Neutrino Oscillation Parameters: Future

The Neutrino Oscillation Workshop (NOW2018) included a session addressing neutrino oscillation parameters in the future. This session included discussion of planned and proposed experiments, detector technologies, and analysis techniques to better measure neutrino oscillation parameters. Constraint of systematic uncertainty in future precision measurements was a topic of particular interest. This proceedings is a brief summary of the presentations in the Oscillation Parameters: Future session; readers are directed to individual contributions to the proceedings for more detailed information

Unitarity of the leptonic mixing matrix

Tesis doctoral inédita. Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Teórica. Fecha de lectura: 28-06-201

N_eff in low-scale seesaw models versus the lightest neutrino mass

We evaluate the contribution to N_eff of the extra sterile states in low-scale type I seesaw models (with three extra sterile states). We explore the full parameter space and find that at least two of the heavy states always reach thermalization in the early Universe, while the third one might not thermalize provided the lightest neutrino mass is below O(10(-3) eV). Constraints from cosmology therefore severely restrict the spectra of heavy states in the range 1 eV-100 MeV. The implications for neutrinoless double beta decay are also discussed

Low-scale seesaw models versus N-eff

We consider the contribution of the extra sterile states in generic low-scale seesaw models to extra radiation, parametrized by N-eff. We find that the value of Neff is roughly independent of the seesaw scale within a wide range. We explore the full parameter space in the case of two extra sterile states and find that these models are strongly constrained by cosmological data for any value of the seesaw scale below O(100 MeV)

Looking at the axionic dark sector with ANITA

The ANITA experiment has recently observed two anomalous events emerging from well below the horizon. Even though they are consistent with tau cascades, a high-energy Standard Model or Beyond the Standard Model explanation is challenging and in tension with other experiments. We study under which conditions the reflection of generic radio pulses can reproduce these signals. Furthermore, we propose that these pulses can be resonantly produced in the ionosphere via axion-photon conversion. This naturally explains the direction and polarization of the events and avoids other experimental bounds

Probing non-unitary mixing and CP-violation at a Neutrino Factory

A low energy non-unitary leptonic mixing matrix is a generic feature of many extensions of the Standard Model. In such a case, the task of future precision neutrino oscillation experiments is more ambitious than measuring the three mixing angles and the leptonic (Dirac) CP-phase, i.e., the accessible parameters of a unitary leptonic mixing matrix. A non-unitary mixing matrix has 13 parameters that affect neutrino oscillations, out of which four are CP-violating. In the scheme of Minimal Unitarity Violation (MUV) we analyse the potential of a Neutrino Factory for determining or constraining the parameters of the non-unitary leptonic mixing matrix, thereby testing the origin of CP-violation in the lepton sector.Comment: 21 pages, 8 eps figures, REVTeX

Effective portals to heavy neutral leptons

The existence of right-handed neutrinos, or heavy neutral leptons (HNLs), is strongly motivated by the observation of neutrino masses and mixing. The mass of these new particles could lie below the electroweak scale, making them accessible to low-energy laboratory experiments. Additional new physics at high energies can mediate new interactions between the Standard Model particles and HNLs, and is most conveniently parametrized by the neutrino Standard Model Effective Field Theory, or νSMEFT for short. In this work, we consider the dimension six νSMEFT operators involving one HNL field in the mass range of O (1) MeV < MN < O (100) GeV. By recasting existing experimental limits on the production and decay of new light particles, we constrain the Wilson coefficients and new physics scale of each operator as a function of the HNL mass.1The authors would like to thank the Instituto de Física Teórica (IFT UAM-CSIC) in Madrid for support via the Centro de Excelencia Severo Ochoa Program under Grant CEX2020-001007-S, during the Extended Workshop “Neutrino Theories”, where this work developed. The research of MH was supported by Perimeter Institute for Theoretical Physics. Research at Perimeter Institute is supported by the Government of Canada through the Department of Innovation, Science and Economic Development and by the Province of Ontario through the Ministry of Research, Innovation and Science. JLP acknowledges support from Generalitat Valenciana through the plan GenT program (CIDEGENT/2018/019) and from the Spanish Ministerio de Ciencia e Innovacion through the project PID2020-113644GB-I00. EFM and MGL were also supported by the Spanish Research Agency (Agencia Estatal de Investigación) through the grant PID2019-108892RB-I00 funded by MCIN/AEI/ 10.13039/501100011033. EFM, MGL, and JLP also acknowledge support from European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreements No 860881-HIDDeN and No 101086085- ASYMMETRY. JHG warmly thanks the hospitality of Albert de Roeck and the EP Neutrino group during his stay at CERN; where this project has been completed PID2019-108892RB-I0

Global bounds on the Type-III Seesaw

We derive general bounds on the Type-III Seesaw parameters from a global fit to flavor and electroweak precision data. We explore and compare three Type-III Seesaw realizations: a general scenario, where an arbitrary number of heavy triplets is integrated out without any further assumption, and the more constrained cases in which only 3 or 2 (minimal scenario) additional heavy states are included. The latter assumption implies rather non-trivial correlations in the Yukawa flavor structure of the model so as to reproduce the neutrino masses and mixings as measured in neutrino oscillations experiments and thus qualitative differences can be found with the more general scenario. In particular, we find that, while the bounds on most elements of the dimension 6 operator coefficients are of order 10−4 for the general and 3-triplet cases, the 2-triplet scenario is more strongly constrained with bounds between 10−5 and 10−7 for the different flavours. We also discuss how these correlations affect the present CMS constraints on the Type-III Seesaw in the minimal 2-triplet scenario

Leptogenesis in GeV-scale seesaw models

We revisit the production of leptonic asymmetries in minimal extensions of the Standard Model that can explain neutrino masses, involving extra singlets with Majorana masses in the GeV scale. We study the quantum kinetic equations both analytically, via a perturbative expansion up to third order in the mixing angles, and numerically. The analytical solution allows us to identify the relevant CP invariants, and simplifies the exploration of the parameter space. We find that sizeable lepton asymmetries are compatible with non-degenerate neutrino masses and measurable active-sterile mixings

Bounds on lepton non-unitarity and heavy neutrino mixing

We present an updated and improved global fit analysis of current flavor and electroweak precision observables to derive bounds on unitarity deviations of the leptonic mixing matrix and on the mixing of heavy neutrinos with the active flavours. This new analysis is motivated by new and updated experimental results on key observables such as $V_{ud}$, the invisible decay width of the $Z$ boson and the $W$ boson mass. It also improves upon previous studies by considering the full correlations among the different observables and explicitly calibrating the test statistic, which may present significant deviations from a $\chi^2$ distribution. The results are provided for three different Type-I seesaw scenarios: the minimal scenario with only two additional right-handed neutrinos, the next to minimal one with three extra neutrinos, and the most general one with an arbitrary number of heavy neutrinos that we parametrize via a generic deviation from a unitary leptonic mixing matrix. Additionally, we also analyze the case of generic deviations from unitarity of the leptonic mixing matrix, not necessarily induced by the presence of additional neutrinos. This last case relaxes some correlations among the parameters and is able to provide a better fit to the data. Nevertheless, inducing only leptonic unitarity deviations avoiding both the correlations implied by the right-handed neutrino extension as well as more strongly constrained operators is challenging and would imply significantly more complex UV completions.Comment: 27 pages + appendices, 7 figures, 7 table