On a Laplacian which acts on symmetric tensors
  In the present paper we show properties of a little-known Laplacian operator acting on symmetric tensors. This operator is an analogue of the well known Hodge-de Rham Laplacian which acts on exterior differential forms. Moreover, this operator admits the Weitzenb\"ock decomposition and we study it using the analytical method, due to Bochner, of proving vanishing theorems for the null space of a Laplace operator admitting a Weitzenb\"ock decomposition and further of estimating its lowest eigenvalue. 
J. Mikesh, S. E. Stepanov, I.I. Tsyganok
math.DG