Scalar Modes Of Gravitational Waves Research Articles

Condition for directly testing scalar modes of gravitational waves by four detectors

General metric theories in a four-dimensional spacetime allow at most six polarization states (two spin-0, two spin-1, and two spin-2) of gravitational waves (GWs). If a sky location of a GW source with the electromagnetic counterpart satisfies a single equation that we propose in this paper, both the spin-1 modes and spin-2 ones can be eliminated from a certain combination of strain outputs at four ground-based GW interferometers (e.g., a network of aLIGO-Hanford, aLIGO-Livingston, Virgo, and KAGRA), where this equation describes curves on the celestial sphere. This means that, if a GW source is found in the curve (or its neighborhood practically), a direct test of scalar (spin-0) modes separately from the other (vector and tensor) modes becomes possible in principle. The possibility of such a direct test is thus higher than an earlier expectation (Hagihara et al., Phys. Rev. D 100, 064010 (2019)), in which they argued that the vector modes could not be completely eliminated. We discuss also that adding the planned LIGO-India detector as a fifth detector will increase the feasibility of scalar polarization tests.

Gravitational waves in F(R) gravity: Scalar waves and the chameleon mechanism

We discuss the scalar mode of gravitational waves emerging in the context of $F(R)$ gravity by taking into account the chameleon mechanism. Assuming a toy model with a specific matter distribution to reproduce the environment of detection experiment by a ground-based gravitational wave observatory, we find that chameleon mechanism remarkably suppresses the scalar wave in the atmosphere of Earth, compared with the tensor modes of the gravitational waves. We also discuss the possibility to detect and constrain scalar waves by the current gravitational observatories and advocate a necessity of the future space-based observations.

Singularity Phenomena in Viable f(R) Gravity

The curvature singularity in viable f(R) gravity models is examined when the background density is dense. This singularity could be eliminated by adding the $R^{2}$ term in the Lagrangian. Some of cosmological consequences, in particular the source for the scalar mode of gravitational waves, are discussed.

Stochastic Background of Relic Scalar Gravitational Waves tuned by Extended Gravity

A stochastic background of relic gravitational waves is achieved by the so called adiabatically-amplified zero-point fluctuations process derived from early inflation. It provides a distinctive spectrum of relic gravitational waves. In the framework of scalar-tensor gravity, we discuss the scalar modes of gravitational waves and the primordial production of this scalar component which is generated beside tensorial one. Then we analyze different viable $f(R)$-gravities towards the Solar System tests and stochastic gravitational waves background. The aim is to achive experimental bounds for the theory at local and cosmological scales in order to select models capable of addressing the accelerating cosmological expansion without cosmological constant but evading the weak field constraints. It is demonstrated that viable $f(R)$-gravities under consideration not only satisfy the local tests, but additionally, pass the PPN-and stochastic gravitational waves bounds for large classes of parameters.

STOCHASTIC BACKGROUND OF RELIC SCALAR GRAVITATIONAL WAVES FROM SCALAR–TENSOR GRAVITY

A stochastic background of relic gravitational waves is achieved by the so-called adiabatically-amplified zero-point fluctuations process derived from early inflation. In principle, it provides a distinctive spectrum of relic gravitational waves. In the framework of scalar–tensor gravity, we discuss the scalar modes of gravitational waves and the primordial production of this scalar component which is generated besides tensorial one. We also discuss the upper limit for such a relic scalar component with respect to the WMAP constraints.

SCALAR GRAVITATIONAL WAVES FROM SCALAR-TENSOR GRAVITY: PRODUCTION AND RESPONSE OF INTERFEROMETERS

Scalar-tensor gravity admits the existence of scalar modes of gravitational waves (SGWs). The mechanism of production and the response of interferometers to these scalar components of gravitational waves can be studied in three different gauges in the massless case: the transverse-traceless (TT) gauge, the so-called "Shibata, Nakao and Nakamura" (SNN) gauge, and the local Lorentz gauge. The response of interferometers to massless SGWs is invariant in these different gauges. Our work generalizes previous results which, in the study of the coupling between interferometers and massless SGWs, started from the assumption that the wavelength of the SGW is much larger than the distance between the test masses. Furthermore, considering situations motivated by string-dilaton gravity, the effect of a small mass term on the response of the interferometer is taken into account. In this case (massive SGW), we have a longitudinal effect, the response of an arm of an interferometer, which is aligned in the wave propagation direction is computed. The value of the longitudinal response function for non-relativistic massive SGW at high frequencies is very high: this fact opens the doors to the interesting possibility of detection of "massive" part of the signal, if advanced projects will achieve high sensitivities. Finally, by using previous results and the geometry of the system, the generalized coupling between interferometers (like VIRGO or LIGO) and massless SGWs is studied. The total frequency response function to massless SGWs incoming from arbitrary directions is studied.

Response of interferometric detectors to scalar gravitational waves

We rigorously analyze the frequency response functions and antenna sensitivity patterns of three types of interferometric detectors to the scalar mode of gravitational waves which is predicted to exist in the scalar-tensor theory of gravity. By a straightforward treatment, we show that the antenna sensitivity pattern of the simple Michelson interferometric detector depends strongly on the wavelength ${\ensuremath{\lambda}}_{\mathrm{SGW}}$ of the scalar mode of the gravitational waves if ${\ensuremath{\lambda}}_{\mathrm{SGW}}$ is comparable to an arms length of the interferometric detector. For the Delay-Line and Fabry-Perot interferometric detectors with an arms length much shorter than ${\ensuremath{\lambda}}_{\mathrm{SGW}},$ however, the antenna sensitivity patterns depend weakly on ${\ensuremath{\lambda}}_{\mathrm{SGW}}$ even though ${\ensuremath{\lambda}}_{\mathrm{SGW}}$ is comparable to the effective path length of those interferometers. This agrees with the result obtained by Maggiore and Nicolis.