First Search for Nontensorial Gravitational Waves from Known Pulsars

Abstract

We present results from the first directed search for nontensorial gravitational waves. While general relativity allows for tensorial (plus and cross) modes only, a generic metric theory may, in principle, predict waves with up to six different polarizations. This analysis is sensitive to continuous signals of scalar, vector, or tensor polarizations, and does not rely on any specific theory of gravity. After searching data from the first observation run of the advanced LIGO detectors for signals at twice the rotational frequency of 200 known pulsars, we find no evidence of gravitational waves of any polarization. We report the first upper limits for scalar and vector strains, finding values comparable in magnitude to previously published limits for tensor strain. Our results may be translated into constraints on specific alternative theories of gravity.

The Polarizations of Gravitational Waves

“…In fact, GW170814 was the first GW event to test the polarization content of GWs. The analysis revealed that the pure tensor polarizations are favored against pure vector and pure scalar polarizations [4,15]. With the advent of more advanced detectors, there exists a better chance to pin down the polarization content and thus, the nature of gravity in the near future.…”

Constraining extra gravitational wave polarizations with Advanced LIGO, Advanced Virgo, and KAGRA and upper bounds from GW170817

“…Figure 1 shows the sky map, which is the contour map for the coefficients of the scalar modes in the null streams by Eqs. (9) and (10). At some positions in the contour map, one can recognize an octapolar behavior of some curves.…”

“…Therefore, let us examine how often the simultaneous suppression of the four vector coefficients in Eqs. (9) and (10) can occur.…”

“…Therefore, an upper bound on the vector GWs can be placed as |h V + h W | < 6 ×10 −23 , where we use an approximation as P a F V a ∼ P a F W a ∼ 1/3 in Eq. (9). If the GW detector network including KAGRA observes a GW170817-like event with an EM counterpart in the future, the use of two null streams will be able to put a tighter constraint on the vector modes separately.…”

“…Therefore, many attempts for GW polarization tests by using not only bursts, pulsars, compact binary coalescences, but also stochastic sources have been discussed (e.g. [6][7][8][9][10][11][12]).…”