Clarifying spherical collapse in coupled dark energy cosmologies

The spherical collapse model is often used to follow the evolution of overdensities into the nonlinear regime. We describe the correct approach to be used in coupled dark energy cosmologies, where a fifth force, different from gravity and mediated by the dark energy scalar field, influences the collapse. We reformulate the spherical collapse description by deriving it directly from the set of nonlinear hydrodynamical Navier Stokes equations. By comparing with the corresponding relativistic equations, we show how the fifth force should be taken into account within the spherical collapse picture and clarify the problems arising when an inhomogeneous scalar field is considered within a spherical collapse picture. We then apply our method to the case of coupled quintessence, where the fifth force acts among cold dark matter particles, and to growing neutrino quintessence, where the fifth force acts between neutrinos. Furthermore, we review this method when applied to standard cosmologies and apply our analysis to minimally coupled quintessence and check past results for early dark energy parametrizations.Comment: 16 pages, 13 figures, published in Physical Review D, minor changes and correction

Dark Matter, Modified Gravity and the Mass of the Neutrino

It has been suggested that Einstein's theory of General Relativity can be modified to accomodate mismatches between the gravitational field and luminous matter on a wide range of scales. Covariant theories of modified gravity generically predict the existence of extra degrees of freedom which may be interpreted as dark matter. We study a subclass of these theories where the overall energy density in these extra degrees of freedom is subdominant relative to the baryon density and show that they favour the presence of massive neutrinos. For some specific cases (such as a flat Universes with a cosmological constant) one finds a conservative lower bound on the neutrinos mass of $m_\nu>0.31$ eV.Comment: 5 pages, 2 figures, 2 tables, submitted to Phys. Rev.

Measuring the galaxy power spectrum with multiresolution decomposition -- II. diagonal and off-diagonal power spectra of the LCRS galaxies

The power spectrum estimator based on the discrete wavelet transform (DWT) for 3-dimensional samples has been studied. The DWT estimator for multi-dimensional samples provides two types of spectra with respect to diagonal and off-diagonal modes, which are very flexible to deal with configuration-related problems in the power spectrum detection. With simulation samples and mock catalogues of the Las Campanas redshift survey (LCRS), we show (1) the slice-like geometry of the LCRS doesn't affect the off-diagonal power spectrum with ``slice-like'' mode; (2) the Poisson sampling with the LCRS selection function doesn't cause more than 1-$\sigma$ error in the DWT power spectrum; and (3) the powers of peculiar velocity fluctuations, which cause the redshift distortion, are approximately scale-independent. These results insure that the uncertainties of the power spectrum measurement are under control. The scatter of the DWT power spectra of the six strips of the LCRS survey is found to be rather small. It is less than 1-$\sigma$ of the cosmic variance of mock samples in the wavenumber range $0.1 < k < 2$ h Mpc$^{-1}$. To fit the detected LCRS diagonal DWT power spectrum with CDM models, we find that the best-fitting redshift distortion parameter $\beta$ is about the same as that obtained from the Fourier power spectrum. The velocity dispersions $\sigma_v$ for SCDM and $\Lambda$CDM models are also consistent with other $\sigma_v$ detections with the LCRS. A systematic difference between the best-fitting parameters of diagonal and off-diagonal power spectra has been significantly measured. This indicates that the off-diagonal power spectra are capable of providing information about the power spectrum of galaxy velocity field.Comment: AAS LaTeX file, 41 pages, 10 figures included, accepted for publication in Ap

An imaging K-band survey - I: The catalogue, star and galaxy counts

We present results from a large area (552\,\sqamin) imaging $K$-band survey to a 5$\sigma$ limit of $K\simeq 17.3$. We have optical-infrared colours of almost all the objects in the sample. Star-galaxy discrimination is performed and the results used to derive the infrared star and galaxy counts. $K$-band ``no-evolution'' galaxy-count models are constructed and compared with the observed data. In the infrared, there is no counterpart for the large excess of faint galaxies over the no-evolution model seen in optical counts. However, we show that the $K$ counts can be remarkably insensitive to evolution under certain reasonable assumptions. Finally, model predictions for $K$-selected redshift surveys are derived.Comment: MNRAS in press. 21 pages plain TeX; figs plus table 4 available via anonymous ftp from /pub/kgb/paper1/sissa.uu at ftp.ast.cam.ac.u

The Angular Power Spectrum of EDSGC Galaxies

We determine the angular power spectrum, C_l, of the Edinburgh/Durham Southern Galaxy Catalog (EDSGC) and use this statistic to constrain cosmological parameters. Our methods for determining C_l, and the parameters that affect it are based on those developed for the analysis of cosmic microwave background maps. We expect them to be useful for future surveys. Assuming flat cold dark matter models with a cosmological constant (constrained by COBE/DMR and local cluster abundances), and a scale--independent bias, b, we find good fits to the EDSGC angular power spectrum with 1.11 < b < 2.35 and 0.2 < Omega_m < 0.55 at 95% confidence. These results are not significantly affected by the ``integral constraint'' or extinction by interstellar dust, but may be by our assumption of Gaussianity.Comment: 11 pages, 9 figures, version to appear in Ap

Cluster Correlation in Mixed Models

We evaluate the dependence of the cluster correlation length r_c on the mean intercluster separation D_c, for three models with critical matter density, vanishing vacuum energy (Lambda = 0) and COBE normalized: a tilted CDM (tCDM) model (n=0.8) and two blue mixed models with two light massive neutrinos yielding Omega_h = 0.26 and 0.14 (MDM1 and MDM2, respectively). All models approach the observational value of sigma_8 (and, henceforth, the observed cluster abundance) and are consistent with the observed abundance of Damped Lyman_alpha systems. Mixed models have a motivation in recent results of neutrino physics; they also agree with the observed value of the ratio sigma_8/sigma_25, yielding the spectral slope parameter Gamma, and nicely fit LCRS reconstructed spectra. We use parallel AP3M simulations, performed in a wide box (side 360/h Mpc) and with high mass and distance resolution, enabling us to build artificial samples of clusters, whose total number and mass range allow to cover the same D_c interval inspected through APM and Abell cluster clustering data. We find that the tCDM model performs substantially better than n=1 critical density CDM models. Our main finding, however, is that mixed models provide a surprisingly good fit of cluster clustering data.Comment: 22 pages + 10 Postscript figures. Accepted for publication in Ap

A Survey of Bariatric Surgical Patients\u27 Experiences with Behavioral and Psychological Services

The following study assessed behavioral and psychological services currently being used by bariatric patients before and after surgery. A convenience sample of N = 380 was generated through solicitation on an online support website; inclusion criteria included having had surgery in the United States after implementation of accreditation standards in 2005. Participants completed an Internet-based survey that assessed services completed, satisfaction with services, perceived impact of surgery on mental and physical health as well as diet and physical activity behaviors, and current reported diet and physical activity behaviors. Overall, participants reported completing more services before surgery, and afterwards the most commonly reported completed services were support groups and dietary consultation; more than half of participants did not meet with either a mental health professional or exercise professional following surgery. Participants expressed high satisfaction with surgery, and perceived that surgery had a positive impact on health and health behaviors. Linear regression analysis showed that satisfaction with surgery was largely predicted by percent weight loss, though it is also possible that perceived benefits to mental and physical health also contributed to satisfaction levels. Self-reported physical activity levels were increased dramatically following surgery; however, these results must be interpreted carefully due to potential sample bias and over-reporting. Because participants in the current sample reported completing few behavioral and psychological services after surgery, it is recommended that bariatric facilities and insurance providers consider requiring patients to complete post-surgical behavioral modification programs that target improvement of diet and physical activity behaviors and overall lifestyle change