A Study of Differences in Calculated Capacity when Using Single-, Mixed- or Multiple-Bounce GSCM Schemes

The paper looks for differences in MIMO system capacity when using either single-, mixed-, or multiple-bounce geometry based stochastic channel models (GSCMs). The investigation considers Saleh-Valenzuela temporal indoor model, expanded for angular domain. In the model omnidirectional and idealized sector antennas were used as array elements. The single-bounce assumption, combination of single and multiple bounces, and pure random multiple bounces assumption were compared within “temporally identical” environment regarding the overall MIMO capacity. Assumption of clustered scatterers/reflectors is used in all three cases. The comparison is performed in statistical sense, using a large number of stochastically generated temporal models. The model is two- dimensional, i.e. neither elevation angle nor polarization/ depolarization was considered

Effects of Unstable Dark Matter on Large-Scale Structure and Constraints from Future Surveys

In this paper we explore the effect of decaying dark matter (DDM) on large-scale structure and possible constraints from galaxy imaging surveys. DDM models have been studied, in part, as a way to address apparent discrepancies between the predictions of standard cold dark matter models and observations of galactic structure. Our study is aimed at developing independent constraints on these models. In such models, DDM decays into a less massive, stable dark matter (SDM) particle and a significantly lighter particle. The small mass splitting between the parent DDM and the daughter SDM provides the SDM with a recoil or "kick" velocity vk, inducing a free-streaming suppression of matter fluctuations. This suppression may be probed via weak lensing power spectra measured by a number of forthcoming imaging surveys that aim primarily to constrain dark energy. Using scales on which linear perturbation theory alone is valid (multipoles < 300), surveys like Euclid or LSST can be sensitive to vk > 90 km/s for lifetimes ~ 1-5 Gyr. To estimate more aggressive constraints, we model nonlinear corrections to lensing power using a simple halo evolution model that is in good agreement with numerical simulations. In our most ambitious forecasts, using multipoles < 3000, we find that imaging surveys can be sensitive to vk ~ 10 km/s for lifetimes < 10 Gyr. Lensing will provide a particularly interesting complement to existing constraints in that they will probe the long lifetime regime far better than contemporary techniques. A caveat to these ambitious forecasts is that the evolution of perturbations on nonlinear scales will need to be well calibrated by numerical simulations before they can be realized. This work motivates the pursuit of such a numerical simulation campaign to constrain dark matter with cosmological weak lensing.Comment: 15 pages, 7 figures. Submitted to PR

Probing the Shape of the Galactic Halo with Hyper-Velocity Stars

Precise proper motion measurements (sigma_mu ~ 10 mkas/yr) of the recently discovered hyper-velocity star (HVS) SDSS J090745.0+024507 would yield significant constraints on the axis ratios and orientation of a triaxial model for the Galactic halo. Triaxiality of dark matter halos is predicted by Cold Dark Matter models of galaxy formation and may be used to probe the nature of dark matter. However, unless the distance to this star is determined to better than 10%, these constraints suffer from one-dimensional degeneracies, which we quantify. We show how proper motion measurements of several HVSs could simultaneously resolve the distance degeneracies of all such stars and produce a detailed picture of the triaxial halo. Additional HVSs may be found from radial velocity surveys or from parallax/proper-motion data derived from GAIA. High-precision proper-motion measurements of these stars using the Space Interferometry Mission (SIM PlanetQuest) would substantially tighten the constraints they yield on the Galactic potential.Comment: 7 pages, matches printed versio

Cold Dark Matter Substructure and Galactic Disks I: Morphological Signatures of Hierarchical Satellite Accretion

(Abridged) We conduct a series of high-resolution, dissipationless N-body simulations to investigate the cumulative effect of substructure mergers onto thin disk galaxies in the context of the LCDM paradigm of structure formation. Our simulation campaign is based on a hybrid approach. Substructure properties are culled directly from cosmological simulations of galaxy-sized cold dark matter (CDM) halos. In contrast to what can be inferred from statistics of the present-day substructure populations, accretions of massive subhalos onto the central regions of host halos, where the galactic disk resides, since z~1 should be common occurrences. One host halo merger history is subsequently used to seed controlled numerical experiments of repeated satellite impacts on an initially-thin Milky Way-type disk galaxy. We show that these accretion events produce several distinctive observational signatures in the stellar disk including: a ring-like feature in the outskirts; a significant flare; a central bar; and faint filamentary structures that (spuriously) resemble tidal streams. The final distribution of disk stars exhibits a complex vertical structure that is well-described by a standard ``thin-thick'' disk decomposition. We conclude that satellite-disk encounters of the kind expected in LCDM models can induce morphological features in galactic disks that are similar to those being discovered in the Milky Way, M31, and in other disk galaxies. These results highlight the significant role of CDM substructure in setting the structure of disk galaxies and driving galaxy evolution. Upcoming galactic structure surveys and astrometric satellites may be able to distinguish between competing cosmological models by testing whether the detailed structure of galactic disks is as excited as predicted by the CDM paradigm.Comment: Accepted version to appear in ApJ, 24 pages, 8 figures, LaTeX (uses emulateapj.cls). Comparison between the simulated ring-like features and the Monoceros ring stellar structure in the Milky Way performed; conclusions unaltere

Self Calibration of Tomographic Weak Lensing for the Physics of Baryons to Constrain Dark Energy

Numerical studies indicate that uncertainties in the treatment of baryonic physics can affect predictions for shear power spectra at a level that is significant for forthcoming surveys such as DES, SNAP, and LSST. Correspondingly, we show that baryonic effects can significantly bias dark energy parameter measurements. Eliminating such biases by neglecting information in multipoles beyond several hundred leads to weaker parameter constraints by a factor of approximately 2 to 3 compared with using information out to multipoles of several thousand. Fortunately, the same numerical studies that explore the influence of baryons indicate that they primarily affect power spectra by altering halo structure through the relation between halo mass and mean effective halo concentration. We explore the ability of future weak lensing surveys to constrain both the internal structures of halos and the properties of the dark energy simultaneously as a first step toward self calibrating for the physics of baryons. This greatly reduces parameter biases and no parameter constraint is degraded by more than 40% in the case of LSST or 30% in the cases of SNAP or DES. Modest prior knowledge of the halo concentration relation greatly improves even these forecasts. Additionally, we find that these surveys can constrain effective halo concentrations near m~10^14 Msun/h and z~0.2 to better than 10% with shear power spectra alone. These results suggest that inferring dark energy parameters with measurements of shear power spectra can be made robust to baryonic effects and may simultaneously be competitive with other methods to inform models of galaxy formation. (Abridged)Comment: 18 pages, 11 figures. Minor changes reflecting referee's comments. Results and conclusions unchanged. Accepted for publication in Physical Review