Testing Fundamental Physics with B-modes of Cosmic Microwave Background anisotropy

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The origins of the universe we live in and the early epochs of its existence has always fascinated people. With discovery and observations of the cosmic microwave background, it is now possible to take a "photograph" of the universe when it was about 400,000 years old. While the picture starts as a visible light, universe expansion cools the light down and it reaches us in the form of the microwaves at the present day. Physics processes in the early universe get imprinted in spatial fluctuations of the intensity and polarization of the cosmic microwave radiation. We see primordial gravitational potential fluctuations as intensity and "straight" patterns in polarization, while primordial gravitational waves would look like "curly" patterns. These are known as B-modes, and we have not seen them yet. The goal of my research is to work on their detection. You do not get to see just cosmic microwave background, as a lot of astrophysical sources in our galaxy are also bright in these frequencies. Two of them are highly polarized - the thermal dust that aligns itself with galactic magnetic field, and the synchrotron radiation produced by charged particles as they rotate around in the magnetic field. They are much brighter than the signal we are looking for, but they can be distinguished from the cosmic microwave background by the colour of light they emit. It is a bit like trying to make out a Milky Way on a clear night in a city, being blinded by coloured lights all around you, except now it is the Milky Way that blinds us. It appears to be possible to characterize the dust and synchrotron polarization, and to try to remove it from the picture. Dust grains align themselves to magnetic field like countless compass needles, and it is possible to reconstruct the direction of the magnetic field in our galaxy from polarization of light they produce. This gives a smooth polarization fraction pattern on the sky sourced by large-scale magnetic field features around us, and once that is subtracted the remainder is quite random, and can be dealt with as the usual noise. Polarization fraction pattern of synchrotron traces similar features, but the physics is more complex, so it needs further investigation. I propose to study these two astrophysical foregrounds, and develop new methods to remove them using the knowledge we gained. With Simons Observatory being build, and proposed CMB-S4 we will have a very low noise picture of the microwave sky, and the ability to see primordial cosmic microwave background will depend on how well we could subtract the foregrounds. As a member of both collaborations, I work with my colleagues on modelling and data analysis. If we see primordial gravitational waves, it would be a big step forward in understanding the early universe, and fundamental physics driving it. It could be a "smoking gun" confirmation of inflation at high energy scales, or it could push the scale of inflation low, as string theory models tend to prefer.