Latest Papers in General Relativity

General Relativity And Quantum Cosmology

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The GstLAL Search Analysis Methods for Compact Binary Mergers in Advanced LIGO's Second and Advanced Virgo's First Observing Runs (1901.08580v1)

Surabhi Sachdev, Sarah Caudill, Heather Fong, Rico K. L. Lo, Cody Messick, Debnandini Mukherjee, Ryan Magee, Leo Tsukada, Kent Blackburn, Patrick Brady, Patrick Brockill, Kipp Cannon, Sydney J. Chamberlin, Deep Chatterjee, Jolien D. E. Creighton, Patrick Godwin, Anuradha Gupta, Chad Hanna, Shasvath Kapadia, Ryan N. Lang, Tjonnie G. F. Li, Duncan Meacher, Alexander Pace, Stephen Privitera, Laleh Sadeghian, Leslie Wade, Madeline Wade, Alan Weinstein, Sophia Liting Xiao

2019-01-24

After their successful first observing run (September 12, 2015 - January 12, 2016), the Advanced LIGO detectors were upgraded to increase their sensitivity for the second observing run (November 30, 2016 - August 26, 2017). The Advanced Virgo detector joined the second observing run on August 1, 2017. We discuss the updates that happened during this period in the GstLAL-based inspiral pipeline, which is used to detect gravitational waves from the coalescence of compact binaries both in low latency and an offline configuration. These updates include deployment of a zero-latency whitening filter to reduce the over-all latency of the pipeline by up to 32 seconds, incorporation of the Virgo data stream in the analysis, introduction of a single-detector search to analyze data from the periods when only one of the detectors is running, addition of new parameters to the likelihood ratio ranking statistic, increase in the parameter space of the search, and introduction of a template mass-dependent glitch-excision thresholding method.

On the Constraint Structure of Vacuum Energy Sequestering (1812.11625v2)

Andrew Svesko, George Zahariade

2018-12-30

We carry out the Hamiltonian analysis of the local vacuum energy sequestering model - a manifestly local and diffeomorphism invariant extension of general relativity which has been shown to remove the radiatively unstable contribution to the vacuum energy generated by matter loops. We find that the degravitation of this UV sensitive quantity is enforced via global relations that are a consequence of the model's peculiar constraint structure. We also show that the model propagates the proper number of degrees of freedom and thus locally reduces to general relativity on-shell.

Evidence for Modified Newtonian Dynamics from Cavendish-type gravitational constant experiments (1901.02604v2)

Norbert Klein

2019-01-09

Recent experimental results for the gravitational constant G from Cavendish-type experiments were analysed in the framework of MOND (Modified Newtonian Dynamics). The basic assumption for the analysis is that MOND corrections apply only to the component of the gravitational field which leads to an accelerated motion of the pendulum body according to Newtons second law. The analysis is based on numerical solutions of the MOND corrected differential equation for a linear pendulum at small acceleration magnitudes of the order of Milgroms fundamental acceleration parameter a_0 = 10^-10 m/s^2 for the case of a mixed gravitational and electromagnetic pendulum restoring force. The results from the pendulum simulations were employed to fit experimental data from recent Cavendish-type experiments with reported discrepancies between G values determined by different measurement methods for a similar experimental setup, namely time of swing, angular acceleration feedback, electrostatic servo and static deflection methods. The analysis revealed that the reported discrepancies can be explained by MOND corrections with one single fit parameter. In fact, the MOND corrected results from all Cavendish experiments published over the last decade were found to be consistent with a value of G = 6.6742 x 10^-11 m^3 kg^-1 s^-2 within a standard deviation of 14 ppm.

The post-Newtonian gravitomagnetic spin-octupole moment of an oblate rotating body and its effects on an orbiting test particle; are they measurable in the Solar System? (1810.09288v3)

Lorenzo Iorio

2018-10-22

We analytically work out the orbital effects induced by the gravitomagnetic spin-octupole moment of an extended spheroidal rotating body endowed with angular momentum and quadrupole mass moment . Our results, proportional to , hold for an arbitrary orientation of the body's symmetry axis and a generic orbital configuration of the test particle. Such effects may be measurable, in principle, with a dedicated spacecraft-based mission to Jupiter. For a moderately eccentric and fast path, the gravitomagnetic precessions of the node and the pericenter of a dedicated orbiter could be as large as or even depending on the orientation of its orbital plane in space. Numerical simulations of the Earth-probe range-rate signal confirm such expectations since its magnitude reaches the level after just 1 day. The precision of the current two-way Ka-band Doppler measurements of the spacecraft Juno, presently orbiting Jupiter, amounts to after seconds. Also other general relativistic effects could be measurable, including also those proportional to , never put to the test so far. Most of the competing Newtonian signals due to the classical multipoles of the planet's gravity field have quite different temporal signatures with respect to the post-Newtonian ones, making, thus, potentially easier disentangling them.

Cross-correlations between scalar perturbations and magnetic fields in bouncing universes (1807.05530v3)

Debika Chowdhury, L. Sriramkumar, Marc Kamionkowski

2018-07-15

Bouncing scenarios offer an alternative to the inflationary paradigm for the generation of perturbations in the early universe. Recently, there has been a surge in interest in examining the issue of primordial magnetogenesis in the context of bouncing universes. As in the case of inflation, the conformal invariance of the electromagnetic action needs to be broken in bouncing scenarios in order to generate primordial magnetic fields which correspond to observed strengths today. The non-minimal coupling, which typically depends on a scalar field that possibly drives the homogeneous background, leads to a cross-correlation at the level of the three-point function between the perturbation in the scalar field and the magnetic fields. This has been studied in some detail in the context of inflation and, specifically, it has been established that the three-point function satisfies the so-called consistency relation in the squeezed limit. In this work, we study the cross-correlation between the magnetic fields and the perturbation in an auxiliary scalar field in a certain class of bouncing scenarios. We consider couplings that lead to scale invariant spectra of the magnetic field and evaluate the corresponding cross-correlation between the magnetic field and the perturbation in the scalar field. We find that, when compared to de Sitter inflation, the dimensionless non-Gaussianity parameter that characterizes the amplitude of the cross-correlations proves to be considerably larger in bouncing scenarios. We also show that the aforementioned consistency condition governing the cross-correlation is violated in the bouncing models. We discuss the implications of our results.

Signature of horizon dynamics in binary black hole gravitational waveforms (1901.08516v1)

Ssohrab Borhanian, K. G. Arun, Harald P. Pfeiffer, B. S. Sathyaprakash

2019-01-24

Gravitational waves from merging binary black holes carry the signature of the strong field dynamics of the newly forming common horizon. This signature presents itself in the amplitudes and phases of various spherical harmonic modes as deviations from the point particle description provided by post-Newtonian theory. Understanding the nature of these departures will aid in (a) formulating better models of the emitted waveforms in the strong field regime of the dynamics, and (b) relating the waveforms observed at infinity to the common horizon dynamics. In this work we have used a combination of numerical relativity simulations and post-Newtonian theory to search for the modes of radiation whose amplitude is most affected by the strong field phase of the evolution. These modes are identified to carry the signature of the strong field regime due to significant deviations of the numerical data from the leading order post-Newtonian predictions. We find that modes with large amplitudes or with spherical harmonic indices are least modified from their dominant post-Newtonian behavior, while the weaker modes are modified to the greatest extent. The addition of spins to the binary components only affects the current-multipole modes with at the order of interest and does seem to stabilize some of these modes, the mode being the exception. This mode is the most promising candidate to observe the signature of strong field dynamics as it shows the deviations from post-Newtonian behavior equally for binaries with non-spinning and aligned spinning black holes.

Proposal for an Optical Test of the Einstein Equivalence Principle (1811.04835v2)

Daniel R. Terno, Francesco Vedovato, Matteo Schiavon, Alexander R. H. Smith, Piergiovanni Magnani, Giuseppe Vallone, Paolo Villoresi

2018-11-12

The Einstein Equivalence Principle (EEP) underpins all metric theories of gravity. Its key element is the local position invariance of non-gravitational experiments, which entails the gravitational red-shift. Precision measurements of the gravitational red-shift tightly bound violations of the EEP only in the fermionic sector of the Standard Model, however recent developments of satellite optical technologies allow for its investigation in the electromagnetic sector. Proposals exploiting light interferometry traditionally suffer from the first-order Doppler effect, which dominates the weak gravitational signal necessary to test the EEP, making them unfeasible. Here, we propose a novel scheme to test the EEP, which is based on a double large-distance optical interferometric measurement. By manipulating the phase-shifts detected at two locations at different gravitational potentials it is possible to cancel-out the first-order Doppler effect and observe the gravitational red-shift implied by the EEP. We present the detailed analysis of the proposal within the post-Newtonian framework and the simulations of the expected signals obtained by using two realistic satellite orbits. Our proposal to overcome the first-order Doppler effect in optical EEP tests is feasible with current technology.

Quantum and classical effects in a light-clock falling in Schwarzschild geometry (1901.08000v2)

Maximilian P. E. Lock, Ivette Fuentes

2019-01-23

Quantum theory and relativity offer different conceptions of time. To explore the conflict between them, we study a quantum version of the light-clock commonly used to illustrate relativistic time dilation. This semiclassical model combines elements of both theories. We show for Gaussian states of the light field that the clock times are independent of the initial state. We calculate the discrepancy between two such clocks when one is held in a gravitational field and the other is left to fall a certain distance. Contrasting our results with the case of pointlike observers in general relativity, as well as classical light-clocks, we find both quantitative and qualitative differences. We find that the quantum contribution to the discrepancy between the two clocks increases with the gravitational field strength, and results in a minimum resolution of the dropped clock (distinct from the quantum uncertainty in its measurement).

Quantum cosmology of a Hořava-Lifshitz model coupled to radiation (1901.04640v2)

G. Oliveira-Neto, L. G. Martins, G. A. Monerat, E. V. Corrêa Silva

2019-01-15

In the present paper, we canonically quantize an homogeneous and isotropic Ho\v{r}ava-Lifshitz cosmological model, with constant positive spatial sections and coupled to radiation. We consider the projectable version of that gravitational theory without the detailed balance condition. We use the ADM formalism to write the gravitational hamiltonian of the model and the Schutz variational formalism to write the perfect fluid hamiltonian. We find the Wheeler-DeWitt equation for the model. That equation depends on several parameters. We study the case where the values of the parameters are chosen, such that, the solutions to the Wheeler-DeWitt equation are bounded. Initially, we solve it using the {\it Many Worlds} interpretation. Using wavepackets computed with the solutions to the Wheeler-DeWitt equation, we obtain the scalar factor expected value . We show that this quantity oscillate between maxima and minima values and never go to zero. That result gives an indication that the model is free from singularities, at the quantum level. We improve this result by showing that if we subtract a standard deviation of from , this quantity is still positive. Then, we use the {\it DeBroglie-Bohm} interpretation. We compute the Bohm's trajectories for the scale factor and show that it never goes to zero. We show that each trajectory agrees with the corresponding . We also compute the quantum potential. That quantity helps understanding why the scale factor never vanishes.

A moment approach to compute quantum-gravity effects in the primordial universe (1901.08391v1)

David Brizuela, Unai Muniain

2019-01-24

An approach to compute quantum-gravity corrections to the scalar and tensorial power spectra of the inflationary perturbations is presented. The analysis of the Wheeler-DeWitt equation is performed by a decomposition of the wave function into its infinite set of moments, which must obey certain system of (first-class) constraints. Considering a semiclassical approximation, the system is truncated at second order in moments and an appropriate gauge-fixing condition is introduced, which allows us to interpret the scale factor of the universe as an internal time. The evolution of the different fluctuations and correlations is then explicitly considered for a de Sitter universe. An approximate analytical solution is obtained for the corrections of the power spectra, which produces an enhancement of power for large scales. Remarkably, the result is in agreement with previous studies in the literature that made use of very different semiclassical approximations. Finally, the numerical implementation of the system is also considered to verify the validity of the analytical solution.

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