Curtailing the dark side in non-standard neutrino interactions
Received: February
Curtailing the dark side in non-standard neutrino interactions
Thomas Schwetzg 0 1 2 7
Pilar Coloma 0 1 2 5 7
Peter B. Denton 0 1 2 4 5 7
M.C. Gonzalez-Garcia 0 1 2 3 7
Michele Maltoni 0 1 2 7
Stony Brook 0 1 2 7
NY 0 1 2 7
U.S.A. 0 1 2 7
Open Access, c The Authors.
0 Pg. Lluis Companys 23 , 08010 Barcelona , Spain
1 Universitat de Barcelona , Diagonal 647, E-08028 Barcelona , Spain
2 Blegdamsvej 17 , DK-2100, Copenhagen , Denmark
3 C.N. Yang Institute for Theoretical Physics, Stony Brook University
4 Niels Bohr International Academy, University of Copenhagen, The Niels Bohr Institute
5 Theoretical Physics Department, Fermi National Accelerator Laboratory
6 15 , Cantoblanco, E-28049 Madrid , Spain
7 Calle de Nicolas Cabrera 13
In presence of non-standard neutrino interactions the neutrino avor evolution equation is a ected by a degeneracy which leads to the so-called LMA-Dark solution. It requires a solar mixing angle in the second octant and implies an ambiguity in the neutrino mass ordering. Non-oscillation experiments are required to break this degeneracy. We perform a combined analysis of data from oscillation experiments with the neutrino scattering experiments CHARM and NuTeV. We nd that the degeneracy can be lifted if the non-standard neutrino interactions take place with down quarks, but it remains for up quarks. However, CHARM and NuTeV constraints apply only if the new interactions take place through mediators not much lighter than the electroweak scale. For light mediators we consider the possibility to resolve the degeneracy by using data from future coherent neutrino-nucleus scattering experiments. We nd that, for an experiment using a stoppedpion neutrino source, the LMA-Dark degeneracy will either be resolved, or the presence of new interactions in the neutrino sector will be established with high signi cance.
interactions; f Instituto de F sica Teorica UAM/CSIC; Universidad Autonoma de Madrid
1 Introduction The NSI formalism 2 3
NSI in neutrino oscillations and the LMA-D degeneracy
Neutrino scattering and heavy versus light NSI mediators
Current experimental constraints
Oscillation experiments
Global t to current experiments | heavy NSI mediators
A future experiment on coherent neutrino-nucleus scattering
Expected combined sensitivity after inclusion of COHERENT
NSI from a light mediator
NSI from a heavy mediator
Summary and conclusions
A Resolving LMA-D by COHERENT data
Experiments measuring the avor composition of solar and atmospheric neutrinos, as well
as neutrinos produced in nuclear reactors and in accelerators, have established that lepton
avor is not conserved in neutrino propagation. Instead, it oscillates with a wavelength
which depends on distance and energy, because neutrinos are massive and the mass states
are admixtures of the avor states [1{3]. At present all con rmed oscillation signatures can
be well described with the three avor neutrinos ( e,
) being quantum superpositions
masses mi leading to two distinctive splittings (see ref. [4] for the latest determination of
the neutrino masses and mixings).
Under the assumption that the Standard Model (SM) is the low energy e ective model
of a complete high energy theory, neutrino masses emerge naturally as the rst observable
consequence from higher dimensional operators. It is particularly remarkable that the
indeed the Weinberg operator [5], which after electroweak symmetry breaking leads to a
suppression of neutrino masses with the scale of new physics , as m
O(v2= )
where v is the Higgs vacuum expectation value. In this framework higher dimensional
operators may also lead to observable consequences at low energies in the neutrino sector.
are lepton avor indices, f; f 0 are SM charged fermions and
are the Dirac
gamma matrices. Here, PL is the left-handed projection operator while P can be either
PL or PR (the right-handed projection operator). These operators would lead to the
socalled Non-Standard Interactions (NSI) in the neutrino sector [6{8] (for recent reviews,
see [9, 10]). They are expected to arise generically from the exchange of some mediator state
assumed to be heavier that the characteristic momentum transfer in the process. Operators
in eq. (1.2) lead to the modi cation of neutrino production and detection mechanisms via
new charged-current interactions (NSI-CC), while operators in eq. (1.1) induce new
neutralcurrent processes (NSI-NC).
The operators in eq. (1.1) can modify the forward-coherent scattering (i.e., at zero
momentum transfer) of neutrinos as they propagate through matter via so-called
MikheevSmirnov-Wolfenstein (MSW) mechanism [6, 11]. Consequently their e ect can be signi
cantly enhanced in oscillation experiments where neutrinos travel large regions of matter,
such as is the case for solar and atmospheric neutrinos. Indeed, the global analysis of data
from oscillation experiments in the framework of mass induced oscillations in presence of
NSI currently provides some (...truncated)