34 research outputs found
Signs of magnetic accretion in X-ray pulsars
The spin-down mechanism of accreting neutron stars is discussed with an
application to one of the best studied X-ray pulsars GX 301-2. We show that the
maximum possible spin-down torque applied to a neutron star from the accretion
flow can be evaluated as . The spin-down rate of the neutron star in GX 301-2 can be
explained provided the magnetospheric radius of the neutron star is smaller
than its canonical value. We calculate the magnetospheric radius considering
the mass-transfer in the binary system in the frame of the magnetic accretion
scenario suggested by V.F. Shvartsman. The spin-down rate of the neutron star
expected within this approach is in a good agreement with that derived from
observations of GX 301-2.Comment: accepted for publication in Astronomy Report
Big Bang nucleosynthesis and physics beyond the Standard Model
The Hubble expansion of galaxies, the 2.73\dK blackbody radiation
background and the cosmic abundances of the light elements argue for a hot,
dense origin of the universe --- the standard Big Bang cosmology --- and enable
its evolution to be traced back fairly reliably to the nucleosynthesis era when
the temperature was of \Or(1) MeV corresponding to an expansion age of
\Or(1) sec. All particles, known and hypothetical, would have been created at
higher temperatures in the early universe and analyses of their possible
effects on the abundances of the synthesized elements enable many interesting
constraints to be obtained on particle properties. These arguments have
usefully complemented laboratory experiments in guiding attempts to extend
physics beyond the Standard SU(3)_{\c}{\otimes}SU(2)_{\L}{\otimes}U(1)_{Y}
Model, incorporating ideas such as supersymmetry, compositeness and
unification. We first present a pedagogical account of relativistic cosmology
and primordial nucleosynthesis, discussing both theoretical and observational
aspects, and then proceed to examine such constraints in detail, in particular
those pertaining to new massless particles and massive unstable particles.
Finally, in a section aimed at particle physicists, we illustrate applications
of such constraints to models of new physics.Comment: 156 pages LaTeX, including 18 PostScript figures; uses ioplppt.sty,
epsf, and personal style file (incl.); Revised and updated to include, e.g.
implications of new deuterium observations in primordial clouds; 2-up
PostScript version (78 pages) available at
ftp://ftp.physics.ox.ac.uk/pub/local/users/sarkar/BBNreview.ps.gz ; to appear
in Reports on Progress in Physic