Publications

We perform exact half-line path integral quantization of flat, homogeneous cosmological models containing a perfect fluid acting as an internal clock, in a D + 1 dimensional minisuperspace setup.

We explore the question, whether the accelerated detector is sensitive to the Planck order shift in its causal domain? This question is addressed in the context of a nested sequence of Rindler observers, where the vacua of preceding Rindler frames appear thermally populated to a shifted Rindler frame. The Bogoliubov analysis relies on the global notion of the quantum field theory and turns out to be insensitive to the local character of these horizon shifts. We investigate this system by means of the Unruh-DeWitt detector and show that this local probe of the quantum field theory is sensitive enough to capture the horizon shifts of the order of the Planck scale.

Sharply peaked quantum states are conjectured to be conducive to the notion of a quantum-corrected spacetime. We investigate this conjecture for a flat-FLRW model with perfect fluid, where a generalized ordering scheme is considered for the gravitational Hamiltonian. We study the implications of different ordering choices on the dynamics of the quantum Universe. We demonstrate that the imprints of the operator ordering ambiguity are minimal, and quantum fluctuations are small in the case of sharply peaked states, leading to a consistent notion of a quantum-corrected spacetime defined via the expectation value of the scale factor. Surprisingly, the ordering imprints survive far away from the singularity through the quantum fluctuations in the quantum-corrected spacetime for broadly peaked states.

We investigate the viability of an effective quantum-corrected spacetime defined by expectation value of the metric variables in quantum cosmology. For this effective geometry, we ask; how the ordering choice affects this notion, what are the quantum fluctuations in this {\it quantum geometry}, and whether its observables have any correspondence with the true {\it quantum observables}. Surprisingly, we find that the ordering choices not only affect physics near singularity but creep well into the classical regime.

We investigate the status of the conformal map between Einstein and Jordan frames of a scalar-tensor theory at the quantum level with the focus on the apparent paradox: the classical conformal map allows an always expanding Einstein frame to map to a Jordan frame that is always contracting, and at some point, the formalism maps a classical system (fluctuations are ignorable) to a quantum system (fluctuations are not ignorable). We find that the conformal map holds at the quantum level, and despite having drastically different cosmological evolution, the rise in quantum characteristics in a collapsing frame implies the same in its expanding counterpart.

We study the mode decomposition of a unitarily evolving wave packet that represents the quantum dynamics of the dust cloud in Lema\^itre-Tolman-Bondi geometry. We showed that the infrared sector of the dust profile predominantly contributes to the emission during the collapsing phase and therefore, is most relevant for the Hawking radiation.