PhD defense: On Quantum Corrections in String Compactifications Effective Actions and Black Holes

Out of the four known fundamental forces, gravity is the most mysterious one. While the three other fundamental forces fit together very nicely with quantum mechanics - yet another cornerstone of modern physics - this does not seem to be as straightforward for gravity. Gravity at tiny length scales, which requires a quantum theory of gravity, is qualitatively different from the remaining forces; standard techniques do not lead to the desired success.

String theory is able to circumvent these problems by introducing the string, a one dimensional, extended object as fundamental degree of freedom. As of now, string theory is the most serious candidate for a theory which unifies gravity and quantum mechanics. Ever since its inception, theoretical physicists made an effort to make the bridge between the formal aspects of string theory and the real world which we observe.

In this thesis, we have made progress in understanding scenarios, which try to make contact with the real world (a process called 'compactification’). The overarching theme covered in this dissertation is the computation of certain quantum effects, which can help in making the aforementioned bridge between the formal machinery of string theory, and the real world which we observe.