Search for Tensor, Vector, and Scalar Polarizations in the Stochastic Gravitational-Wave Background

Abstract

The detection of gravitational waves with Advanced LIGO and Advanced Virgo has enabled novel tests of general relativity, including direct study of the polarization of gravitational waves. While general relativity allows for only two tensor gravitational-wave polarizations, general metric theories can additionally predict two vector and two scalar polarizations. The polarization of gravitational waves is encoded in the spectral shape of the stochastic gravitational-wave background, formed by the superposition of cosmological and individually unresolved astrophysical sources. Using data recorded by Advanced LIGO during its first observing run, we search for a stochastic background of generically polarized gravitational waves. We find no evidence for a background of any polarization, and place the first direct bounds on the contributions of vector and scalar polarizations to the stochastic background. Under log-uniform priors for the energy in each polarization, we limit the energy densities of tensor, vector, and scalar modes at 95% credibility to Ω_{0}^{T}<5.58×10^{-8}, Ω_{0}^{V}<6.35×10^{-8}, and Ω_{0}^{S}<1.08×10^{-7} at a reference frequency f_{0}=25 Hz.

Effective field theory of black hole quasinormal modes in scalar-tensor theories

“…Another important constraint that scalar-tensor theories need to contend with is the lack of evidence for additional polarizations in the gravitational wave spectra observed so far [29,30]. This, however, should be mostly viewed as a constraint on the strength of their coupling to baryons rather than on their actual existence [31,32].…”

Exact amplitudes of six polarization modes for gravitational waves

“…This milestone in gravitational wave research opens a window to probe the highly dynamical and strong-field regimes of gravity [10,11]. In addition, the aLIGO and Virgo also allow the precision study of the polarization modes of the gravitational waves, particularly the bound of the non-tensorial modes [12,13]. The analysis for known galactic pulsars put the constraint on the strain of the scalar and vector modes to be below 1.5 × 10 −26 at 95% credibility [13], which is the first direct upper limit for a non-tensorial strain.…”

“…In addition, the aLIGO and Virgo also allow the precision study of the polarization modes of the gravitational waves, particularly the bound of the non-tensorial modes [12,13]. The analysis for known galactic pulsars put the constraint on the strain of the scalar and vector modes to be below 1.5 × 10 −26 at 95% credibility [13], which is the first direct upper limit for a non-tensorial strain. This upper bound provides a guideline to modify the beyond-GR theories of gravity.…”

Continuous gravitational waves and magnetic monopole signatures from single neutron stars

“…Recent observation of gravitational waves (GWs) by the LIGO-VIRGO collaboration [1,2] have ushered in a new era of multi-messenger astronomy. Apart from its significant astrophysical [3][4][5] and cosmological [6,7] implications, gravitational wave astronomy also has the potential to illuminate many important questions in fundamental physics [8][9][10][11][12]. A fast emerging area in this context is the endeavour to detect continuous GWs from single neutron stars.…”