High energy cosmic ray signature of quark nuggets

It has been recently proposed that dark matter in the Universe might consist of nuggets of quarks which populate the nuclear desert between nucleons and neutron star matter. It is further suggested that the Centauro events which could be the signature of particles with atomic mass A approx. 100 and energy E approx. 10 to 15th power eV might also be related to debris produced in the encounter of two neutron stars. A further consequence of the former proposal is examined, and it is shown that the production of relativistic quark nuggets is accompanied by a substantial flux of potentially observable high energy neutrinos

Costs, Institutional Mobility Barriers, and Market Structure: Advertising Agencies as Multiproduct Firms

What accounts for the diversity and limited concentration that has long characterized the organization of the advertising agency industry? This question is addressed by treating an advertising agency as a multiproduct firm. The firm's product line or service mix is defined in terms of the set of different media categories where an agency places the advertising messages which it creates on behalf of its clients. Evidence is presented indicating that the structure of demand and costs in the advertising agency industry conforms to the conditions that MacDonald and Slivinski (1987) showed were required for an industry to sustain an equilibrium with diversified firms. Building on this framework, we formulate a set of three hypotheses relating to the realization of product-specific scale and scope economies. The first two hypotheses posit that given low fixed costs and minimal entry barriers, both media-specific scale and scope economies are available and can be exploited by relatively small-size agencies. The third hypothesis suggests that large agencies may experience diseconomies of scope as a consequence of excessive diversification induced by two pervasive industry institutional phenomena: (i) 'bundling' of agency services to match client demand for a mix of media advertising; and (ii) 'conflict policy' which prohibits an agency from serving competing accounts and operates as a mobility constraint. Utilizing a multiproduct cost function, we estimate media-specific scale and scope economies for a cross-section of 401 U.S. agencies in 1987. The results obtained support the set of three hypotheses outlined above.

Dark Matter Seeding in Neutron Stars

We present a mechanism that may seed compact stellar objects with stable lumps of quark matter, or {\it strangelets}, through the self-annihilation of gravitationally accreted WIMPs. We show that dark matter particles with masses above a few GeV may provide enough energy in the nuclear medium for quark deconfinement and subsequent strangelet formation. If this happens this effect may then trigger a partial or full conversion of the star into a strange star. We set a new limit on the WIMP mass in the few-GeV range that seems to be consistent with recent indications in dark matter direct detection experiments.Comment: 3 pages, 1 figure. Prepared for 19th Particles and Nuclei International Conference (PANIC 2011), Boston, USA 25-29 Jul 201

On prospects for dark matter indirect detection in the Constrained MSSM

In the framework of the Constrained MSSM we derive the most probable ranges of the diffuse gamma radiation flux from the direction of the Galactic center and of the positron flux from the Galactic halo due to neutralino dark matter annihilation. We find that, for a given halo model, and assuming flat priors, the 68% probability range of the integrated gamma-ray flux spans about one order of magnitude, while the 95% probability range can be much larger and extend over four orders of magnitude (even exceeding five for a tiny region at small neutralino mass). The detectability of the signal by GLAST depending primarily on the cuspiness of the halo profile. The positron flux, on the other hand, appears to be too small to be detectable by PAMELA, unless the boost factor is at least of order ten and/or the halo profile is extremely cuspy. We also briefly discuss the sensitivity of our results to the choice of priors

Galaxy Mergers at z>1 in the HUDF: Evidence for a Peak in the Major Merger Rate of Massive Galaxies

We present a measurement of the galaxy merger fraction and number density from observations in the Hubble Ultra Deep Field for 0.5<z<2.5. We fit the combination of broadband data and slitless spectroscopy of 1308 galaxies with stellar population synthesis models to select merging systems based on a stellar mass of >10^10 M_sol. When correcting for mass incompleteness, the major merger fraction is not simply proportional to (1+z)^m, but appears to peak at z_frac~=1.3+-0.4. From this merger fraction, we infer that ~42% of massive galaxies have undergone a major merger since z~1. We show that the major merger number density peaks at z_dens~1.2, which marks the epoch where major merging of massive galaxies is most prevalent. This critical redshift is comparable to the peak of the cosmic star formation rate density, and occurs roughly 2.6 Gyr earlier in cosmic time than the peak in the number density of X-ray selected active galactic nuclei. These observations support an indirect evolutionary link between merging, starburst, and active galaxies.Comment: Accepted to ApJ. 7 pages, 6 figures, 1 table. Uses and includes emulateapj.cls. In the initial submission, Figures 1 and 2 where switche

Reconstruction of primordial density fields

The Monge-Ampere-Kantorovich (MAK) reconstruction is tested against cosmological N-body simulations. Using only the present mass distribution sampled with particles, and the assumption of homogeneity of the primordial distribution, MAK recovers for each particle the non-linear displacement field between its present position and its Lagrangian position on a primordial uniform grid. To test the method, we examine a standard LCDM N-body simulation with Gaussian initial conditions and 6 models with non-Gaussian initial conditions: a chi-squared model, a model with primordial voids and four weakly non-Gaussian models. Our extensive analyses of the Gaussian simulation show that the level of accuracy of the reconstruction of the nonlinear displacement field achieved by MAK is unprecedented, at scales as small as about 3 Mpc. In particular, it captures in a nontrivial way the nonlinear contribution from gravitational instability, well beyond the Zel'dovich approximation. This is also confirmed by our analyses of the non-Gaussian samples. Applying the spherical collapse model to the probability distribution function of the divergence of the displacement field, we also show that from a well-reconstructed displacement field, such as that given by MAK, it is possible to accurately disentangle dynamical contributions induced by gravitational clustering from possible initial non-Gaussianities, allowing one to efficiently test the non-Gaussian nature of the primordial fluctuations. In addition, a simple application of MAK using the Zel'dovich approximation allows one to also recover accurately the present-day peculiar velocity field on scales of about 8 Mpc.Comment: Version to appear in MNRAS, 24 pages, 21 figures appearing (uses 35 figure files), 1 tabl

Intermedia Substitutability and Market Demand by National Advertisers

We assess substitutable and complementary relationships among eight national advertising media classes, as well as the magnitude of their own-price elasticities. We use a translog demand model, whose parameters we estimate by three-stage least squares, based on 1960-94 annual U.S. data.We find aggregate demand by national advertisers for each of the eight media is own-price inelastic, and that cross-price elasticities suggest slightly more substitute than complementary relationships, although both are rather weak. These patterns are consistent with long prevailing institutional arrangements and media selection practices.

An Australia telescope survey for CMB anisotropies

We have surveyed six distinct `empty fields' using the Australia Telescope Compact Array in an ultra-compact configuration with the aim of imaging, with a high brightness sensitivity, any arcmin-scale brightness-temperature anisotropies in the background radio sky. The six well-separated regions were observed at a frequency of 8.7 GHz and the survey regions were limited by the ATCA primary beams which have a full width at half maximum of 6 arcmin at this frequency; all fields were observed with a resolution of 2 arcmin and an rms thermal noise of 24 microJy/beam. After subtracting foreground confusion detected in higher resolution images of the fields, residual fluctuations in Stokes I images are consistent with the expectations from thermal noise and weaker (unidentified) foreground sources; the Stokes Q and U images are consistent with expectations from thermal noise. Within the sensitivity of our observations, we have no reason to believe that there are any Sunyaev-Zeldovich holes in the microwave sky surveyed. Assuming Gaussian-form CMB anisotropy with a `flat' spectrum, we derive 95 per cent confidence upper limits of Q_flat < 10--11 microK in polarized intensity and Q_flat < 25 microK in total intensity. The ATCA filter function peaks at l=4700 and has half maximum values at l=3350 and 6050.Comment: 17 pages, includes 8 figures and 6 tables, accepted for publication in MNRA