Description of the Riemannian geometry in the presence of conical defects

A consistent approach to the description of integral coordinate-invariant functionals of the metric on manifolds scrM_α with conical defects (or singularities) of the topology C_α×Σ is developed. According to the proposed prescription scrM_α are considered as limits of the converging sequences of smooth spaces. This enables one to give a strict mathematical meaning to a number of invariant integral quantities on scrM_α and make use of them in applications. In particular, an explicit representation for the Euler numbers and Hirtzebruch signature in the presence of conical singularities is found. Also, a higher dimensional Lovelock gravity on scrM_α is shown to be well defined and the gravitational action in this theory is evaluated. Another series of applications is related to the computation of black hole entropy in the higher derivative gravity and in quantum two-dimensional models. This is based on its direct statistical-mechanical derivation in the Gibbons-Hawking approach, generalized to the singular manifolds scrM_α, and gives the same results as in the other methods.