Un effet de moir\'e sur les espaces sym\'etriques de type non-compact
  We prove that if $X$ is a symmetric space of the noncompact type, just as adding Helgason waves which propagate in all direction yields an elementary spherical function for $X$, a Helgason wave can be produced by adding elementary spherical functions whose centers cluster along a horocycle in $X$. 
Alexandre Afgoustidis
math.GR math.CA