1,035,633 research outputs found

    A multi-transition molecular line study of inward motions towards massive star-forming cores

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    A multi-transition 3 mm 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), 12^{12}CO(1-0) and optically thin lines C18^{18}O(1-0), 13^{13}CO(1-0) were observed towards each source. The normalized velocity differences (δ\deltaVCS_{\rm CS}, δ\deltaVHCO+_{\rm HCO^{+}}) between the peak velocities of optically thick lines and optically thin line C18^{18}O(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 >0.2 >0.2 \: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?

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    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 ∼1100\sim 1100 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 ∼1075\sim 1075 days for its orbital period and of ∼0.3MJup\sim 0.3 M_{\rm Jup} 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

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    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

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    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

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    We classify the supersymmetric solutions of minimal N=2N=2 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 Λ<0\Lambda<0 non-null case, the canonical form of the metric is described by a fibration over a three-dimensional base space that has U(1)\text{U}(1) 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 Λ<0\Lambda<0 null case, the supersymmetric solutions define an integrable null K\"ahler structure. In the Λ>0\Lambda>0 non-null case, the manifold is a fibration over a Lorentzian Gauduchon-Tod base space. Finally, in the Λ>0\Lambda>0 null class, the metric is contained in the Kundt family, and it turns out that the holonomy is reduced to Sim(1)×Sim(1){\rm Sim}(1)\times{\rm Sim}(1). 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

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    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

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    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 n=0n=0 and ∣n∣=1|n|=1 Landau levels, it is ruled out in higher ∣n∣|n| Landau levels. Unlike graphene, the fractional quantum Hall effect in topological insulators is predicted to show an interesting asymmetry between n=1n=1 and n=−1n=-1 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

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    We study the effect of an electric charge in the middle of a ring of electrons in a magnetic field such as ν=1/2\nu = 1/2. 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 ν=1/2\nu=1/2 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.
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