of establishing conservative upper limits on the modification to gravity.Comment: 12 pages, 10 figures; v2: revised version accepted by Phys. Rev.