D. Harari

On the Evolution of Global Strings in the Early Universe

Abstract We find that a bent global string straightens itself out by dissipation into Nambu-Goldstone (NG) bosons in the order of one oscillation time and that the spectrum of radiated NG bosons is 1/ k . In the early universe, the assumption that there is one global string per causal horizon is justified after an initial period during which the effect of the primordial plasma on the motion of the strings is non-negligible. We find that the upper bound that axion radiation by strings places on the axion decay constant is comparable to, but not more stringent than the one derived from coherent oscillations of the axion field, i.e. ∫ a ≲ 10 12 GeV. We also discuss the model-dependence of this bound.

Effects of a Nambu-Goldstone boson on the polarization of radio galaxies and the cosmic microwave background

Abstract A coupling gϕE·B to a pseudoscalar field ϕ affects the polarization properties of electromagnetic waves as they propagate through background fields. We analyse the bounds imposed on g from astronomical polarization measurements. If ϕ is the Nambu-Goldstone boson field of a global symmetry spontaneously broken at an energy scale v, the g= Nα πv , with N a model-dependent numerical coefficient. For an exactly massless Nambu-Goldstone boson that N⪆50 is incompatible with the observed correlation between polarization properties and shape of distant radio galaxies and quasars, unless there was inflation after the breakdown of the global symmetry. We also show that propagation through intervening magnetic fields induces a small degree of linear polarization in the cosmic microwave background.

On the ultrahigh energy cosmic ray horizon

We compute the ultrahigh energy cosmic ray horizon, i.e. the distance up to which cosmic ray sources may significantly contribute to the fluxes above a certain threshold on the observed energies. We obtain results both for proton and heavy nuclei sources.

B polarization of the CMB from Faraday rotation

We study the effect of Faraday rotation due to a uniform magnetic field on the polarization of the cosmic microwave background. Scalar fluctuations give rise only to parity-even E-type polarization of the cosmic microwave background. However in the presence of a magnetic field, a nonvanishing parity-odd B-type polarization component is produced through Faraday rotation. We derive the exact solution for the E and B modes generated by scalar perturbations including the Faraday rotation effect of a uniform magnetic field, and evaluate their cross correlations with temperature anisotropies. We compute the angular autocorrelation function of the B-modes in the limit that the Faraday rotation is small. We find that uniform primordial magnetic fields of present strength around B{sub 0}=10{sup -9} G rotate E-modes into B-modes with amplitude comparable to those due to the weak gravitational lensing effect at frequencies around {nu}=30 GHz. The strength of B-modes produced by Faraday rotation scales as B{sub 0}/{nu}{sup 2}. We evaluate also the depolarizing effect of Faraday rotation upon the cross correlation between temperature anisotropy and E-type polarization.

The superstring, diff S1/S1, and holomorphic geometry

Abstract We incorporate superstrings into the non-perturbative formulation of string field theories based on Kahler geometry recently proposed by Bowick and Rajeev. The string field is conjectured to be the Kahler potential of loop space, its equation of motion given by the vanishing of the curvature of a product bundle constructed over a graded Diff S 1 /S 1 , as required for reparametrization invariance of the theory. We find that bosonic and fermionic loops in a Minkowski background solve the equation for the Kahler potential only in ten dimensions. We use geometric quantization techniques to calculate the curvature of the super-holomorphic vector bundle, since they emphasize the role of the complex geometry, and flag manifold techniques to calculate the curvature of the line bundle over super-Diff S 1 /S 1 .

Depolarization of the cosmic microwave background by a primordial magnetic field and its effect upon temperature anisotropy

We estimate the depolarizing effect of a primordial magnetic field upon the cosmic microwave background radiation due to differential Faraday rotation across the last scattering surface. The degree of linear polarization of the CMB is significantly reduced at frequencies around and below 30 GHz

Anisotropies of ultrahigh energy cosmic rays diffusing from extragalactic sources

(B_* /10^{-2}{\rm Gauss})^{1/2}

Anisotropies of ultrahigh energy cosmic ray nuclei diffusing from extragalactic sources

, where

A spin‐ 1/2 particle formalism in curved space–time

B_*

Effects of the galactic magnetic field upon large scale anisotropies of extragalactic cosmic rays

is the value of the primordial field at recombination. The depolarizing mechanism reduces the damping of anisotropies due to photon diffusion on small angular scales. The