10,392 research outputs found
The Role of Kinetic Energy Flux in the Convective Urca Process
The previous analysis of the convective Urca neutrino loss process in
degenerate, convective, quasi-static, carbon-burning cores by Barkat and
Wheeler omitted specific consideration of the role of the kinetic energy flux.
The arguments of Barkat and Wheeler that steady-state composition gradients
exist are correct, but chemical equilibrium does not result in net cooling.
Barkat and Wheeler included a "work" term that effectively removed energy from
the total energy budget that could only have come from the kinetic energy,
which must remain positive. Consideration of the kinetic energy in the
thermodynamics of the convective Urca process shows that the convective Urca
neutrinos reduce the rate of increase of entropy that would otherwise be
associated with the input of nuclear energy and slow down the convective
current, but, unlike the "thermal" Urca process do not reduce the entropy or
temperature.Comment: 16 pages, AAS LaTex, in press, Astrophysical Journal, September 20,
Vol 52
Phase field modeling of electrochemistry II: Kinetics
The kinetic behavior of a phase field model of electrochemistry is explored
for advancing (electrodeposition) and receding (electrodissolution) conditions
in one dimension. We described the equilibrium behavior of this model in [J. E.
Guyer, W. J. Boettinger, J.A. Warren, and G. B. McFadden, ``Phase field
modeling of electrochemistry I: Equilibrium'', cond-mat/0308173]. We examine
the relationship between the parameters of the phase field method and the more
typical parameters of electrochemistry. We demonstrate ohmic conduction in the
electrode and ionic conduction in the electrolyte. We find that, despite making
simple, linear dynamic postulates, we obtain the nonlinear relationship between
current and overpotential predicted by the classical ``Butler-Volmer'' equation
and observed in electrochemical experiments. The charge distribution in the
interfacial double layer changes with the passage of current and, at
sufficiently high currents, we find that the diffusion limited deposition of a
more noble cation leads to alloy deposition with less noble species.Comment: v3: To be published in Phys. Rev. E v2: Attempt to work around
turnpage bug. Replaced color Fig. 4a with grayscale 13 pages, 7 figures in 10
files, REVTeX 4, SIunits.sty, follows cond-mat/030817
The Convective Urca Process with Implicit Two-Dimensional Hydrodynamics
Consideration of the role of the convective flux in the thermodymics of the
convective Urca neutrino loss process in degenerate, convective, quasi-static,
carbon-burning cores shows that the convective Urca process slows down the
convective current around the Urca-shell, but, unlike the "thermal" Urca
process, does not reduce the entropy or temperature for a given convective
volume. Here we demonstrate these effects with two-dimensional numerical
hydrodynamical calculations. These two-dimensional implicit hydrodynamics
calculations invoke an artificial speeding up of the nuclear and weak rates.
They should thus be regarded as indicative, but still qualitative. We find
that, compared to a case with no Urca-active nuclei, the case with Urca effects
leads to a higher entropy in the convective core because the energy released by
nuclear burning is confined to a smaller volume by the effective boundary at
the Urca shell. All else being equal, this will tend to accelerate the
progression to dynamical runaway. We discuss the open issues regarding the
impact of the convective Urca process on the evolution to the "smoldering
phase" and then to dynamical runaway.Comment: 22 pages, 11 figures, accepted for publication in the Astrophysical
Journa
Extreme Supernova Models for the Superluminous Transient ASASSN-15lh
The recent discovery of the unprecedentedly superluminous transient
ASASSN-15lh (or SN 2015L) with its UV-bright secondary peak challenges all the
power-input models that have been proposed for superluminous supernovae. Here
we examine some of the few viable interpretations of ASASSN-15lh in the context
of a stellar explosion, involving combinations of one or more power inputs. We
model the lightcurve of ASASSN-15lh with a hybrid model that includes
contributions from magnetar spin-down energy and hydrogen-poor circumstellar
interaction. We also investigate models of pure circumstellar interaction with
a massive hydrogen-deficient shell and discuss the lack of interaction features
in the observed spectra. We find that, as a supernova ASASSN-15lh can be best
modeled by the energetic core-collapse of a ~40 Msun star interacting with a
hydrogen-poor shell of ~20 Msun. The circumstellar shell and progenitor mass
are consistent with a rapidly rotating pulsational pair-instability supernova
progenitor as required for strong interaction following the final supernova
explosion. Additional energy injection by a magnetar with initial period of 1-2
ms and magnetic field of 0.1-1 x 10^14 G may supply the excess luminosity
required to overcome the deficit in single-component models, but this requires
more fine-tuning and extreme parameters for the magnetar, as well as the
assumption of efficient conversion of magnetar energy into radiation. We thus
favor a single-input model where the reverse shock formed in a strong SN
ejecta-CSM interaction following a very powerful core-collapse SN explosion can
supply the luminosity needed to reproduce the late-time UV-bright plateau.Comment: 8 pages, 3 figure
Wigner-Yanase skew information as tests for quantum entanglement
A Bell-type inequality is proposed in terms of Wigner-Yanase skew
information, which is quadratic and involves only one local spin observable at
each site. This inequality presents a hierarchic classification of all states
of multipartite quantum systems from separable to fully entangled states, which
is more powerful than the one presented by quadratic Bell inequalities from
two-entangled to fully entangled states. In particular, it is proved that the
inequality provides an exact test to distinguish entangled from nonentangled
pure states of two qubits. Our inequality sheds considerable light on
relationships between quantum entanglement and information theory.Comment: 5 page
Two-photon decays of hadronic molecules
In many calculations of the two--photon decay of hadronic molecules, the
decay matrix element is estimated using the wave function at the origin
prescription, in analogy to the two-photon decay of parapositronium. We
question the applicability of this procedure to the two-photon decay of
hadronic molecules for it introduces an uncontrolled model dependence into the
calculation. As an alternative approach, we propose an explicit evaluation of
the hadron loop. For shallow bound states, this can be done as an expansion in
powers of the range of the molecule binding force. In the leading order one
gets the well-known point-like limit answer. We estimate, in a self-consistent
and gauge invariant way, the leading range corrections for the two-photon decay
width of weakly bound hadronic molecules emerging from kaon loops. We find them
to be small. The role of possible short-ranged operators and of the width of
the scalars remains to be investigated.Comment: LaTeX2e, 26 pages, new figure and additional appendix added, version
to appear in Phys.Rev.
Regular black holes with flux tube core
We consider a class of black holes for which the area of the two-dimensional
spatial cross-section has a minimum on the horizon with respect to a
quasiglobal (Krusckal-like) coordinate. If the horizon is regular, one can
generate a tubelike counterpart of such a metric and smoothly glue it to a
black hole region. The resulting composite space-time is globally regular, so
all potential singuilarities under the horizon of the original metrics are
removed. Such a space-time represents a black hole without an apparent horizon.
It is essential that the matter should be non-vacuum in the outer region but
vacuumlike in the inner one. As an example we consider the noninteracting
mixture of vacuum fluid and matter with a linear equation of state and scalar
phantom fields. This approach is extended to distorted metrics, with the
requirement of spherical symmetry relaxed.Comment: 15 pages. 2 references adde
New interpretation of variational principles for gauge theories. I. Cyclic coordinate alternative to ADM split
I show how there is an ambiguity in how one treats auxiliary variables in
gauge theories including general relativity cast as 3 + 1 geometrodynamics.
Auxiliary variables may be treated pre-variationally as multiplier coordinates
or as the velocities corresponding to cyclic coordinates. The latter treatment
works through the physical meaninglessness of auxiliary variables' values
applying also to the end points (or end spatial hypersurfaces) of the
variation, so that these are free rather than fixed. [This is also known as
variation with natural boundary conditions.] Further principles of dynamics
workings such as Routhian reduction and the Dirac procedure are shown to have
parallel counterparts for this new formalism. One advantage of the new scheme
is that the corresponding actions are more manifestly relational. While the
electric potential is usually regarded as a multiplier coordinate and Arnowitt,
Deser and Misner have regarded the lapse and shift likewise, this paper's
scheme considers new {\it flux}, {\it instant} and {\it grid} variables whose
corresponding velocities are, respectively, the abovementioned previously used
variables. This paper's way of thinking about gauge theory furthermore admits
interesting generalizations, which shall be provided in a second paper.Comment: 11 page
Timeless path integral for relativistic quantum mechanics
Starting from the canonical formalism of relativistic (timeless) quantum
mechanics, the formulation of timeless path integral is rigorously derived. The
transition amplitude is reformulated as the sum, or functional integral, over
all possible paths in the constraint surface specified by the (relativistic)
Hamiltonian constraint, and each path contributes with a phase identical to the
classical action divided by . The timeless path integral manifests the
timeless feature as it is completely independent of the parametrization for
paths. For the special case that the Hamiltonian constraint is a quadratic
polynomial in momenta, the transition amplitude admits the timeless Feynman's
path integral over the (relativistic) configuration space. Meanwhile, the
difference between relativistic quantum mechanics and conventional
nonrelativistic (with time) quantum mechanics is elaborated on in light of
timeless path integral.Comment: 41 pages; more references and comments added; version to appear in
CQ
SN 2005hj: Evidence for Two Classes of Normal-Bright SNe Ia and Implications for Cosmology
HET Optical spectra covering the evolution from about 6 days before to about
5 weeks after maximum light and the ROTSE-IIIb unfiltered light curve of the
"Branch-normal" Type Ia Supernova SN 2005hj are presented. The host galaxy
shows HII region lines at redshift of z=0.0574, which puts the peak unfiltered
absolute magnitude at a somewhat over-luminous -19.6. The spectra show weak and
narrow SiII lines, and for a period of at least 10 days beginning around
maximum light these profiles do not change in width or depth and they indicate
a constant expansion velocity of ~10,600 km/s. We analyzed the observations
based on detailed radiation dynamical models in the literature. Whereas delayed
detonation and deflagration models have been used to explain the majority of
SNe Ia, they do not predict a long velocity plateau in the SiII minimum with an
unvarying line profile. Pulsating delayed detonations and merger scenarios form
shell-like density structures with properties mostly related to the mass of the
shell, M_shell, and we discuss how these models may explain the observed SiII
line evolution; however, these models are based on spherical calculations and
other possibilities may exist. SN 2005hj is consistent with respect to the
onset, duration, and velocity of the plateau, the peak luminosity and, within
the uncertainties, with the intrinsic colors for models with M_shell=0.2 M_sun.
Our analysis suggests a distinct class of events hidden within the
Branch-normal SNe Ia. If the predicted relations between observables are
confirmed, they may provide a way to separate these two groups. We discuss the
implications of two distinct progenitor classes on cosmological studies
employing SNe Ia, including possible differences in the peak luminosity to
light curve width relation.Comment: ApJ accepted, 31 page
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