799 research outputs found
Ultra-High Energy Cosmic Rays from Young Neutron Star Winds
The long-held notion that the highest-energy cosmic rays are of distant
extragalactic origin is challenged by observations that events above eV do not exhibit the expected high-energy cutoff from photopion
production off the cosmic microwave background. We suggest that these
unexpected ultra-high-energy events are due to iron nuclei accelerated from
young strongly magnetized neutron stars through relativistic MHD winds. We find
that neutron stars whose initial spin periods are shorter than ms, where is the surface magnetic field, can
accelerate iron cosmic rays to greater than eV. These ions can
pass through the remnant of the supernova explosion that produced the neutron
star without suffering significant spallation reactions. For plausible models
of the Galactic magnetic field, the trajectories of the iron ions curve
sufficiently to be consistent with the observed arrival directions of the
highest energy events.Comment: 11 pages, 1 figure, replaced with revised version, some references
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On Constraining Electroweak-Baryogenesis with Inhomogeneous Primordial Nucleosynthesis
Primordial nucleosynthesis calculations are shown to be able to provide
constraints on electroweak baryogenesis which produce a highly inhomogeneous
distribution of the baryon-to-photon ratio. Such baryogenesis scenarios
overproduce 4He and/or 7Li and can be ruled out whenever a fraction
f<3*10e-6(100 GeV/T)^3 of nucleated bubbles of broken-symmetry phase
contributes > 10% of the baryon number within the horizon volume.Comment: 16 pages, 3 figures (figures available by email), UCRL-JC-11522
Nucleation of quark matter bubbles in neutron stars
The thermal nucleation of quark matter bubbles inside neutron stars is
examined for various temperatures which the star may realistically encounter
during its lifetime. It is found that for a bag constant less than a critical
value, a very large part of the star will be converted into the quark phase
within a fraction of a second. Depending on the equation of state for neutron
star matter and strange quark matter, all or some of the outer parts of the
star may subsequently be converted by a slower burning or a detonation.Comment: 13 pages, REVTeX, Phys.Rev.D (in press), IFA 93-32. 5 figures (not
included) available upon request from [email protected]
Cosmic Rays at the highest energies
After a century of observations, we still do not know the origin of cosmic
rays. I will review the current state of cosmic ray observations at the highest
energies, and their implications for proposed acceleration models and secondary
astroparticle fluxes. Possible sources have narrowed down with the confirmation
of a GZK-like spectral feature. The anisotropy observed by the Pierre Auger
Observatory may signal the dawn of particle astronomy raising hopes for high
energy neutrino observations. However, composition related measurements point
to a different interpretation. A clear resolution of this mystery calls for
much larger statistics than the reach of current observatories.Comment: 8 pages, 4 figures, in the Proceedings of TAUP 201
Curvature energy effects on strange quark matter nucleation at finite density
We consider the effects of the curvature energy term on thermal strange quark
matter nucleation in dense neutron matter. Lower bounds on the temperature at
which this process can take place are given and compared to those without the
curvature term.Comment: PlainTex, 6 pp., IAG-USP Rep.5
Plasma waves driven by gravitational waves in an expanding universe
In a Friedmann-Robertson-Walker (FRW) cosmological model with zero spatial
curvature, we consider the interaction of the gravitational waves with the
plasma in the presence of a weak magnetic field. Using the relativistic
hydromagnetic equations it is verified that large amplitude magnetosonic waves
are excited, assuming that both, the gravitational field and the weak magnetic
field do not break the homogeneity and isotropy of the considered FRW
spacetime.Comment: 14 page
On The Origin of Very High Energy Cosmic Rays
We discuss the most recent developments in our understanding of the
acceleration and propagation of cosmic rays up to the highest energies. In
particular we specialize our discussion to three issues: 1) developments in the
theory of particle acceleration at shock waves; 2) the transition from galactic
to extragalactic cosmic rays; 3) implications of up-to-date observations for
the origin of ultra high energy cosmic rays (UHECRs).Comment: Invited Review Article to appear in Modern Physics Letters A, Review
Sectio
Equation of State for Helium-4 from Microphysics
We compute the free energy of helium-4 near the lambda transition based on an
exact renormalization-group equation. An approximate solution permits the
determination of universal and nonuniversal thermodynamic properties starting
from the microphysics of the two-particle interactions. The method does not
suffer from infrared divergences. The critical chemical potential agrees with
experiment. This supports a specific formulation of the functional integral
that we have proposed recently. Our results for the equation of state reproduce
the observed qualitative behavior. Despite certain quantitative shortcomings of
our approximation, this demonstrates that ab initio calculations for collective
phenomena become possible by modern renormalization-group methods.Comment: 9 pages, 6 figures, revtex updated version, journal referenc
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