Quadratic differential operators, Bicharacters and $\bullet$ Products
  For a commutative cocommutative Hopf algebra we study the relationship between a certain linear map defined via a bicharacter, an exponential of a quadratic differential operator and a $\bullet$ product obtained via twisting by a bicharacter. This new relationship between $\bullet$ products and exponentials of quadratic differential operators was inspired by studying the exponential of a particular quadratic differential operator introduced by I. Frenkel, Lepowsky and Meurman in "Vertex operator algebras and the Monster", and used in the theory of twisted modules of lattice vertex algebras. 
Iana I. Anguelova and Maarten J. Bergvelt
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