Magnetic moments of Dirac and Majorana neutrinos

We present two models where the magnetic moment of the electron neutrino can be as high as the experimental bound of 10⁻¹⁰ Bohr magnetons. The models, one in which the neutrinos are Dirac particles and the other where they are Majorana particles possessing transition moments, are consistent with known experiments and are realizations of a recent suggestion by Voloshin, Vysotsky and Okun to explain the solar neutrino experiment.     

Neutral particles in light of the Majorana-Ahluwalia ideas

The first part of this article presents an overview of the theory and phenomenology of truly neutral particles based on the papers of Majorana, Racah, Furry, McLennan, and Case. The recent development of the construct undertaken by Ahluwalia could be relevant for the explanation of the present experimental situation in neutrino physics and astrophysics. Then the new fundamental wave equations for self-/anti-self-conjugate type II spinors proposed by Ahluwalia are recast into covariant form. The connection with Foldy-Nigam-Bargmann-Wightman-Wigner (FNBWW)-type quantum field theory is found. Possible applications to the problem of neutrino oscillations are discussed.On leave of absence from Department of Theoretical and Nuclear Physics, Saratov State University, Saratov, Russia. E-mail: dvoeglazov@mainl.jinr.dubna.su.     

2002年诺贝尔物理奖介绍:中微子振荡实验

描述粒子相互作用基本理论是标准模型，按照标准模型，中微子没有静止质量．如果中微子有静止质量，将表现为中微子振荡．戴维斯和小柴昌俊由于确定地发现中微子振荡而获2002年诺贝尔物理奖。     

General neutrino mass spectrum and mixing properties in seesaw mechanisms

Neutrinos stand out among the elementary particles because of their unusually small masses.Various seesaw mechanisms attempt to explain this fact.In this work,applying insights from matrix theory,we are in a position to treat variants of seesaw mechanisms in a general manner.Specifically,using Weyl's inequalities,we discuss and rigorously prove under which conditions the seesaw framework leads to a mass spectrum with exactly three light neutrinos.We find an estimate of the mass of heavy neutrinos to be the mass obtained by neglecting light neutrinos,shifted at most by the maximal strength of the coupling to the light neutrino sector.We provide analytical conditions allowing one to prescribe that precisely two out of five neutrinos are heavy.For higher-dimensional cases the inverse eigenvalue methods are used.In particular,for the CP-invariant scenarios we show that if the neutrino sector has a valid mass matrix after neglecting the light ones,i.e.if the respective mass submatrix is positive definite,then large masses are provided by matrices with large elements accumulated on the diagonal.Finally,the Davis-Kahan theorem is used to show how masses affect the rotation of light neutrino eigenvectors from the standard Euclidean basis.This general observation concerning neutrino mixing,together with results on the mass spectrum properties,opens directions for further neutrino physics studies using matrix analysis.     

Localizability of tachyonic particles and neutrinoless double beta decay

The quantum field theory of superluminal (tachyonic) particles is plagued by a number of problems, which include the Lorentz non-invariance of the vacuum state, the ambiguous separation of the field operator into creation and annihilation operators under Lorentz transformations, and the necessity of a complex reinterpretation principle for quantum processes. Another unsolved question concerns the treatment of subluminal components of a tachyonic wave packet in the field-theoretical formalism, and the calculation of the time-ordered propagator. After a brief discussion on related problems, we conclude that rather painful choices have to be made in order to incorporate tachyonic spin- \frac12\frac{1}{2} particles into field theory. We argue that the field theory needs to be formulated such as to allow for localizable tachyonic particles, even if that means that a slight unitarity violation is introduced into the S matrix, and we write down field operators with unrestricted momenta. We find that once these choices have been made, the propagator for the neutrino field can be given in a compact form, and the left-handedness of the neutrino as well as the right-handedness of the antineutrino follow naturally. Consequences for neutrinoless double beta decay and superluminal propagation of neutrinos are briefly discussed.     

Exotic fermions in Kadyshevsky’s theory and the possibility to detect them

As it is known, the principal research interest of V.G. Kadyshevsky was the development of a geometric approach to quantum field theory with a constraint imposed on the mass spectrum of elementary particles. Non-Hermitian operators arising in this case seemed to be a major obstacle to the development of a consistent theory. These issues have been resolved recently, and the introduction of the pseudo-Hermitian algebraic approach to the construction of quantum theory was a major advance in this physical research. The central point of such theories is the construction of PT-symmetric non-Hermitian Hamiltonians with real eigenvalues. It is important to note that both purely theoretical and experimental studies (e.g., in non-Hermitian optics) are found among the many published papers on this subject. Therefore, we believe that the development of pseudo-Hermitian relativistic quantum theory with a maximal mass may provide favorable opportunities to discuss the possible experimental verification of theoretical results obtained in this field. Kadyshevsky himself regarded the hypothesis of existence of new particles, which he called exotic fermions, as an important prediction of his theory. The possibility of discovery of exotic neutrinos in precision experiments on the determination of the neutrino mass is discussed in the present study.     

Studying the D ∗ K molecular structure of D^{+}_{s1}(2460) in the Bethe–Salpeter approach

To explain both the possible superluminal neutrino propagation and all the known phenomenological constraints/observations on Lorentz violation, the Background-Dependent Lorentz Violation (BDLV) has been proposed. We study the BDLV in a model-independent way. Assuming that the Lorentz violation on the Earth is much larger than those on the interstellar scale, we automatically escape all the astrophysical constraints on Lorentz violation. For the BDLV from the effective field theory, we present a simple model and discuss the possible solutions to the theoretical challenges of the superluminal neutrino propagation such as the Bremsstrahlung effects for muon neutrinos and the pion decays. Also, we address the Lorentz violation constraints from the LEP and KamLAMD experiments. For the BDLV from the Type IIB string theory with D3-branes and D7-branes, we point out that the D3-branes are flavour blind, and all the SM particles are the conventional particles as in the traditional SM when they do not interact with the D3-branes. Thus, we not only can naturally avoid all the known phenomenological constraints on Lorentz violation, but also can naturally explain all the theoretical challenges. Interestingly, the energy-dependent photon velocities may be tested at the experiments.     

Neutrino Oscillations: Entanglement,Energy-Momentum Conservation and QFT

We consider several subtle aspects of the theory of neutrino oscillations which have been under discussion recently. We show that the S-matrix formalism of quantum field theory can adequately describe neutrino oscillations if correct physics conditions are imposed. This includes space-time localization of the neutrino production and detection processes. Space-time diagrams are introduced, which characterize this localization and illustrate the coherence issues of neutrino oscillations. We discuss two approaches to calculations of the transition amplitudes, which allow different physics interpretations: (i) using configuration-space wave packets for the involved particles, which leads to approximate conservation laws for their mean energies and momenta; (ii) calculating first a plane-wave amplitude of the process, which exhibits exact energy-momentum conservation, and then convoluting it with the momentum-space wave packets of the involved particles. We show that these two approaches are equivalent. Kinematic entanglement (which is invoked to ensure exact energy-momentum conservation in neutrino oscillations) and subsequent disentanglement of the neutrinos and recoiling states are in fact irrelevant when the wave packets are considered. We demonstrate that the contribution of the recoil particle to the oscillation phase is negligible provided that the coherence conditions for neutrino production and detection are satisfied. Unlike in the previous situation, the phases of both neutrinos from Z ⁰ decay are important, leading to a realization of the Einstein-Podolsky-Rosen paradox.     

Oscillations Do Not Distinguish Between Massive and Tachyonic Neutrinos

It is shown that the hypothesis of tachyonic neutrinos leads to the same oscillations effect as if they were usual massive particles. Therefore, the experimental evidence of neutrino oscillations does not distinguish between massive and tachyonic neutrinos. Thus, in view of the fact that the results of the direct neutrino mass measurements are not decisive, the question about the nature of neutrinos remains still open.     

Quantum dissipation in vacuum neutrino oscillation

The pattern of neutrino oscillations changes when one considers these particles evolving as an open quantum system. In this article we derive seven possibilities that change the two-generation neutrino survival probability due to quantum dissipation and decoherence. We find entirely original probabilities assuming that these effects can be parametrized by the addition of only one phenomenological constant keeping complete positivity. We observe that a relaxation effect of the system shows an unusual mechanism of flavor conversion, the appearance of CP-violation effects for Majorana neutrinos, besides an appreciable change in the behavior of high energy neutrinos.     

Singletons,Physics in AdS Universe and Oscillations of Composite Neutrinos

The study starts with the kinematical aspects of singletons and massless particles. It extends to the beginning of a field theory of composite elementary particles and its relations with conformal field theory, including very recent developments and speculations about a possible interpretation of neutrino oscillations and CP violation in this context. This framework was developed during the past twenty years. Based on our deformation philosophy of physical theories, it deals with elementary particles composed of singletons in anti-De Sitter spacetime.     

Mixing between gravitational and weak interactions through the massive gravitino

The interactions of the Goldstone neutrino, in a globally supersymmetric theory, are shown to depend only on the mass spectrum. If supersymmetry is realized locally, the Goldstone neutrino is eliminated by the super-Higgs mechanism; the gravitino (spin $\text{3}\text{2}$ partner of the gravition) becomes massive, leading to a mixing between gravitational and weak interactions. Weak interactions of the gravitino, for example weak decays of heavy new particles, can be recovered as a special case of gravitational ones.     

Neutrino astronomy and massive long-lived particles from the big bang

We consider the neutrino flux from the decay of long-lived big-bang particles. The red-shift z_tr at which the neutrino transparency of the universe sets in is calculated as a function of neutrino energy: z_tr 1 × 10⁵ for TeV neutrinos and z_tr 3 × 10⁶ for 10 MeV neutrinos. One might expect the production of detectable neutrino flux at z z_tr, but, as demonstrated in this paper, the various upper limits, most notably due to nucleosynthesis and diffuse X- and gamma-rays, preclude this possibility. Unless the particle decay is strongly dominated by the pure neutrino channel, observable neutrino flux can be produced only at the current epoch, corresponding to red-shift z ≈ 0. For the thermal relics which annihilate through the gauge bosons of SU(3)×SU(2)×U(1) group, the neutrino flux can be marginally detectable at 0.1 < E_v < 10 TeV. As an example of non-thermal relics we consider gravitinos. If gravitinos are the lightest supersymmetric particles (LSP) they can produce the detectable neutrino flux in the form of a neutrino line with energy , where M_G is the gravitino mass. The flux strongly depends on the mechanisms of R-parity violation. It is shown that heavy gravitinos (M_G 100 GeV) can make up the dark matter in the universe.     

Hadron final states in deep-inelastic leptoproduction on nuclei

We discuss some aspects of the formation of inclusive hadron final states in deep-inelastic electro-, muo- and neutrinoproduction on nuclear targets.The inclusive final states are known to possess a remarkable Q² independence in interactions with free nucleons. Nevertheless, we prove that the nuclear spectra and mean multiplicities should have a rather specific and appreciable dependence on Q². In leptoproduction on heavy nuclei the yields of particles in nucleus fragmentation rise by a factor of two, as at the fixed energy transfer v one passes from incoherent scattering to diffraction scattering, and the total multiplicities change by 20–40%. The effects predicted seem to be detectable with the current and the near-future experimental facilities. Fermilab bubble chamber neutrino experiments and the coming SPS muon and neutrino experiments deserve special attention in this respect. We also comment on the possibilities offered by leptoproduction on nuclei for testing some absorption models.     

Neutrinoless double beta-decay

The neutrinoless double β-decay of nuclei is reviewed. We discuss neutrino mixing and 3 × 3 PMNS neutrino mixing matrix. Basic theory of neutrinoless double β-decay is presented in some details. Results of different calculations of nuclear matrix element are discussed. Experimental situation is considered. The Appendix is dedicated to E. Majorana (brief biography and his paper in which the theory of Majorana particles is given)     

Trimoun production in neutrino and muon interactions from structure at the lepton vertex

The direct production of three charged leptons by an incident high-energy neutrino can arise from approximately local structure effects at the lepton vertex, and be accompanied by limited energy-momentum transfer to the target nucleon. We estimate the relative rate in a simple model which illustrates this class of mechanisms, and then enumerate several unambiguous experimental tests, such as the absence of neutrinos in the final state, which distinguish this mechanism from those involving the production and weak decay of real new particles.     

Nearly degenerate mass and bimaximal mixing of neutrinos in the SO(3) gauge model of leptons

A realistic scheme for masses and mixing of leptons is investigated in the model with gauged SO(3) lepton flavor symmetry. Within this scheme, a nearly bimaximal neutrino mixing pattern with a maximal CP-violating phase is found to be the only possible solution for reconciling both solar and atmospheric neutrino flux anomalies. Three Majorana neutrino masses are nearly degenerate and large enough to play a significant cosmological role. Lepton flavor-violating effects via SO(3) gauge interactions can be as large as the present experimental limits. Masses of the SO(3) gauge bosons are bounded to be above 24 TeV when the SO(3) gauge boson mixing angle and coupling constant are taken to be the same as those ( and g) in the electroweak theory. Received: 10 February 1999 / Published online: 8 September 1999     

Neutrino–Electron Processes in a Magnetic Field and Their Crossing Symmetry

We have studied the neutrino–electron processes in a matter with an external magnetic field of an arbitrary strength. Invariant squares of S-matrix elements, which have been obtained for such reactions using the technique based on the density matrix of a particle propagating in an external magnetic field, are valid in an arbitrary frame of reference moving along the magnetic field lines. The transition probabilities obtained can easily be generalized to the processes of interaction of a neutrino with other charged leptons and protons. The probabilities of the processes have been integrated over the transverse momenta of charged particles for the rates of neutrino–electron reactions as well as the energy and momentum transferred in them from the medium to neutrinos. The expressions obtained are written in the unified form for all neutrino–electron processes.