5,588 research outputs found
EVOLUTION OF A STRING NETWORK IN BACKGROUNDS WITH ROLLING HORIZONS
We discuss the temporal variation of the equation of state of a classical
string network, evolving in a background in which the Hubble radius 1/H shrinks
to a minimum and then re-expands to infinity. We also present a method to look
for self-consistent non-vacuum string backgrounds, correponding to the
simultaneous solution of the gravi-dilaton backgrounds equations and of the
string equations of motion.Comment: 19 pages, plain tex, no figures, to appear in "String gravity and
physics at the Planck energy scale" (World Scientific, Singapore, 1995
Eigenvalues of the volume operator in loop quantum gravity
We present a simple method to calculate certain sums of the eigenvalues of
the volume operator in loop quantum gravity. We derive the asymptotic
distribution of the eigenvalues in the classical limit of very large spins
which turns out to be of a very simple form. The results can be useful for
example in the statistical approach to quantum gravity.Comment: 12 pages, version accepted in Class. Quantum Gra
Rotational Corrections to and Isovector Magnetic Moment of the Nucleon
The rotational corrections to the axial vector constant and the
isovector magnetic moment of the nucleon are studied in the Nambu --
Jona-Lasinio model. We follow a semiclassical quantization procedure in terms
of path integrals in which we can include perturbatively corrections in powers
of angular velocity . We find non-zero order
corrections from both the valence and the Dirac sea quarks. These corrections
are large enough to resolve the long-standing problem of a strong
underestimation of both and in the leading order. The axial
constant is well reproduced, whereas the isovector magnetic moment
is still underestimated by 25 \%.Comment: (Revtex), 10 pages (3 figures available on request), report
RUB-TPII-53/9
Black hole entropy for the general area spectrum
We consider the possibility that the horizon area is expressed by the general
area spectrum in loop quantum gravity and calculate the black hole entropy by
counting the degrees of freedom in spin-network states related to its area.
Although the general area spectrum has a complex expression, we succeeded in
obtaining the result that the black hole entropy is proportional to its area as
in previous works where the simplified area formula has been used. This gives
new values for the Barbero-Immirzi parameter () which are larger than that of previous works.Comment: 5 page
Multi-Magnon Scattering in the Ferromagnetic XXX-Model with Inhomogeneities
We determine the transition amplitude for multi-magnon scattering induced
through an inhomogeneous distribution of the coupling constant in the
ferromagnetic XXX-model. The two and three particle amplitudes are explicitely
calculated at small momenta. This suggests a rather plausible conjecture also
for a formula of the general n-particle amplitude.Comment: 21 pages, latex, no figure
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