Periodic Riemannian manifold with preassigned gaps in spectrum of   Laplace-Beltrami operator
  It is known (E.L. Green (1997), O. Post (2003)) that for an arbitrary $m\in\mathbb{N}$ one can construct a periodic non-compact Riemannian manifold $M$ with at least $m$ gaps in the spectrum of the corresponding Laplace-Beltrami operator $-\Delta_M$. In this work we want not only to produce a new type of periodic manifolds with spectral gaps but also to control the edges of these gaps. The main result of the paper is as follows: for arbitrary pairwise disjoint intervals $(\a_j,\b_j)\subset[0,\infty)$, $j=1,...,m$ ($m\in\mathbb{N}$), for an arbitrarily small $\delta>0$ and for an arbitrarily large $L>0$ we construct a periodic non-compact Riemannian manifold $M$ with at least $m$ gaps in the spectrum of the operator $-\Delta_{M}$, moreover the edges of the first $m$ gaps belong to $\delta$-neighbourhoods of the edges of the intervals $(\a_j,\b_j)$, while the remaining gaps (if any) are located outside the interval $[0,L]$. 
Andrii Khrabustovskyi
math.SP math-ph math.AP math.DG math.MP