Low-x hadronic final states at HERA

Measurements of the hadronic final state at HERA are reviewed, which aim at the investigation of the parton dynamics of the proton at small Bjorken x.Comment: 7 pages, latex, 8 figures as ps/eps file

The Dawn of Galaxies

The development of primordial inhomogeneities into the non-linear regime and the formation of the first astrophysical objects within dark matter halos mark the transition from a simple, neutral, cooling universe -- described by just a few parameters -- to a messy ionized one -- the realm of radiative, hydrodynamic, and star formation processes. The recent measurement by the WMAP satellite of a large optical depth to electron scattering implies that this transition must have begun very early, and that the universe was reionized at redshift z_ion=17\pm 5. It is an early generation of extremely metal-poor massive stars and/or `seed' accreting black holes in subgalactic halos that may have generated the ultraviolet radiation and mechanical energy that reheated and reionized most of the hydrogen in the cosmos. The detailed thermal, ionization, and chemical enrichment history of the universe during the crucial formative stages around z=10-20 depends on the power-spectrum of density fluctuations on small scales, the stellar initial mass function and star formation efficiency, a complex network of poorly understood `feedback' mechanisms, and remains one of the crucial missing links in galaxy formation and evolution studies.Comment: 14 pages, 4 figures, to appear in the proceedings of the XXI Texas Symposium on Relativistic Astrophysics held on December 9--13 2002, in Florence, Ital

Confronting QCD Instantons with HERA Data

The sensitivity of existing HERA data on the hadronic final state in deep-inelastic scattering (DIS) to processes induced by QCD instantons is systematically investigated. The maximally allowed fraction of such processes in DIS is found to be on the percent level in the kinematic domain 0.0001 < x-Bjorken < 0.01 and 5 < Q squared < 100 GeV squared. The best limits are obtained from the multiplicity distribution.Comment: 5 pages, latex, entire paper w. tex, style and figure

The Dark Matter Annihilation Signal from Galactic Substructure: Predictions for GLAST

We present quantitative predictions for the detectability of individual Galactic dark matter subhalos in gamma-rays from dark matter pair annihilations in their centers. Our method is based on a hybrid approach, employing the highest resolution numerical simulations available (including the recently completed one billion particle Via Lactea II simulation) as well as analytical models for the extrapolation beyond the simulations' resolution limit. We include a self-consistent treatment of subhalo boost factors, motivated by our numerical results, and a realistic treatment of the expected backgrounds that individual subhalos must outshine. We show that for reasonable values of the dark matter particle physics parameters (M_X ~ 50 - 500 GeV and ~ 10^-26 - 10^-25 cm^3/s) GLAST may very well discover a few, even up to several dozen, such subhalos, at 5 sigma significance, and some at more than 20 sigma. We predict that the majority of luminous sources would be resolved with GLAST's expected angular resolution. For most observer locations the angular distribution of detectable subhalos is consistent with a uniform distribution across the sky. The brightest subhalos tend to be massive (median Vmax of 24 km/s) and therefore likely hosts of dwarf galaxies, but many subhalos with Vmax as low as 5 km/s are also visible. Typically detectable subhalos are 20 - 40 kpc from the observer, and only a small fraction are closer than 10 kpc. The total number of observable subhalos has not yet converged in our simulations, and we estimate that we may be missing up to 3/4 of all detectable subhalos.Comment: 19 pages, 12 figures, ApJ accepted, a version with higher resolution figures can be downloaded from http://www.sns.ias.edu/~mqk/transfer/VL2_GLAST_predictions.pd

Formation and evolution of galaxy dark matter halos and their substructure

We use the ``Via Lactea'' simulation to study the co-evolution of a Milky Way-size LambdaCDM halo and its subhalo population. While most of the host halo mass is accreted over the first 6 Gyr in a series of major mergers, the physical mass distribution [not M_vir(z)] remains practically constant since z=1. The same is true in a large sample of LambdaCDM galaxy halos. Subhalo mass loss peaks between the turnaround and virialization epochs of a given mass shell, and declines afterwards. 97% of the z=1 subhalos have a surviving bound remnant at the present epoch. The retained mass fraction is larger for initially lighter subhalos: satellites with maximum circular velocities Vmax=10 km/s at z=1 have today about 40% of their mass back then. At the first pericenter passage a larger average mass fraction is lost than during each following orbit. Tides remove mass in substructure from the outside in, leading to higher concentrations compared to field halos of the same mass. This effect, combined with the earlier formation epoch of the inner satellites, results in strongly increasing subhalo concentrations towards the Galactic center. We present individual evolutionary tracks and present-day properties of the likely hosts of the dwarf satellites around the Milky Way. The formation histories of ``field halos'' that lie today beyond the Via Lactea host are found to strongly depend on the density of their environment. This is caused by tidal mass loss that affects many field halos on eccentric orbits.Comment: 20 pages, 18 figures. Figures 6,7 and 8 corrected in this version, for details see the erratum in ApJ 679, 1680 and http://www.ucolick.org/~diemand/vl/publ/vlevolerr.pdf. Data, movies and images are available at http://www.ucolick.org/~diemand/vl

LOOPUS Mob-D: System concept for a public mobile satellite system providing integrated digital services for the Northern Hemisphere from an elliptical orbit

A new concept for a satellite based public mobile communications system, LOOPUS Mob-D, is introduced, whereby most of the classical problems in mobile satellite systems are approached in a different way. The LOOPUS system will offer a total capacity of 6000 high rate channels in three service areas (Europe, Asia, and North America), covering the entire Northern Hemisphere with a set of group special mobile (GSM) compatible mobile services, eventually providing the 'office in the car'. Special characteristics of the LOOPUS orbit and the communications network architecture are highlighted