3,911 research outputs found
On the O II ground configuration energy levels
The most accurate way to measure the energy levels for the O II 2p^3 ground
configuration has been from the forbidden lines in planetary nebulae. We
present an analysis of modern planetary nebula data that nicely constrain the
splitting within the ^2D term and the separation of this term from the ground
^4S_{3/2} level. We extend this method to H II regions using high-resolution
spectroscopy of the Orion nebula, covering all six visible transitions within
the ground configuration. These data confirm the splitting of the ^2D term
while additionally constraining the splitting of the ^2P term. The energies of
the ^2P and ^2D terms relative to the ground (^4S) term are constrained by
requiring that all six lines give the same radial velocity, consistent with
independent limits placed on the motion of the O+ gas and the planetary nebula
data.Comment: 20 pages, 3 figures. To be published in Ap
Getting Super-Excited with Modified Dispersion Relations
We demonstrate that in some regions of parameter space, modified dispersion
relations can lead to highly populated excited states, which we dub as
"super-excited" states. In order to prepare such super-excited states, we
invoke dispersion relations that have negative slope in an interim sub-horizon
phase at high momenta. This behaviour of quantum fluctuations can lead to large
corrections relative to the Bunch-Davies power spectrum, which mimics highly
excited initial conditions. We identify the Bogolyubov coefficients that can
yield these power spectra. In the course of this computation, we also point out
the shortcomings of the gluing method for evaluating the power spectrum and the
Bogolyubov coefficients. As we discuss, there are other regions of parameter
space, where the power spectrum does not get modified. Therefore, modified
dispersion relations can also lead to so-called "calm excited states" as well.
We conclude by commenting on the possibility of obtaining these modified
dispersion relations within the Effective Field Theory of Inflation.Comment: 1+19 pages, 4 figure
Nonuniqueness for the kinetic Fokker-Planck equation with inelastic boundary conditions
We describe the structure of solutions of the kinetic Fokker-Planck equations
in domains with boundaries near the singular set in one-space dimension. We
study in particular the behaviour of the solutions of this equation for
inelastic boundary conditions which are characterized by means of a coefficient
describing the amount of energy lost in the collisions of the particles
with the boundaries of the domain. A peculiar feature of this problem is the
onset of a critical exponent rc which follows from the analysis of McKean (cf.
[26]) of the properties of the stochastic process associated to the
Fokker-Planck equation under consideration. In this paper, we prove rigorously
that the solutions of the considered problem are nonunique if and
unique if . In particular, this nonuniqueness explains the
different behaviours found in the physics literature for numerical simulations
of the stochastic differential equation associated to the Fokker-Planck
equation. In the proof of the results of this paper we use several asymptotic
formulas and computations in the companion paper [16].Comment: 64 pages, 1 figure. Previous version has been split into tw
Fluorescent Excitation of Spectral Lines in Planetary Nebulae
Fluorescent excitation of spectral lines is demonstrated as a function of
temperature-luminosity and the distance of the emitting region from the central
stars of planetary nebulae. The electron densities and temperatures are
determined, and the method is exemplified through a detailed analysis of
spectral observations of a high excitation PN, NGC 6741, observed by Hyung and
Aller(1997). Fluorescence should also be important in the determination of
element abundances. It is suggested that the method could be generally applied
to determine or constrain the luminosity and the region of spectral emission in
other intensively radiative sources such as novae, supernovae, and active
galactic nuclei.Comment: 5 pages, 4 figures (fig.4 in color), ApJ (in press
Trajectory of test particle around a slowly rotating relativistic star emitting isotropic radiation
We explored the motion of test particles near slowly rotating relativistic
star having a uniform luminosity. In order to derive the test particle's
equations of motion, we made use of the radiation stress-energy tensor first
constructed by Miller and Lamb \cite{ML96}. From the particle's trajectory
obtained through the numerical integration of the equations of motion, it is
found that for sufficiently high luminosity, "suspension orbit" exists, where
the test particle hovers around at uniform angular velocity in the same
direction as the star's spin. Interestingly, it turned out that the radial
position of the "suspension orbit" was determined by the luminosity and the
angular momentum of the star alone and was independent of the initial positions
and the specific angular momentum of the particle. Also found is that there
exist not only the radiation drag but also "radiation counter-drag" which
depends on the stellar radius and the angular momentum and it is this radiation
counter-drag that makes the test particle in the "suspension orbit" to hover
around at uniform angular velocity which is greater than that induced by the
Lense-Thirring effect (i.e., general relativistic dragging of inertial frame).Comment: 23 pages, 7 figures, to appear in Phys. Rev. D
A Reexamination of Electron Density Diagnostics for Ionized Gaseous Nebulae
We present a comparison of electron densities derived from optical forbidden
line diagnostic ratios for a sample of over a hundred nebulae. We consider four
density indicators, the [O II] , [S II]
, [Cl III] and [Ar IV]
doublet ratios. Except for a few H II regions for
which data from the literature were used, diagnostic line ratios were derived
from our own high quality spectra. For the [O II] doublet ratio, we find that
our default atomic data set, consisting of transition probabilities (Aij) from
Zeippen (1982} and collision strengths from Pradhan (1976), fit the
observations well, although at high electron densities, the [O II]doublet ratio
yields densities systematically lower than those given by the [S II] doublet
ratio, suggesting that the ratio of Aij of the [O II]
doublet,, given by Zeippen (1982) may need to be
revised upwards by ~6%. Our analysis also shows that the more recent
calculations of [O II] A value by Zeippen (1987a) and collision strengths by
McLaughlin & Bell (1998) are inconsistent with the observations at the high and
low density limits, respectively, and can therefore be ruled out. We confirm
the earlier result of Copetti & Writzl (2002) that the [O II] A values
calculated by Wiese et al. (1996) yield electron densities systematically lower
than those deduced from the [S II] doublet ratio and that the discrepancy is
most likely caused by errors in the A values calculated by Wiese et al. Using
our default atomic data set for [\ion{O}{ii}], we find that N_{\rm
e}([\ion{O}{ii}]) \la N_{\rm e}([\ion{S}{ii}]) \approx N_{\rm
e}([\ion{Cl}{iii}])< N_{\rm e}([\ion{Ar} {iv}]).Comment: 15 pages, 13 figures, 7 tables, accepted for publication in A&
Extended Effective Field Theory of Inflation
We present a general framework where the effective field theory of single
field inflation is extended by the inclusion of operators with mass dimension 3
and 4 in the unitary gauge. These higher dimensional operators introduce
quartic and sextic corrections to the dispersion relation. We study the regime
of validity of this extended effective field theory of inflation and the effect
of these higher dimensional operators on CMB observables associated with scalar
perturbations, such as the speed of sound, the amplitude of the power spectrum
and the tensor-to-scalar ratio. Tensor perturbations remain instead, unaltered.Comment: new version matches the published version, includes adding few
citations and correcting few typo
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