Research Interests

Cosmologists (including myself) seem to believe that most of universe is composed of a dark clumpy component (dark matter) and a smooth anti-gravitating dark fluid (dark energy). Naturally, there is a lot of speculation about the nature of these dark components. I seem to spend a lot of time, trying to rule out some of these candidates and putting constraints on others. For more details see:

I have also spent quite some time worrying about how the presence of non-linear cosmological perturbations can (or cannot) affect the standard cosmological evolution, in both early and late universe. For more details see:

Being our most direct probe of the early universe, Cosmic Microwave Background (CMB) is arguably the most significant source of information that has led to our current understanding of modern cosmology. Being a cosmologist, naturally, many of my studies have been related to the CMB in one way or another. Most of my work on CMB, however, concentrates on secondary anisotropies, or foregrounds, that are generated in the low redshift universe. For more details see:

Accretion Disks are among the most enigmatic and (thus) interesting phenomena in Astrophysics. They can occur in vastly different situations, ranging from galaxies being swallowed by their central super-massive black holes, to a stars being consumed by a massive companion, and yet they share very similar underlying processes. I have worked on projects, trying to understand the accretion mechanism, and the nature of accretion disks close to the horizon of a black hole. For more details see:   

The hot gas trapped within clusters of galaxies, with temperatures as hot as a hundred million degrees, contain most of the thermal energy of the universe. I try to understand various properties of this intracluster gas, specifically through its impact on the cosmic microwave background (Sunyaev-Zel’dovich effect), as well as its X-ray emission. For more details see:

Understanding Dark Matter and Dark Energy

Understanding Accretion Disks

Cosmic Microwave Background (CMB)

Cosmological Back-Reaction and the Role of Non-linearities

Understanding the Intracluster Medium

· My Publications on Dark Matter and Dark Energy

· My Publications on the Intracluster Medium

· My Publications on Cosmological Back-reaction

· My Publications on Accretion Disks

· My Publications on Cosmic Microwave background

I dabble in Astrophysics, Cosmology, and Physics of gravity.  I am obsessed with observational hints that could help address problems in fundamental physics. In particular, I have found anomalous signatures of dark energy and dark baryons in the cosmic microwave background radiation. With other collaborators, I have also developed a curious theory for an incompressible dark energy, named cuscuton (after the Latin name for the parasitic plant of dodder). I am currently trying my hand in solving the cosmological constant problem through a new theory of gravity that can surprisingly relate the formation of astrophysical black holes to today’s acceleration of cosmic expansion. In a related inquiry, I am also exploring the relation of cuscuton and quantum gravity.  

Here are the broad areas of my research in Astrophysics and Cosmology. There is, of course, a lot of overlap between different areas, which can be seen by common papers listed under different fields.

Was Einstein right? or is there more to gravity than his celebrated theory of General Relativity? The huge discrepancy between the predicted quantum vacuum, and the observed one (known as the cosmological constant problem) suggests “yes”.  I am very excited about this possibility, and its possible implications for the cosmology and quantum theory of gravity. For more details see:

Modified Gravity and the Cosmological Constant Problem

· My Publications on Modified Gravity