66,352 research outputs found
Entropy of Horizons, Complex Paths and Quantum Tunneling
In any spacetime, it is possible to have a family of observers following a
congruence of timelike curves such that they do not have access to part of the
spacetime. This lack of information suggests associating a (congruence
dependent) notion of entropy with the horizon that blocks the information from
these observers. While the blockage of information is absolute in classical
physics, quantum mechanics will allow tunneling across the horizon. This
process can be analysed in a simple, yet general, manner and we show that the
probability for a system with energy to tunnel across the horizon is
where is the surface gravity of the
horizon. If the surface gravity changes due to the leakage of energy through
the horizon, then one can associate an entropy with the horizon where
and is the active gravitational mass of the
system. Using this result, we discuss the conditions under which, a small patch
of area of the horizon contributes an entropy ,
where is the Planck area.Comment: published versio
Understanding the radio emission geometry of PSR B0329+54
We have analyzed high-quality single pulse data of PSR B0329+54 at 325 MHz
and 606 MHz to study the structure of the emission beam. Using the
window-threshold technique, which is suitable for detecting weak emission
components, we have detected 4 additional emission components in the pulse
window. Three of these are new components and the fourth is a confirmation of a
recently proposed component. Hence PSR B0329+54 is now known to have 9 emission
components - the highest among all known pulsars. The distribution of the pulse
components around the central core component indicates that the emission beam
consists of four nested cones. The asymmetry in the location of the conal
components in the leading versus trailing parts of the profile is interpreted
as being due to aberration and retardation in the pulsar magnetosphere. These
measurements allow us to determine the precise location of the 4 conal rings of
emission. We find that the successive outer cones are emitted at higher
altitudes in the magnetosphere. Further, for any given cone, the emission
height at the lower frequency is found to be more than that at the higher
frequency. The inferred heights range from ~160 km to ~1150 km. The set of
``active'' field lines, from which most of the conal radiation appears to
originate, are found to be confined to a region located within ~0.5 to ~0.6 of
the polar cap radius. We discuss the implications of our new findings on our
understanding of the pulsar emission geometry and its impact on the emission
mechanisms.Comment: 20 pages, 5 figures. Accepted for Astrophysical Journa
Chronological Inversion Method for the Dirac Matrix in Hybrid Monte Carlo
In Hybrid Monte Carlo simulations for full QCD, the gauge fields evolve
smoothly as a function of Molecular Dynamics time. Here we investigate improved
methods of estimating the trial or starting solutions for the Dirac matrix
inversion as superpositions of a chronological sequence of solutions in the
recent past. By taking as the trial solution the vector which minimizes the
residual in the linear space spanned by the past solutions, the number of
conjugate gradient iterations per unit MD time is decreased by at least a
factor of 2. Extensions of this basic approach to precondition the conjugate
gradient iterations are also discussed.Comment: 35 pages, 18 EPS figures A new "preconditioning" method, derived from
the Chronological Inversion, is described. Some new figures are appended.
Some reorganization of the material has taken plac
Non-perturbative improvement of bilinears in unquenched QCD
We describe how the improvement of quark bilinears generalizes from quenched
to unquenched QCD, and discuss which of the additional improvement constants
can be determined using Ward Identities.Comment: LATTICE99 (Improvement and Renormalization). 3 pages, no figures.
Corrected error (improvement coefficient is not needed
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