Neutrino masses

Current measurements of the large-scale structure of galaxies are able to place an $\sim 0.5 ~ \rm eV$ upper limit on the absolute mass scale of neutrinos. An order-of-magnitude improvement in raw sensitivity, together with an insensitivity to systematic effects, is needed to reach the lowest value allowed by particle physics experiments. We consider the prospects of determining both the neutrino mass scale and the number of of massive neutrinos using future redshift surveys, specifically those undertaken with the Square Kilometre Array (SKA), with and without additional constraints from the upcoming Planck CMB experiment. If the sum of the neutrino masses $\sum m_i \gtsimeq 0.25 ~ \rm eV$ then the imprint of neutrinos on large-scale structure (LSS) should be enough, on its own, to establish the neutrino mass scale and, considered alongside CMB constraints, it will also determine the number of massive neutrinos $N_{\nu}$, and hence the mass hierarchy. If $\sum m_i \sim 0.05 ~ \rm eV$, at the bottom end of the allowed range, then a combination of LSS, CMB and particle physics constraints should be able to determine $\sum m_i$, $N_{\nu}$ and the hierarchy. If $\sum m_i$ is in the specific range $0.1-0.25 ~ \rm eV$, then a combination of LSS, CMB and particle physics experiments should determine $\sum m_i$, but not $N_{\nu}$ or the hierarchy. Once an SKA-like LSS survey is available there are good prospects of obtaining a full understanding of the conventional neutrino sector, and a chance of finding evidence for sterile neutrinos.

In some classes of flavour models based on unified theories with a type I see-saw mechanism, the prediction for the mass of the lightest right-handed neutrino is in conflict with the lower bound from the requirement of successful thermal leptogenesis. We investigate how lifting the absolute neutrino mass scale by adding a type II see-saw contribution proportional to the unit matrix can solve this problem. Generically, lifting the neutrino mass scale increases the prediction for the mass of the lightest right-handed neutrino while the decay asymmetry is enhanced and washout effects are reduced, relaxing the lower bound on the mass of the lightest right-handed neutrino from thermal leptogenesis. For instance in classes of unified theories where the lightest right-handed neutrino dominates the type I see-saw contribution, we find that thermal leptogenesis becomes possible if the neutrino mass scale is larger than about 0.15 eV, making this scenario testable by neutrinoless double beta decay experiments in the near future.

Among three typical energy scales, a neutrino mass scale (mν∼0.1 eV), a GUT scale (MGUT∼1016 GeV), and a TeV scale (MNP∼1 TeV), there is a fascinating relation, i.e. . The TeV scale, MNP, is a new physics scale beyond the standard model which is regarded as supersymmetry in this letter. We suggest a simple supersymmetric neutrinophilic Higgs doublet model, which realizes the above relation dynamically as well as the suitable mν through a tiny vacuum expectation value of the neutrinophilic Higgs doublet without additional scales other than MNP and MGUT. A gauge coupling unification, which is an excellent feature in the supersymmetric standard model, is preserved automatically in this setup.

The most direct way to get information on neutrino masses is the investigation of weak decays and tritium is the best candidate due to its high specific activity and low endpoint energy. The relevance of this approach is based on the following arguments: • Neutrinos are not massless as we have convincing evidence for neutrino oscillations from experiments detecting atmospheric and solar neutrinos. The signals are interpreted as differences in the squares of neutrino masses from which a lower bound for the neutrino masses can be derived. • As these differences are rather small one can set limits for all neutrino masses from the lowest upper bound which is set by the Mainz group from tritium β decay: mv2 = −1.6 ± 2.5 ± 2.1 eV2/c4 corresponding to an upper limit of mv < 2.2 eV/c2 (95 % C.L.). Hence the sum of the three neutrino masses is less than about 7 eV/c2 The results are of interest for cosmology as neutrinos are part of the hot dark matter. The minimum total mass deduced from oscilation experiments is about equal to the sum of the stellar masses. The present upper bound from the direct mass measurements is about equal to the limit given by structure formation. The result of the two presently working experiments in Mainz and Troitsk and their systematic uncertainties will be presented. These experiment have almost reached their sensitivity limits. A next generation experiment KATRIN will be set up at Forschungszentrum Karlsruhe. Its aim is to push the sensitivity limit to mv < 0.3 eV/c2 (90 % C.L.). This would fully cover the cosmologically relevant parameter space and set the neutrino mass scale to discriminate between models with degenerated and hierachical neutrino mass scenarios.

This paper aims at solving several open questions in current neutrino physics: the neutrino mass hierarchy, the Dirac CP violating phase, the absolute mass of neutrinos, the nature of neutrinos (Dirac or Majorana), the Majorana matrix and the absolute value of the effective Majorana neutrino mass. In the research presented in this paper, we have shown that the precise definition of the mass splittings between neutrino mass eigenstates, done in the latest analysis of experimental data, can be of crucial importance for defining the nature of neutrino mass hierarchy. The Standard Model has three generations of fundamental matter particles. Three generations of the charged lepton mass show a hierarchical structure: mτ > mμ > me. Owing to that, there is a belief and it is considered that neutrinos may follow such hierarchical structure. In our calculations, we have also included the latest data obtained, based on the processing of measurement results, which showed that even with such data, obtained results favor the normal neutrino mass hierarchy. As for the individual neutrino mass calculated in this paper, in today’s neutrino physics it is only known that neutrino mass scale is bounded only from above, and both the Dirac and the Majorana character of neutrinos are compatible with all observations. Among some of the questions resolved in this paper, which are related to the properties of neutrinos, a positive answer was also given to the question of whether light neutrinos are self-conjugate particles or not.

We analyse in detail the scalar triplet contribution to the low-energy lepton flavour violating (LFV) and lepton number violating (LNV) processes within a TeV-scale left-right symmetric framework. We show that in both type-I and type-II seesaw dominance for the light neutrino masses, the triplet of mass comparable to or smaller than the largest right-handed neutrino mass scale can give sizeable contribution to the LFV processes, except in the quasi-degenerate limit of light neutrino masses, where a suppression can occur due to cancellations. In particular, a moderate value of the heaviest neutrino to scalar triplet mass ratio $r\lesssim {\cal O}(1)$ is still experimentally allowed and can be explored in the future LFV experiments. Similarly, the contribution of a relatively light triplet to the LNV process of neutrinoless double beta decay could be significant, disfavouring a part of the model parameter space otherwise allowed by LFV constraints. Nevertheless, we find regions of parameter space consistent with both LFV and LNV searches, for which the values of the total effective neutrino mass can be accessible to the next generation ton-scale experiments. Such light triplets can also be directly searched for at the LHC, thus providing a complementary probe of this scenario. Finally, we also study the implications of the triplet contribution for the left-right symmetric model interpretation of the recent diboson anomaly at the LHC.

The evidence for non‐vanishing neutrino masses from solar and atmospheric neutrinos provides the first solid hint towards physics beyond the standard model. A full reconstruction of the neutrino spectrum may well provide a key to the theoretical structures underlying the standard model such as supersymmetry, grand unification or extra space dimensions. In this article we discuss the impact of absolute neutrinos masses on physics beyond the standard model. We review the information obtained from neutrino oscillation data and discuss the prospects of the crucial determination of the absolute neutrino mass scale, as well as the intriguing connection with the Z‐burst model for extreme‐energy cosmic rays.

We determine the forecast errors on the absolute neutrino mass scale and the equation of state of dark energy by combining synthetic data from the Dark Energy Survey (DES) and the Cosmic Microwave Background (CMB) Planck surveyor. We use angular clustering of galaxies for DES in 7 redshift shells up to $z\sim 1.7$ including cross-correlations between different redshift shells. We study models with massless and massive neutrinos and three different dark energy models: $\Lambda$CDM ($w=-1$), wCDM (constant $w$), and waCDM (evolving equation of state parameter $w(a)=w_0 + w_{a}(1-a)$). We include the impact of uncertainties in modeling galaxy bias using a constant and a redshift-evolving bias model. For the $\Lambda$CDM model we obtain an upper limit for the sum of neutrino masses from DES+Planck of $\Sigma m_\nu < 0.08$ eV (95\% C.L.) for a fiducial mass of $\Sigma m_\nu = 0.047$ eV, with a 1$\sigma$ error of 0.02 eV, assuming perfect knowledge of galaxy bias. For the wCDM model the limit is $\Sigma m_\nu < 0.10 $ eV. For a wCDM model where galaxy bias evolves with redshift, the upper limit on the sum of neutrino masses increases to 0.19 eV. DES will be able to place competitive upper limits on the sum of neutrino masses of 0.1-0.2 eV and could therefore strongly constrain the inverted mass hierarchy of neutrinos. In a wCDM model the 1$\sigma$ error on constant $w$ is $\Delta w= 0.03$ from DES galaxy clustering and Planck. Allowing $\Sigma m_\nu$ as a free parameter increases the error on $w$ by a factor of 2, with $\Delta w=0.06$. In a waCDM model, in which the dark energy equation of state varies with time, the errors are $\Delta w_0 = 0.2$ and $\Delta w_a = 0.42$. Including neutrinos and redshift dependent galaxy bias increases the errors to $\Delta w_0 = 0.35$ and $\Delta w_a = 0.89$.

The absolute neutrino mass scale is currently unknown, but can be constrained from cosmology. The WiggleZ high redshift star-forming blue galaxy sample is less sensitive to systematics from non-linear structure formation, redshift-space distortions and galaxy bias than previous surveys. We obtain a upper limit on the sum of neutrino masses of 0.60eV (95% confidence) for WiggleZ+Wilkinson Microwave Anisotropy Probe. Combining with priors on the Hubble Parameter and the baryon acoustic oscillation scale gives an upper limit of 0.29eV, which is the strongest neutrino mass constraint derived from spectroscopic galaxy redshift surveys.

Two-loop effects on the right-handed neutrino masses can have an impact on the low-energy phenomenology, especially when the right-handed neutrino mass spectrum is very hierarchical at the cut-off scale. In this case, the physical masses of the lighter right-handed neutrinos can be dominated by quantum effects induced by the heavier ones. Further, if the heaviest right-handed neutrino mass is at around the Planck scale, two-loop effects on the right-handed neutrino masses generate, through the seesaw mechanism, an active neutrino mass which is in the ballpark of the experimental values. In this paper we investigate extensions of the Planck-scale lepton number breaking scenario by additional Higgs doublets (inert or not). We find that under reasonable assumptions these models lead simultaneously to an overall neutrino mass scale and to a neutrino mass hierarchy in qualitative agreement with observations.

The search for neutrinoless double β decay probes lepton number conservation with high sensitivity and investigates the neutrino nature and mass scale. Experiments presently in preparation will cover the quasi-degeneracy region of the neutrino mass pattern. Probing the inverted hierarchy region requires improved sensitivities and next-generation experiments, based either on large expansions of the present searches or on new ideas. We examine here a novel technology relying on ZnMoO4 scintillating bolometers, which can provide an experiment with background close to zero in the ton × year exposure scale. The promising performance of a pilot detector is presented, both in terms of energy resolution and background control. A preliminary study of the sensitivities of future experiments shows that the inverted hierarchy region is within the reach of the technique here proposed. A realistic phased approach program towards a next-generation search is presented and briefly discussed.

The tiny neutrino masses and the associated large lepton mixings provide an interesting puzzle and a likely window to the physics beyond the standard model. This is certainly true if neutrinos are Majorana particles, since then, unlike in the Dirac case, the standard model is not a complete theory. The Majorana case leads to lepton number violation manifested through neutrinoless-double-beta decay and same-sign dileptons potentially accessible to colliders such as the LHC. This is covered at length. I discuss in these lectures possible theories of neutrino mass whose predictions are dictated by their structure only and this points strongly to grand unification. I cover in detail both SU(5) and SO(10) grand unified theories, and study the predictions of their minimal versions. The main message I wish to bring across is a serious hope of probing the origin of neutrino mass in near future, through the combined effort of high-energy collider and low-energy lepton number and lepton flavor violation experiments.

We study neutrino mass matrices with one texture equality and the neutrino mixing matrix having either its first ( T M 1 ) or second ( T M 2 ) column identical to that of the tribimaximal mixing matrix. We found that out of total fifteen possible neutrino mass matrices with one texture equality, only six textures are compatible with T M 1 mixing and six textures are compatible with T M 2 mixing in the light of the current neutrino oscillation data. These textures have interesting implications for the presently unknown parameters such as the neutrino mass scale, effective Majorana neutrino mass, effective neutrino mass, the atmospheric mixing, and the Dirac- and Majorana-type CP violating phases. We, also, present the S 3 group motivation for some of these textures.

Neutrino masses are yet unknown. We discuss the present state of effective electron antineutrino mass fromβdecay experiments; effective Majorana neutrino mass from neutrinoless double-beta decay experiments; neutrino mass squared differences from neutrino oscillation: solar, atmospheric, reactor, and accelerator-based experiments; sum of neutrino masses from cosmological observations. Current experimental challenges in the determination of neutrino masses are briefly discussed. The main focus is devoted to contemporary experiments.

We present a brief summary of the parallel Session IV, “Neutrino masses, states and interactions”, of the Neutrino Oscillation Workshop 2022. Topics covered in this session include recent experimental and theoretical results on searches for neutrinoless double beta decay, coherent elastic neutrino-nucleus scattering, developments in measurements of the absolute neutrino mass scale and phenomenological implications of: neutrino nonstandard interactions, heavy neutral leptons, nontrivial neutrino electromagnetic properties and radiative models of neutrino mass generation.