The Multi-parameter Test of Gravitational Wave Dispersion with Principal Component Analysis

In this work, we consider a conventional test of gravitational wave(GW) propagation which is based on the phenomenological parameterized dispersion relation to describe potential departures from General Relativity(GR)along the propagation of GWs. But different from tests conventionally performed previously, we vary multiple deformation coefficients simultaneously and employ the principal component analysis(PCA) method to remedy the strong degeneracy among deformation coefficients and obtain informative posteriors. The dominant PCA components can be better measured and constrained, and thus are expected to be more sensitive to potential departures from the waveform model. Using this method we analyze ten selected events and get the result that the combined posteriors of the dominant PCA parameters are consistent with GR within 99.7% credible intervals. The standard deviation of the first dominant PCA parameter is three times smaller than that of the original dispersion parameter of the leading order. However, the multi-parameter test with PCA is more sensitive to not only potential deviations from GR but also systematic errors of waveform models. The difference in results obtained by using different waveform templates hints that the demands of waveform accuracy are higher to perform the multiparameter test with PCA. Whereas, it cannot be strictly proven that the deviation is indeed and only induced by systematic errors. It requires more thorough research in the future to exclude other possible reasons in parameter estimation and data processing.

Neutron star mass-radius relation with gravitational field shielding by a scalar field

The currently well-developed models for equations of state （EoSs） have been severely impacted by recent measurements of neutron stars with a small radius and/or large mass. To explain these measurements, the theory of gravitational field shielding by a scalar field is applied. This theory was recently developed in accor- dance with the five-dimensional （5D） fully covariant Kaluza-Klein （KK） theory that has successfully unified Einstein＇s general relativity and Maxwell＇s electromagnetic theory. It is shown that a massive, compact neutron star can generate a strong scalar field, which can significantly shield or reduce its gravitational field, thus making it more massive and more compact. The mass-radius relation developed under this type of modified gravity can be consistent with these recent measurements of neutron stars. In addition, the effect of gravitational field shielding helps explain why the supernova explosions of some very massive stars （e.g.9 40 MQ as measured recently） actually formed neutron stars rather than black holes as expected. The EoS models, ruled out by measurements of small radius and/or large mass neutron stars according to the the- ory of general relativity, can still work well in terms of the 5D fully covariant KK theory with a scalar field.

The Nature of Space and of Gravitation

Many recent highly precise and unmistakable observational facts achieved thanks to the tightly synchronized clocks of the GPS, provide consistent evidence that the gravitational fields are created by velocity fields of real space itself, a vigorous and very stable quantum fluid like spatial medium, the same space that rules the propagation of light and the inertial motion of matter. It is shown that motion of this real space in the ordinary three dimensions round the Earth, round the Sun and round the galactic centers throughout the universe, according to velocity fields closely consistent with the local main astronomical motions, correctly induces the gravitational dynamics observed within these gravitational fields. In this spacedynamics the astronomical bodies all closely rest with respect to the real space, which forth-rightly leads to the observed null results of the Michelson light anisotropy experiments as well as to the absence of effects of the solar and galactic gravitational fields on the rate of clocks moving with Earth as recently discovered with the help of the GPS clocks. This spacedynamics exempts us from explaining the circular orbital motions of the planets round the Sun, likewise the rotation of Earth exempted people from explaining the diurnal transit of the heavens in the days of Copernicus and Galileo, because it is space itself that so moves. This spacedynamics also eliminates the need of dark matter and dark energy to explain respectively the galactic gravitational dynamics and the accelerated expansion of the universe. It also straightforwardly accounts in terms of well known and genuine physical effects for all the other observed effects, caused by the gravitational fields on the velocity of light and on the rate of clocks, including all the new effects recently discovered with the help of the GPS. It moreover simulates the non-Euclidean metric underlying Einstein’s spacetime curvature. This spacedynamics is the crucial innovation in the current world conception that definitively resolves all at once the troubles afflicting the current theories of space and gravitation.

Does black hole spin play a key role in the FSRQ/BL Lac dichotomy?

Blazars are characterized by large intensity and spectral variations across the electromagnetic spectrum It is believed that jets emerging from them are almost aligned with the line-of-sight. The major- ity of identified extragalactic sources in γ-ray catalogs of EGRET and Fermi are blazars. Observationally, blazars can be divided into two classes： fiat spectrum radio quasars （FSRQs） and BL Lacs. BL Lacs usually exhibit lower γ-ray luminosity and harder power law spectra at γ-ray energies than FSRQs. We attempt to explain the high energy properties of FSRQs and BL Lacs from Fermi γ-ray space telescope observations. It was argued previously that the difference in accretion rates is mainly responsible for the large mismatch in observed luminosity in ＂7-ray. However, when intrinsic luminosities are derived by correcting for beaming effects, this difference in 7-ray luminosity between the two classes is significantly reduced. In order to ex- plain this difference in intrinsic luminosities, we propose that spin plays an important role in the luminosity distribution dichotomy of BL Lacs and FSRQs. As the outflow power of a blazar increases with increasing spin of a central black hole, we suggest that the spin plays a crucial role in making BL Lac sources low luminous and slow rotators compared to FSRQ sources.

Statistical Mechanical Entropy of a （4 ＋ n）-Dimensional Static Spherically Symmetric Black Hole

Considering corrections to all orders in the Planck length on the quantum state density from the generalized uncertainty principle and using the quantum state density to all degrees of freedom including extra dimensions, we calculate the statistical entropy of the scalar field in the higher-dimensional static spherically symmetric black hole spacetime without any artificial cutoff. Calculation shows that the entropy is proportional to the horizon area. The coefficient of proportionality is 1/4 when the minimal length parameter is selected appropriately.

On static and spherically symmetric solutions of Starobinsky model

We investigate the problem of static and spherically symmetric solutions in the Starobinsky gravity model.By extending the Lichnerowicz and Israel theorems, William Nelson has demonstrated that the Schwarzschild solution is the unique static, spherically symmetric and asymptotically flat black hole solution in the Starobinsky model.However, Hong Lüet al.find that there are sign errors in the proof of Nelson.This raises the problem of whether Nelson’s proof is correct or not.In order to answer this question, we explore the corresponding solutions by using the Taylor series expansion method.We find that Nelson’s conclusion is indeed correct despite the flaw in the proof.

Second post-Minkowskian order harmonic metric for a moving Kerr-Newman black hole

We apply the Lorentz boosting method to the Kerr-Newman metric in harmonic coordinates, and obtain the second post-Minkowskian order harmonic metric for a moving Kerr-Newman black hole with an arbitrary constant speed. This metric may be useful for investigating observable relativistic effects due to the motion of the moving source. As an application, the post-Newtonian equations of motion for a particle and a photon in the far field of this black hole are calculated.