Dynamical mechanism for varying light velocity as a solution to cosmological problems

A dynamical model for varying light velocity in cosmology is developed, based on the idea that there are two metrics in spacetime. One metric g_μν describes the standard gravitational vacuum, and the other describes the geometry through which matter fields propagate. Matter propagating causally with respect to can provide acausal contributions to the matter stress-energy tensor in the field equations for g_μν, which, as we explicitly demonstrate with perfect fluid and scalar field matter models, provides a mechanism for the solution of the horizon, flatness and magnetic monopole problems in an FRW universe. The field equations also provide a ‘graceful exit' to the inflationary epoch since below an energy scale (related to the mass of ψ_μ) we recover exactly the standard FRW field equations.     

Newman-Penrose Formalism and Gravitational Impulsive and Shock Waves

Vacuum spacetimes endowed with two commuting spacelike Killing vector fields are considered. Subject to the hypothesis that there exists a shearfree null geodesic congruence orthogonal to the two-surface generated by the two commuting spacelike Killing vector fields,it is shown that, with a specific choice of null tetrad, the Newman-Penrose equations are reduced to an ordinary differential equation of Riccati type. fiom the consideration of this differential equation, exact solutions of the vacuum Einstein field equations with distribution valued Weyl curvature describing the propagation of gravitational impulsive and shock wave of variable polarization are then constructed.     

193T1超形变带K=1/2的可能性

分析了脱耦合项对于原子核转动惯量的重要影响.总结了奇质量核K=1/2带转动惯量变化规律的新特点.在此基础上讨论了¹⁹³T1中3条新的超形变带的内部结构.目前尚无足够证据能够确认它们都是K=1/2带.     

Different approaches to the study of the gravitational radiation emitted by astrophysical sources

Stars and black holes are sources of gravitational radiation in many phases of their life, and the signals they emit exhibit features that are characteristic of the generating process. Emitted since the beginning of star formation, these signals also contribute to create a stochastic background of gravitational waves. We shall show how the spectral properties of this background can be estimated in terms of the energy spectrum of each single event and of the star formation rate history, which is now deducible from astronomical observations. We shall further discuss the process of scattering of masses by stars and black holes, showing that, unlike black holes, stars emit signals that carry a clear signature of the nature of the source.     

Gravitational Deflection of Massive Particles by a Schwarzschild Black Hole in Radiation Gauge*

The exact metric of a Schwarzschild black hole in the true radiation gauge was recently reported.In this work, we base on this gravity and calculate the gravitational deflection of relativistic massive particles up to the fourth post-Minkowskian order. It is found that the result is consistent with the previous formulations for both the case of dropping the fourth-order contribution and the case of light deflection. Our result might be helpful for future high-accuracy observations.     

The delay time of gravitational wave – gamma-ray burst associations

The first gravitational wave (GW) – gamma-ray burst (GRB) association, GW170817/GRB 170817A, had an offset in time, with the GRB trigger time delayed by ~1.7 s with respect to the merger time of the GW signal. We generally discuss the astrophysical origin of the delay time, Δt, of GW-GRB associations within the context of compact binary coalescence (CBC) – short GRB (sGRB) associations and GW burst – long GRB (lGRB) associations. In general, the delay time should include three terms, the time to launch a clean (relativistic) jet, Δt_jet; the time for the jet to break out from the surrounding medium, Δt_bo; and the time for the jet to reach the energy dissipation and GRB emission site, Δt_GRB. For CBC-sGRB associations, Δtjet and Δt_bo are correlated, and the final delay can be from 10 ms to a few seconds. For GWB-lGRB associations, Δt_jet and Δt_bo are independent. The latter is at least ~10 s, so that Δt of these associations is at least this long. For certain jet launching mechanisms of lGRBs, Δt can be minutes or even hours long due to the extended engine waiting time to launch a jet. We discuss the cases of GW170817/GRB 170817A and GW150914/GW150914-GBM within this theoretical framework and suggest that the delay times of future GW/GRB associations will shed light into the jet launching mechanisms of GRBs.     

OJ287: Post-Newtonian Calculation in Harmonic Coordinate and Pulsar Timing Residual Confirmation

We calculate and discuss the motion of the binary black hole OJ287 based on Post-Newtonian approximation in a harmonic coordinate. With gravitational waveform obtained, theoretical timing residual of PSR B1855+09 induced by gravitational radiation of OJ287 is presented and compared with observed data, further shows that hypothesis referring to OJ287 as a binary BH system might be proper. The energy flux of gravitational radiation from binary is also provided, from which we find that the flux changes sign successively: ?_N >0, ?_1PN <0, ?_2PN >0, in agreement with the relative signs of forces of each PN order, revealed in the previous work.     

Models of G time variations in diverse dimensions

A review of different cosmological models in diverse dimensions leading to a relatively small time variation in the effective gravitational constant G is presented. Among them: the 4-dimensional (4-D) general scalar-tensor model, the multidimensional vacuum model with two curved Einstein spaces, the multidimensional model with the multicomponent anisotropic “perfect fluid”, the S-brane model with scalar fields and two form fields, etc. It is shown that there exist different possible ways of explaining relatively small time variations of the effective gravitational constant G compatible with present cosmological data (e.g. acceleration): 4-dimensional scalar-tensor theories or multidimensional cosmological models with different matter sources. The experimental bounds on Ġ may be satisfied either in some restricted interval or for all allowed values of the synchronous time variable.      

High-resolution solid-state NMR of anisotropically mobile molecules under very low-power H decoupling and moderate magic-angle spinning

We show that for observing high-resolution heteronuclear NMR spectra of anisotropically mobile systems with order parameters less than 0.25, moderate magic-angle spinning (MAS) rates of 11 kHz combined with ¹H decoupling at 1–2 kHz are sufficient. Broadband decoupling at this low ¹H nutation frequency is achieved by composite pulse sequences such as WALTZ-16. We demonstrate this moderate MAS low-power decoupling technique on hydrated POPC lipid membranes, and show that 1 kHz ¹H decoupling yields spectra with the same resolution and sensitivity as spectra measured under 50 kHz ¹H decoupling when the same acquisition times (50 ms) are used, but the low-power decoupled spectra give higher resolution and sensitivity when longer acquisition times (>150 ms) are used, which are not possible with high-power decoupling. The limits of validity of this approach are explored for a range of spinning rates and molecular mobilities using more rigid membrane systems such as POPC/cholesterol mixed bilayers. Finally, we show ¹⁵N and ¹³C spectra of a uniaxially diffusing membrane peptide assembly, the influenza A M2 transmembrane domain, under 11 kHz MAS and 2 kHz ¹H decoupling. The peptide ¹⁵N and ¹³C intensities at low-power decoupling are 70–80% of the high-power decoupled intensities. Therefore, it is possible to study anisotropically mobile lipids and membrane peptides using liquid-state NMR equipment, relatively large rotors, and moderate MAS frequencies.