Nonstandard neutrino interactions from a triplet seesaw model

We investigate nonstandard neutrino interactions (NSIs) in the triplet seesaw model featuring nontrivial correlations between NSI parameters and neutrino masses and mixing parameters. We show that sizable NSIs can be generated as a consequence of a nearly degenerate neutrino mass spectrum. Thus, these NSIs could lead to quite significant signals of lepton flavor violating decays such as ${\mu }^{-}\to e^{-}{\nu }_e{\overline{\nu }}_{\mu }$ and ${\mu }^{+}\to e^{+}{\overline{\nu }}_e{\nu }_{\mu }$ at a future neutrino factory, effects adding to the uncertainty in determination of the Earth matter density profile, as well as characteristic patterns of the doubly charged Higgs decays observable at the Large Hadron Collider.

Figure 1

Tree-level Feynman diagrams with the exchange of heavy triplet fields. The corresponding diagrams are responsible for (a) a light neutrino Majorana mass term, (b) nonstandard neutrino interactions, (c) NSIs of four charged leptons, and (d) self-coupling of the SM Higgs doublet.

Figure 2

The upper bounds (at 90% C.L.) on the NSI parameters governed by Eq. (8) with respect to the lightest neutrino mass $m_1$. Given $m_1$, the ratio $m_{\Delta }/{\lambda }_{\varphi }$ in Eq. (8) (or ${\lambda }_{\varphi }^{-1}$ if $m_{\Delta }$ is fixed) is pushed up unless any of the bounds in Table  is saturated. The solid curves correspond to constraints on $|{\epsilon }_{\alpha \beta }^m|$ parameters, while the dashed curve shows the bound on the $|{\epsilon }_{e\mu }^{e\mu }|$ (or $|{\epsilon }_{\mu e}^{\mu e}|$) parameter. Equations (13, 14) yield the asymptotic values of $|{\epsilon }_{e\mu }^{e\mu }|$ and $|{\epsilon }_{ee}^m|$ in the ND region (shaded). The wiggles on the curves are numerical artifacts given by the granularity of the scan over the parameter space.

Figure 3

Sensitivity limits (at 90% C.L.) on the parameter $\epsilon \equiv |{\epsilon }_{e\mu }^{e\mu }|$ as a function of the distance ($L$) from the source to the near detector. The solid and dashed curves correspond to ${sin}^{2}2{\theta }_{13}=0.01$ and 0.1, respectively.