On the Gravitomagnetic Time Delay

We study the gravitational time delay in ray propagation due to rotating masses in the linear approximation of general relativity. Simple expressions are given for the gravitomagnetic time delay that occurs when rays of radiation cross a slowly rotating shell and propagate in the field of a distant rotating source. Moreover, we calculate the local gravitational time delay in the Goedel universe. The observational consequences of these results in the case of weak gravitational lensing are discussed.Comment: 15 pages, 1 figure, revised version submitted to Phys. Lett.

Quantum Zeno effect and the detection of gravitomagnetism

In this work we introduce two experimental proposals that could shed some light upon the inertial properties of intrinsic spin. In particular we will analyze the role that the gravitomagnetic field of the Earth could have on a quantum system with spin 1/2. We will deduce the expression for Rabi transitions, which depend, explicitly, on the coupling between the spin of the quantum system and the gravitomagnetic field of the Earth. Afterwards, the continuous measurement of the energy of the spin 1/2 system is considered, and an expression for the emerging quantum Zeno effect is obtained. Thus, it will be proved that gravitomagnetism, in connection with spin 1/2 systems, could induce not only Rabi transitions but also a quantum Zeno effect.Comment: Essay awarded with an ``honorable mention'' in the Annual Essay Competition of the Gravity Research Foundation for the year 2000, four new references, discussion enlarged, 9 pages. Accepted in International Journal of Modern Physics

On the Earth's tidal perturbations for the LARES satellite

Frame dragging, one of the outstanding phenomena predicted by General Relativity, is efficiently studied by means of the laser-ranged satellites LARES, LAGEOS and LAGEOS 2. The accurate analysis of the orbital perturbations of Earth's solid and ocean tides has been relevant for increasing the accuracy in the test of frame-dragging using these three satellites. The Earth's tidal perturbations acting on the LARES satellite are obtained for the 110 significant modes of corresponding Doodson number and are exhibited to enable the comparison to those of the LAGEOS and LAGEOS-2 satellites. For LARES we represent 29 perturbation modes for l=2,3,4 for ocean tides.Comment: 14 pages, 9 figures, to appear in Eur Phys J Plus (subm. Sept 20, 2017

Focus Point on Tests of General Relativity and Alternative Gravity Theories

Testing of fundamental physical theories at ever higher accuracy is a continuous process and hence General Rela-tivity and the development of alternative gravity theories have always been among the interests of experimentalists,astronomers and theoreticians. The empirical basis of General Relativity is linked to an immense scope of areas, fromthe equivalence principle up to, say, the variation of the gravitational constant and of other physical constants.In 1960s the General Relativity was transferred from abstract mathematical construction to a driving force in anew area of research –relativistic astrophysics— dealing with a sequence of impressive observational discoveries, suchas quasars, cosmic microwave background radiation, pulsars, compact binary stars, etc. Practically at the same time,the development of rockets and space technologies provided means for new types of tests of General Relativity, suchas Lunar laser ranging and signal time delays. Let us recall a remark attributed to Einstein at the end of a discussionwith Thirring in 1918 in regard to a test of frame-dragging:What a pity the earth has no moon in an orbit just outsideits atmosphere!Currently, laser-ranged satellites are among the important tools for testing tiny predictions of GeneralRelativity, such as frame-dragging. Some alternative gravitational theories agree with all the current tests of GeneralRelativity but predict different results for frame-dragging.A new phase of studies on extensions of General Relativity and alternative gravity theories started with thediscovery of the dark sector –dark energy and dark matter— as of dominating content of the Universe. Cosmology,therefore, became an area of broad applications of alternative gravity theories. Informative constraints on gravitytheories are also obtained monitoring S2 and other stars in the vicinity of the massive black hole in the Galacticcenter. Thus, it is now hardly possible to mention cosmic structures, from the Solar system up to the dynamics ofgalaxies and clusters of galaxies, for which alternative gravity theories have not been probed.The discovery of gravitational waves, one hundred years after the formulation of General Relativity, further stim-ulated the consideration of alternative gravity theories. The particular importance of this new window is in that itenables to test the strong-field General Relativity,i.e.the effects close to the event horizon.Finally, testing the Equivalence Principle is a probe for gravitational theories at fundamental level and a main steptowards any quantum gravity theory.The papers included in thisFocus Pointnaturally cover a minor fraction of the above-mentioned areas; neverthelessthey contain timely accounts on broad topics, from tests on the Equivalence Principle, to orbital dynamics of extendedbodies in inspiraling binary systems, up to cosmology

Constraining spacetime torsion with LAGEOS

We compute the corrections to the orbital Lense-Thirring effect (or frame-dragging) in the presence of spacetime torsion. We derive the equations of motion of a test body in the gravitational field of a rotating axisymmetric massive body, using the parametrized framework of Mao, Tegmark, Guth and Cabi. We calculate the secular variations of the longitudes of the node and of the pericenter. We also show how the LAser GEOdynamics Satellites (LAGEOS) can be used to constrain torsion parameters. We report the experimental constraints obtained using both the nodes and perigee measurements of the orbital Lense-Thirring effect. This makes LAGEOS and Gravity Probe B (GPB) complementary frame-dragging and torsion experiments, since they constrain three different combinations of torsion parameters

LARES/WEBER-SAT and the equivalence principle

It has often been claimed that the proposed Earth artificial satellite LARES/WEBER-SAT-whose primary goal is, in fact, the measurement of the general relativistic Lense-Thirring effect at a some percent level-would allow to greatly improve, among (many) other things, the present-day (10^-13) level of accuracy in testing the equivalence principle as well. Recent claims point towards even two orders of magnitude better, i.e. 10^-15. In this note we show that such a goal is, in fact, unattainable by many orders of magnitude being, instead, the achievable level of the order of 10^-9.Comment: LaTex, 4 pages, no figures, no tables, 26 references. Proofs corrections included. To appear in EPL (Europhysics Letters

Testing gravity at the Second post-Newtonian level through gravitational deflection of massive particles

Expression for second post-Newtonian level gravitational deflection angle of massive particles is obtained in a model independent framework. Several of its important implications including the possibility of testing gravitational theories at that level are discussed.Comment: 5 pages, couple of equations of the previous version are correcte

Gravitomagnetism in the Kerr-Newman-Taub-NUT spacetime

We study the motion of test particles and electromagnetic waves in the Kerr-Newman-Taub-NUT spacetime in order to elucidate some of the effects associated with the gravitomagnetic monopole moment of the source. In particular, we determine in the linear approximation the contribution of this monopole to the gravitational time delay and the rotation of the plane of the polarization of electromagnetic waves. Moreover, we consider "spherical" orbits of uncharged test particles in the Kerr-Taub-NUT spacetime and discuss the modification of the Wilkins orbits due to the presence of the gravitomagnetic monopole.Comment: 12 pages LaTeX iopart style, uses PicTex for 1 Figur

10-Ethynyl-2,3,6,6a,9,10-hexa­hydro-1H-6,9-methano­pyrrolo[2,1-i][2,1]benzo­thia­zol-10-ol 5,5-dioxide

In the title compound, C13H15NO3S, the sole classical hydrogen-bond donor is involved in an intra­molecular O—H⋯N hydrogen bond. In the crystal structure, pairs of mol­ecules related by inversion centres are linked by pairs of weak inter­molecular C—H⋯O inter­actions; these centrosymmetric pairs are, in turn, linked further by weak inter­molecular C—H⋯O inter­actions, forming two-dimensional sheets oriented parallel to (101)

Geodetic precession and strong gravitational lensing in the dynamical Chern-Simons modified gravity

We have investigated the geodetic precession and the strong gravitational lensing in the slowly-rotating black hole in the dynamical Chern-Simons modified gravity theory. We present the formulas of the orbital period $T$ and the geodetic precession angle $\Delta\Theta$ for the timelike particles in the circular orbits around the black hole, which shows that the change of the geodetic precession angle with the Chern-Simons coupling parameter $\xi$ is converse to the change of the orbital period with $\xi$ for fixed $a$. We also discuss the effects of the Chern-Simons coupling parameter on the strong gravitational lensing when the light rays pass close to the black hole and obtain that for the stronger Chern-Simons coupling the prograde photons may be captured more easily, and conversely, the retrograde photons is harder to be captured in the slowly-rotating black hole in the dynamical Chern-Simons modified gravity. Supposing that the gravitational field of the supermassive central object of the Galaxy can be described by this metric, we estimated the numerical values of the main observables for gravitational lensing in the strong field limit.Comment: 19 pages, 5 figures, more clarifications and references added, accepted for publication in Classical and Quantum Gravit