Dr Siegl's research interests are in the areas of analysis and mathematical physics. His main research interests are spectral theory, functional analysis and partial differential equations. More specifically he is interested in non-self-adjoint differential operators, often arising in physical problems with energy losses.

He has published more than 30 articles, received prizes for his Ph.D., the Ambizione grant for excellent young researchers from the Swiss National Science Foundation and organized several conferences focused on his research area.