1,035,633 research outputs found
A multi-transition molecular line study of inward motions towards massive star-forming cores
A multi-transition 3mm molecular line single-pointing and mapping survey
was carried out towards 29 massive star-forming cores in order to search for
the signature of inward motions. Up to seven different transitions, optically
thick lines HCO(1-0), CS(2-1), HNC(1-0), HCN(1-0), CO(1-0) and
optically thin lines CO(1-0), CO(1-0) were observed towards each
source. The normalized velocity differences (V,
V) between the peak velocities of optically thick lines
and optically thin line CO(1-0) for each source were derived. Prominent
inward motions are probably present in either HCO(1-0) or CS(2-1) or
HNC(1-0) observations in most sources. Our observations show that there is a
significant difference in the incidence of blue shifted line asymmetric line
profiles between CS(2-1) and HCO(1-0). The HCO(1-0) shows the highest
occurrence of obvious asymmetric feature, perhaps owing to different optical
depth between CS(2-1) and HCO(1-0). HCO(1-0) appears to be the best
inward motion tracer. The mapping observations of multiple line transitions
enable us to identify six strong infall candidates G123.07-6.31, W75(OH),
S235N, CEP-A, W3(OH), NGC7538. The infall signature is extended up to a linear
scale pc.Comment: 11 pages, 10 figures, 3 tables, accepted for publication in MNRA
Possible solution to the riddle of HD 82943 multiplanet system: the three-planet resonance 1:2:5?
We carry out a new analysis of the published radial velocity data for the
planet-hosting star HD82943. We include the recent Keck/HIRES measurements as
well as the aged but much more numerous CORALIE data. We find that the CORALIE
radial velocity measurements are polluted by a systematic annual variation
which affected the robustness of many previous results. We show that after
purging this variation, the residuals still contain a clear signature of an
additional days periodicity. The latter variation leaves
significant hints in all three independent radial velocity subsets that we
analysed: the CORALIE data, the Keck data acquired prior to a hardware upgrade,
and the Keck data taken after the upgrade.
We mainly treat this variation as a signature of a third planet in the
system, although we cannot rule out other interpretations, such as long-term
stellar activity. We find it easy to naturally obtain a stable three-planet
radial-velocity fit close to the three-planet mean-motion resonance 1:2:5, with
the two main planets (those in the 1:2 resonance) in an aligned apsidal
corotation. The dynamical status of the third planet is still uncertain: it may
reside in as well as slightly out of the 5:2 resonance. We obtain the value of
days for its orbital period and of for its
minimum mass, while the eccentric parameters are uncertain.Comment: 18 pages, 5 tables, 18 figures; accepted for publication in MNRA
QSD IV : 2+1 Euclidean Quantum Gravity as a model to test 3+1 Lorentzian Quantum Gravity
The quantization of Lorentzian or Euclidean 2+1 gravity by canonical methods
is a well-studied problem. However, the constraints of 2+1 gravity are those of
a topological field theory and therefore resemble very little those of the
corresponding Lorentzian 3+1 constraints. In this paper we canonically quantize
Euclidean 2+1 gravity for arbitrary genus of the spacelike hypersurface with
new, classically equivalent constraints that maximally probe the Lorentzian 3+1
situation. We choose the signature to be Euclidean because this implies that
the gauge group is, as in the 3+1 case, SU(2) rather than SU(1,1). We employ,
and carry out to full completion, the new quantization method introduced in
preceding papers of this series which resulted in a finite 3+1 Lorentzian
quantum field theory for gravity. The space of solutions to all constraints
turns out to be much larger than the one as obtained by traditional approaches,
however, it is fully included. Thus, by suitable restriction of the solution
space, we can recover all former results which gives confidence in the new
quantization methods. The meaning of the remaining "spurious solutions" is
discussed.Comment: 35p, LATE
Signature reversal invariance
We consider the signature reversing transformation of the metric tensor g_ab
goes to -g_ab induced by the chiral transformation of the curved space gamma
matrices gamma_a goes to gamma gamma_a in spacetimes with signature (S,T),
which also induces a (-1)^T spacetime orientation reversal. We conclude: (1) It
is a symmetry only for chiral theories with S-T= 4k, with k integer. (2)
Yang-Mills theories require dimensions D=4k with T even for which even rank
antisymmentric tensor field strengths and mass terms are also allowed. For
example, D=10 super Yang-Mills is ruled out. (3) Gravititational theories
require dimensions D=4k+2 with T odd, for which the symmetry is preserved by
coupling to odd rank field strengths. In D=10, for example, it is a symmetry of
N=1 and Type IIB supergravity but not Type IIA. A cosmological term and also
mass terms are forbidden but non-minimal R phi^2 coupling is permitted. (4)
Spontaneous compactification from D=4k+2 leads to interesting but different
symmetries in lower dimensions such as D=4, so Yang-Mills terms, Kaluza-Klein
masses and a cosmological constant may then appear. As a well-known example,
IIB permits AdS_5 x S^5.Comment: LaTex, 31 pages; v3: Extended discussion of fermions without
vielbeins. Version to appear in Nucl. Phys.
Geometry of Killing spinors in neutral signature
We classify the supersymmetric solutions of minimal gauged supergravity
in four dimensions with neutral signature. They are distinguished according to
the sign of the cosmological constant and whether the vector field constructed
as a bilinear of the Killing spinor is null or non-null. In neutral signature
the bilinear vector field can be spacelike, which is a new feature not arising
in Lorentzian signature. In the non-null case, the canonical form
of the metric is described by a fibration over a three-dimensional base space
that has holonomy with torsion. We find that a generalized
monopole equation determines the twist of the bilinear Killing field, which is
reminiscent of an Einstein-Weyl structure. If, moreover, the electromagnetic
field strength is self-dual, one gets the Kleinian signature analogue of the
Przanowski-Tod class of metrics, namely a pseudo-hermitian spacetime determined
by solutions of the continuous Toda equation, conformal to a scalar-flat
pseudo-K\"ahler manifold, and admitting in addition a charged conformal Killing
spinor. In the null case, the supersymmetric solutions define an
integrable null K\"ahler structure. In the non-null case, the
manifold is a fibration over a Lorentzian Gauduchon-Tod base space. Finally, in
the null class, the metric is contained in the Kundt family, and it
turns out that the holonomy is reduced to .
There appear no self-dual solutions in the null class for either sign of the
cosmological constant.Comment: 40 pages, uses JHEP3.cls. v2: Appendix and ref. added. v3: Published
versio
p-mode frequencies in solar-like stars : I. Procyon A
As a part of an on-going program to explore the signature of p-modes in
solar-like stars by means of high-resolution absorption lines pectroscopy, we
have studied four stars (alfaCMi, etaCas A, zetaHer A and betaVir). We present
here new results from two-site observations of Procyon A acquired over twelve
nights in 1999. Oscillation frequencies for l=1 and l=0 (or 2) p-modes are
detected in the power spectra of these Doppler shift measurements. A frequency
analysis points out the dificulties of the classical asymptotic theory in
representing the p-mode spectrum of Procyon A
The stability of the fractional quantum Hall effect in topological insulators
With the recent observation of graphene-like Landau levels at the surface of
topological insulators, the possibility of fractional quantum Hall effect,
which is a fundamental signature of strong correlations, has become of
interest. Some experiments have reported intra-Landau level structure that is
suggestive of fractional quantum Hall effect. This paper discusses the
feasibility of fractional quantum Hall effect from a theoretical perspective,
and argues that while this effect should occur, ideally, in the and
Landau levels, it is ruled out in higher Landau levels. Unlike
graphene, the fractional quantum Hall effect in topological insulators is
predicted to show an interesting asymmetry between and Landau
levels due to spin-orbit coupling.Comment: 8 pages, 2 figure
nu=1/2 quantum Hall effect in the Aharonov-Casher geometry in a mesoscopic ring
We study the effect of an electric charge in the middle of a ring of
electrons in a magnetic field such as . In the absence of the
central charge, a residual current should appear due to an Aharanov-Bohm
effect. As the charge varies, periodic currents should appear in the ring. We
evaluate the amplitude of these currents, as well as their period as the
central charge varies. The presence of these currents should be a direct
signature of the existence of a statistical gauge field in the
quantum Hall effect. Numerical diagonalizations for a small number of electrons
on the sphere are also carried out. The numerical results up to 9 electrons are
qualitatively consistent with the mean field picture.Comment: 23 pages,14 included postscript figures, submitted to Phys. Rev.
- …