Monday

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 that 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 compare two potential formalisms – one using the “plus” and “cross” signals and the other using the gravitational wave Stokes’ parameters – and their strengths and weaknesses in decomposing various backgrounds, including primordial and astrophysical signals. I will also discuss the relative sensitivity of gravitational wave detectors – such as pulsar timing arrays and the proposed (e)LISA satellites – to these modes.