Studies in Quantum Field Theory in Curved Spacetime and its implications for Compact Stars

Mandal, Susobhan (2023) Studies in Quantum Field Theory in Curved Spacetime and its implications for Compact Stars. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Susobhan Mandal (17RS045)) 17RS045.pdf - Submitted Version Restricted to Repository staff only Download (950kB)

Abstract

The recent multi-messenger observation of gravitational waves makes it now possible to probe the matter dynamics in extreme conditions and strong gravity within the neutron stars and white dwarfs. These stars are extremely dense compact astrophysical objects whose matter constituents are believed to be the degenerate fermions. These compact stars are stable in nature, as they are supported against the self-gravitational pull through the degeneracy pressure generated by the degenerate fermions. For white dwarfs, the dominating fermion constituents are degenerate electrons whereas, for neutron stars, the main constituents are primarily degenerate neutrons. The other possible constituents of neutron stars are protons, electrons, muons, and different mesons. Since these stars are compact and highly massive, the general relativistic corrections to the matter field dynamics become important and cannot be neglected. In this thesis, the foremost theme is to study the equation of state of matter inside these stars using the framework of thermal field theory in curved spacetime in which the condition of local thermal equilibrium is used explicitly. In this thesis, two kinds of effects of curved spacetime on matter equations of states are studied, namely the gravitational time-dilation and the general relativistic frame-dragging. Among these two effects, the time-dilation effect is shown to be the stronger one. Further, using these equation of states of matter, the mass-radius relations of these stars are obtained numerically. Using the equations of states computed in the curved spacetime of these compact stars, we show the enhancement of mass of the stars for a given radius. Moreover, the enhancement of angular momentum due to the effect of gravitational time-dilation is also shown. In the case of slowly rotating stars, we also explain the origin of seed magnetism due to explicit spin-degeneracy breaking due to the rotation of the star.

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