160 research outputs found
Possible way out of the Hawking paradox: Erasing the information at the horizon
We show that small deviations from spherical symmetry, described by means of
exact solutions to Einstein equations, provide a mechanism to "bleach" the
information about the collapsing body as it falls through the aparent horizon,
thereby resolving the information loss paradox. The resulting picture and its
implication related to the Landauer's principle in the presence of a
gravitational field, is discussed.Comment: 11 pages, Latex. Some comments added to answer to some raised
questions. Typos corected. Final version, to appear in Int. J. Modern. Phys.
Measuring longitudinal amplitudes for electroproduction of pseudoscalar mesons using recoil polarization in parallel kinematics
We propose a new method for measuring longitudinal amplitudes for
electroproduction of pseudoscalar mesons that exploits a symmetry relation for
polarization observables in parallel kinematics. This polarization technique
does not require variation of electron scattering kinematics and avoids the
major sources of systematic errors in Rosenbluth separation.Comment: intended for Phys. Rev. C as a Brief Repor
Quasifree Pion Electroproduction from Nuclei in the Region
We present calculations of the reaction in the
distorted wave impulse approximation. The reaction allows for the study of the
production process in the nuclear medium without being obscured by the details
of nuclear transition densities. First, a pion electroproduction operator
suitable for nuclear calculations is obtained by extending the Blomqvist-Laget
photoproduction operator to the virtual photon case. The operator is gauge
invariant, unitary, reference frame independent, and describes the existing
data reasonably well. Then it is applied in nuclei to predict nuclear cross
sections under a variety of kinematic arrangements. Issues such as the effects
of gauge-fixing, the interference of the resonance with the
background, sensitivities to the quadrupole component of the
excitation and to the electromagnetic form factors, the role of final-state
interactions, are studied in detail. Methods on how to experimentally separate
the various pieces in the coincidence cross section are suggested. Finally, the
model is compared to a recent SLAC experiment.Comment: 27 pages in REVTEX, plus 22 PS figures embedded using psfig.sty
(included), uuencode
Supersymmetric 3-branes on smooth ALE manifolds with flux
We construct a new family of classical BPS solutions of type IIB supergravity
describing 3-branes transverse to a 6-dimensional space with topology R^2*ALE.
They are characterized by a non-trivial flux of the supergravity 2-forms
through the homology 2-cycles of a generic smooth ALE manifold. Our solutions
have two Killing spinors and thus preserve N=2 supersymmetry. They are
expressed in terms of a quasi harmonic function H (the ``warp factor''), whose
properties we study in the case of the simplest ALE, namely the Eguchi-Hanson
manifold. The equation for H is identified as an instance of the confluent Heun
equation. We write explicit power series solutions and solve the recurrence
relation for the coefficients, discussing also the relevant asymptotic
expansions. While, as in all such N=2 solutions, supergravity breaks down near
the brane, the smoothing out of the vacuum geometry has the effect that the
warp factor is regular in a region near the cycle. We interpret the behavior of
the warp factor as describing a three-brane charge ``smeared'' over the cycle
and consider the asymptotic form of the geometry in that region, showing that
conformal invariance is broken even when the complex type IIB 3-form field
strength is assumed to vanish. We conclude with a discussion of the basic
features of the gauge theory dual.Comment: latex, 36 pages (26 + appendix). Some statements on the gauge dual
made more precise. Final version to appear on NP
Non-Hermitian Rayleigh-Schroedinger Perturbation Theory
We devise a non-Hermitian Rayleigh-Schroedinger perturbation theory for the
single- and the multireference case to tackle both the many-body problem and
the decay problem encountered, for example, in the study of electronic
resonances in molecules. A complex absorbing potential (CAP) is employed to
facilitate a treatment of resonance states that is similar to the
well-established bound-state techniques. For the perturbative approach, the
full CAP-Schroedinger Hamiltonian, in suitable representation, is partitioned
according to the Epstein-Nesbet scheme. The equations we derive in the
framework of the single-reference perturbation theory turn out to be identical
to those obtained by a time-dependent treatment in Wigner-Weisskopf theory. The
multireference perturbation theory is studied for a model problem and is shown
to be an efficient and accurate method. Algorithmic aspects of the integration
of the perturbation theories into existing ab initio programs are discussed,
and the simplicity of their implementation is elucidated.Comment: 10 pages, 1 figure, RevTeX4, submitted to Physical Review
Relations between the K_{l3} and tau --> K pi nu_tau decays
We investigate the relations between the K_{l3} and tau --> K pi nu_tau
decays using the meson dominance approach. First, the experimental branching
fractions (BF) for K^-_{e3} and K^0_{e3} are used to fix two normalization
constants (isospin invariance is not assumed). Then, the BF of tau^- -->
K^*(892)^- nu_tau is calculated in agreement with experiment. We further argue
that the nonzero value of the slope parameter lambda_0 of the K^-_{mu3} and
K^0_{mu3} form factors f_0(t) implies the existence of the tau^- -->
K_0^*(1430)^- nu_tau decay. We calculate its BF, together with BF's of the
K^-_{mu3}, K^0_{mu3}, tau- --> K^- pi^0 nu_tau, and tau- --> antiK^0 pi^0
nu_tau decays, as a function of the lambda_0 parameter. At some value of
lambda_0, different for charged and neutral kaons, calculated BF's seem to
match existing data and a prediction is obtained for the tau^- --> K pi nu
decays going through the K_0^*(1430)^- resonance.Comment: 14 pages, RevTeX, epsf.sty, 3 embedded figure
Effective Lagrangian Approach to the Theory of Eta Photoproduction in the Region
We investigate eta photoproduction in the resonance region
within the effective Lagrangian approach (ELA), wherein leading contributions
to the amplitude at the tree level are taken into account. These include the
nucleon Born terms and the leading -channel vector meson exchanges as the
non-resonant pieces. In addition, we consider five resonance contributions in
the - and - channel; besides the dominant , these are:
and . The amplitudes for the
and the photoproduction near threshold have significant
differences, even as they share common contributions, such as those of the
nucleon Born terms. Among these differences, the contribution to the
photoproduction of the -channel excitation of the is the most
significant. We find the off-shell properties of the spin-3/2 resonances to be
important in determining the background contributions. Fitting our effective
amplitude to the available data base allows us to extract the quantity
, characteristic of the
photoexcitation of the resonance and its decay into the
-nucleon channel, of interest to precise tests of hadron models. At the
photon point, we determine it to be from
the old data base, and from a
combination of old data base and new Bates data. We obtain the helicity
amplitude for to be from the old data base, and from the combination of the old data base and new Bates
data, compared with the results of the analysis of pion photoproduction
yielding , in the same units.Comment: 43 pages, RevTeX, 9 figures available upon request, to appear in
Phys. Rev.
3D finite compartment modeling of formation and healing of bruises may identify methods for age determination of bruises
Simulating the spatial and temporal behavior of bruises may identify methods that allow accurate age determination of bruises to assess child abuse. We developed a numerical 3D model to simulate the spatial kinetics of hemoglobin and bilirubin during the formation and healing of bruises. Using this model, we studied how skin thickness, bruise diameter and diffusivities affect the formation and healing of circular symmetric bruises and compared a simulated bruise with a natural inhomogeneous bruise. Healing is faster for smaller bruises in thinner and less dense skin. The simulated and natural bruises showed similar spatial and temporal dynamics. The different spatio-temporal dynamics of hemoglobin and bilirubin allows age determination of model bruises. Combining our model predictions with individual natural bruises may allow optimizing our model parameters. It may particularly identify methods for more accurate age determination than currently possible to aid the assessment of child abuse
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