1,791 research outputs found
Collapse of Positronium and Vacuum Instability
A hypercritical value for the magnetic field is determined, which provides
the full compensation of the positronium rest mass by the binding energy in the
maximum symmetry state and disappearance of the energy gap separating the
electron-positron system from the vacuum. The compensation becomes possible
owing to the falling to the center phenomenon. The structure of the vacuum is
described in terms of strongly localized states of tightly mutually bound (or
confined) pairs. Their delocalization for still higher magnetic field, capable
of screening its further growth, is discussed.Comment: Talk given at 12th Lomonosov Conference on Elementary Particle
Physics, Moscow, August 25-30, 2005 to be published in Proceedings with World
Scientific Publishing Co (Singapore). 5 pages. LATEX requires 12 Lomcon.sty
and cite.st
PULSARS WITH STRONG MAGNETIC FIELDS: POLAR GAPS, BOUND PAIR CREATION AND NONTHERMAL LUMINOSITIES
Modifications to polar-gap models for pulsars are discussed for the case
where the surface magnetic field, , of the neutron star is strong. For
B\ga4\times10^8\rm\,T, the curvature -quanta emitted tangentially to
the curved force lines of the magnetic field are captured near the threshold of
bound pair creation and are channelled along the magnetic field as bound
electron-positron pairs (positronium). The stability of such bound pairs
against ionization by the parallel electric field, , in the polar
cap, and against photoionization is discussed. Unlike free pairs, bound pairs
do not screen near the neutron star. As a consequence, the energy
flux in highly relativistic particles and high-frequency (X-ray and/or
-ray) radiation from the polar gaps can be much greater than in the
absence of positronium formation. We discuss this enhancement for (a)
Arons-type models, in which particles flow freely from the surface, and find
any enhancement to be modest, and (b) Ruderman-Sutherland-type models, in which
particles are tightly bound to the surface, and find that the enhancement can
be substantial. In the latter case we argue for a self-consistent,
time-independent model in which partial screening of maintains it
close to the threshold value for field ionization of the bound pairs, and in
which a reverse flux of accelerated particles maintains the polar cap at a
temperature such that thermionic emission supplies the particles needed for
this screening. This model applies only in a restricted range of periods,
, and it implies an energy flux in high-energy particles that can
correspond to a substantial fraction of the spin-down power of the pulsar.
Nonthermal, high-frequency radiation has been observed from six radio pulsarsComment: TEX file, 47 pages. Accepted by Australian J. Phy
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