Astrophysics

Observational cosmology, with particular focus on the formation and evolution of large scale structures in our universe like clusters of galaxies as large as 500 million light years. “Weighing” the universe, and mapping out the mysterious dark matter it contains.

String- and M-theory inspired scenarios for the cosmology of the early universe. Replacing the unphysical Big Bang-like beginning of our universe with bouncing scenarios of accelerated expansion followed by familiar evolution.

Physics beyond the standard model: theories of elementary particles with extra space dimensions (large, small, warped and flat); supersymmetry; grand unification; dark matter; inflation and dark energy; as well as relationships between the different subjects.

Cosmology as a natural meeting ground for fundamental theory (e.g. superstring theory or quantum gravity) and observations. Exploring how seeds laid down in the very early universe developed into the large scale structure we observe in the universe today.

The origin and evolution of the largest observable structures in the universe (much larger than entire galaxies); understanding why the expansion of the universe is accelerating. Observational techniques: cosmic microwave background, gravitational lensing and gravity waves.

What, exactly, happened around the time of the Big Bang? Exploring new models inspired by superstring theory and supergravity, e.g. ones in which we live on “branes” that collide with a “big bang”. Satellite experiments to test such models.

Cosmology and cosmological implications of quantum gravity. Observable effects in cosmology help to identify the limits of general relativity, which could potentially be surpassed by modified theories of gravity and/or quantum gravity.

Implications of high-energy elementary particle physics for physics of the early universe and its evolution (Big Bang, creation of matter, formation of galaxies, etc). And vice-versa: implications of observable cosmological data for fundamental physics.

Collisions and subsequent decays of higher dimensional branes leave behind three-dimensional branes, one of which could play the role of our universe. This process also leads to the production of one-dimensional branes, D-strings, and fundamental ones (F-strings), known as cosmic superstrings. In the first part of this talk, I will discuss the mechanism we have proposed in order to explain the origin of the space-time dimensionality, while in the second part I will review formation and dynamics of cosmic superstrings.

Near the Planckian scales, quantum gravity is expected to drastically change the structure of spacetime, one feature of which may be noncomutativity of the coordinates. Based on the recent advances in quantum field theories on such noncommutative spaces, I will consider the fluctuations of inflaton and look for possible noncommutative corrections in the CMB. Anisotropy and non-gaussianity are the result. The resultant distribution is then compared with ACBAR, CBI and WMAP data to constrain the scale of noncommutativity parameter.

I describe a number of techniques that allow for the generation of (near) scale-invariant fluctuations in the early Universe without inflation or ekpyrosis. The basic ingredient is a decaying maximal speed of propagation, for which a Universal law is found. Connections are made with k-essence, the cuscaton, and the DBI action. However the simplest realizations result from bimetric theories and deformed dispersion relations and DSR. A number of implications to theories of quantum gravity are discussed.

In addition to its ability to probe Inflation, CMB polarization offers the intriguing possibility to detect CP-symmetry violation. In some sense these predictions, if true, would be more surprising than confirmation of the inflationary paradigm -- for which ample, albeit circumstantial, evidence already exists. Moreover, recent theoretical predictions imply that, not only are parity violating CMB polarization effects possible, but that they have already been detected at 3\sigma confidence levels in existing polarization data. I will present a worked example showing the impact of experimental systematic effects on such measurements, and present a robust test to help determine the veracity of the theoretical predictions. I will show that the CP-symmetry violating observables are more susceptible to certain systematic effects, and discuss the future prospects for such CMB polarization probes of fundamental physics.