Astronomy Colloquium (2016 Fall Semester)

* Date

Sep. 1

* Speaker

Dong-Hoon Kim

* Title

Primordial Gravitational Waves and Rescattered Electromagnetic Radiation in the Cosmic Microwave Background

* Abstract

Understanding the interaction ofprimordial gravitational waves (GWs) with the Cosmic MicrowaveBackground (CMB) plasma is important for observational cosmology. I present aneffect apparently overlooked as yet. We consider a single free electric chargeand suppose that it can be agitated by primordial GWs propagating through theCMB plasma, resulting in periodic, regular motion along particular directions.Light reflected by the charge will be partially polarized, and this willimprint a characteristic pattern on the CMB. We study this effect byconsidering a simple model in which anisotropic incident electromagnetic (EM)radiation is rescattered by a charge sitting in spacetime perturbed by GWs andbecomes polarized. As the charge is driven to move along particular directions,we calculate its dipole moment to determine the leading-order rescattered EMradiation. The Stokes parameters of the rescattered radiation exhibit a netlinear polarization. We investigate how this polarization effect can beschematically represented out of the Stokes parameters. We work out therepresentations of gradient modes (E-modes) and curl modes (B-modes) to producepolarization maps.

Although the polarization effect resultsfrom GWs, we find that its representations, the E- and B-modes, do notpractically reflect the GW properties such as strain amplitude, frequency andpolarization states.