94,213 research outputs found
Black Composite M-branes
We generalise all the known supersymmetric composite M-branes to the
corresponding black configurations. Thermodynamical formulae is written by
using the simple rules to construct these black branes.Comment: 14 pages, latex. Revised version to appear in Nuclear Physics
Black hole dynamics from instanton strings
A D-5-brane bound state with a self-dual field strength on a 4-torus is
considered. In a particular case this model reproduces the D5-D1 brane bound
state usually used in the string theory description of 5-dimensional black
holes. In the limit where the brane dynamics decouples from the bulk the Higgs
and Coulomb branches of the theory on the brane decouple. Contrasting with the
usual instanton moduli space approximation to the problem the Higgs branch
describes fundamental excitations of the gauge field on the brane. Upon
reduction to 2-dimensions it is associated with the so-called instanton
strings. Using the Born-Infeld action for the D-5-brane we determine the
coupling of these strings to a minimally coupled scalar in the black hole
background. The supergravity calculation of the cross section is found to agree
with the D-brane absorption probability rate calculation. We consider the near
horizon geometry of our black hole and elaborate on the corresponding duality
with the Higgs branch of the gauge theory in the large N limit. A heuristic
argument for the scaling of the effective string tension is given.Comment: 37 pages, latex. Typos corrected, SUSY field configuration argued to
be valid even when DBI corrections are important and two references adde
The temporal changes of the pulsational periods of the pre-white dwarf PG 1159-035
PG 1159-035, a pre-white dwarf with T=140000 K, is the prototype of the
PG1159 spectroscopic class and the DOV pulsating class. Changes in the star
cause variations in its oscillation periods. The measurement of temporal change
in the oscillation periods, dP/dt, allows us to estimate directly rates of
stellar evolutionary changes, such as the cooling rate and the envelope
contraction rate, providing a way to test and refine evolutionary models for
pre-white dwarf pulsating stars.
We measured 27 pulsation modes period changes. The periods varied at rates of
between 1 and 100 ms/yr, and several can be directly measured with a relative
standard uncertainty below 10%. For the 516.0 s mode (the highest in amplitude)
in particular, not only the value of dP/dt can be measured directly with a
relative standard uncertainty of 2%, but the second order period change,
d(dP/dt)/dt, can also be calculated reliably. By using the (O-C) method we
refined the dP/dt and estimated the d(dP/dt)/dt for six other pulsation
periods. As a first application, we calculated the change in the PG 1559-035
rotation period, dP_rot/dt = -2.13*10^{-6} s/s, the envelope contraction rate
dR/dt = -2.2*10^{-13} solar radius/s, and the cooling rante dT/dt =
-1.42*10^{-3} K/s.Comment: 8 pages; 2 figures; 2 tables; appendix with 2 table
Birth of a Closed Universe of Negative Spatial Curvature
We propose a modified form of the spontaneous birth of the universe by
quantum tunneling. It proceeds through topology change and inflation, to
eventually become a universe with closed spatial sections of negative curvature
and nontrivial global topology.Comment: 10 pages, 1 figure. Revised version with better comments on assumed
topology chang
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