Solar system constraints on multifield theories of modified dynamics

Any viable theory of modified Newtonian dynamics (MOND) as modified gravity is likely to require fields in addition to the usual tensor field of General Relativity. For these theories, the MOND phenomenology emerges as an effective fifth force probably associated with a scalar field. Here, I consider the constraints imposed on such theories by Solar system phenomenology, primarily by the absence of significant deviations from inverse-square attraction in the inner Solar system as well as detectable local preferred frame effects. The current examples of multifield theories can be constructed to satisfy these constraints and such theories lead inevitably to an anomalous non-inverse-square force in the outer Solar system.     

Describing neutron stars by the relativistic mean field theory

Neutron stars are studied in the framework of the relativistic mean field theory of interacting nucleons, hyperons, and mesons. Within the hadronic freedom, the cores of neutron stars are found to be dominated by hyperons when the density is sufficiently high. The influence of hyperon coupling constants on the transition from a neutron star to a hyperon-dominated strange neutron star is also investigated. It is found that the transition density gets its minimum value when the ratio of hyperon coupling constant to nucleon's takes the value of 0.65, and the calculated maximum mass of the neutron star is 1.4 M which lies within the range of the observational results.     

最新规范的参考系及有关问题

在简要阐明参考系、参考架及其历史重大进程的基础上,对几种重要的、最新规范的参考系/参考架(质心天球参考系和地心天球参考系、国际天球参考系、国际地球参考系、太阳系动力学参考系等)的定义、实现和特点作了评述和分析,并对最新规范中与参考系、参考架有关的某些新概念的定义和新模式的应用(自2003年开始贯彻),如:天球中介极(CIP)、天球历书原点(CEO)、地球历书原点(TEO)、地球自转角的新定义、岁差-章动新模式的应用,作了阐述和讨论。     

Radiative acceleration in Schwarzschild space–times

We examine the radial motion of a material particle in the intense radiation field of a static spherically symmetric compact object with spherical emitting surface outside the Schwarzschild radius. This paper generalizes previous work which dealt with radial motion in the Thomson limit, where the radiation force is simply proportional to the radiative flux. In the general case the average time component of the 4-momentum transferred to the particle is not negligible compared with its rest mass. Consequently, we find that the frequency dependence of the radiation force owing to Compton scattering for highly energetic photons gives rise to an increase in the effective mass of the test particle. In this work we outline the effects of this frequency dependence and compare these with the results in the Thomson limit. We present the frequency dependent saturation velocity curves for a range of stellar luminosities and radiation frequencies and present the resulting phase-space diagrams corresponding to the radial test particle trajectories. In particular, the stable equilibrium points which exist in the Thomson limit are found to be absent in the general case.     

Does the plasma composition affect the long-term evolution of relativistic jets?

We study the influence of the matter content of extragalactic jets on their morphology, dynamics and emission properties. For this purpose we consider jets of extremely different compositions, including pure leptonic and baryonic plasmas. Our work is based on two-dimensional relativistic hydrodynamic simulations of the long-term evolution of powerful extragalactic jets propagating into a homogeneous environment. The equation of state used in the simulations accounts for an arbitrary mixture of electrons, protons and electron–positron pairs. Using the hydrodynamic models, we have also computed synthetic radio maps and the thermal bremsstrahlung X-ray emission from their cavities.
Although there is a difference of about three orders of magnitude in the temperatures of the cavities inflated by the simulated jets, we find that both the morphology and the dynamic behaviour are almost independent of the assumed composition of the jets. Their evolution proceeds in two distinct epochs. During the first one, multidimensional effects are unimportant and the jets propagate ballistically. The second epoch starts when the first larger vortices are produced near the jet head, causing the beam cross-section to increase and the jet to decelerate. The evolution of the cocoon and cavity is in agreement with a simple theoretical model. The beam velocities are relativistic  ( Γ ≃4)  at kiloparsec scales, supporting the idea that the X-ray emission of several extragalactic jets may be due to relativistically boosted CMB photons. The radio emission of all models is dominated by the contribution of the hotspots. All models exhibit a depression in the X-rays surface brightness of the cavity interior, in agreement with recent observations.