\noindent{\bf Mathematisches Oberseminar} {\it PDG und
Spektraltheorie} (WiSe 2014/15).

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\noindent{\bf Date:} 22.01.2015.

\noindent{\bf Time and place:} 14:15 in B 134.

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\noindent{\bf Speaker:} Robert Seiringer (IST Austria).

\noindent{\bf Titel:} {\it Validity of spin wave theory for the quantum Heisenberg model.}


\noindent{\bf Abstract:}

\noindent We consider the quantum ferromagnetic Heisenberg model in
three dimensions, for all spins $S\geq1/2$. We rigorously prove the
validity of the spin-wave approximation for the excitation spectrum,
at the level of the first non-trivial contribution to the free energy
at low temperatures. The proof combines a bosonic representation of
the model introduced by Holstein \& Primakoff with probabilistic
estimates, localization bounds and functional inequalities. (Joint
work with Michele Correggi and Alessandro Giuliani) 

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Thomas {\O}stergaard S{\o}rensen

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