Particle theory

Abstract:

Using the South Pole Acoustic Test Setup (SPATS) and a retrievable transmitter deployed in holes drilled for the IceCube experiment, we have measured the attenuation of acoustic signals by South Pole ice at depths between 190 m and 500 m. Three data sets, using different acoustic sources, have been analyzed and give consistent results. The method with the smallest systematic uncertainties yields an amplitude attenuation coefficient α = 3.20 ± 0.57 km-1 between 10 and 30 kHz, considerably larger than previous theoretical estimates. Expressed as an attenuation length, the analyses give a consistent result for λ ≡ 1/α of ∼300 m with 20% uncertainty. No significant depth or frequency dependence has been found. © 2010 Elsevier B.V. All rights reserved.

Abstract:

The question of the transition to global isotropy from our anisotropic local universe is studied using the Union 2 catalogue of Type Ia supernovae (SNeIa). We construct a 'residual' statistic sensitive to systematic shifts in their brightness in different directions and use this to search in different redshift slices for a preferred direction on the sky in which the SNeIa are brighter or fainter relative to the standard Λcold dark matter (ΛCDM) cosmology. At low redshift (z < 0.05), we find that an isotropic model such as ΛCDM is barely consistent with the SNeIa data at 2σ-3σ. A maximum-likelihood analysis of peculiar velocities confirms this finding - there is a bulk flow of 260 kms-1 extending out to z~ 0.06, which disagrees with ΛCDM at 1σ-2σ. Since the Shapley concentration is believed to be largely responsible for this bulk flow, we make a detailed study of the infall region: the SNeIa falling away from the Local Group towards Shapley are indeed significantly dimmer than those falling towards us on to Shapley. Convergence to the CMB rest frame must occur well beyond Shapley (z > 0.06) so this low-redshift bulk flow will systematically bias any reconstruction of the expansion history of the Universe. At higher redshifts z > 0.15 the agreement between the SNeIa data and the ΛCDM model does improve, however, the sparseness and low quality of the data mean that the latter cannot be singled out as the preferred cosmological model. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Abstract:

We compare predictions for high energy neutrino and anti-neutrino deep inelastic scattering cross-sections within the conventional DGLAP formalism of next-to-leading order QCD, using the latest parton distribution functions such as CT10, HERAPDF1.5 and MSTW08 and taking account of PDF uncertainties. From this we derive a benchmark cross-section and uncertainty which is consistent with the results obtained earlier using the ZEUS-S PDFs. We advocate the use of this for analysing data from neutrino telescopes, in order to facilitate comparison between their results.

Abstract:

We present the results of searches for dipolar-type anisotropies in different energy ranges above 2.5 × 10¹⁷ eV with the surface detector array of the Pierre Auger Observatory, reporting on both the phase and the amplitude measurements of the first harmonic modulation in the right-ascension distribution. Upper limits on the amplitudes are obtained, which provide the most stringent bounds at present, being below 2% at 99% C.L. for EeV energies. We also compare our results to those of previous experiments as well as with some theoretical expectations. © 2011 Published by Elsevier B.V.

Abstract:

We report on the search for electromagnetic and hadronic showers ("cascades") produced by a diffuse flux of extraterrestrial neutrinos in the AMANDA neutrino telescope. Data for this analysis were recorded during 1001 days of detector livetime in the years 2000-2004. The observed event rates are consistent with the background expectation from atmospheric neutrinos and muons. An upper limit is derived for the diffuse flux of neutrinos of all flavors assuming a flavor ratio of νe:νμ: ντ = 1:1:1 at the detection site. The all-flavor flux of neutrinos with an energy spectrum Φ ∝ E-2 is less than 5.0 × 10-7 GeV s-1 sr-1 cm-2 at a 90% C.L. Here, 90% of the simulated signal would fall within the energy range 40 TeV to 9 PeV. We discuss flux limits in the context of several specific models of extraterrestrial and prompt atmospheric neutrino production. © 2010 Elsevier B.V. All rights reserved.