Narrow Results

The supersymmetric standard model of particle interactions is extended to include two Higgs triplet superfields at the TeV scale, carrying two units of lepton number. Realistic tree-level Majorana neutrino masses are obtained in the presence of soft, i.e. bilinear, R-parity nonconservation.

The current status of solar neutrino measurements and their oscillation interpretation is reviewed.

The renormalization group equations (RGEs) of the mass matrices of quarks and leptons in an SO(10) model with two-Higgs scalars in the Yukawa coupling are studied. This model is the minimal model of SUSY and non-SUSY SO(10) GUT which can reproduce all the experimental data. Non-SUSY SO(10) GUT model has the intermediate energy phase, Pati–Salam phase, and passes through the symmetry breaking pattern, SO(10) → SU(2)_L × SU(2)_R × SU(4)_C → SU(2)_L × U(1)_Y × SU(3)_C. Though minimal, it has, after the Pati–Salam phase, four Higgs doublets in Yukawa interactions. We consider the RGEs of the Yukawa coupling constants of quarks and charged leptons and of the coupling constants of the dimension-five operators of neutrinos corresponding to the above symmetry breaking pattern. The scalar quartic interactions are also incorporated.

The double-beta decay process has been widely investigated in the last two decades due to the possible lepton number nonconservation decay modes that may occur. An experimental evidence of these modes would lead to the conclusion that neutrino is a massive Majorana particle. At present, when the nonzero neutrino mass is convincingly proved by neutrino oscillation experiments, the double-beta decay investigations are the most promising for determining the absolute value of the neutrino mass. In this paper we give a brief review of some recent nuclear double-beta decay investigations in connection with neutrino mass. We discuss the potential of this process to search for beyond standard model physics, the QRPA-based methods for computing the relevant nuclear matrix elements and the derivation of neutrino masses both from double-beta decay and neutrino oscillation data and in agreement with the present cosmological constraints.

We discuss the implications of a new scalar field coupled to neutrinos.

We demonstrate that an SU(2)_L×U(1)_Y model with the same particle content as Standard Model (SM) and discrete reflection symmetry between second and third generations of leptons gives rise to charged lepton and neutrino mass matrices which can accommodate the present solar, atmospheric, WMAP neutrino experimental results. The model predicts the value of |U₁₃| which could be tested in neutrino factories and the effective Majorana neutrino mass <m_ee> which is at the lower end of the present experimental value. Neutrino masses are generated through dim=5 operators and the scale of which are constrained by the value of <m_ee>. If, in future neutrinoless double beta decay experiments namely, MOON, EXO, GENIUS shift the lower bound on <m_ee> by one order, the present model will fail to accommodate the solar neutrino mixing angle due to LMA solution.

We present and discuss the properties and the main results of a cosmological model with a spontaneously-broken chiral symmetry. The model contains and relates dynamically, two spin-zero fields. The scalar field can provide the dynamical basis for inflation in the early universe. The pseudoscalar, Goldstone field can provide an early, small residual vacuum energy density, the absolute value of which we estimate to be similar to the present, empirically small vacuum energy density. The small energy scale for this effective cosmological constant is estimated separately, by relating it dynamically to the empirical, small scale of neutrino mass. CP invariance is broken spontaneously. This provides a natural basis for the early generation of an antineutrino–neutrino asymmetry, whose magnitude we estimate, and find to be significant.

We demonstrate that "Bimaximal + Democratic" type neutrino mass matrix can accommodate the deviation of θ_⊙ from its maximal value along with the other present-day neutrino experimental results, namely, atmospheric, CHOOZ, neutrinoless double beta decay (ββ_0ν) and result obtained from WMAP experiment. We define a function χ_p in terms of solar and atmospheric neutrino mass squared differences and solar neutrino mixing angle (obtained from different experiments and our proposed texture). The masses and mixing angles are expressed in terms of three parameters in our proposed texture. The allowed region of the texture parameters is obtained through minimization of the above function. The proposed texture crucially depends on the value of the experimental results of ββ_0ν experiment among all other above-mentioned experiments. If, in future, ββ_0ν experiments, namely, MOON, EXO, GENIUS shift the lower bound on 〈m_ee〉 at the higher side by one order, the present texture will be ruled out.

The unjustly neglected method of exactly solving generalized electroweak models — with an original spontaneous symmetry breaking mechanism based on the gauge group SU(n)_L⊗U(1)_Y — is applied here to a particular class of chiral 3-3-1 models. This procedure enables us, without resorting to any approximation, to express the boson mass spectrum and charges of the particles involved therein as a straightforward consequence of both a proper parametrization of the Higgs sector and a new generalized Weinberg transformation. We prove that the resulting values can accommodate the experimental ones just by tuning a sole parameter. Furthermore, if we take into consideration both the left-handed and right-handed components of the neutrino (included in a lepton triplet along with their corresponding left-handed charged partner), then we are in the position to propose an original method for the neutrino to acquire a very small but nonzero mass without spoiling the previously achieved results in the exact solution of the model. In order to be compatible with the existing phenomenological data, the range of that sole parameter imposes a large order of magnitude for the vev〈ϕ〉~10⁴ TeV in our method. Consequently, the new bosons of the model have to be very massive.

Combining one established idea with two recent ones, it is pointed out for the first time that three of the outstanding problems of particle physics and cosmology, i.e. neutrino mass, dark matter, and baryogenesis, may have a simple common solution, arising from the interactions of a single term, with experimentally verifiable consequences.

We prove that, even at a low TeV scale, the canonical seesaw mechanism can be naturally implemented in the exact solution of a particular 3-3-1 gauge model, since a very small alteration ε in the parameter matrix of the Higgs sector is taken into account. Therefore, this new parameter can act as an appropriate mass source for neutrinos, while, due to the main parameter a, all the previously achieved results in the exact solution of the model are recovered. Moreover, this mathematical artifice does separate the boson mass spectrum from the neutrino mass issue, hence giving more flexibility in tuning the model. Possible phenomenological results and their implications — such as dark matter plausible candidates that can occur — are also briefly discussed.

We analyze with the Bayesian method the solar and KamLAND neutrino data in terms of neutrino oscillations. We show that Bayesian credible regions with a flat prior in the plane strongly support the LMA solution, in agreement with the usual chi-square analysis. Other reasonable priors are considered in order to test the stability of the LMA solution. We show that priors which favor small or large values of the mixing angle lead to minor changes of the allowed LMA region, affecting mainly its large-tan²θ₁₂ part.

This is a brief review of spectroscopic studies of neutrino-less double beta decays (0νββ) and the MOON (Mo Observatory Of Neutrinos) project. It aims at studying the Majorana nature of neutrinos and the mass spectrum by spectroscopic studies of 0νββ with ν-mass sensitivity of 〈m_ν〉 ≈ 30 meV. The solid scintillator option of the MOON detector is a super ensemble of multi-layer modules, each being composed by a scintillator plate and two tracking detector planes. Thin ββ source films are interleaved between the detector planes. High localization of the two β tracks enables one to select true signals and reject BG ones by spatial and time correlation analyses. MOON with detector ≠ ββ source is used for studying 0νββ decays from ¹⁰⁰Mo, ⁸²Se and other ββ isotopes with large nuclear sensitivity (large Q_ββ). Real-time exclusive measurements of low energy solar neutrinos can also be made by observing inverse β rays from solar-ν captures of ¹⁰⁰Mo in delayed coincidence with the subsequent β decay of ¹⁰⁰Tc.

From several neutrino oscillation experiments, we understand now that neutrinos have mass. However, we really do not know what mechanism is responsible for producing this neutrino mass. Current or planned neutrino experiments utilize neutrino beams and long-baseline detectors to explore flavor mixing but do not address the question of the origin of neutrino mass. In order to begin answering that question, neutrino interactions need to be explored at much higher energies. This paper outlines a program to explore neutrinos and their interactions with various particles through a series of experiments involving colliding neutrino beams.

We consider a small, metastable maximum vacuum expectation value b₀ of order of a few eV, for a pseudoscalar Goldstone-like field, which is related to the scalar inflaton field ϕ in an idealized model of a cosmological, spontaneously-broken chiral symmetry. The b field allows for relating semi-quantitatively three distinct quantities in a cosmological context.

(a) A very small, residual vacuum energy density or effective cosmological constant of , for λ ~ 3×10^-14, the same as an empirical inflaton self-coupling.

(b) A tiny neutrino mass, less than b₀.

(c) A possible small variation downward of the proton to electron mass ratio over cosmological time. The latter arises from the motion downward of the b field over cosmological time, toward a nonzero value. Such behavior is consistent with an equation of motion.

We argue that hypothetical b quanta, potentially inducing new long-range forces, are absent, because of negative, effective squared mass in an equation of motion for b-field fluctuations. The assumed flatness of a potential maximum involves a small inverse-time parameter μ ≪ 1/t₀, where t₀ is the present age of the universe.

The neutral member of a Majorana fermion triplet (Σ⁺, Σ⁰, Σ^-) is proposed as a candidate for the dark matter of the Universe. It may also serve as the seesaw anchor for obtaining a radiative neutrino mass.

The Supersymmetric Standard Model is a benchmark theoretical framework for particle physics, yet it suffers from a number of deficiencies, the main one among which is the strong CP problem. Solving this with an axion in the context of selected new particles, it is shown in three examples that other problems go away automatically as well, resulting in (-)^L and (-)^3B conservation, viable combination of two dark-matter candidates, successful baryogenesis, seesaw neutrino masses, and verifiable experimental consequences at the TeV energy scale.

The inverse seesaw mechanism of neutrino mass, i.e. , where ∊_L is small, is discussed in the context of the U(1)_Σ model. This is a gauge extension of the Standard Model of particle interactions with lepton triplets (Σ⁺, Σ⁰, Σ^-) as (Type III) seesaw anchors for obtaining small Majorana neutrino masses.

A minimalistic scenario is developed to explain dark matter and tiny but nonzero neutrino masses. A new scalar called SLIM plays the role of the dark matter. Neutrinos achieve Majorana mass through a one-loop diagram. This scenario can be realized for both real and complex SLIM. Simultaneously explaining the neutrino mass and dark matter abundance constrains the scenario. In particular for real SLIM, an upper bound of a few MeV on the masses of the new particles and a lower bound on their coupling is obtained which make the scenario testable. The low energy scenario can be embedded within various SU(2)× U(1) symmetric models. A specific example is introduced and its phenomenological consequences are discussed.

The neutrino oscillations probabilities depend on mass squared differences; in the case of three-neutrino mixing, there are two independent differences, which have been measured experimentally. In order to calculate the absolute masses of neutrinos, we have conjectured a third relation, in the form of a sum of squared masses. The calculated masses look plausible and are in good agreement with the upper bounds coming from astrophysics.