Phenomenological constraints on low-scale gravity

TL;DR

This paper analyzes constraints on the gravity scale in extra-dimensional theories, highlighting the strongest bounds from neutrino oscillations and more reliable bounds from flavor-conserved processes, with bounds ranging from 10^5 to 10^18 GeV.

Contribution

It provides a comprehensive comparison of various phenomenological constraints on the gravity scale, emphasizing the impact of broken symmetries on these bounds.

Findings

Neutrino oscillations impose the strongest lower bounds on the gravity scale.

Flavor-conserved processes yield more reliable but weaker bounds.

Bounds vary from 10^5 GeV to 10^18 GeV depending on assumptions.

Abstract

We study the constraints on gravity scale $M_P$ in extra-dimension gravitational theory, obtained from gravity-induced processes. The obtained constraints are subdivided into strong (though not robust) and reliable (though less strong). The strong constraints can be in principle relaxed due to some broken gauge symmetries, e.g. family symmetry. The strongest constraint is given by neutrino oscillations. For different assumptions the lower bound on $M_P$ is $10^{15} - 10^{18}$ GeV. However, it can be, in principle, reduced by broken family symmetry. More reliable bounds are due to flavor-conserved operators or those which change the flavors within one family. These bounds, obtained using the electron mass and width of $\pi \to e\nu$ decay, are $1\times 10^5$ GeV and $5\times 10^5$ GeV, for these two cases, respectively.