Detecting dark energy in long baseline neutrino oscillations

In this paper, we discuss a possibility of studying properties of dark energy in long baseline neutrino oscillation experiments. We consider two types of models of neutrino dark energy. For one type of models the scalar field is taken to be quintessence-like and for the other phantom-like. In these models the scalar fields couple to the neutrinos to give rise to spatially varying neutrino masses. We will show that the two types of models predict different behaviors of the spatial variation of the neutrino masses inside the Earth and consequently result in different signals in long baseline neutrino oscillation experiments.     

Neutrino oscillations as a probe of dark energy

We consider a class of theories in which neutrino masses depend significantly on environment, as a result of interactions with the dark sector. Such theories of mass varying neutrinos were recently introduced to explain the origin of the cosmological dark energy density and why its magnitude is apparently coincidental with that of neutrino mass splittings. In this Letter we argue that in such theories neutrinos can exhibit different masses in matter and in vacuum, dramatically affecting neutrino oscillations. As an example of modifications to the standard picture, we consider simple models that may simultaneously account for the LSND anomaly, KamLAND, K2K, and studies of solar and atmospheric neutrinos, while providing motivation to continue to search for neutrino oscillations in short baseline experiments such as BooNE.     

Dark energy and neutrino CPT-violation

In this paper we study dynamical CPT-violation in the neutrino sector as induced by the dark energy of the universe. Specifically we consider a dark energy model where the dark energy scalar derivatively interacts with the right-handed neutrinos. This type of derivative coupling leads to cosmological CPT-violation during the evolution of the background field of the dark energy. We calculate the induced CPT-violation of left-handed neutrinos and find that the CPT-violation produced in this way is consistent with the present experimental limit and sensitive to future neutrino oscillation experiments such as the neutrino factory. PACS 95.36.+x; 14.60.St     

Minimal supergravity scalar neutrino dark matter and inverse seesaw neutrino masses

We show that within the inverse seesaw mechanism for generating neutrino masses, minimal supergravity naturally provides the scalar neutrino as the lightest superparticle. We also demonstrate that such schemes naturally reconcile the small neutrino masses with the correct relic scalar neutrino dark matter abundance and accessible direct detection rates in nuclear recoil experiments. This way, inverse seesaw minimal supergravity offers a common solution to the generation of the neutrino mass and to the origin of dark matter.     

Linking solar and long baseline terrestrial neutrino experiments

We show that, in the framework of three light neutrino species with hierarchical masses and assuming no fine tuning between the entries of the neutrino mass matrix, one can use the solar neutrino data to obtain information on the element U(e3) of the lepton mixing matrix. Conversely, a measurement of U(e3) in atmospheric or long baseline accelerator or reactor neutrino experiments would help discriminate between possible oscillation solutions of the solar neutrino problem.     

Matter effects and CP-violation at neutrino factories

Neutrino factories allow precise measurements of neutrino masses, leptonic mixing angles, leptonic CP-violation and matter effects. Some aspects of matter effects and their role in the disentanglement of parameters in very long baseline neutrino oscillation experiments are discussed.     

Results from solar, atmospheric and K2K experiments and future possibilities with T2K

Recent results from solar, reactor, atmospheric and long baseline (K2K) experiments are discussed. With the improved data statistics and analyses, our knowledge on the neutrino masses and mixing angles are steadily improving. T2K is the next generation neutrino oscillation experiment between J-PARC in Tokai and Super-Kamiokande. This experiment will start in 2009. This experiment is expected to improve the current knowledge on the neutrino masses and mixings substantially.     

Sneutrino dark matter in gauged inverse seesaw models for neutrinos

Extending the minimal supersymmetric standard model to explain small neutrino masses via the inverse seesaw mechanism can lead to a new light supersymmetric scalar partner which can play the role of inelastic dark matter (IDM). It is a linear combination of the superpartners of the neutral fermions in the theory (the light left-handed neutrino and two heavy standard model singlet neutrinos) which can be very light with mass in ~5-20 GeV range, as suggested by some current direct detection experiments. The IDM in this class of models has keV-scale mass splitting, which is intimately connected to the small Majorana masses of neutrinos. We predict the differential scattering rate and annual modulation of the IDM signal which can be testable at future germanium- and xenon-based detectors.     

Leptogenesis and dark matter unified in a non-SUSY model for neutrino masses

We propose a unified explanation for the origin of dark matter and baryon number asymmetry on the basis of a non-supersymmetric model for the neutrino masses. Neutrino masses are generated in two distinct ways, that is, a tree-level seesaw mechanism with a single right-handed neutrino, and one-loop radiative effects by a new additional doublet scalar. A spontaneously broken U(1)^′ brings about a Z₂ symmetry which restricts couplings of this new scalar and controls the neutrino masses. It also guarantees the stability of a CDM candidate. We examine two possible candidates for the CDM. We also show that the decay of a heavy right-handed neutrino related to the seesaw mechanism can generate baryon number asymmetry through leptogenesis.     

Dark matter particle production in b-->s transitions with missing energy

Dedicated underground experiments searching for dark matter have little sensitivity to GeV and sub-GeV masses of dark matter particles. We show that the decay of B mesons to K(K(*)) and missing energy in the final state can be an efficient probe of dark matter models in this mass range. We analyze the minimal scalar dark matter model to show that the width of the decay mode with two dark matter scalars B-->KSS may exceed the decay width in the standard model channel, B-->Knunu , by up to 2 orders of magnitude. Existing data from B physics experiments almost entirely exclude dark matter scalars with masses less than 1 GeV. Expected data from B factories probe the range of dark matter masses up to 2 GeV.     

Leptonic flavor and CP violation

Recent neutrino oscillation data teach us that the neutrinos have masses and that they mix. We discuss two ways that can be used to probe other non-standard leptonic physics. We show that non-standard neutrino interaction can be probed in neutrino oscillation experiments and discuss sneutrino-antisneutrino mixing.     

CP Phase Effects in Long Baseline Neutrino Experiments

Neutrino oscillation experiments are analyzed within the two-flavor frame work which is defined by 1 mass-squared difference and 1 mixing angle. In three flavor neutrino oscillation, there are 6 parameter, 2 mass squared differences, 3 mixing angle and 1 CP phase. In this article, we give the observing CP violating phase effects in neutrino oscillation probability in long baseline neutrino experiments.     

Neutrino masses and the dark energy equation of state: relaxing the cosmological neutrino mass bound

At present, cosmology provides the nominally strongest constraint on the masses of standard model neutrinos. However, this constraint is extremely dependent on the nature of the dark energy component of the Universe. When the dark energy equation of state parameter is taken as a free (but constant) parameter, the neutrino mass bound is sigma m(v) < or = 1.48 eV (95% C.L.), compared with sigma m(v) < or = 0.65 eV (95% C.L.) in the standard model where the dark energy is in the form of a cosmological constant. This has important consequences for future experiments aimed at the direct measurement of neutrino masses. We also discuss prospects for future cosmological measurements of neutrino masses.     

Dark matter,neutrino mass,cutoff for cosmic-ray neutrino,and the Higgs boson invisible decay from a neutrino portal interaction

We study an effective theory beyond the standard model(SM) where either of the two additional gauge singlets, a Majorana fermion and a real scalar, constitutes all or some fraction of dark matter. In particular, we focus on the masses of the two singlets in the range of O(10) MeV-O(10) GeV with a neutrino portal interaction, which plays an important role not only in particle physics but also in cosmology and astronomy. We point out that the thermal dark matter abundance can be explained by(co-)annihilation, where the dark matter with a mass greater than 2 GeV can be tested in future lepton colliders, CEPC, ILC, FCC-ee and CLIC, in the light of the Higgs boson invisible decay. When the gauge singlets are lighter than O(100) MeV, the interaction can affect the neutrino propagation in the universe due to its annihilation with cosmic background neutrino into the gauge singlets. Although in this case it can not be the dominant dark matter, the singlets are produced by the invisible decay of the Higgs boson at such a rate which is fully within reach of future lepton colliders. In particular, a high energy cutoff of cosmic-ray neutrino,which may account for the non-detection of Greisen-Zatsepin-Kuzmin(GZK) neutrino or the non-observation of the Glashow resonance, can be set. Interestingly, given the cutoff and the mass(range) of WIMPs, a neutrino mass can be"measured" kinematically.     

Exploring neutrino mass and mass hierarchy in interacting dark energy models

We investigate how the dark energy properties impact the constraints on the total neutrino mass in interacting dark energy(IDE)models. In this study, we focus on two typical interacting dynamical dark energy models, i.e., the interacting w cold dark matter(IwCDM) model and the interacting holographic dark energy(IHDE) model. To avoid the large-scale instability problem in IDE models, we apply the parameterized post-Friedmann approach to calculate the perturbation of dark energy. We employ the Planck 2015 cosmic microwave background temperature and polarization data, combined with low-redshift measurements on baryon acoustic oscillation distance scales, type Ia supernovae, and the Hubble constant, to constrain the cosmological parameters. We find that the dark energy properties could influence the constraint limits on the total neutrino mass. Once dynamical dark energy is considered in the IDE models, the upper bounds of ∑mν will be changed. By considering the values of χ^2min , we find that in these IDE models the normal hierarchy case is slightly preferred over the inverted hierarchy case;for example, △χ^2= 2.720 is given in the IHDE+∑mν model. In addition, we also find that in the Iw CDM+∑mν model β = 0 is consistent with current observational data inside the 1σ range, and in the IHDE+∑mν model β > 0 is favored at more than 2σ level.     

Cosmology with massive neutrinos coupled to dark energy

Cosmological consequences of a coupling between massive neutrinos and dark energy are investigated. In such models, the neutrino mass is a function of a scalar field, which plays the role of dark energy. The evolution of the background and cosmological perturbations are discussed. We find that mass-varying neutrinos can leave a significant imprint on the anisotropies in the cosmic microwave background and even lead to a reduction of power on large angular scales.     

Reconciling cold dark matter with COBE/IRAS plus solar and atmospheric neutrino data

We present a model where an unstable MeV Majorana tau neutrino can naturally reconcile the cold dark matter model (CDM) with cosmological observations of large and small scale density fluctuations and, simultaneously, with data on solar and atmospheric neutrinos. The solar neutrino deficit is explained through long wavelength, so-called just-so oscillations involving conversions of ν_e into both ν_μ and a sterile species ν_s , while atmospheric neutrino data are explained through ν_μ to ν_e conversions. Future long baseline neutrino oscillation experiments, as well as some reactor experiments will test this hypothesis. The model is based on the spontaneous violation of a global lepton number symmetry at the weak scale. This symmetry plays a key role in generating the cosmologically required decay of the ν_τ with lifetime τ_ντ ≈ 10²-10⁴ seconds, as well as the masses and oscillations of the three light neutrinos ν_e, ν_μ and ν_s required in order to account for solar and atmospheric neutrino data. It also leads to the invisibly decaying Higgs signature that can be searched at LEP and future particle colliders.     

Neutrino Mass Hierarchy and CP Violation in Long Baseline Neutrino Experiment

We discuss the CP violation in long base line neutrino oscillation experiments. The direct measurement of CP violation is the difference of transitions probability between CP conjugate channels. The sign of Δ ₃₁ is not yet determined, we assume two mass hierarchy conditions, normal (Δ ₃₁>0) and inverted (Δ ₃₁<0). In this paper, we study the CP violation and neutrino mass hierarchy effect in vacuum and matter for long baseline BNL experiments. By an appropriate chose of experimental parameter, neutrino energy and traveled distance. We find that, in matter normal mass hierarchy en-chanced maximum CP violation over their invert mass hierarchy value by 12 %.     

Probing the Majorana nature of TeV-scale radiative seesaw models at collider experiments

A general feature of TeV-scale radiative seesaw models, in which tiny neutrino masses are generated via loop corrections, is an extended scalar (Higgs) sector. Another feature is the Majorana nature; e.g., introducing right-handed neutrinos with TeV-scale Majorana masses under the discrete symmetry, or otherwise introducing some lepton number violating interactions in the scalar sector. We study phenomenological aspects of these models at collider experiments. We find that, while properties of the extended Higgs sector of these models can be explored to some extent, the Majorana nature of the models can also be tested directly at the International Linear Collider via the electron–positron and electron–electron collision experiments.