ABSTRACT
The extra dimensions were introduced to unify gravity with other gauge interactions. Since we do not experience any new dimensions beyond our four space–time dimensions, these extra dimensions were assumed to be compact. This would make these extra dimensions invisible at our present energies. Any probe having energy of the order of the compactication scale, which is the inverse of the radius of compacti-cation, can only see these extra dimensions. Usually the compactication scale is considered to be about the Planck scale, so all new excited states become heavy and decouple from low-energy physics.
