H. Rubinstein

Optical properties of the South pole ice at depths between 0.8 and 1 kilometer.

The optical properties of the ice at the geographical South Pole have been investigated at depths between 0.8 and 1 kilometer. The absorption and scattering lengths of visible light (∼515 nanometers) have been measured in situ with the use of the laser calibration setup of the Antarctic Muon and Neutrino Detector Array (AMANDA) neutrino detector. The ice is intrinsically extremely transparent. The measured absorption length is 59 � 3 meters, comparable with the quality of the ultrapure water used in the Irvine-Michigan-Brookhaven and Kamiokande proton-decay and neutrino experiments and more than twice as long as the best value reported for laboratory ice. Because of a residual density of air bubbles at these depths, the trajectories of photons in the medium are randomized. If the bubbles are assumed to be smooth and spherical, the average distance between collisions at a depth of 1 kilometer is about 25 centimeters. The measured inverse scattering length on bubbles decreases linearly with increasing depth in the volume of ice investigated.

Optical properties of deep ice at the South Pole: absorption.

We discuss recent measurements of the wavelength-dependent absorption coefficients in deep South Pole ice. The method uses transit-time distributions of pulses from a variable-frequency laser sent between emitters and receivers embedded in the ice. At depths of 800-1000 m scattering is dominated by residual air bubbles, whereas absorption occurs both in ice itself and in insoluble impurities. The absorption coefficient increases approximately exponentially with wavelength in the measured interval 410-610 nm. At the shortest wavelength our value is approximately a factor 20 below previous values obtained for laboratory ice and lake ice; with increasing wavelength the discrepancy with previous measurements decreases. At ~415 to ~500 nm the experimental uncertainties are small enough for us to resolve an extrinsic contribution to absorption in ice: submicrometer dust particles contribute by an amount that increases with depth and corresponds well with the expected increase seen near the Last Glacial Maximum in Vostok and Dome C ice cores. The laser pulse method allows remote mapping of gross structure in dust concentration as a function of depth in glacial ice.We discuss recent measurements of the wavelength-dependent absorption coefficients in deep South Pole ice. The method uses transit time distributions of pulses from a variable-frequency laser sent between emitters and receivers embedded in the ice. At depths of 800 to 1000 m scattering is dominated by residual air bubbles, whereas absorption occurs both in ice itself and in insoluble impurities. The absorption coefficient increases approximately exponentially with wavelength in the measured interval 410 to 610 nm. At the shortest wavelength our value is about a factor 20 below previous values obtained for laboratory ice and lake ice; with increasing wavelength the discrepancy with previous measurements decreases. At around 415 to 500 nm the experimental uncertainties are small enough for us to resolve an extrinsic contribution to absorption in ice: submicron dust particles contribute by an amount that increases with depth and corresponds well with the expected increase seen near the Last Glacial Maximum in Vostok and Dome C ice cores. The laser pulse method allows remote mapping of gross structure in dust concentration as a function of depth in glacial ice.

Distortion of the acoustic peaks in the CMBR due to a primordial magnetic field

Abstract In this paper we study the effect of a magnetic field on the fluctuation spectrum of the cosmic microwave background. We find that upcoming measurements might give interesting bounds on large scale magnetic fields in the early Universe. If the effects are seen, it might be possible to establish the presence of different fields in different patches of the sky. Absence of any effect, will provide by one order of magnitude a better limit for a primordial field, now given by nucleosynthesis.

Revisiting nucleosynthesis constraints on primordial magnetic fields

Abstract In view of several conflicting results, we reanalyze the effects of magnetic fields on the primordial nucleosynthesis. In the case the magnetic field is homogeneous over a horizon volume, we show that the main effects of the magnetic field are given by the contribution of its energy density to the Universe expansion rate and the effect of the field on the electrons quantum statistics. Although, in order to get an upper limit on the field strength, the weight of the former effect is numerically larger, the latter cannot be neglected. Including both effects in the PN code we get the upper limit B ≤ 1 × 10 11 Gauss at the temperature T = 10 9 K. We generalize the considerations to case when instead the magnetic is inhomogeneous on the horizon length. We show that in these cases only the effect of the magnetic field on the electron statistics is relevant. If the coherence length of the magnetic field at the end of the PN is in the range 10 ⪡ L 0 ⪡ 10 11 cm our upper limit is B ≤ 1 × 10 12 Gauss.

UV and optical light transmission properties in deep ice at the South Pole

Both absorption and scattering of light at wavelengths 410 to 610 nanometers were measured in the South Pole ice at depths 0.8 to 1 kilometer with the laser calibration system of the Antarctic Muon And Neutrino Detector Array (AMANDA). At the shortest wavelengths the absorption lengths exceeded 200 meters - an order of magnitude longer than has been reported for laboratory ice. The absorption shows a strong wavelength dependence while the scattering length is found to be independent of the wavelength, consistent with the hypothesis of a residual density of air bubbles in the ice. The observed linear decrease of the inverse scattering length with depth is compatible with an earlier measurement by the AMANDA collaboration (at ∼515 nanometers).

Limits on possible magnetic fields at nucleosynthesis time

Abstract In this paper we discuss limits on magnetic fields that could have been present at nucleosynthesis time. We considered several effects that could be relevant modifing light elements relic abundances. They include: changes in reaction rates, mass shifts due to strong and electromagnetic interactions, variation of the expansion rate of the Universe due to both the magnetic field energy density and the increasing of the electrons density in overcritical magnetic fields. We find that the latter is the main effect. It was not taken into account in previous calculations. The allowed field intensity at the end of nucleosynthesis ( T = 1 × 10 9 K) is B ≤ 3 × 10 10 gauss.

Evolution and radiation from superconducting cosmic strings

Abstract We study the evolution of cosmic superconducting strings and their decay. We show that they pass by three stages. The last one produces high-energy particles. The size of the loop at this stage is less than 30 pc. If particles can leave the string, and μ 22 is the linear density necessary to explain galaxy formation, the strings are shown to produce isotropic γ radiation in excess of present bounds. However, we show that the produced particles degrade drastically in energy in the magnetic field of the string so that high-energy particles are not produced.

Proton β decay in large magnetic fields

Abstract Both electromagnetic and strong interactions contribute to make, in magnetic fields of the order of B > 1014 T, the neutron stable against beta decay and for somewhat larger fields the proton becomes unstable to a decay into a neutron via β emission. Changes in chiral condensates due to such fields and an unexpectedly large field dependence of hadronic magnetic moments would modify these arguments. Fields of such magnitude may exist in colliding neutron stars and in the vicinity of cosmic strings. Possible astrophysical consequences are discussed.

Dependence of lattice hadron masses on external magnetic fields

Abstract We study the variation of the hadron masses in the presence of external magnetic fields of strength of the order of the masses themselves. We identify the main factors affecting the lattice simulation results: • - the boundary discontinuities for eB ⪡ 2 π / L 2 a 2 . • - the SU(6) choice of the hadron wave function. We confirm qualitatively the earlier theoretical ansatz on the linear behaviour of the masses with the magnetic field and, as a by-product, we improve the lattice measurements of the nucleon magnetic moments. However our systematic and statistical errors preclude us from measuring the theoretically predicted field strength at which the proton becomes heavier than the neutron.

Large magnetic field instabilities induced by magnetic dipole transitions

Abstract We present a new mechanism that will limit very high magnetic fields which have been conjectured to exist in connection with some astrophysical phenomena. Low lying strongly interacting particles and resonances mixing with each other via magnetic dipole QED couplings force a vacuum instability for large external magnetic fields. These mixings limit fields to a few GeV 2 .