Solving the hierarchy problem with brane crystals

The brane world scenario advocated by Arkani-Hamed et al. transmutes the hi erarchy problem into explaining why extra dimensions have sizes much larger than the fundamental scale. In this Letter we discuss possible solutions t o this problem by considering the compactified dimensions to be populated b y a large number of branes in a crystal lattice. The experimental consequen ces of this scenario are described, including the presence of large energy gaps in the spectrum of Kaluza-Klein modes. (C) 2001 Published by Elsevier Science B.V.