35,284 research outputs found
Jantzen coefficients and simplicity of generalized Verma modules
The main purpose of the paper is to establish new tools in the study of
. We introduce the Jantzen coefficients of
generalized Verma modules. It comes from the Jantzen's simplicity criteria for
generalized Verma modules and has a deep relation with the structure of
. We develop a reduction process to compute those
coefficients. For which we need to consider generalized Verma modules induced
from maximal parabolic subalgebras having maximal nontrivial singularity, so
called basic generalized Verma modules. The classification of such modules is
obtained in this paper. As the first application of our results, we give a
refinement of Jantzen's simplicity criteria.Comment: 43 pages, 4 figure
On the non-thermal kappa-distributed electrons in planetary nebulae and HII regions: the kappa index and its correlations with other nebular properties
Recently, a suspicion arose that the free electrons in planetary nebulae
(PNe) and HII regions might have non-thermal energy distributions. In this
scenario, a kappa index is introduced to characterize the electron energy
distributions, with smaller kappa values indicating larger deviations from
Maxwell-Boltzmann distributions. Assuming that this is the case, we determine
the kappa values for a sample of PNe and HII regions by comparing the
intensities of [OIII] collisionally excited lines and the hydrogen Balmer jump.
We find the average kappa indices of PNe and HII regions to be 27 and 32,
respectively. Correlations between the resultant kappa values and various
physical properties of the nebulae are examined to explore the potential origin
of non-thermal electrons in photoionized gaseous nebulae. However, no positive
result is obtained. Thus the current analysis does not lend to support to the
idea that kappa-distributed electrons are present in PNe and HII regions.Comment: 23 pages, 6 figures, accepted for publication in Ap
H I Free-Bound Emission of Planetary Nebulae with Large Abundance Discrepancies: Two-Component Models versus Kappa-distributed electrons
The "abundance discrepancy" problem in the study of planetary nebulae (PNe),
viz., the problem concerning systematically higher heavy-element abundances
derived from optical recombination lines relative to those from collisionally
excited lines, has been under discussion for decades, but no consensus on its
solution has yet been reached. In this paper we investigate the hydrogen
free-bound emission near the Balmer jump region of four PNe that are among
those with the largest abundance discrepancies, aiming to examine two recently
proposed solutions to this problem: two-component models and Kappa electron
energy distributions. We find that the Balmer jump intensities and the spectrum
slopes cannot be simultaneously matched by the theoretical calculations based
upon single Maxwell-Boltzmann electron-energy distributions, whereas the
fitting can be equally improved by introducing Kappa electron energy
distributions or an additional Maxwell-Boltzmann component. We show that
although H I free-bound emission alone cannot distinguish the two scenarios, it
can provide important constraints on the electron energy distributions,
especially for cold and low-Kappa plasmas.Comment: 23 pages, 10 figures, accepted for publication in Ap
Nuclear suppression of meson yields with large at the RHIC and the LHC
We calculate meson transverse momentum spectra in p+p collisions as
well as their nuclear suppressions in central A+A collisions both at the RHIC
and the LHC in LO and NLO with the QCD-improved parton model. We have included
the parton energy loss effect in hot/dense QCD medium with the effectively
medium-modified fragmentation functions in the higher-twist approach of
jet quenching. The nuclear modification factors of meson in central
Au+Au collisions at the RHIC and central Pb+Pb collisions at the LHC are
provided, and a nice agreement of our numerical results at NLO with the ALICE
measurement is observed. Predictions of yield ratios of neutral mesons such as
, and at large in relativistic
heavy-ion collisions are also presented for the first time.Comment: 7 pages, 8 figure
meson production of high-energy nuclear collisions at NLO
The transverse momentum spectrum of meson in relativistic heavy-ion
collisions is studied at the next-to-leading-order (NLO) within the
perturbative QCD, where the jet quenching effect in the QGP is incorporated
with the effectively medium-modified fragmentation functions using the
higher-twist approach. We show that the theoretical simulations could give nice
descriptions of PHENIX data on meson in both and central collisions at the RHIC, and also provide numerical predictions of
spectra in central collisions with ~TeV at the
LHC. The ratios of in and in central
collisions at ~GeV are found to overlap in a wide region, which
matches well the measured ratio by PHENIX. We demonstrate that,
at the asymptotic region when the ratios of
in both and are almost determined only by
quark jets fragmentation and thus approach to the one in
scattering; in addition, the almost identical gluon (quark) contribution
fractions to and to result in a rather moderate variation of
distribution at intermediate and high region in
relative to that in ; while a slightly higher at small
in can be observed due to larger suppression of gluon
contribution fraction to as compared to the one to . The
theoretical prediction for at the LHC has also been presented.Comment: 7 pages, 8 figures, 2 typos corrected, revision for publicatio
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