Universal extra dimension, proposed and first studied in 2000, assume, at variance with the ADD and RS approaches, that all fields propagate universally in the extra dimensions.
Multiple time dimensions, i.e. the possibility that there might be more than one dimension of time, has occasionally been discussed in physics and philosophy, although those models have to deal with the problem of causality.
^Rizzo, Thomas G. (2004). "Pedagogical Introduction to Extra Dimensions". SLAC Summer Institute. arXiv:hep-ph/0409309. Bibcode:2004hep.ph....9309R.
^For a pedagogical introduction, see M. Shifman (2009). Large Extra Dimensions: Becoming acquainted with an alternative paradigm. Crossing the boundaries: Gauge dynamics at strong coupling. Singapore: World Scientific. arXiv:0907.3074. Bibcode:2010IJMPA..25..199S. doi:10.1142/S0217751X10048548.