Loop bounds on non-standard neutrino interactions

Abstract

We reconsider the bounds on non-standard neutrino interactions with matter which can be derived by constraining the four-charged-lepton operators induced at the loop level. We find that these bounds are model dependent. Naturalness arguments can lead to much stronger constraints than those presented in previous studies, while no completely model-independent bounds can be derived. We will illustrate how large loop-contributions to four-charged-lepton operators are induced within a particular model that realizes gauge invariant non-standard interactions and discuss conditions to avoid these bounds. These considerations mainly affect the O(10 −4 ) constraint on the non-standard coupling strength ε eµ , which is lost. The only model-independent constraints that can be derived are O(10 −1 ). However, significant cancellations are required in order to saturate this bound. * biggio@mppmu.mpg.de †

Non-standard neutrino interactions at one loop

“…After performing the rescaling (18) and the field rotation (20), the kinetic terms are canonical and the charged lepton mass matrix is diagonal, whereas the interaction terms are not diagonal. For later convenience, we rotate the neutrino fields as ν L → L m ν L , in order to keep them as much aligned as possible with their charged partners.…”

“…This fact triggered renewed interest at present neutrino facilities [14][15][16][17][18][19]. The typical bounds on production and detection NSIs are about ε µτ ∼ 10 −2 [20,21]. Higher sensitivities, of ε µτ ∼ < 10 −3 are within the reach of future neutrino experiments [22][23][24][25][26][27][28][29][30].…”

Interim Design Report

“…If the running time is doubled, no significant improvement is gained, indicating that the limiting factor is not statistics. These bounds are a significant improvement upon the current bounds [161,162], but not as strong as those which the Neutrino Factory can obtain.…”

“…Model-independent experimental constraints on the ε s,d,m αβ range from 10 −4 to O(1) [16,[159][160][161][162], while model-dependent limits are often much tighter [163,164] since, in concrete models, NSI in the neutrino sector are usually accompanied by non-standard effects in the charged-lepton sector that are constrained, for example, by rare decay searches or measurements of the weak mixing angle.…”

New physics searches at near detectors of neutrino oscillation experiments

“…There are several such operators [16][17][18][19][20][21][22][23][24][25], depending on the production mechanism of the neutrino beam (π decay for conventional neutrino beams and super-beam experiments, β decay for β-beam and reactor experiments and µ decays for neutrino factories). We will classify the new physics operators in three different categories:…”