Guenter Sigl

Primordial magnetic fields from cosmological first order phase transitions

We give an improved estimate of primordial magnetic fields generated during cosmological first order phase transitions. We examine the charge distribution at the nucleated bubble wall and its dynamics. We consider instabilities on the bubble walls developing during the phase transition. It is found that damping of these instabilities due to viscosity and heat conductivity caused by particle diffusion can be important in the QCD phase transition, but is probably negligible in the electroweak transition. We show how such instabilities together with the surface charge densities on bubble walls excite magnetic fields within a certain range of wavelengths. We discuss how these magnetic seed fields may be amplified by magneto hydrodynamics effects in the turbulent fluid. The strength and spectrum of the primordial magnetic field at the present time for the cases where this mechanism was operative during the electroweak or the QCD phase transition are estimated. On a 10 Mpc comoving scale, field strengths of the order 10{sup {minus}29} G for electroweak and 10{sup {minus}20} G for QCD, could be attained for reasonable phase transition parameters. {copyright} {ital 1997} {ital The American Physical Society}

Decoherence in supernova neutrino transformations suppressed by deleptonization

In the dense-neutrino region at 50-400 km above the neutrino sphere in a supernova, neutrino-neutrino interactions cause large flavor transformations. We study when the multiangle nature of the neutrino trajectories leads to flavor decoherence between different angular modes. We consider a two-flavor mixing scenario between {nu}{sub e} and another flavor {nu}{sub x} and assume the usual hierarchy F{sub {nu}{sub e}}>F{sub {nu}{sub e}}>F{sub {nu}{sub x}}=F{sub {nu}{sub x}} for the number fluxes. We define {epsilon}=(F{sub {nu}{sub e}}-F{sub {nu}{sub e}})/(F{sub {nu}{sub e}}-F{sub {nu}{sub x}}) as a measure for the deleptonization flux which is the one crucial parameter. The transition between the quasi-single-angle behavior and multiangle decoherence is abrupt as a function of {epsilon}. For typical choices of other parameters, multiangle decoherence is suppressed for {epsilon} > or approx. 0.3, but a much smaller asymmetry suffices if the neutrino mass hierarchy is normal and the mixing angle small. The critical {epsilon} depends logarithmically on the neutrino luminosity. In a realistic supernova scenario, the deleptonization flux is probably enough to suppress multiangle decoherence.

Extremely high-energy neutrinos, neutrino hot dark matter, and the highest energy cosmic rays

Extremely high energy (,10 22 eV) cosmic neutrino beams initiate high energy particle cascades in the background of relic neutrinos from the big bang. We perform numerical calculations to show that such cascades could contribute more than 10% to the observed cosmic ray flux above 3 3 10 19 eV if neutrinos have ,eV masses. The required intensity of primary neutrinos could be consistent with astrophysical models for their production if the maximum neutrino energy reaches to ,10 22 eV and the massive neutrino dark matter is locally clustered. Future observations of ultrahigh energy cosmic rays will lead to an indirect but practical search for neutrino dark matter. [S0031-9007(98)07941-1] PACS numbers: 98.70.Sa, 95.35. + d, 95.85.Ry, 98.70.Vc It has been claimed that pure cold dark matter (CDM) leads to a larger baryon fraction (Vb) than predicted by big bang nucleosynthesis (BBN) if the observed hot x-rayemitting gas represents a fair sample of the universe [1]. An admixture of hot dark matter (HDM) with CDM shifts the estimates of the baryon fraction closer to that by BBN. In addition, this mixed cold 1 hot dark matter model (CHDM) has been shown to agree well with the cosmic microwave background (CMB) spectrum measured by

Microwave background constraints on mixing of photons with hidden photons

Various extensions of the Standard Model predict the existence of hidden photons kinetically mixing with the ordinary photon. This mixing leads to oscillations between photons and hidden photons, analogous to the observed oscillations between different neutrino flavors. In this context, we derive new bounds on the photon-hidden photon mixing parameters using the high precision cosmic microwave background spectral data collected by the Far Infrared Absolute Spectrophotometer instrument on board of the Cosmic Background Explorer. Requiring the distortions of the CMB induced by the photon-hidden photon mixing to be smaller than experimental upper limits, this leads to a bound on the mixing angle χ0 10−7−10−5 for hidden photon masses between 10−14 eV and 10−7 eV. This low-mass and low-mixing region of the hidden photon parameter space was previously unconstrained.

Indirect detection of Kaluza-Klein dark matter

We investigate prospects for indirect detection of Kaluza-Klein dark matter, focusing on the annihilation radiation of the first Kaluza-Klein excitation of the hypercharge gauge boson

Ultrahigh-energy cosmic rays : Physics and astrophysics at extreme energies

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Ultra-high energy cosmic ray propagation in the local supercluster

in the galactic halo; in particular we estimate neutrino, gamma-ray and synchrotron fluxes. Comparing the predicted fluxes with observational data we are able to constrain the

Ultrahigh energy cosmic rays from neutrino emitting acceleration sources

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Probing grand unified theories with cosmic ray, gamma-ray and neutrino astrophysics

mass (and therefore the compactification scale). The constraints depend on the specific model adopted for the dark matter density profile. For a Navarro, Frenk, and White profile the analysis of synchrotron radiation puts a lower bound on the

Cosmological neutrino signatures for grand unification scale physics

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