Effective Field Theory of a Locally Noncommutative Space-Time and Extra Dimensions

We assume that the noncommutativity starts to be visible continuously from a scale ${\mathrm{\Lambda }}_{NC}$. According to this assumption, a two-loop effective action is derived for noncommutative ${\varphi }^4$ and ${\varphi }^3$ theories from a Wilsonian point of view. We show that these effective theories are free of UV/IR mixing phenomena. We also investigate the positivity constraint on coefficients of higher dimension operators present in the effective theory. This constraint makes the low energy theory to be UV completion of a full theory. Finally, we discuss noncommutativity and extra dimensions. In our effective theories formulated on noncommutative extra dimensions, if the campactification scale ${\mathrm{\Lambda }}_c$ is less than the scale ${\mathrm{\Lambda }}_{NC}$, the theory will not suffer from UV/IR mixing.