Remarks on Time-Space Noncommutative Field Theories

We propose a physical interpretation of the perturbative breakdown of unitarity in time-like noncommutative field theories in terms of production of tachyonic particles. These particles may be viewed as a remnant of a continuous spectrum of undecoupled closed-string modes. In this way, we give a unified view of the string-theoretical and the field-theoretical no-go arguments against time-like noncommutative theories. We also perform a quantitative study of various locality and causality properties of noncommutative field theories at the quantum level.Comment: 19 pages, LaTe

Directional detection of Dark Matter

Among the many experimental techniques available, those providing directional information have the potential of yielding an unambiguous observation of WIMPs even in the presence of insidious backgrounds. A measurement of the distribution of arrival direction of WIMPs can also discriminate between Galactic Dark Matter halo models. In this article, I will discuss the motivation for directional detectors and review the experimental techniques used by the various experiments. I will then describe one of them, the DMTPC detector, in more detail.Comment: 17 pages, 11 postscript figures, mini-review submitted to Modern Physics Letters A (MPLA). Submitted to Modern Physics Letters A (MPLA

Deciding Where to Publish or Present Your Work

Are you having trouble choosing the best place to publish or present your work? Which publications have the biggest impact? This workshop will provide a general overview of factors to consider when choosing venues to publish and present. We will include a discussion of available tools and resources you can use to gather information and make informed decisions

Bound on the Dark Matter Density in the Solar System from Planetary Motions

High precision planet orbital data extracted from direct observation, spacecraft explorations and laser ranging techniques enable to put a strong constraint on the maximal dark matter density of a spherical halo centered around the Sun. The maximal density at Earth's location is of the order $10^5$ ${\rm GeV/cm^3}$ and shows only a mild dependence on the slope of the halo profile, taken between 0 and -2. This bound is somewhat better than that obtained from the perihelion precession limits.Comment: 7 pages, 1 figur

Soft L_e-L_mu-L_tau flavour symmetry breaking and sterile neutrino keV Dark Matter

We discuss how a $L_e-L_\mu-L_\tau$ flavour symmetry that is softly broken leads to keV sterile neutrinos, which are a prime candidate for Warm Dark Matter. This is to our knowledge the first model where flavour symmetries are applied simultaneously to active and sterile neutrinos explaining at the same time active neutrino properties and this peculiar Dark Matter scenario. The essential point is that different scales of the symmetry breaking and the symmetry preserving entries in the mass matrix lead to one right-handed neutrino which is nearly massless compared to the other two. Furthermore, we naturally predict vanishing $\theta_{13}$ and maximal $\theta_{23}$, while the correct value of $\theta_{12}$ must come from the mixing of the charged leptons. We can furthermore predict an exact mass spectrum for the light neutrinos, which will be testable in the very near future.Comment: 14 page

Dark matter effects in vacuum spacetime

We analyze a toy model describing an empty spacetime in which the motion of a test mass (and the trajectories of photons) evidence the presence of a continuous and homogeneous distribution of matter; however, since the energy-momentum tensor vanishes, no real matter or energy distribution is present at all. Thus, a hypothetical observer will conclude that he is immersed in some sort of dark matter, even though he has no chance to directly detect it. This suggests yet another possibility of explaining the elusive dark matter as a purely dynamical effect due to the curvature of spacetime.Comment: 5 pages, 2 figures, expanded with comments about the exact motion and curvature invariant

Discrete Matter, Far Fields, and Dark Matter

We show that in cosmology the gravitational action of the far away matter has quite relevant effects, if retardation of the forces and discreteness of matter (with its spatial correlation) are taken into account. The expansion rate is found to be determined by the density of the far away matter, i.e., by the density of matter at remote times. This leads to the introduction of an effective density, which has to be five times larger than the present one, if the present expansion rate is to be accounted for. The force per unit mass on a test particle is found to be of the order of 0.2cH_0. The corresponding contribution to the virial of the forces for a cluster of galaxies is also discussed, and it is shown that it fits the observations if a decorrelation property of the forces at two separated points is assumed. So it appears that the gravitational effects of the far away matter may have the same order of magnitude as the corresponding local effects of dark matter.Comment: 16 pages, 1 figure. LaTex documen

The Effect of Substructure on Mass Estimates of Galaxies

Large galaxies are thought to form hierarchically, from the accretion and disruption of many smaller galaxies. Such a scenario should naturally lead to galactic phase-space distributions containing some degree of substructure. We examine the errors in mass estimates of galaxies and their dark halos made using the projected phase-space distribution of a tracer population (such as a globular cluster system or planetary nebulae) due to falsely assuming that the tracers are distributed randomly. The level of this uncertainty is assessed by applying a standard mass estimator to samples drawn from 11 random realizations of galaxy halos containing levels of substructure consistent with current models of structure formation. We find that substructure will distort our mass estimates by up to ~20% - a negligible error compared to statistical and measurement errors in current derivations of masses for our own and other galaxies. However, this represents a fundamental limit to the accuracy of any future mass estimates made under the assumption that the tracer population is distributed randomly, regardless of the size of the sample or the accuracy of the measurements.Comment: 9 pages, 8 figures, Astrophysical Journal, in pres

CIRS: Cluster Infall Regions in the Sloan Digital Sky Survey I. Infall Patterns and Mass Profiles

We use the Fourth Data Release of the Sloan Digital Sky Survey to test the ubiquity of infall patterns around galaxy clusters and measure cluster mass profiles to large radii. We match X-ray cluster catalogs with SDSS, search for infall patterns, and compute mass profiles for a complete sample of X-ray selected clusters. Very clean infall patterns are apparent in most of the clusters, with the fraction decreasing with increasing redshift due to shallower sampling. All 72 clusters in a well-defined sample limited by redshift (ensuring good sampling) and X-ray flux (excluding superpositions) show infall patterns sufficient to apply the caustic technique. This sample is by far the largest sample of cluster mass profiles extending to large radii to date. Similar to CAIRNS, cluster infall patterns are better defined in observations than in simulations. Further work is needed to determine the source of this difference. We use the infall patterns to compute mass profiles for 72 clusters and compare them to model profiles. Cluster scaling relations using caustic masses agree well with those using X-ray or virial mass estimates, confirming the reliability of the caustic technique. We confirm the conclusion of CAIRNS that cluster infall regions are well fit by NFW and Hernquist profiles and poorly fit by singular isothermal spheres. This much larger sample enables new comparisons of cluster properties with those in simulations. The shapes (specifically, NFW concentrations) of the mass profiles agree well with the predictions of simulations. The mass inside the turnaround radius is on average 2.19$\pm$0.18 times that within the virial radius. This ratio agrees well with recent predictions from simulations of the final masses of dark matter haloes.Comment: 34 pages, 24 figures, accepted for publication in AJ, full resolution version available at http://www.astro.yale.edu/krines