Gravitational waves are tiny perturbations in space-time that propagate at the speed of light. Their direct detection in 2015 by Advanced LIGO has started a new era of astronomy and it is assumed that there are sufficient sources to incoherently sum to an all pervasive background which can be studied statistically.
These waves have many properties that are analogous to photons – especially in terms of their polarisation. Both types of wave have two polarisations: “plus” and “cross” for gravitational waves and “vertical” and “horizontal” for photons. However, these are coordinate system dependent and so analysis of photon polarisation backgrounds (such as measurements of the CMB) is done in terms of coordinate independent “E” and “B” modes. In an almost mathematically identical way, a gravitational wave background can be considered in terms of similar modes.
In this talk I will discuss the relative sensitivity of the proposed (e)LISA satellite to these modes and what can be learned about the backgrounds. For example, a pure stochastic background would lead to statistically identical E and B power spectra so a significant difference between the relative strengths of the two modes would imply there is something more complicated about the background, such as a preferred direction.