Probing a stationary non-Gaussian background of stochastic gravitational waves with pulsar timing arrays

Abstract

We introduce the concept of stationary graviton non-Gaussianity (nG), an observable that can be probed in terms of 3-point correlation functions of a stochastic gravitational wave (GW) background. When evaluated in momentum space, stationary nG corresponds to folded bispectra of graviton nG. We determine 3-point overlap functions for testing stationary nG with pulsar timing array GW experiments, and we obtain the corresponding optimal signal-tonoise ratio. For the first time, we consider 3-point overlap functions including scalar graviton polarizations (which can be motivated in theories of modified gravity); moreover, we also calculate 3-point overlap functions for correlating pulsar timing array with ground based GW detectors. The value of the optimal signal-to-noise ratio depends on the number and position of monitored pulsars. We build geometrical quantities characterizing how such ratio depends on the pulsar system under consideration, and we evaluate these geometrical parameters using data from the IPTA collaboration. We quantitatively show how monitoring a large number of pulsars can increase the signal-to-noise ratio associated with measurements of stationary graviton nG. arXiv:1910.04758v1 [gr-qc]

Characterizing the cosmological gravitational wave background: Anisotropies and non-Gaussianity

“…The characterization of the non-Gaussian properties of the SGWB is a potential tool to discriminate whether a SGWB has a primordial or astrophysical origin. The primoridal 3-point function of the GW field, hh 3 i, is unobservable, due to the decoherence of the associated phase (because of the propagation, and the finite duration of the measurement [23,24]), with, possibly, the exception of very specific shapes [30,39]. It is more convenient to consider the non-Gaussianity associated with the GW energy density angular distribution, which is not affected by this problem [25].…”

“…In light of this fact, a measurement of non-Gaussianity would be a signal of large scale coherency, that would likely point to a cosmological origin of the signal. Previous works showed that inflation can result in a sizeable and nonvanishing 3-point function hh 3 i for the graviton wave function, but that this is generically nonobservable in interferometers [23,24], due to the decoherence of the phase the GW wave-function h induced by the GW propagation, and due to the finite duration of the measurement (see [30] for a possible exception to this conclusion, occurring for a very specific shape of the bispectrum). Since the phase does not affect the GW energy density, we argue that the energy density is a much better variable to study the statistics of the SGWB.…”

Pulsar Based Alternative Timing Source for Grid Synchronization and Operation

“…In the case of measuring pulsar X-ray emission, NASA's Station Explorer for X-ray Timing and Navigation Technology (SEXTANT) mission, involved demonstrating real-time on-board X-ray Pulsar Navigation [7]. In astrophysics, a Pulsar Timing Array (PTA) was designed to detect and analyze variations in the arrival times of pulsar generated signals which may be caused by gravitational waves [8]- [10].…”

Modern Topics in Scalar Field Cosmology

“…6 An example of a slow-roll potential. Acceleration occurs when the potential energy of the field, V (φ), dominates over the kinetic energy term 1 2φ 2 . Inflation ends at φ end when the kinetic energy increases to be approximately equal to the potential term, 1 2φ 2 ≈ V .…”

“…4. 2 The structure of the 3-point function in eq (4.2.14) requires that the three GWs entering in the correlator originate from a common directionn in the sky. In the graphical representation above, we show with the red spot the common region of emission of three GWs (which can be of cosmological origin); with the blue blob the region containing GW detectors (which can be of astrophysical size, as in the case of PTA experiments).…”