Revisiting metric perturbations in tensor-vector-scalar theory

I revisit cosmological perturbations in Bekenstein's tensor-vector-scalar theory (TeVeS). Considering only scalar modes in the conformal Newtonian gauge, the extra degrees of freedom are expressed in a way suitable for studying modifications at the level of the metric potentials. Assuming a universe in the matter-dominated phase, I discuss the mechanism responsible for boosting structure growth, and confirm the vector field as its key ingredient. Using a semi-analytic approach, I further characterize the evolution of density perturbations and the potentials on sub- and superhorizon scales.Comment: 12 pages, 6 figures; updated Figs. 3, 5, and 6, improved discussion of potential and density growth, accepted versio

Growth rate of cosmological perturbations at z ~ 0.1 from a new observational test

Spatial variations in the distribution of galaxy luminosities, estimated from redshifts as distance proxies, are correlated with the peculiar velocity field. Comparing these variations with the peculiar velocities inferred from galaxy redshift surveys is a powerful test of gravity and dark energy theories on cosmological scales. Using ~ 2 $\times$ 10$^{5}$ galaxies from the SDSS Data Release 7, we perform this test in the framework of gravitational instability to estimate the normalized growth rate of density perturbations f$\sigma_{8}$ = 0.37 +/- 0.13 at z ~ 0.1, which is in agreement with the $\Lambda$CDM scenario. This unique measurement is complementary to those obtained with more traditional methods, including clustering analysis. The estimated accuracy at z ~ 0.1 is competitive with other methods when applied to similar datasets.Comment: 4 pages, 2 figures, matches version accepted for publication in PR

A multistream model for quantum plasmas

The dynamics of a quantum plasma can be described self-consistently by the nonlinear Schroedinger-Poisson system. Here, we consider a multistream model representing a statistical mixture of N pure states, each described by a wavefunction. The one-stream and two-stream cases are investigated. We derive the dispersion relation for the two-stream instability and show that a new, purely quantum, branch appears. Numerical simulations of the complete Schroedinger-Poisson system confirm the linear analysis, and provide further results in the strongly nonlinear regime. The stationary states of the Schroedinger-Poisson system are also investigated. These can be viewed as the quantum mechanical counterpart of the classical Bernstein-Greene-Kruskal modes, and are described by a set of coupled nonlinear differential equations for the electrostatic potential and the stream amplitudes.Comment: 20 pages, 10 figure

Speed from light: growth rate and bulk flow at z ~ 0.1 from improved SDSS DR13 photometry

Observed galaxy luminosities (derived from redshifts) hold information on the large-scale peculiar velocity field in the form of spatially correlated scatter, which allows for bounds on bulk flows and the growth rate of matter density perturbations using large galaxy redshift surveys. We apply this luminosity approach to galaxies from the recent SDSS Data Release 13. Our goal is twofold. First, we take advantage of the recalibrated photometry to identify possible systematic errors relevant to our previous analysis of earlier data. Second, we seek improved constraints on the bulk flow and the normalized growth rate f$\sigma_{8}$ at z ~ 0.1. Our results confirm the robustness of our method. Bulk flow amplitudes, estimated in two redshift bins with 0.02 < z$_{1}$ < 0.07 < z$_{2}$ < 0.22, are generally smaller than in previous measurements, consistent with both the updated photometry and expectations for the $\Lambda$CDM model. The obtained growth rate, f$\sigma_{8}$ = 0.48 +/- 0.16, is larger than, but still compatible with, its previous estimate, and closer to the reference value of Planck. Rather than precision, the importance of these results is due to the fact that they follow from an independent method that relies on accurate photometry, which is a top requirement for next-generation photometric catalogs.Comment: 7 pages, 3 figures, 2 tables; accepted for publication in MNRAS after minor revisio