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arXiv2007

Scalar perturbations in Randall-Sundrum braneworld cosmology

We study the evolution of scalar perturbations in the radiation-dominated era of Randall-Sundrum braneworld cosmology by numerically solving the coupled bulk and brane master wave equations. We find that density perturbations with wavelengths less than a critical value (set by the bulk curvature length) are amplified during horizon re-entry. Conversely, we explicitly confirm from simulations that the spectrum is identical to GR on large scales. Although this magnification is not relevant for the cosmic microwave background or measurements of large scale structure, it may have some bearing on the formation of primordial black holes in Randall-Sundrum models.

astro-ph↗

arXiv2007

Giant Radio Galaxies as a probe of the cosmological evolution of the IGM, I. Preliminary deep detections and low-resolution spectroscopy with the SALT

A problem of the cosmological evolution of the IGM is recalled and a necessity to find distant (z>0.5) giant radio galaxies (GRGs) with the lobe energy densities lower than about 10^{-14} J m^{-3} to solve this problem is emphasized. Therefore we undertake a search for such GRGs on the southern sky hemisphere using the SALT. In this paper we present a selected sample of the GRG candidates and the first deep detections of distant host galaxies, as well as the low-resolution spectra of the galaxies identified on the DSS frames. The data collected during the Performance Verification (P-V) phase show that 21 of 35 galaxies with the spectroscopic redshift have the projected linear size greater than 1 Mpc (for H_{0}=71 km\s\Mpc). However their redshifts do not exceed the value of 0.4 and the energy density in only two of them is less than 10^{-14} J m^{-3}. A photometric redshift estimate of one of them (J1420-0545) suggests a linear extent larger than 4.8 Mpc, i.e. a larger than that of 3C236, the largest GRG known up to now.

astro-ph↗

arXiv2007

The ANTARES Detector: Electronics and Readout

In this paper, we illustrate the main features of the electronics and data acquisition systems of the ANTARES apparatus, a large volume, deep-sea neutrino telescope under construction in the Mediterranean Sea off the coast of Toulon, France. The apparatus consists of an array of 900 large-area photomultipliers arranged on 12 detection lines, 5 of which are in data acquisition since January 2007. The schedule is to complete the apparatus construction in early 2008.

astro-ph↗

arXiv2008

Uncertainties of the antiproton flux from Dark Matter annihilation in comparison to the EGRET excess of diffuse gamma rays

The EGRET excess of diffuse Galactic gamma rays shows all the features expected from dark matter annihilation (DMA): a spectral shape given by the fragmentation of mono-energetic quarks, which is the same in all sky directions and an intensity distribution of the excess expected from a standard dark matter halo, predicted by the rotation curve. From the EGRET excess one can predict the flux of antiprotons from DMA. However, how many antiprotons arrive at the detector strongly depends on the propagation model. The conventional isotropic propagation models trap the antiprotons in the Galaxy leading to a local antiproton flux far above the observed flux. According to Bergstrom et. al. this excludes the DMA interpretation of the EGRET excess. Here it is shown that more realistic anisotropic propagation models, in which most antiprotons escape by fast transport in the z-direction, are consistent with the B/C ratio, the antiproton flux and the EGRET excess from DMA.

astro-ph↗

arXiv2007

Deep-space laser-ranging missions ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) and ASTROD I for astrodynamics and astrometry

Deep-space laser ranging will be ideal for testing relativistic gravity, and mapping the solar-system to an unprecedented accuracy. ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) and ASTROD I are such missions. ASTROD I is a mission with a single spacecraft; it is the first step of ASTROD with 3 spacecraft. In this talk, after a brief review of ASTROD and ASTROD I, we concentrate of the precision of solar astrodynamics that can be achieved together with implications on astrometry and reference frame transformations. The precision planetary ephemeris derived from these missions together with second post-Newtonian test of relativistic gravity will serve as a foundation for future precise astrometry observations. Relativistic frameworks are discussed from these considerations.

astro-ph↗

arXiv2007

Baryogenesis -- 40 Years Later

The classical picture of GUT baryogenesis has been strongly modified by theoretical progress concerning two nonperturbative features of the standard model: the phase diagram of the electroweak theory, and baryon and lepton number changing sphaleron processes in the high-temperature symmetric phase of the standard model. We briefly review three viable models, electroweak baryogenesis, the Affleck-Dine mechanism and leptogenesis and discuss the prospects to falsify them. All models are closely tied to the nature of dark matter, especially in supersymmetric theories. In the near future results from LHC and gamma-ray astronomy will shed new light on the origin of the matter-antimatter asymmetry of the universe.

hep-ph↗

arXiv2007

The IceCube Collaboration: contributions to the 30th International Cosmic Ray Conference (ICRC 2007)

This paper bundles 40 contributions by the IceCube collaboration that were submitted to the 30th International Cosmic Ray Conference ICRC 2007. The articles cover studies on cosmic rays and atmospheric neutrinos, searches for non-localized, extraterrestrial electron, muon and tau neutrino signals, scans for steady and intermittent neutrino point sources, searches for dark matter candidates, magnetic monopoles and other exotic particles, improvements in analysis techniques, as well as future detector extensions. The IceCube observatory will be finalized in 2011 to form a cubic-kilometer ice-Cherenkov detector at the location of the geographic South Pole. At the present state of construction, IceCube consists of 52 paired IceTop surface tanks and 22 IceCube strings with a total of 1426 Digital Optical Modules deployed at depths up to 2350 m. The observatory also integrates the 19 string AMANDA subdetector, that was completed in 2000 and extends IceCube's reach to lower energies. Before the deployment of IceTop, cosmic air showers were registered with the 30 station SPASE-2 surface array. IceCube's low noise Digital Optical Modules are very reliable, show a uniform response and record waveforms of arriving photons that are resolvable with nanosecond precision over a large dynamic range. Data acquisition, reconstruction and simulation software are running in production mode and the analyses, profiting from the improved data quality and increased overall sensitivity, are well under way.

astro-ph↗

arXiv2007

CPT violations in Astrophysics and Cosmology

In this paper it is given a brief review of the current limits on the magnitude of CPT and Lorentz Invariance violations, currently predicted in connection with quantum gravity and string/M-theory, that can be derived from astrophysical and cosmological data. Even if not completely unambiguous, these observational tests of fundamental physics are complementary to the ones obtained by accelerator experiments and by ground or space based direct experiments, because potentially can access very high energies and large distances.

astro-ph↗

arXiv2007

KM3NeT: A Next Generation Neutrino Telescope in the Mediterranean Sea

To complement the IceCube neutrino telescope currently under construction at the South Pole, the three Mediterranean neutrino telescope projects ANTARES, NEMO and NESTOR have joined forces to develop, construct and operate a km^3-scale neutrino telescope in the Mediterranean Sea. Since February 2006, the technical specifications and performance of such a detector are studied in the framework of a 3-year EU-funded Design Study. In 2009 a technical design report will be released laying the foundations for the construction of the detector. In the following, the current status of the Design Study is presented and examples of solutions for the technical challenges are discussed.

astro-ph↗

arXiv2007

More on the bending of light !

Recently, Rindler and Ishak have argued that the bending of light is, in principle, changed by the presence of a cosmological constant since one must consider not only the null geodesic equation, but also the process of measurement. I agree with the fact that both must be considered. Here, on the basis of the mathematically exact solution to the classical bending problem, and independent of the cosmological constant, I clarify the approximate argument found in the vast majority of texts (new and old) for the measured value of the bending of light for a single source and show that the result is in part due to the almost perfect cancelation of two terms, one of which is seldom considered. When one considers two sources, this cancelation is of no consequence, and, for example, if the sources are opposite with the same associated apsidal distance, the approximate argument gives the rigorously correct answer (up to numerical evaluation), an answer which is unaffected by the presence of a cosmological constant.

gr-qc↗

arXiv2007

Open Clusters in the log Age vs. M_V plane

In the log Age vs. integrated absolute magnitude (M_V) plane, the open clusters of the Milky Way form a well-defined band parallel to theoretical sequences decribing the passive evolution of Simple Stellar Populations and display a pretty sharp upper threshold in mass (M ~ 2X 10^4 M_{sun}) over a 4 dex range of ages.

astro-ph↗

arXiv2007

X-ray Observations of Galaxies: The Importance of Deep High-Resolution Observations

X-ray observations of galaxies have grown from a curiosity into a full-fledged field of astronomy. These observations provide unique information on black holes, binary stars, and the hot phase of the ISM, which can be used to constrain the chemical evolution of the Universe, and the joint evolution of galaxies and massive black holes. These exciting results are due in large part to the high-resolution capability of {\it Chandra}. To follow on {\it Chandra} and push forward this science past the present capabilities, our community must build a high-resolution (sub-arcsecond) large-area (several square meters) X-ray telescope.

astro-ph↗

arXiv2007

Extreme Habitability: Formation of Habitable Planets in Systems with Close-in Giant Planets and/or Stellar Companions

With more than 260 extrasolar planetary systems discovered to-date, the search for habitable planets has found new grounds. Unlike our solar system, the stars of many of these planets are hosts to eccentric or close-in giant bodies. Several of these stars are also members of moderately close ($<$40 AU) binary or multi-star systems. The formation of terrestrial objects in these "extreme" environments is strongly affected by the dynamics of their giant planets and/or their stellar companions. These objects have profound effects on the chemical structure of the disk of planetesimals and the radial mixing of these bodies in the terrestrial regions of their host stars. For many years, it was believed that such effects would be so destructive that binary stars and also systems with close-in giant planets would not be able to form and harbor habitable bodies. Recent simulations have, however, proven otherwise. I will review the results of the simulations of the formation and long-term stability of Earth-like objects in the habitable zones of such "extreme" planetary systems, and discuss the possibility of the formation of terrestrial planets, with significant amounts of water, in systems with hot Jupiters, and also around the primaries of moderately eccentric close binary stars.

astro-ph↗

arXiv2007

"Gauge" in General Relativity: Second-order general relativistic gauge-invariant perturbation theory

As in the case of the other gauge field theories, there is so called ``gauge'' also in general relativity. This ``gauge'' is unphysical degree of freedom. There are two kinds of ``gauges'' in general relativity. These are called the first- and the second-kind of gauges, respectively. The gauge of the first kind is just coordinate system on a single manifold. On the other hand, the gauge of the second kind arises in the general relativistic perturbations. Through the precise distinction of these two concepts of ``gauges'', we develop second-order gauge-invariant general relativistic perturbation theory.

gr-qc↗

arXiv2007

Supersymmetric Dark Matter Candidates - The Lightest Neutralino, the Gravitino, and the Axino

In supersymmetric extensions of the Standard Model, the lightest neutralino, the gravitino, and the axino can appear as the lightest supersymmetric particle and as such provide a compelling explanation of the non-baryonic dark matter in our Universe. For each of these dark matter candidates, I review the present status of primordial production mechanisms, cosmological constraints, and prospects of experimental identification.

hep-ph↗

arXiv2008

Expected z>5 QSO number counts in large area deep near-infrared surveys

The QSO luminosity function at z>5 provides strong constraints on models of joint evolution of QSO and their hosts. However, these observations are challenging because the low space densities of these objects necessitate surveying of large areas, in order to obtain statistically meaningful samples, while at the same time cosmological redshifting and dimming means that rather deep Near Infrared (NIR) imaging must be carried out. Several upcoming and proposed facilities with wide-field NIR imaging capabilities will open up this new region of parameter space. In this paper we present predictions for the expected number counts of z>5 QSOs, based on simple empirical and semi-empirical models of QSO evolution, as a function of redshift, depth and surveyed area. We compute the evolution of observed-frame QSO magnitudes and colors in a representative photometric system covering the wavelength range 550nm<lambda<1800nm, and combine this information with different estimates for the evolution of the QSO luminosity function. We conclude that planned ground-based surveys such as Pan-STARRS and VISTA should be able to detect a large number of luminous QSOs up to z<7.5, but that space-based missions such as EUCLID (formerly SPACE/DUNE) or SNAP are probably required in order to obtain substantial samples at higher redshift. We also use our models to predict the expected number counts for future X-ray space missions (such as XEUS and Constellation-X), and show that because of their small field-of-view, these telescopes are unlikely to discover significant numbers of AGN at very high redshift. However, X-ray follow-up of objects detected at longer wavelength will be an important means of confirming their identity as AGN and constraining obscuration.

astro-ph↗

arXiv2007

Evolution over Time of Magentic Dynamo Driven UV & X-ray Emissions of dG-M Stars and Effects on Hosted Planets

The evolution over time of the magnetic activity and the resulting X-ray and UV coronal and chromospheric emissions of main-sequence dG, dK, and dM stars with widely different ages are discussed. Young cool stars spin rapidly and have correspondingly very robust magnetic dynamos and strong coronal and chromospheric X-ray - UV (XUV) emissions. However, these stars spin-down with time as they lose angular momentum via magnetized winds and their magnetic generated activity and emissions significantly decrease. Studies of dK-dM stars over a wide range of ages and rotations show similar (but not identical) behavior. Particular emphasis is given to discussing the effects that XUV emissions have on the atmospheres and evolution of solar system planets as well as the increasing number of extrasolar planets found hosted by dG-dM stars. The results from modeling the early atmospheres of Venus, Earth and Mars using recently determined XUV irradiances and inferred winds of the young Sun are also briefly discussed. For example, the loss of water from juvenile Venus and Mars can be explained by action of the strong XUV emissions and robust winds of the young Sun. We also examine the effects of strong X-ray and UV coronal and chromospheric emissions (and frequent flares) that dM stars have on possible planets orbiting within their shrunken habitable zones (HZs) - located close to the low luminosity host stars (HZ < ~0.4 AU). Dwarf M stars make interesting targets for further study because of their deep outer convective zones (CZs), efficient dynamos, frequent flares and strong XUV emissions. Furthermore, a large fraction of dM stars are very old (>5 Gyr), which present intriguing possibilities for the development of highly advanced modes of intelligent life on planets that may orbit them.

astro-ph↗

arXiv2007

Detection of Very-High Energy Gamma-Rays from the BL Lac Object PG 1553+113 with the MAGIC Telescope

The MAGIC telescope has observed very-high energy gamma-ray emission from the BL Lac object PG 1553+113 in 2005 and 2006 at an overall significance is 8.8 sigma. The light curve shows no significant flux variations on a daily timescale. The flux level during 2005 was, however, significantly higher as compared to 2006. The differential energy spectrum between approx. 90 GeV and 500 GeV is well described by a power law with a spectral index of -4.2+-0.3. The photon energy spectrum and spectral modeling allow to pose upper limits of z=0.74 and z=0.56, respectively, on the yet undetermined redshift of PG 1553+113. Recent VLT observations of this blazar show featureless spectra in the near-IR, thus no direct redshift could be determined from these measurements.

astro-ph↗