The LIGO Scientific Collaboration publications and further tests of GR:

[beecee]

https://www.lsc-group.phys.uwm.edu/ppcomm/Papers.html

Tests of general relativity with the binary black hole signals from the LIGO-Virgo catalog GWTC-1

Summary:

Mar 11, 2019

https://www.ligo.org/science/Publication-O2TGR/index.php

 

SUMMARY

All of the tests performed here have shown that the black hole mergers observed by Advanced LIGO and Virgo are compatible with the predictions of General Relativity. Furthermore, by combining information from the most confident black hole mergers observed to date, we have improved our previous constraints on possible deviations from General Relativity by factors up to 2.4. The future will bring many more observations of black hole binaries, providing even more information on these measurements. Furthermore, we are developing a variety of new ways of testing General Relativity with these signals. We will continue testing Einstein's theory!

the paper:

https://arxiv.org/pdf/1903.04467.pdf

11 Mar 2019

Tests of General Relativity with the Binary Black Hole Signals from the LIGO-Virgo Catalog GWTC-1

The LIGO Scientific Collaboration and the Virgo Collaboration The detection of gravitational waves by Advanced LIGO and Advanced Virgo provides an opportunity to test general relativity in a regime that is inaccessible to traditional astronomical observations and laboratory tests. We present four tests of the consistency of the data with binary black hole gravitational waveforms predicted by general relativity. One test subtracts the best-fit waveform from the data and checks the consistency of the residual with detector noise. The second test checks the consistency of the low- and high-frequency parts of the observed signals. The third test checks that phenomenological deviations introduced in the waveform model (including in the post-Newtonian coefficients) are consistent with zero. The fourth test constrains modifications to the propagation of gravitational waves due to a modified dispersion relation, including that from a massive graviton. We present results both for individual events and also results obtained by combining together particularly strong events from the first and second observing runs of Advanced LIGO and Advanced Virgo, as collected in the catalog GWTC-1. We do not find any inconsistency of the data with the predictions of general relativity and improve our previously presented combined constraints by factors of 1.1 to 2.4. In particular, we bound the mass of the graviton to be mg ≤ 5.0 × 10−23 eV/c 2 (90% credible level), an improvement of a factor of 1.5 over our previously presented results. Additionally, we check that the four gravitational-wave events published for the first time in GWTC-1 do not lead to stronger constraints on alternative polarizations than those published previously.

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A search for the isotropic stochastic background with Advanced LIGO's second observing run

Mar 7, 2019

Summary:

https://www.ligo.org/science/Publication-O2StochIso/index.php

SEARCHING FOR A GRAVITATIONAL WAVE BACKGROUND DURING ADVANCED LIGO'S SECOND OBSERVING RUN:

The search for the isotropic stochastic gravitational wave background during Advanced LIGO's second run (November 2016 - August 2017) did not reveal any evidence of the background. However, thanks to the increase in sensitivity of the detector due to hardware and software upgrades, new upper limits were placed on the energy density of the background. This showed an increase in sensitivity by a factor of about 3 relative to the first observing run with Advanced LIGO. In addition to the improved upper limits on the stochastic background, we were also able to place new limits on the string tension of Nambu-Goto cosmic strings and to test the polarization content in the SGWB. Since General Relativity (GR) says that gravitational waves should have one specific type of polarization mode (called tensor modes), we can test the data to find the 'likelihood' that Nature also produces vector and scalar modes of gravitational wave signals. The presence of these other modes would suggest physics beyond GR. Although we cannot test Einstein's theory directly until the SGWB has been detected, we can place constraints on the presence of a background with any kind of polarization modes. The current results are consistent with predictions from General Relativity.

the paper:

https://arxiv.org/pdf/1903.02886.pdf

A search for the isotropic stochastic background using data from Advanced LIGO’s second observing run:

The LIGO Scientific Collaboration and The Virgo Collaboration:

The stochastic gravitational-wave background is a superposition of sources that are either too weak or too numerous to detect individually. In this study we present the results from a crosscorrelation analysis on data from Advanced LIGO’s second observing run (O2), which we combine with the results of the first observing run (O1). We do not find evidence for a stochastic background, so we place upper limits on the normalized energy density in gravitational waves at the 95% credible level of ΩGW < 6.0 × 10−8 for a frequency-independent (flat) background and ΩGW < 4.8 × 10−8 at 25 Hz for a background of compact binary coalescences. The upper limit improves over the O1 result by a factor of 2.8. Additionally, we place upper limits on the energy density in an isotropic background of scalar- and vector-polarized gravitational waves, and we discuss the implication of these results for models of compact binaries and cosmic string backgrounds. Finally, we present a conservative estimate of the correlated broadband noise due to the magnetic Schumann resonances in O2, based on magnetometer measurements at both the LIGO Hanford and LIGO Livingston observatories. We find that correlated noise is well below the O2 sensitivity.

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All-sky search for continuous gravitational waves from isolated neutron stars using Advanced LIGO O2 data

the paper:

https://arxiv.org/pdf/1903.01901.pdf

We present results of an all-sky search for continuous gravitational waves (CWs), which can be produced by fast spinning neutron stars with an asymmetry around their rotation axis, using data from the second observing run of the Advanced LIGO detectors. Three different semi-coherent methods are used to search in a gravitational-wave frequency band from 20 to 1922 Hz and a first frequency derivative from −1 × 10−8 to 2 × 10−9 Hz/s. None of these searches has found clear evidence for a CW signal, so upper limits on the gravitational-wave strain amplitude are calculated, which for this broad range in parameter space are the most sensitive ever achieved.

VI. CONCLUSIONS:

In this paper we have presented the first results of an all-sky search for CW signals using Advanced LIGO O2 data with three different pipelines, covering a frequency range from 20 to 1922 Hz and a first frequency derivative from −1 × 10−8 to 2 × 10−9 Hz/s. For this broad range in parameter space, this is the most sensitive search up to 1500 Hz. Each search found many outliers which were followed-up but none of them resulted in a credible astrophysical CW signal. On the contrary, they were ascribable to noise disturbances, to hardware injections, or consistent with noise fluctuations. Although no detections have been made, we have placed interesting 95% CL upper limits on the gravitational wave strain amplitude h0, the most sensitive being ' 1.7 × 10−25 in the 123-124 Hz region, as shown in Fig. 3. The improved results over the O1 search are due to the better sensitivity of the detectors, the use of a longer dataset and improvements of the pipelines. By converting the upper limits to an astrophysical reach, as shown in Fig. 4, we see that the searches presented in this paper provide already astrophysical interesting results. For instance, in the “bucket” region (around ' 150 Hz), we would be able to detect a CW signal from a neutron star within a distance of 100 pc if its ellipticity were at least 10−6 . Similarly, in the middle frequency range, around ' 500 Hz, we would be able to detect the CW signal up to a distance of 1 kpc, with > 10−6 . Finally at higher frequencies, around ' 1500 Hz, the same signal would be detectable up to a distance of 10 kpc if > 10−6 and 1 kpc if > 10−7 . Such levels of ellipticity are comparable or below the maximum value we may expect for neutron stars described by a standard equation of state [64]. Further all-sky analyses are planned on O2 data, by extending the parameter space and looking at sub-threshold candidates. The O3 observing run is foreseen to start in April 2019 and will last for approximately 1 year. The full network of LIGO and Virgo detectors is being upgraded and improved, and we expect that the noise floor in O3 run will be significantly better than for O2. This, and the foreseen longer run duration, will make future searches more sensitive, increasing the chances of a CW detection or allowing us to place tighter constraints on the non-asymmetries of neutron stars in our galaxy and to put constraints on the unseen neutron star population.

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The incredible science continues!