Note on the gauge symmetries of unimodular gravity

© 2016 American Physical Society.
The origin of this work lies in a question by Gerardus ’t Hooft at the Shapes of Gravity meeting held in Nijmegen in 2016. It has been partially supported by the European Union FP7 ITN INVISIBLES (Marie Curie Actions, PITN- GA-2011- 289442) and (HPRN-CT-200-00148); COST action MP1405 (Quantum Structure of Spacetime), COST action MP1210 (The String Theory Universe) as well as by FPA2012-31880 (MICINN, Spain), FPA2014-54154-P (MICINN, Spain), and S2009ESP-1473 (CA Madrid). This project has received funding from the European Union’ s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant Agreement No. 690575. This project has also received funding from the European Union’ s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie Grant Agreement No. 674896. The authors acknowledge the support of the Spanish MINECO Centro de Excelencia Severo Ochoa program under Grant No. SEV-2012-0249.