Brane oscillations and the cosmic coincidence problem

We show that, under general assumptions, in six-dimensional brane-world models with compactified large extra dimensions, the energy density of brane oscillations scales as that of cold dark matter and its present value is compatible with observations. Such value is obtained from the only dimensional scale in the theory, namely, the fundamental scale of gravity in six dimensions $M_6\sim 1$ TeV, without any fine-tuning or the introduction of additional mass scales apart from the large size of the extra dimensions. It has been suggested that the same kind of models could provide also the correct magnitude of the cosmological constant. This observation can be relevant for the resolution of the cosmic coincidence problem in the brane-world scenario.Comment: 5 pages, RevTeX. Comments on the renormalization of the branon mass included. Final version to appear in Phys.Rev.D (R

Solar Wakes of Dark Matter Flows

We analyze the effect of the Sun's gravitational field on a flow of cold dark matter (CDM) through the solar system in the limit where the velocity dispersion of the flow vanishes. The exact density and velocity distributions are derived in the case where the Sun is a point mass. The results are extended to the more realistic case where the Sun has a finite size spherically symmetric mass distribution. We find that regions of infinite density, called caustics, appear. One such region is a line caustic on the axis of symmetry, downstream from the Sun, where the flow trajectories cross. Another is a cone-shaped caustic surface near the trajectories of maximum scattering angle. The trajectories forming the conical caustic pass through the Sun's interior and probe the solar mass distribution, raising the possibility that the solar mass distribution may some day be measured by a dark matter detector on Earth. We generalize our results to the case of flows with continuous velocity distributions, such as that predicted by the isothermal model of the Milky Way halo.Comment: 30 pages, 8 figure

The Large Magellanic Cloud and the Distance Scale

The Magellanic Clouds, especially the Large Magellanic Cloud, are places where multiple distance indicators can be compared with each other in a straight-forward manner at considerable precision. We here review the distances derived from Cepheids, Red Variables, RR Lyraes, Red Clump Stars and Eclipsing Binaries, and show that the results from these distance indicators generally agree to within their errors, and the distance modulus to the Large Magellanic Cloud appears to be defined to 3% with a mean value of 18.48 mag, corresponding to 49.7 Kpc. The utility of the Magellanic Clouds in constructing and testing the distance scale will remain as we move into the era of Gaia.Comment: 23 pages, accepted for publication in Astrophysics and Space Science. From a presentation at the conference The Fundamental Cosmic Distance Scale: State of the Art and the Gaia Perspective, Naples, May 201

Toward an internally consistent astronomical distance scale

Accurate astronomical distance determination is crucial for all fields in astrophysics, from Galactic to cosmological scales. Despite, or perhaps because of, significant efforts to determine accurate distances, using a wide range of methods, tracers, and techniques, an internally consistent astronomical distance framework has not yet been established. We review current efforts to homogenize the Local Group's distance framework, with particular emphasis on the potential of RR Lyrae stars as distance indicators, and attempt to extend this in an internally consistent manner to cosmological distances. Calibration based on Type Ia supernovae and distance determinations based on gravitational lensing represent particularly promising approaches. We provide a positive outlook to improvements to the status quo expected from future surveys, missions, and facilities. Astronomical distance determination has clearly reached maturity and near-consistency.Comment: Review article, 59 pages (4 figures); Space Science Reviews, in press (chapter 8 of a special collection resulting from the May 2016 ISSI-BJ workshop on Astronomical Distance Determination in the Space Age

The 1995 pilot campaign of PLANET: searching for microlensing anomalies through precise, rapid, round-the-clock monitoring

PLANET (the Probing Lensing Anomalies NETwork) is a worldwide collaboration of astronomers whose primary goal is to monitor microlensing events densely and precisely in order to detect and study anomalies that contain information about Galactic lenses and sources that would otherwise be unobtainable. The results of PLANET's highly successful first year of operation are presented here. Details of the observational setup, observing procedures, and data-reduction procedures used to track the progress in real time at the three participating observing sites in 1995 are discussed. The ability to follow several events simultaneously with a median sampling interval of 1.6 hr and a photometric precision of better than 0.10 mag even at I = 19 has been clearly demonstrated. During PLANET's 1995 pilot campaign, ten microlensing events were monitored, resulting in the most precise and densely-sampled light curves to date the binary nature of one of these, MACHO 95-BLG-12, was recognized by PLANET on the mountain. Another event, OGLE 95-BLG-04, displayed chromaticity that may betray the presence of blending with unresolved stars projected onto the same resolution element. Although lasting only about a month, the campaign may allow constraints to be placed on the number of planets with mass ratios to the parent star of 0.01 or greater