Neutrino Mass Research Articles

Connecting (g − 2)μ to neutrino mass in the extended neutrinophilic 2HDM

One simple way to lower the scale of the seesaw mechanism that generates neutrino masses is to attribute part of their smallness to a suppressed vacuum expectation value of a second Higgs doublet as in the neutrinophilic 2HDM or in the type IB seesaw model. On that structure we add one charged singlet scalar to induce a chirally enhanced contribution to (g – 2)μ with the same righthanded neutrinos of the seesaw. We discuss the interplay of generating the necessary contribution to the latter with lepton flavor violation which is also necessarily brought to low scale. We show that it is possible to explain (g –2)μ even for heavy neutrino masses of order of a few TeV.

Tree-level UV completions for NRSMEFT d = 6 and d = 7 operators

We study ultra-violet completions for operators in standard model effective field theory extended with right-handed neutrinos (NRSMEFT). Using a diagrammatic method, we generate systematically lists of possible tree-level completions involving scalars, fermions or vectors for all operators at d = 6 and d = 7, which contain at least one right-handed neutrino. We compare our lists of possible UV models to the ones found for pure SMEFT. We also discuss how the observation of LNV processes via NRSMEFT operators at the LHC can be related to Majorana neutrino masses of the standard model neutrinos.

Tachyonic Neutrinos: From the Cosmic Rays to Extragalactic Supernovae

The possibility of neutrinos moving at faster-than-light speeds can be modeled using terms in the Lagrangian that violate Lorentz symmetry, but the question of whether m2<0 and v>c tachyonic neutrinos exist is an empirical question. It remains unresolved despite evidence from cosmic ray and other data that the electron neutrino has an effective mν2≈−0.25eV2, which would require that one or more mass states is also tachyonic. In 2013, the 3+3 model of the neutrino masses, which includes one tachyonic mass state, was proposed based on supernova SN 1987A neutrino data. Here, we update evidence for tachyonic electron neutrinos and the 3+3 model and discuss one test which could prove conclusive. The update of earlier evidence includes many new elements, including new data which make the earlier cosmic ray evidence more robust, new results on cosmic ray composition, the ankle of the spectrum, leptonic cosmic ray data, and the statistical significance of finding the three large neutrino masses stipulated in the 3+3 model. Barring a galactic supernova, which occur only around twice a century, a decisive test of the 3+3 model could involve observing an extragalactic supernova neutrino burst, that is, a cluster of neutrinos in a specific time window well beyond what chance would predict. Even though existing searches for such bursts have yielded only upper limits on the extragalactic supernova frequency within a certain distance, it is shown that the choice of a one-day window for possible neutrino clusters in time might be far more sensitive. A search using a one-day time window could be conducted using existing data, and if a signal is found it would confirm the 3+3 model. Of course, the absence of any day-long neutrino burst would not disprove the model, since it could mean only that the nearest supernova during the period when detectors were active was simply too far to be detected. Finally, apart from testing the 3+3 model, an alternative type of search is suggested using existing hadronic cosmic ray data (from the IceCube Collaboration) that might verify the tachyonic neutrino hypothesis.

New magic neutrino mass textures with three free parameters

Motivated by current experiments on searching for neutrinoless double beta decays, we study the phenomenological consequences and testability of the constraint relation “Mii=Mjj+Meμ+Meτ”, for i,j=e,μ,τ, on the magic neutrino mass matrix elements. This hypothesis is inspired by the μ−τ symmetry and gives rise to six different Majorana neutrino mass textures, including two textures one-zero. These obtained textures are diagonalized by the well-known trimaximal mixing which provides nonzero and nonmaximal reactor and atmospheric angles, respectively. Depending on the predominance of the e-row or μ-τ block, the preferred neutrino mass hierarchy and the lower limits on the |Mii| effective Majorana masses for each magic matrix are determined. Furthermore, in light of the global-fit results of neutrino oscillation parameters as reported by NuFIT 5.1, we also study the testability of these textures at the proposed neutrinoless double beta decay experiments such as KamLAND-Zen, GERDA Phase-II and nEXO, by incorporating the effective Majorana neutrino masses |Mij| that are generated through these neutrino mass matrices.

Fermionic dark matter in Dynamical Scotogenic Model

In the Dynamical Scotogenic Model, the global B − L symmetry is supposed to be broken spontaneously resulting in a massless Goldstone boson called majoron, and massive right handed neutrinos which participate in the generation of light neutrino massses at one-loop. One of them being the lightest stable particle can be a thermal dark matter candidate. We discuss how the dark matter phenomenology differs from the original Scotogenic model, taking into account all the constraints coming from the observed neutrino masses and mixing, lepton flavor violations such as μ → eγ, μ → eJ, astrophysical and cosmological observations of stellar cooling and Neff, as well as collider signatures such as Higgs invisible decays. We find that the dark matter annihilation to majorons plays an important role to produce the right relic abundance.

The FLAMINGO project: cosmological hydrodynamical simulations for large-scale structure and galaxy cluster surveys

ABSTRACT We introduce the Virgo Consortium’s FLAMINGO suite of hydrodynamical simulations for cosmology and galaxy cluster physics. To ensure the simulations are sufficiently realistic for studies of large-scale structure, the subgrid prescriptions for stellar and AGN feedback are calibrated to the observed low-redshift galaxy stellar mass function and cluster gas fractions. The calibration is performed using machine learning, separately for each of FLAMINGO’s three resolutions. This approach enables specification of the model by the observables to which they are calibrated. The calibration accounts for a number of potential observational biases and for random errors in the observed stellar masses. The two most demanding simulations have box sizes of 1.0 and 2.8 Gpc on a side and baryonic particle masses of 1 × 108 and $1\times 10^9\, \text{M}_\odot$, respectively. For the latter resolution, the suite includes 12 model variations in a 1 Gpc box. There are 8 variations at fixed cosmology, including shifts in the stellar mass function and/or the cluster gas fractions to which we calibrate, and two alternative implementations of AGN feedback (thermal or jets). The remaining 4 variations use the unmodified calibration data but different cosmologies, including different neutrino masses. The 2.8 Gpc simulation follows 3 × 1011 particles, making it the largest ever hydrodynamical simulation run to z = 0. Light-cone output is produced on-the-fly for up to 8 different observers. We investigate numerical convergence, show that the simulations reproduce the calibration data, and compare with a number of galaxy, cluster, and large-scale structure observations, finding very good agreement with the data for converged predictions. Finally, by comparing hydrodynamical and ‘dark-matter-only’ simulations, we confirm that baryonic effects can suppress the halo mass function and the matter power spectrum by up to ≈20 per cent.

The JUNO water Cherenkov detector system

The Jiangmen Underground Neutrino Observatory (JUNO) is a 20 kton liquid scintillator detector with the primary physics goal of the neutrino mass ordering determination. The detector will be built in a laboratory 650-m underground. The pool is filled with 34 kton ultrapure water outside the central detector as a water Cherenkov detector for cosmic muon detection. 2400 MCP-PMTs detect the water Cherenkov light produced by cosmic muons. The inner surface of the water veto is covered with a Tyvek reflector to increase the light collection efficiency. A water system is used for water purification and circulation to maintain high water quality for optimal detector performance. A set of radon removal equipment will be integrated with the water system to reduce the radon-induced background in the central detector. Based on prototype studies, the radon concentration in water could be reduced to less than 10 mBq/m3. The cosmic muon detection efficiency of the water Cherenkov detector can reach 99.5%. With this veto system, the cosmic muon-induced fast neutron background can also be reduced to the level of about ∼0.1/day level.

Precision CMB constraints on eV-scale bosons coupled to neutrinos

The cosmic microwave background (CMB) has proven to be an invaluable tool for studying the properties and interactions of neutrinos, providing insight not only into the sum of neutrino masses but also the free streaming nature of neutrinos prior to recombination. The CMB is a particularly powerful probe of new eV-scale bosons interacting with neutrinos, as these particles can thermalize with neutrinos via the inverse decay process, nu bar{nu } rightarrow X, and suppress neutrino free streaming near recombination – even for couplings as small as lambda _{nu } sim {mathcal {O}}(10^{-13}). Here, we revisit CMB constraints on such bosons, improving upon a number of approximations previously adopted in the literature and generalizing the constraints to a broader class of models. This includes scenarios in which the boson is either spin-0 or spin-1, the number of interacting neutrinos is either N_{textrm{int}} = 1,2 or 3, and the case in which a primordial abundance of the species is present. We apply these bounds to well-motivated models, such as the singlet majoron model or a light U(1)_{L_{mu }-L_{tau }} gauge boson, and find that they represent the leading constraints for masses m_Xsim 1, {textrm{eV}}. Finally, we revisit the extent to which neutrino-philic bosons can ameliorate the Hubble tension, and find that recent improvements in the understanding of how such bosons damp neutrino free streaming reduces the previously found success of this proposal.

Nu Electroweak baryogenesis: the scalar singlet strikes back

We perform a comprehensive scan of the parameter space of a general singlet scalar extension of the Standard Model to identify the regions which can lead to a strong first-order phase transition, as required by the electroweak baryogenesis mechanism. We find that taking into account bubble nucleation is a fundamental constraint on the parameter space and present a conservative and fast estimate for it so as to enable efficient parameter space scanning. The allowed regions turn out to be already significantly probed by constraints on the scalar mixing from Higgs signal strength measurements. We also consider the addition of new neutrino singlet fields with Yukawa couplings to both scalars and forming heavy (pseudo)-Dirac pairs, as in the linear or inverse Seesaw mechanisms for neutrino mass generation. We find that their inclusion does not alter the allowed parameter space from early universe phenomenology in a significant way. Conversely, there are allowed regions of the parameter space where the presence of the neutrino singlets would remarkably modify the collider phenomenology, yielding interesting new signatures in Higgs and singlet scalar decays.

Untying the Growth Index to Relieve the σ8 Discomfort

The matter fluctuation parameter σ8 is, by model construction, degenerate with the growth index γ. Here, we study the effect on the cosmological parameter constraints by treating each independently from one another, considering σ8 as a free and non-derived parameter along with a free γ. We then try to constrain all parameters using three probes that span from deep to local redshifts, namely the CMB spectrum, the growth measurements from redshift space distortions fσ8, and the galaxy cluster counts. We also aim to assess the impact of this relaxation on the σ8 tension between its inferred CMB value in comparison to that obtained from local cluster counts. We also propose a more sophisticated correction, along with the classical one, that takes into account the impact of cosmology on the growth measurements when the parameters are varied in the Monte Carlo process, which consist in adjusting the growth to keep the observed power spectrum, integrated over all angles and scales, as invariant with the background evolution. We found by using the classical correction that untying the two parameters does not shift the maximum likelihood of either σ8 or γ, but it rather enables larger bounds with respect to when σ8 is a derived parameter, and that when considering CMB + fσ8, or when further combining with cluster counts albeit with tighter bounds. Precisely, we obtain σ8=0.809±0.043 and γ=0.613±0.046 in agreement with Planck’s constraint for the former and compatible with ΛCDM for the latter but with bounds wide enough to accommodate both values subject to the tensions. Allowing for massive neutrinos does not change the situation much. On the other hand, considering a tiered correction yields σ8=0.734±0.013 close to ∼1 σ for the inferred local values albeit with a growth index of γ=0.636±0.022 at ∼2 σ from its ΛCDM value. Allowing for massive neutrinos in this case yielded σ8=0.756±0.024, still preferring low values but with much looser constraints on γ=0.549±0.048 and a slight preference for Σmν∼0.19. We conclude that untying σ8 and γ helps in relieving the discomfort on the former between the CMB and local probes, and that careful analysis should be followed when using data products treated in a model-dependent way.

Tri-hypercharge: a separate gauged weak hypercharge for each fermion family as the origin of flavour

We propose a tri-hypercharge (TH) extension of the Standard Model (SM) in which a separate gauged weak hypercharge is associated with each fermion family. In this way, every quark and lepton multiplet carries unique gauge quantum numbers under the extended gauge group, providing the starting point for a theory of flavour. If the Higgs doublets only carry third family hypercharge, then only third family renormalisable Yukawa couplings are allowed. However, non-renormalisable Yukawa couplings may be induced by the high scale Higgs fields (hyperons) which break the three hypercharges down to the SM hypercharge, providing an explanation for fermion mass hierarchies and the smallness of CKM quark mixing. Following a similar methodology, we study the origin of neutrino masses and mixing in this model. Due to the TH gauge symmetry, the implementation of a seesaw mechanism naturally leads to a low scale seesaw, where the right-handed neutrinos in the model may be as light as the TeV scale. We present simple examples of hyperon fields which can reproduce all quark and lepton (including neutrino) masses and mixing. After a preliminary phenomenological study, we conclude that one of the massive Z′ bosons can be as light as a few TeV, with implications for flavour-violating observables, LHC physics and electroweak precision observables.

Physics implication from higher weak isospin decomposition

The SU(3)_Lotimes U(1)_X symmetry actually studied is directly broken to the electroweak symmetry SU(2)_Lotimes U(1)_Y by a Higgs triplet, predicting a relevant new physics at TeV scale. This work argues, by contrast, that the higher weak isospin SU(3)_L might be broken at a high energy scale, much beyond 1 TeV, by a Higgs octet to an intermediate symmetry SU(2)_Lotimes U(1)_{T_8} at TeV, before the latter U(1)_{T_8} recombined with U(1)_X defines (i.e., broken to) U(1)_Y by a Higgs singlet. The new physics coupled to SU(3)_L breaking phase is decoupled, whereas what remains is a novel family-nonuniversal abelian model, U(1)_{T_8}otimes U(1)_X, significantly overhauling the standard model as well as yielding consistent results for neutrino mass, dark matter, W-mass anomaly, and FCNC, differently from the usual 3-3-1 model.

Ultraviolet extensions of the Scotogenic model

The Scotogenic model is a popular scenario that induces radiative Majorana neutrino masses and includes a weakly-interacting dark matter candidate. We classify all possible ultraviolet extensions of the Scotogenic model in which (i) the dark ℤ2 parity emerges at low energies after the spontaneous breaking of a global U(1)L lepton number symmetry, and (ii) the low-energy effective theory contains a naturally small lepton number breaking parameter, suppressed by the mass of a heavy mediator integrated out at tree-level. We find 50 such models and discuss two of them in detail to illustrate our setup. We also discuss some general aspects of the phenomenology of the models in our classification, exploring possible lepton flavor violating signals, collider signatures and implications for dark matter. The phenomenological prospects of these scenarios are very rich due to the presence of additional scalar states, including a massless Goldstone boson.

DEMNUni: the imprint of massive neutrinos on the cross-correlation between cosmic voids and CMB lensing

Cosmic voids are a powerful probe of cosmology and are one of the core observables of upcoming galaxy surveys. The cross-correlations between voids and other large-scale structure tracers such as galaxy clustering and galaxy lensing have been shown to be very sensitive probes of cosmology and among the most promising to probe the nature of gravity and the neutrino mass. However, recent measurements of the void imprint on the lensed Cosmic Microwave Background (CMB) have been shown to be in tension with expectations based on LCDM simulations, hinting to a possibility of non-standard cosmological signatures due to massive neutrinos. In this work we use the DEMNUni cosmological simulations with massive neutrino cosmologies to study the neutrino impact on voids selected in photometric surveys, as well as on the void-CMB lensing cross-correlation. We show how the void properties observed in this way (size function, profiles) are affected by the presence of massive neutrinos compared to the neutrino massless case, and show how these can vary as a function of the selection method of the void sample. We comment on the possibility for massive neutrinos to be the source of the aforementioned tension. Finally, we identify the most promising setup to detect signatures of massive neutrinos in the voids-CMB lensing cross-correlation and define a new quantity useful to distinguish among different neutrino masses by comparing future observations against predictions from simulations including massive neutrinos.

Leptogenesis and neutrinoless double beta decay in the scotogenic hybrid textures of neutrino mass matrix

Abstract In our recent work, we identified the hybrid textures that simultaneously account for dark matter (DM) and neutrinoless double beta decay (0νββ). We also obtained bounds on dark matter mass and effective Majorana mass. However, on the same lines, in this work, we explored common parameter spaces amongst the baryon asymmetry of the universe Y, dark matter mass M 1, and effective Majorana mass |Mee |. We use experimental bounds on the relic density of dark matter (Ωh 2) and baryon asymmetry of the universe to identify the suitable hybrid textures. We found that out of the five hybrid textures only three simultaneously satisfy the physics observations of the DM, 0νββ, and leptogenesis. It is interesting to note that these three hybrid textures give a lower bound to the effective Majorana mass |Mee |, which can be probed in current and future experiments like SuperNEMO, KamLAND-Zen, NEXT, and nEXO (5 years) that have sensitivity reaches of 0.05 eV, 0.045 eV, 0.03 eV, and 0.015 eV, respectively.

Saving CNB assisted EDE model at the expense of quantum corrections?

Abstract As it is suggested in [1,2], one can dynamically introduce the coincidence time-scale for EDE in the framework of a particular mass-varying-neutrino-model as a time at which neutrinos constituting the cosmic neutrino background enter the non-relativistic regime. The model does not predict, however, the right amount of EDE density because of smallness of neutrino masses. One may hope to adjust the parameters in such a way as to ensure that the two-loop contributions are kept small while at the same time the effective mass for scalar field that enters the expression of zero-point-energy (for the field trapped in the minimum of effective potential) is sufficient for explaining the needed amount of EDE. Unfortunately, the answer is not in the affirmative.

Diffuse Neutrino Flux Based on the Rates of Core-collapse Supernovae and Black Hole Formation Deduced from a Novel Galactic Chemical Evolution Model

Fluxes of the diffuse supernova neutrino background (DSNB) are calculated based on a new modeling of galactic chemical evolution, where a variable stellar initial mass function (IMF), depending on the galaxy type, is introduced and black hole (BH) formation from the failed supernova is considered for progenitors heavier than 18M ⊙. The flux calculations are performed for different combinations of the star formation rate, nuclear equation of state, and neutrino mass hierarchy, to examine the systematic effects from these factors. In any case, our new model predicts the enhanced DSNB flux at E ν ≳ 30 MeV and E ν ≲ 10 MeV, due to more frequent BH formation and a larger core-collapse rate at high redshifts in early-type galaxies, respectively. Event rate spectra of the DSNB at a detector from the new model are shown, and the detectability at water-based Cherenkov detectors, Super-Kamiokande with a gadolinium dissolution and Hyper-Kamiokande, is discussed. In order to investigate the impacts of the assumptions in the new model, we prepare alternative models, based on different IMF forms and treatments of BH formation, and estimate the discrimination capabilities between the new and alternative models at these detectors.

Development and characterisation of high-resolution microcalorimeter detectors for the ECHo-100k experiment

The goal of the ECHo experiment is a direct determination of the absolute scale of the neutrino mass by the analysis of the end-point region of the 163Ho electron capture (EC) spectrum. The results of the first phase of the experiment, ECHo-1k, have paved the way for the current phase, ECHo-100k, which aims at a sensitivity below 2eV on the effective electron neutrino mass. In order to reach this goal, a new generation of high-resolution magnetic microcalorimeters with embedded 163Ho have been developed and characterised. The design has been optimised to meet all the challenging requirements of the ECHo-100k experimental phase, such as excellent energy resolution, wafer scale implantation and multi-chip operation with multiplexing read-out. We present the optimisation studies, the final design of the detector array and the first characterisation studies. The obtained results demonstrate that the detectors fully match and even surpass the requirements for the current experimental phase, ECHo-100k.

Phenomenology of the simplest linear seesaw mechanism

The linear seesaw mechanism provides a simple way to generate neutrino masses. In addition to Standard Model particles, it includes quasi-Dirac leptons as neutrino mass mediators, and a leptophilic scalar doublet seeding small neutrino masses. Here we review its associated physics, including restrictions from theory and phenomenology. The model yields potentially detectable μ → eγ rates as well as distinctive signatures in the production and decay of heavy neutrinos (Ni) and the charged Higgs boson (H±) arising from the second scalar doublet. We have found that production processes such as e+e−→ NN, e−γ → NH− and e+e−→ H+H− followed by the decay chain {H}^{pm}to {ell}_i^{pm }N , Nto {ell}_j^{pm }{W}^{mp } leads to striking lepton number violation signatures at high energies which may probe the Majorana nature of neutrinos.

The MillenniumTNG Project: the impact of baryons and massive neutrinos on high-resolution weak gravitational lensing convergence maps

ABSTRACT We study weak gravitational lensing convergence maps produced from the MillenniumTNG simulations by direct projection of the mass distribution on the past backwards lightcone of a fiducial observer. We explore the lensing maps over a large dynamic range in simulation mass and angular resolution, allowing us to establish a clear assessment of numerical convergence. By comparing full physics hydrodynamical simulations with corresponding dark-matter-only runs, we quantify the impact of baryonic physics on the most important weak lensing statistics. Likewise, we predict the impact of massive neutrinos reliably far into the non-linear regime. We also demonstrate that the ‘fixed & paired’ variance suppression technique increases the statistical robustness of the simulation predictions on large scales not only for time slices but also for continuously output lightcone data. We find that both baryonic and neutrino effects substantially impact weak lensing shear measurements, with the latter dominating over the former on large angular scales. Thus, both effects must explicitly be included to obtain sufficiently accurate predictions for stage IV lensing surveys. Reassuringly, our results agree accurately with other simulation results where available, supporting the promise of simulation modelling for precision cosmology far into the non-linear regime.