Pion production in high energy cosmic ray collisions

Calculations on pion energy and angle distribution in center of hydrodynamic inelastic model for nucleon-nucleon collisio

Production spectrum of high energy electrons from high energy cosmic ray collisions

Production spectrum of high energy electrons from high energy cosmic ray collision

The phase-space structure of cold dark-matter halos: Insights into the Galactic halo

We study the formation of the Milky Way's halo in a $\Lambda$CDM cosmology by scaling down a high resolution simulation of the formation of a cluster of galaxies. We determine how much phase-space substructure is left over from the objects that merge to build up the present galaxy. We study the debris streams originating from such objects and find that their evolution can be explained simply in terms of the conservation of phase-space density. Analysing the mass growth history of our halo we find that its inner regions have been in place for more than 10 Gyr, but that the growth of the halo as a whole is more gradual, in agreement with other high resolution simulations of dark-matter halos. Recent accretion contributes to the inner 10 kpc of the halo only at the 10$^{-4}$ level. Finally we determine the number of dark-matter streams as a function of distance from the centre of the halo. In the equivalent of the ``Solar vicinity'', we find that the dark-matter is smoothly distributed in space, and that the velocity ellipsoid is formed by hundreds of thousands of streams, most of which have velocity dispersions of the order of 1 km/s or less.Comment: 16 pages, 21 figures, MNRAS in press. Postscript version with high resolution figures available from http://www.mpa-garching.mpg.de/~ahelmi/research/lcdm_cl.html. Minor change

The Dark UNiverse Explorer (DUNE): Proposal to ESA's Cosmic Vision

The Dark UNiverse Explorer (DUNE) is a wide-field space imager whose primary goal is the study of dark energy and dark matter with unprecedented precision. For this purpose, DUNE is optimised for the measurement of weak gravitational lensing but will also provide complementary measurements of baryonic accoustic oscillations, cluster counts and the Integrated Sachs Wolfe effect. Immediate auxiliary goals concern the evolution of galaxies, to be studied with unequalled statistical power, the detailed structure of the Milky Way and nearby galaxies, and the demographics of Earth-mass planets. DUNE is an Medium-class mission which makes use of readily available components, heritage from other missions, and synergy with ground based facilities to minimise cost and risks. The payload consists of a 1.2m telescope with a combined visible/NIR field-of-view of 1 deg^2. DUNE will carry out an all-sky survey, ranging from 550 to 1600nm, in one visible and three NIR bands which will form a unique legacy for astronomy. DUNE will yield major advances in a broad range of fields in astrophysics including fundamental cosmology, galaxy evolution, and extrasolar planet search. DUNE was recently selected by ESA as one of the mission concepts to be studied in its Cosmic Vision programme.Comment: Accepted in Experimental Astronom

Why we need to see the dark matter to understand the dark energy

The cosmological concordance model contains two separate constituents which interact only gravitationally with themselves and everything else, the dark matter and the dark energy. In the standard dark energy models, the dark matter makes up some 20% of the total energy budget today, while the dark energy is responsible for about 75%. Here we show that these numbers are only robust for specific dark energy models and that in general we cannot measure the abundance of the dark constituents separately without making strong assumptions.Comment: 4 pages, to be published in the Journal of Physics: Conference Series as a contribution to the 2007 Europhysics Conference on High Energy Physic

Probing Cosmic Acceleration Beyond the Equation of State: Distinguishing between Dark Energy and Modified Gravity Models

If general relativity is the correct theory of physics on large scales, then there is a differential equation that relates the Hubble expansion function, inferred from measurements of angular diameter distance and luminosity distance, to the growth rate of large scale structure. For a dark energy fluid without couplings or an unusual sound speed, deviations from this consistency relationship could be the signature of modified gravity on cosmological scales. We propose a procedure based on this consistency relation in order to distinguish between some dark energy models and modified gravity models. The procedure uses different combinations of cosmological observations and is able to find inconsistencies when present. As an example, we apply the procedure to a universe described by a recently proposed 5-dimensional modified gravity model. We show that this leads to an inconsistency within the dark energy parameter space detectable by future experiments.Comment: 8 pages, 7 figures; expanded paper; matches PRD accepted version; corrected growth rate formula; main results and conclusion unchange

Direct Detection of Dark Matter Debris Flows

Tidal stripping of dark matter from subhalos falling into the Milky Way produces narrow, cold tidal streams as well as more spatially extended "debris flows" in the form of shells, sheets, and plumes. Here we focus on the debris flow in the Via Lactea II simulation, and show that this incompletely phase-mixed material exhibits distinctive high velocity behavior. Unlike tidal streams, which may not necessarily intersect the Earth's location, debris flow is spatially uniform at 8 kpc and thus guaranteed to be present in the dark matter flux incident on direct detection experiments. At Earth-frame speeds greater than 450 km/s, debris flow comprises more than half of the dark matter at the Sun's location, and up to 80% at even higher speeds. Therefore, debris flow is most important for experiments that are particularly sensitive to the high speed tail of the dark matter distribution, such as searches for light or inelastic dark matter or experiments with directional sensitivity. We show that debris flow yields a distinctive recoil energy spectrum and a broadening of the distribution of incidence direction.Comment: 22 pages, 7 figures; accepted for publication in PR

Neutron capture production rates of cosmogenic 60Co, 59Ni and 36Cl in stony meteorites

Results for neutron flux calculations in stony meteoroids (of various radii and compositions) and production rates for Cl-36, Ni-59, and Co-60 are reported. The Ni-59/Co-60 ratio is nearly constant with depth in most meteorites: this effect is consistent with the neutron flux and capture cross section properties. The shape of the neutron flux energy spectrum, varies little with depth in a meteorite. The size of the parent meteorite can be determined from one of its fragments, using the Ni-59/Co-60 ratios, if the parent meteorite was less than 75 g/cm(2) in radius. If the parent meteorite was larger, a lower limit on the size of the parent meteorite can be determined from a fragment. In C3 chondrites this is not possible. In stony meteorites with R less than 50 g/cm(2) the calculated Co-60 production rates (mass less than 4 kg), are below 1 atom/min g-Co. The highest Co-60 production rates occur in stony meteorites with radius about 250 g/cm(2) (1.4 m across). In meteorites with radii greater than 400 g/cm(2), the maximum Co-60 production rate occurs at a depth of about 175 g/cm(2) in L-chondrite, 125 g/cm(2) in C3 chrondrite, and 190 g/cm(2) in aubrites

Simple quantum cosmology: Vacuum energy and initial state

A static non-singular 10-dimensional closed Friedmann universe of Planck size, filled with a perfect fluid with an equation of state with w = -2/3, can arise spontaneously by a quantum fluctuation from nothing in 11-dimensional spacetime. A quantum transition from this state can initiate the inflationary quantum cosmology outlined in Ref. 2 [General Relativity and Gravitation 33, 1415, 2001 - gr-qc/0103021]. With no fine-tuning, that cosmology predicts about 60 e-folds of inflation and a vacuum energy density depending only on the number of extra space dimensions (seven), G, h, c and the ratio between the strength of gravity and the strength of the strong force. The fraction of the total energy in the universe represented by this vacuum energy depends on the Hubble constant. Hubble constant estimates from WMAP, SDSS, the Hubble Key Project and Sunyaev-Zeldovich and X-ray flux measurements range from 60 to 72 km/(Mpc sec). With a mid-range Hubble constant of 65 km/(Mpc sec), the model in Ref. 2 predicts Omega-sub-Lambda = 0.7Comment: To be published in General Relativity and Gravitation, Vol. 37, May 2005. 5 pages, no figure

Non-monotonic orbital velocity profiles around rapidly rotating Kerr-(anti-)de Sitter black holes

It has been recently demonstrated that the orbital velocity profile around Kerr black holes in the equatorial plane as observed in the locally non-rotating frame exhibits a non-monotonic radial behaviour. We show here that this unexpected minimum-maximum feature of the orbital velocity remains if the Kerr vacuum is generalized to the Kerr-de Sitter or Kerr-anti-de Sitter metric. This is a new general relativity effect in Kerr spacetimes with non-vanishing cosmological constant. Assuming that the profile of the orbital velocity is known, this effect constrains the spacetime parameters.Comment: 9 pages, 4 figures, accepted for Class. Quant. Gra