Gravitational Waves from Sub-Lunar-Mass Primordial Black-Hole Binaries: A New Probe of Extradimensions

In many brane world models, gravity is largely modified at the electroweak scale $\ensuremath{\sim}1\text{ }\text{ }\mathrm{T}\mathrm{e}\mathrm{V}$. In such models, primordial black holes (PBHs) with a lunar mass $M\ensuremath{\sim}{10}^{\ensuremath{-}7}{M}_{\ensuremath{\bigodot}}$ might have been produced when the temperature of the Universe was at $\ensuremath{\sim}1\text{ }\text{ }\mathrm{T}\mathrm{e}\mathrm{V}$. If a significant fraction of the dark halo of our galaxy consists of these lunar mass PBHs, a huge number of BH binaries will exist in our neighborhood. Third generation detectors such as EURO can detect gravitational waves from these binaries, and can also determine their chirp mass. With a new detector designed to be sensitive at high frequency bands $\ensuremath{\gtrsim}1\text{ }\mathrm{k}\mathrm{H}\mathrm{z}$, the existence of extradimensions could be confirmed.