Gravitation and Astrophysics

The following sections are included:

• Preface

• Contents

Due to the weakness of gravity, the accuracy of the Newtonian gravitational constant G is essentially below the accuracy of other fundamental constants. The current value of G, recommended by CODATA in 2006, based on all results available at the end of 2006, is G = (6.67428 ± 0.00067) × 10^-11 m³kg^-1s^-2 with a relative error of 100 ppm. The modern history of G determination is considered. New experiments at a level of accuracy of 10 to 30 ppm are now in progress in some world gravitational laboratories. One of the problems of improving the accuracy of G is a precision measurement of the period of eigen oscillations of the torsion balance. The torsion balance responses to tiny environmental noises, which accordingly result in changes of the torsional oscillation period. The seismic environmental noise in the underground laboratory condition has been studied on the base of data of the Baksan Laser Interferometer. The dependence of the torsion period value and the error of its estimation on the level of the acting seismic noise has been simulated and studied. To measure the Newtonian gravitational constant at the accuracy level of 10 ppm, the environmental seismic noise must be below 10^-2 mGal.

A new determination of Newtonian gravitational constant G is presented by using a torsion pendulum with time-of-swing method. Features of the design include: (1) two SS316 stainless steel spheres with more homogeneous density were used as the source masses; (2) a rectangular glass block was used as the main body of the pendulum; (3) both the pendulum and source masses were set in a vacuum chamber to reduce the error of measuring the relative positions conveniently; (4) exchanging of the configurations between "near" and "far" positions was remotely operated by using a stepper motor; (5) the anelastic effect of the torsion fiber was first measured directly by using two disk pendulums with the help of a high-Q factor quartz fiber. We repeated the G measurements twice independently, and two G values have only a difference of 9 ppm. The combined final value of G was found to be (6.67349±0.00018) × 10^-11 m³kg^-1s^-2 with a relative uncertainty of 26.33 ppm.

In string theories, the law of gravity changes as the distance r is reduced to below the radius of compactification, R. Gravity-only large extra dimensions with R ~ 100 µm could solve the gauge hierarchy problem in grand unification. On the other hand, the observed accelerating expansion of the universe is consistent with a vacuum-energy density 10¹²⁰ times smaller than the value predicted from the quantum corrections to it. This enormous discrepancy could be eliminated if gravitons were 'fat' with the size of the order of 50 µm. Both of these possibilities would lead to a violation of the 1/r² law below 100 µm.

We are conducting a sub-millimeter test of the 1/r² law at 4.2 K. To minimize Newtonian errors, the experiment employs a near-null source, a circular disk of large diameter-to-thickness ratio. Two test masses, also disk-shaped, are positioned on the two sides of the source mass at a nominal distance of 260 µm. The test masses are connected to a SQUID to form a superconducting differential accelerometer. As the source is driven sinusoidally, a violation signal should appear at the second harmonic due to symmetry. The detector is rigidly mounted on the housing and the source mass is suspended separately and driven from outside the housing. The source is driven at its resonance frequency. In this paper, we discuss the design, principle, and progress of this experiment.

For testing gravity and detecting gravitational waves in space, deep-space laser ranging using drag-free spacecraft is a common method. Deep space provides a large arena and a long integration time. Laser technology provides measurement sensitivity, while drag-free technology ensures that gravitational phenomenon to be measured with least spurious noises. In this talk, we give an overview of motivations and methods of various space missions/proposals testing relativistic gravity and detecting gravitational waves, and refer to various references.

LCGT shall be planned to be the large scale cryogenic gravitational wave telescope in order to firstly detect gravitational waves. After the detection, the detector will be served as an astronomical tool to observe the Universe. In collaborative observation by Advanced LIGO, GEO HF and Advanced Virgo projects, LCGT is desired with AIGO to contribute both the enterprise of detecting the gravitational wave events and the worldwide network for gravitational wave astronomy. This paper summarizes the status of LCGT.

An electrostatic-control led torsion pendulum was constructed to test the in-flight performance of an electrostatic inertial sensor on ground. An electrostatic-controlled torque resolution of 6 × 10^-13 N m Hz^-1/2 and a force resolution of 3.6 × 10^-11 N Hz^-1/2 from 2 mHz to 0.1 Hz were achieved.

The Laser Interferometer Space Antenna (LISA) is a joint ESA-NASA mission for detecting low-frequency gravitational waves, by using accurate distance measurements with laser interferometry between three spacecrafts, which will be launched around 2018 and one year later reach their operational orbits around the Sun. In order to operate successfully, it is crucial for the constellation of the three spacecrafts to have extremely high stability. Based on the study of operational orbits for a 2015 launch, we designed the operational orbits of beginning epoch on 2019-03-01, analyzed the acceptable error range of the injection, and introduced the method of orbit design and optimization.

In this article, we present a detailed derivation of the angular resolution of arbitrary sets of LISA (Laser Interferometer Space Antenna) constellations with a toy model for gravitational wave signals, and further generalized to more complicated cases with slowly varying gravitational wave signals of well-defined frequency at any time instant. For future space-borne LISA-like gravitational wave detectors, our results may serve as a conservative quick estimate of the detector's angular resolution and hopefully moreover a reference for the configuration designs.

One challenge in large-scale scientific data analysis is to monitor data in real-time in a distributed environment. For the LIGO (Laser Interferometer Gravitational-wave Observatory) project, a dedicated suit of data monitoring tools (DMT) has been developed, yielding good extensibility to new data type and high flexibility to a distributed environment. Several services are provided, including visualization of data information in various forms and file output of monitoring results.

In this work, a DMT monitor, OmegaMon, is developed for tracking statistics of gravitational-wave (OW) burst triggers that are generated from a specific OW burst data analysis pipeline, the Omega Pipeline. Such results can provide diagnostic information as reference of trigger post-processing and interferometer maintenance.

Using the radio telescopes in Chinese VLBI Network (CVN) and the K5/VSSP32 VLBI system of NICT in Japan, we have developed Total-Phase-Count algorithms that extract open-loop Doppler information from the Chang'E-1 tracking data. Our latest results indicate that Doppler residuals of three-way Doppler are about 3mm/s in Is integration time, relative to an 2.3GHz carrier. This system has also been used in ESA's Mars Express observation in Nov. 2008. In the Chinese-Russian Mars mission (Yinghuo-1) of 2011, the current software algorithms and hardware performance will be improved, and we will attempt to use Total-Phase-Count observable and high precision Doppler shift information to test gravitational waves.

We review the progress in the holographic calculation of shear viscosity for strongly coupled field theories. We focus on the calculation of shear viscosity from the effective coupling of transverse gravitons and present some explicit examples.

From the principle of relativity with two universal invariant parameters c and l, 24 possible kinematical (including geometrical and static) algebras can be obtained. Each algebra is of 10 dimensional, generating the symmetry of a 4 dimensional homogeneous space-time or a pure space. In addition to the ordinary Poincaré algebra, there is another Poincaré algebra among the 24 algebras. New 4d geometries with the new Poincaré symmetry are presented. The motion of free particles on one of the new space-times is discussed.

Physical decomposition of the non-Abelian gauge field has recently solved the two-decade-lasting problem of a gauge-invariant gluon spin. Here we extend this approach to gravitation and attack the century-lasting problem of a covariant gravitational energy density. Counterpart of the gauge field in gravity, the affine connection, is unambiguously separated into a pure geometric term which does not contribute to the curvature tensor, and a gauge-independent physical term which always vanishes in a flat space-time. By this decomposition the conventional pseudo-tensors of the gravitational energy are easily converted to be true tensors, and a physical meaning does exist for the energy density.

We discuss a covariant decomposition of gauge fields into gauge-invariant physical components and gauge-dependent unphysical components. In particular, we consider QED with nonlinear gauge conditions and Yang-Mills gravity with 4-dimensional translational gauge symmetry (T(4) group) in flat space-time. The consistency and intimate relations among decomposition of gauge fields for all times, and gauge conditions and Faddeev-Popov ghost fields are investigated. The gauge invariance of QED and Yang-Mills gravity are revealed by the invariance of physical components under gauge transformations.

We re-express the Kerr metric in standard Bondi-Saches coordinate near null infinity . Using the uniqueness result of characteristic initial value problem, we prove the Kerr metric is the only asymptotic flat, stationary, axial symmetric, algebraic special solution of vacuum Einstein equation.

The relationship between pulsar-like compact stars and gravitational waves is briefly reviewed. Due to regular spins, pulsars could be useful tools for us to detect ~nano-Hz low-frequency gravitational waves by pulsar-timing array technique; besides, they would also be ~kilo-Hz high-frequency gravitational wave radiators because of their compactness. The wave strain of an isolated pulsar depends on the equation state of cold matter at supra-nuclear densities. Therefore, a real detection of gravitational wave should be very meaningful in gravity physics, micro-theory of elementary strong interaction, and astronomy.

In the context of the Randall-Sundrum braneworld, an exhaustive and detailed description of the approach based in the minimal anisotropic consequence onto the brane, which has been successfully used to generate exact interior solutions to Einstein's field equations for static and non-uniform braneworld stars with local and non-local bulk terms, is carefully presented. It is shown that this approach allows the generation of a braneworld version for any known general relativistic solution.

The classical Yang-Mills gravity with translation gauge symmetry in flat space-time was shown to be consistent with experiments in previous papers. We summarize the main features and then discuss the massless ghost particle and its interaction in pure gravity. It is convenient to formulate quantum Yang-Mills gravity by using the Lagrange multiplier method. We discuss the propagator and interactions of ghost vector particles. These results are necessary for the unitarity and gauge invariance of the S-matrix in quantum Yang-Mills gravity.

Gravity is the unique interaction which is universal and attractive, distinctive properties directly connected with energy. Identifying a good expression which describes the (quasi-)local energy-momentum of gravitating systems is still an outstanding fundamental puzzle. The traditional pseudotensor approach is considered here along with the more modern quasi-local idea. Using a covariant Hamiltonian boundary-term approach clarifies the geometric and physical ambiguities. Certain criteria can be used as theoretical tests of any proposed quasi-local energy-momentum expression, including positivity, the spatial and null asymptotic limit, and the small region limit. The argument for the positive energy requirement is recalled and some positive energy proofs are noted. Positivity in general is a very strong criterion, but it is not so easy to prove or disprove. Positivity in the small vacuum region limit is simpler, and is also a quite strong test. In particular none of the traditional pseudotensors passes this test. Two natural quasi-local expressions and some other contrived ones do satisfy this small region requirement. The natural expressions have a positive energy proof for finite regions. Conversely, circumstances in which it is appropriate for the energy to be negative are noted. Our covariant Hamiltonian boundary term quasi-local gravitational energy-momentum expression requires, on the boundary, a choice of a displacement vector and field reference values. We have proposed obtaining the reference values from an energy-optimized isometric embedding of the 2-boundary into Minkowski space. This gives reasonable results at least for spherically symmetric regions.

In this paper, we studied the interactions of dark energy with dark matter, black hole, and wormhole. It was shown that, in phantom case, the interaction terms make arise the new behaviors, such as avoidance from big rip, the decrease of black hole mass, and the increase of the wormhole throat size.

China and Russia are planning to launch a joint Mars mission in 2011. In the joint mission, the 1st Chinese Mars Probe, Yinghuo-1 will explore the space weather of the Mars, and will test the deep space navigation techniques. Different from the close-loop tracking methods in common deep space mission, the open-loop methods like DOR/DOD and 1-way Doppler, are developed and applied to determine the sic orbit and position.

It is well known that moving puncture method and the specific gauge condition are critically important for successful simulation of binary black hole merging. On the contrary, the importance of formalism for numerical relativity is not very clear yet. Both generalized harmonic formalism and BSSN formalism work very well. So the simplicity of Einstein's equations in ADM formalism stimulates us to investigate a naive but interesting problem—can ADM formalism work as stably as BSSN formalism does with the moving puncture method and the advanced gauge condition, which were proved critical important for BSSN formalism's success. We apply this idea to Schwarzschild black hole simulation as a test example. Unfortunately, our result implies that ADM formalism has its intrinsic instable character which may be introduced by the property of the corresponding equations themselves instead of the gauge condition. And more, we find that the so called advanced gauge condition even make the situation worse. So we conclude that one gauge condition works well in one numerical formalism does not mean it works well also in other formalism. Through concrete examples, we give readers a primary sense on the roles that formalism, gauge condition, numerical method and other issues play in the problem of stability of numerical relativity.

We present an analytic solution for density perturbations in the matter component during the matter dominated stage in terms of Gauss' hypergeometric functions for a class of f(R) gravity models of accelerated expansion. By using the analytic solution, we obtain an analytical expression for the matter transfer function at scales much less than the present Hubble scale.

Normal modes, zero modes and super-radiant modes for scalar fields are studied in (2+1)-dimensional BTZ spacetime and in (3+1)-dimensional Kerr-anti-de Sitter spacetime. For BTZ spacetime, normal modes are obtained in solving the eigenvalue equation in numerical and analytical methods. All physical normal modes shown to lie above the zero mode line: 0=frequency - angular velocity × azimuthal angular momentum. For Kerr-anti-de Sitter spacetime, non-existence of zero modes is shown rigorously for the Dirichlet boundary condition. Non-existence of zero modes indicates that super-radiant instability modes are unphysical but super-radiant stability modes are physical.

In this work, the radio, X-ray and γ-ray emissions are compiled for sample of 42 flat spectrum radio quasars-FSRQs, to calculate the effective spectrum indices, namely the radio-X-ray spectrum index α_RX, the radio-γ-ray spectrum index α_RG and the X-ray to γ-ray spectrum index α_XG. Also the correlations among α_RX, α_RG and α_XG are investigated. It is interesting that for 42 FSRQs, which can be used to estimate the γ-ray emissions from the X-ray and the radio emissions. Clear correlations are found between α_XG and α_RX and between α_RG and α_XG respectively. A weak correlation between α_RX and α_RG is found. The results show that the γ-ray emissions are associated with both radio and the X-ray emissions in blazars.

Various refinements of trapped surfaces are summarized, intended to apply near the outer horizon of a black hole, together with their relations. Assuming the null energy condition, minimal trapped implies outer trapped, which implies increasingly trapped. Variations of these three definitions form an interwoven hierarchy.

We present the results from a series of analytical studies on relic gravitational waves (RGW) and the anisotropies and polarization of cosmic background radiation (CMB). The analytical spectrum h(ν) of RGW shows the influences of the dark energy, neutrino free-streaming (NFS), quantum chro-modynamical (QCD) phase transition, e⁺e^- annihilation, and inflation. Various possible detections of, and constraints on RGW are examined. The resulting h(ν) is then used to analytically calculate the spectra of CMB anisotropies and polarizations. The influences of the inflation index, NFS, and baryon on are demonstrated. We also extend analytical calculation of to the case with reionization. The explicit dependence of on the optical depth is obtained, whose degeneracies with the amplitude and index of RGW are shown, and the consequential implications in extracting RGW signal from observed are explored.

The state transitions of black hole (BH) X-ray binaries are discussed based on the evolution of large-scale magnetic fields, in which the combination of three energy mechanisms are involved: (1) the Blandford-Znajek (BZ) process related to the open field lines connecting a rotating BH with remote astrophysical loads, (2) the magnetic coupling (MC) process related to the closed field lines connecting the BH with its surrounding accretion disk, and (3) the Blandford-Payne (BP) process related to the open field lines connecting the disk with remote astrophysical loads. It turns out that each spectral state of the BH binaries corresponds to each configuration of magnetic field in BH magnetosphere, and the main characteristics of low/hard (LH) state, hard intermediate (HIM) state and steep power law (SPL) state are roughly fitted based on the evolution of large-scale magnetic fields associated with disk accretion.

RXTE satellite discovered many kHz quasi-periodic oscillations (QPOs) in X-ray neuron star systems, and these oscillations are often taken as the accreting matter circling around the central compact objects. As the models for kHz QPOs are constructed, the mass and/or radius of these neutron stars can be inferred, by which the comparisons with the star equations of states (EOSs) can be performed.

The Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (formerly GLAST) provides an increase of sensitivity and has detected rapid variation in the γ-ray region. In this work, the variation timescales detected from the γ-ray loud blazars by LAT and EGRET are used to estimate the central black hole masses for 14 blazars. The obtained masses are in a range of (2.07 ~ 15.54) × 10⁷ M_⊙, the Doppler factors are in the range of δ = 1.12 ~ 4.63, which are comparable with those obtained by other authors.

We analyze, in the framework of open quantum systems, the reduced dynamics of a static detector (a two-level atom) outside a two-dimensional black hole in weak interaction with a bath of massless quantum scalar fields in the Hartle-Hawking vacuum. We find that the detector outside the black hole is asymptotically driven to a thermal state at the temperature T, which reduces to the Hawking temperature in the spatial asymptotic region, regardless of its initial state. Our discussion therefore shows that the Hawking effect can be understood as a manifestation of thermalization phenomena in the framework of open quantum systems.

Casimir energies and forces have been calculated in various configurations and boundary conditions. The calculations indicated that the Casimir energy might change its sign depending not only on the boundary conditions but also on geometry and topology of the configuration. With the development of nanotechnology, it is known that repulsive Casimir force is very important in nanodevices. In this paper, we review some research results on repulsive Casimir force, and discuss whether it could be realizable theoretically and experimentally.

The discovery of the accelerated expansion of the universe using Type Ia supernovae (SNe Ia) has stimulated a tremendous amount of interest in the use of SNe Type Ia events as standard cosmological candles, and as a probe of the fundamental physics of dark energy. Recent observations of SNe Ia have indicated a significant population difference depending on the host galaxy. These observational findings are consistent with SNe Ia Ni-56 production in star-forming spiral galaxies some 0.1 solar masses higher – and therefore more luminous – than in elliptical galaxies. We present recent full-star, 3D simulations of Type Ia supernovae which may help explain the nature of this systematic variation in SNe Ia luminosities, as well as the nature of the Ia explosion mechanism. These insights may in turn eventually shed light on the mystery of dark energy itself.

The following sections are included:

• International Organizing Committee

• Local organizing Committee

• List of Participants

• Photos