Circular polarisation of gamma rays as a probe of DM-cosmic ray electron interactions

Dark Matter (DM) constitutes most of the matter in the presently accepted
cosmological model for our Universe. However, despite the increased
sensitivity of direct and indirect DM searches, and the latest LHC run at 13
TeV centre of mass energy, no signal from DM particles has been detected so
far, leading to exclusion limits on the parameter space of DM models.
Conventional indirect searches look for an excess in the electromagnetic
emission from the sky that cannot be attributed to known astrophysical
sources, but polarisation is so far not being explored.

In this talk, I will argue that the photon polarisation is an important
feature to understand new physics interactions. In particular, circular
polarisation can be generated from Beyond the Standard Model (BSM)
interactions if they violate parity and there is an asymmetry in the number
of particles which participate in the interaction. I will consider a
simplified model for fermionic (Majorana) DM and study the circularly
polarised gamma rays below 10 GeV from DM cosmic ray electron interactions.
I will study the differential flux of positive and negative polarised
photons from the Galactic Centre and show that the degree of circular
polarization can reach up to 90%. Finally, I will discuss the detection
prospects of this signal in future experiments.