Research interests

Inflationary cosmology and early universe physics

Our current understanding of the universe on large scales is well described by the LCDM (Lambda-Cold Dark Matter) model, supplemented by an inflationary epoch in the very early universe. Besides providing an elegant explanation to the numerous shortcomings of the hot Big Bang theory, inflation also provides a natural, causal and efficient mechanism for the origin of primordial density perturbations which source the anisotropies in the Cosmic Microwave Background (CMB) radiation and later act as seeds for the formation of the large scale structure in the universe. The inflationary paradigm is thus widely considered a crucial part of the concordance model of cosmology. Our group is interested in exploring the observational features of beyond single field inflationary models and constrain the parameter space using Planck and other datasets.

Primordial black holes and their observational imprints

Primordial black holes (PBH) have emerged as one of the most promising candidates for the cold dark matter in recent times, particularly after the detection of the merger of solar mass black holes by LIGO/VIRGO observations. Primordial black holes open the window for many interesting cosmological and astrophysical counterparts. One can classify broadly them into (i) pre-formation requirements and implications, (ii) formation by collapse and (iii) the post-formation effects and imprints. our group is mostly focused on the first aspect. We study the formation of PBHs and the induced stochastic gravitational wave background (ISGWB) due to the amplified scalar curvature perturbations at smaller scales. In recent papers, we studied the production of PBHs in a specific single field model of inflation and found that they can account for the entire dark matter in the allowed mass windows and the resulting ISGWB can fall within the projected sensitivities of various upcoming GW observatories. We further explored the imprints of non-instantaneous reheating epochs after the end of inflation on the PBHs abundance and ISGWB. Our group is interested in various aspects of PBH formation in different inflationary models and their resulting observational imprints on smaller scales.

Primordial non-Gaussianities

The simplest inflationary models predict a nearly scale invariant spectrum of primordial density fluctuations with very small non-Gaussianities which are in remarkable agreement with the precise measurements of CMB anisotropies. Despite many of these observational accomplishments, there are still large degeneracies in theoretical space of inflationary models. Thus, any ideas which lift these degeneracies are of great importance. The non-Gaussian features associated with the primordial fluctuations are often used to limit and distinguish inflationary models. One usually assumes the initial Gaussian nature of the primordial perturbations to explain the present cosmological observations. But the models that explain the observed universe predict a minimal deviation from Gaussianity. Thus non-Gaussian observables are robust tools to constrain many inflationary models. Since non-Gaussianities arise from the interactions present in the early universe, its detection would give more clues about physics at energy scales as high as the GUT scale. Our group is interested in exploring novel non-Gaussian correlators arising in models containing dynamical gauge fields using semi-classical methods as well as in-in formalism and study their observational consequences.

Dark matter

The constituents of the universe demonstrated by various astrophysical observations, such as galaxy rotation curves, bullet clusters, CMB, etc., have consistently indicated that a massive amount of non-luminous matter called “Dark Matter (DM)” is present in our universe. Over the years, various DM candidates such as Weakly Interacting Massive Particles (WIMP), Sterile neutrinos, Weakly Interacting Slim Particles (WISP), PBH etc. have been proposed. Our group is interested in studying multiple ways to get more information about this elusive component of the universe using indirect detection techniques involving the capture of DM particles by compact stars such as neutron stars (NS), resulting in a rise in its temperature which will be detected in telescopes such as Thirty Meter Telescope (TMT), James Webb Space Telescope (JWST) etc. We also intend to study more on WISPs such as Axion-like Particles (ALPs) by exploring multiple models to explore more of their properties.

CMB anomalies

CMB radiation is the relic of the early universe filling all space in a homogeneous and isotropic fashion. The CMB power spectrum contains information of the small deviations from isotropy and homogeneity (of order 1 part in 100000), which were seeded during the inflationary epoch in the early universe. The precise measurements of the CMB power spectrum from subsequent observations of COBE, WMAP, and Planck suggest that the LCDM model is the concordance model of the universe. However, there exists some persistent features in the CMB power spectrum, called CMB anomalies which remain unexplained by the LCDM model. One novel anomaly that has always existed in the CMB angular power spectrum is the deficit in power at very large scales (or low multipoles). Such a suppression at very large scales (corresponding to the present Hubble scale), can either be a consequence of some unknown/new physics in the very early inflationary epoch resulting in deviations from the scale-invariant inflationary power spectrum at very large scales or could also be due to unknown systematics. In our group, we are interested in the study of such inflationary models that can explain the low multipole suppression in CMB angular power spectrum and constrain such models with recent datasets.

Relativistic effects in large scale structure

In the study of the large-scale structure of the universe, our main focus is on understanding the formation and distribution of cosmological structures in the sky. While it sounds simple and straightforward, the idea involves many minute details, simply because the observations made by galaxy surveys are affected by how the emitted photons coming from the source to the observer undergo some changes in their direction, energy and so on. Simply put, we need to account for additional "relativistic effects" while making observations, so as to reconcile the observations better with our theoretical predictions. The most relevant of such effects is the weak gravitational lensing, that manifests through the change in shape and size of the observed galaxies. With many ongoing surveys like the Dark Energy Survey (DES) and the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), and upcoming ones like Large Synoptic Sky Survey (LSST) and Euclid, we can have a more precise measurement of cosmological structures, for which it is also essential to have a better understanding of the underlying theory that helps us forecast these measurements in the first place.

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