1,321 research outputs found
High Order QED Corrections in Physics of Positronium
High-order perturbative corrections to positronium decays and hyperfine
splitting are briefly reviewed. Theoretical predictions are compared to the
most recent experimental data. Perspectives of future calculations are
discussed.Comment: 8 pages, LaTeX, talk given at Workshop on Positronium Physics, ETH
Honggerberg, Zurich, May 30-31, 2003, a misprint in Eq. (1) correcte
VLA Observations of the "Eye of the Tornado"- the High Velocity \HII Region G357.63-0.06
The unusual supernova remnant candidate G357.7-0.1 and the compact source
G357.63-0.06 have been observed with the Very Large Array at 1.4 and 8.3 GHz.
The H92 line (8.3 GHz) was detected from the compact source with a
surprising velocity of about -210 km/s indicating that this source is an \HII
region, is most likely located at the Galactic center, and is unrelated to the
SNR. The \HI absorption line (1.4 GHz) data toward these sources supports this
picture and suggests that G357.7-0.1 lies farther away than the Galactic
center.Comment: Latex, 14 pages including 4 figures. Accepted to A
Revealing the obscured supernova remnant Kes 32 with Chandra
I report here on the analysis and interpretation of a Chandra observation of
the supernova remnant Kes 32. Kes 32 is rather weak in X-rays due to a large
interstellar absorption, which is found to be ~4E22 cm^-2, larger than
previously reported. Spectral analysis indicates that the ionization age of
this object is very young, with n_e t ~ 4E9 cm^-3s, and a temperature of kT_e ~
1 keV. The X-ray emission peaks at a smaller radius than in the radio. The low
ionization age suggests that Kes 32 is a young remnant. However, a young age is
in contradiction with the relatively large apparent size, which indicates an
age of several thousand years, instead of a few hundred years. This problem is
discussed in connection with Kes 32's unknown distance and its possible
association with the Norma galactic arm.Comment: Accepted for publication in the Astrophysical Journal. 7 pages, 7
figure
Quantum Hall Effect in Quantum Electrodynamics
We consider the quantum Hall effect in quantum electrodynamics and find a
deviation from the quantum mechanical prediction for the Hall conductivity due
to radiative antiscreening of electric charge in an external magnetic field. A
weak universal dependence of the von Klitzing constant on the magnetic field
strength, which can possibly be observed in a dedicated experiment, is
predicted.Comment: 4 pages, 2 figures, LaTeX, perturbative result correcte
Recoil corrections in the hydrogen isoelectronic sequence
A version of the Bethe-Salpeter equation appropriate for calculating recoil
corrections in highly charged hydrogenlike ions is presented. The nucleus is
treated as a scalar particle of charge Z, and the electron treated
relativistically. The known recoil corrections of order are
derived in both this formalism and in NRQED
The Distances of SNR W41 and overlapping HII regions
New HI images from the VLA Galactic Plane Survey show prominent absorption
features associated with the supernovae remnant G23.3-0.3 (SNR W41). We
highlight the HI absorption spectra and the CO emission spectra of eight
small regions on the face of W41, including four HII regions, three non-thermal
emission regions and one unclassified region. The maximum velocity of
absorption for W41 is 782 km/s and the CO cloud at radial velocity
955 km/s is behind W41. Because an extended TeV source, a diffuse X-ray
enhancement and a large molecular cloud at radial velocity 775 km/s are
also projected at the center of W41, these yield the kinematic distance of 3.9
to 4.5 kpc for W41. For HII regions, our analyses reveal that both G23.42-0.21
and G23.07+0.25 are at the far kinematic distances (9.9 kpc and
10.6 kpc respectively) of their recombination-line velocities (1030.5 km/s
and 89.62.1 km/s respectively), G23.07-0.37 is at the near kinematic
distance (4.40.3 kpc) of its recombination-line velocity (82.72.0
km/s), and G23.27-0.27 is probably at the near kinematic distance (4.10.3
kpc) of its recombination-line velocity (76.10.6 km/s).Comment: 11 pages, 3 figs., 2 tables, accepted by A
Order alpha^3 ln(1/alpha) Corrections to Positronium Decays
The logarithmically enhanced alpha^3 ln(1/alpha) corrections to the para- and
orthopositronium decay widths are calculated in the framework of dimensionally
regularized nonrelativistic quantum electrodynamics.In the case of
parapositronium, the correction is negative, approximately doubles the effect
of the leading logarithmic alpha^3 ln^2(1/alpha) one, and is comparable to the
nonlogarithmic O(alpha^2) one. As for orthopositronium, the correction is
positive and almost cancels the alpha^3 ln^2(1/alpha) one. The uncertainties in
the theoretical predictions for the decay widths are reduced.Comment: 10 pages (Latex); missing term added, corrected coefficient B_p used,
numerical results insignificantly change
NGC 3576 and NGC 3603: Two Luminous Southern HII Regions Observed at High Resolution with the Australia Telescope Compact Array
NGC 3576 (G291.28-0.71; l=291.3o, b=-0.7o) and NGC 3603 (G291.58-0.43;
l=291.6o, b=-0.5o) are optically visible, luminous HII regions located at
distances of 3.0 kpc and 6.1 kpc, respectively. We present 3.4 cm Australian
Telescope Compact Array (ATCA) observations of these two sources in the
continuum and the H90a, He90a, C90a and H113b recombination lines with an
angular resolution of 7" and a velocity resolution of 2.6 km/s. All four
recombination lines are detected in the integrated profiles of the two sources.
Broad radio recombination lines are detected in both NGC 3576 (DV_{FWHM}>= 50
km/s) and NGC 3603 (DV_{FWHM}>=70 km/s). In NGC 3576 a prominent N-S velocity
gradient (~30 km/s/pc) is observed, and a clear temperature gradient (6000 K to
8000 K) is found from east to west, consistent with a known IR color gradient
in the source. In NGC 3603, the H90a, He90a and the H113b lines are detected
from 13 individual sources. The Y^+ (He/H) ratios in the two sources range from
0.08+/-0.04 to 0.26+/-0.10. We compare the morphology and kinematics of the
ionized gas at 3.4 cm with the distribution of stars, 10 micron emission and
H_2O, OH, and CH_3OH maser emission. These comparisons suggest that both NGC
3576 and NGC 3603 have undergone sequential star formation.Comment: 24 pages, 12 Postscript figure
Two-Loop Bethe Logarithms
We calculate the two-loop Bethe logarithm correction to atomic energy levels
in hydrogen-like systems. The two-loop Bethe logarithm is a low-energy quantum
electrodynamic (QED) effect involving multiple summations over virtual excited
atomic states. Although much smaller in absolute magnitude than the well-known
one-loop Bethe logarithm, the two-loop analog is quite significant when
compared to the current experimental accuracy of the 1S-2S transition: it
contributes -8.19 and -0.84 kHz for the 1S and the 2S state, respectively. The
two-loop Bethe logarithm has been the largest unknown correction to the
hydrogen Lamb shift to date. Together with the ongoing measurement of the
proton charge radius at the Paul Scherrer Institute its calculation will bring
theoretical and experimental accuracy for the Lamb shift in atomic hydrogen to
the level of 10^(-7).Comment: 4 pages, RevTe
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