Naturally Small Seesaw Neutrino Mass with No New Physics Beyond the TeV Scale

If there is no new physics beyond the TeV energy scale, such as in a theory of large extra dimensions, the smallness of the seesaw neutrino mass, i.e. $m_\nu = m_D^2/m_N$, cannot be explained by a very large $m_N$. In contrast to previous attempts to find an alternative mechanism for a small $m_\nu$, I show how a solution may be obtained in a simple extension of the Standard Model, without using any ingredient supplied by the large extra dimensions. It is also experimentally testable at future accelerators.