@article{PfaeffleStephan2011, author = {Frank Pf{\"a}ffle and Christoph A. Stephan}, title = {The holst action by the spectral action principle}, journal = {Communications in mathematical physics}, volume = {307}, number = {1}, pages = {261 -- 273}, doi = {10.1007/s00220-011-1303-0}, year = {2011}, }