Majorana Neutrino Oscillations in Vacuum

In the context of a type I seesaw scenario which leads to get light left-handed and heavy right-handed Majorana neutrinos, we obtain expressions for the transition probability densities between two flavor neutrinos in the cases of left-handed and right-handed neutrinos. We obtain these expressions in the context of an approach developed in the canonical formalism of Quantum Field Theory for neutrinos which are considered as superpositions of mass-eigenstate plane waves with specific momenta. The expressions obtained for the left-handed neutrino case after the ultra-relativistic limit is taking lead to the standard probability densities which describe light neutrino oscillations. For the right-handed neutrino case, the expressions describing heavy neutrino oscillations in the non-relativistic limit are different respect to the ones of the standard neutrino oscillations. However, the right-handed neutrino oscillations are phenomenologically restricted as is shown when the propagation of heavy neutrinos is considered as superpositions of mass-eigenstate wave packets.

Search for Majorana Neutrino Signal in B_c Meson Rare Decay

We study the B c meson rare decay in order to search for the Majorana neutrino signal. It is found that the corresponding decay rate is sensitive to the Majorana neutrino mass and mixing angles. The signal of B±c→ l±1l±2 M induced by the Majorana neutrino within the mass region mπ<mn<mB may be observed at LHCb.

Study of the Standard Model and Majorana neutrino contributions to

Lepton number violation processes can be induced by the Majorana neutrino exchange, which provide evidence for the Majorana nature of neutrinos. In addition to the natural explanation of the small neutrino masses,Type-I seesaw mechanism predicts the existence of Majorana neutrinos. The aim of this work is to study the B meson rare decays B^+→K^((*))+μ^+μ^-in the Standard Model and its extensions, and then to investigate the same-sign decay process B^+→K^((*)-)μ^+μ^+. The corresponding dilepton invariant mass distributions are calculated. It is found that the dilepton angular distributions could shed light on the properties of new interactions induced by Majorana neutrinos.

The Majorana neutrino mass matrix indicated by the current data

The Majorana neutrino mass matrix combines information from the neutrino masses and the leptonic mixing in the flavor basis. Its invariance under some transformation matrices indicates the existence of certain residual symmetry. We offer an intuitive display of the structure of the Majorana neutrino mass matrix, using the whole set of the oscillation data. The structure is revealed depending on the lightest neutrino mass. We find that there are three regions with distinct characteristics of structure. A group effect and the-τ exchange symmetry are observed. Six types of texture non-zeros are shown. Implications for flavor models are discussed.

Geometry of the effective Majorana neutrino mass in the 0νββ decay

The neutrinoless double-beta （0vββ） decay is a unique process used to identify the Majorana nature of massive neutrinos, and its rate depends on the size of the effective Majorana neutrino mass （m）ee- We put forward a novel ＇coupling-rod＇ diagram to describe （m）ee in the complex plane, by which the effects of the neutrino mass ordering and CP-violating phases on （m）ee are intuitively understood. We show that this geometric language allows us to easily obtain the maximum and minimum of I（m）eel. It remains usable even if there is a kind of new physics contributing to （m）ee, and it can also be extended to describe the effective Majorana masses （m）eμ, （m）eτ, （m）μμ, （m）,μτ and （m）ττ which may appear in some other lepton-number violating processes.

Determining the Neutrino Mass Eigenstates and the Effective Majorana Mass

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.

Active-Sterile Neutrino Oscillations and Leptogenesis

We study coherent active-sterile neutrino oscillations as a possible source of leptogenesis. To this end, we add 3 gauge invariant Weyl_R neutrinos to the Standard Model with both Dirac and Majorana type mass terms. We find that the measured active neutrino masses and mixings, and successful baryogenesis via leptogenesis, may be achieved with fine-tuning, if at least one of the sterile neutrinos has a mass in the approximate range 0.14 to 1.1 GeV.

Majorana中微子与第二类振荡

该文讨论了Ｍａｊｏｒａｎａ中微子和第二类振荡的关系，得出结论：在拉氏量中，只考虑Ｍａｊｏｒａｎａ质量项并不能导致中微子的第二类振荡，必须同时考虑Ｄｉｒａｃ质量项；在Ｎ≥２时，第二类振荡不能单独存在，必然伴随着第一类振荡。

Neutrino Masses and See-Saw Mechanism

A neutrino is a subatomic particle that is very similar to an electron, but has no electrical charge and a very small mass. Neutrinos are one of the most abundant particles in the universe. Because they have very little interaction with matter, however, they are incredibly difficult to detect. We present a study of the physics of neutrinos using the Dirac lagrangian. Based on Lorentz invariance we introduce the notion of Majorana spinor. Then we derive the mass terms for both Dirac and Majorana neutrinos. We further discuss the general framework of the See-Saw mechanism considering a simplification of the problem.

A Study of Dark Matter with Spiral Galaxy Rotation Curves

To constrain the properties of dark matter, we study spiral galaxy rotation curves measured by the THINGS collaboration. A model that describes a mixture of two self-gravitating non-relativistic ideal gases, “baryons” and “dark matter”, reproduces the measured rotation curves within observational uncertainties. The model has four parameters that are obtained by minimizing a x2 between the measured and calculated rotation curves. From these four parameters, we calculate derived galaxy parameters. We find that dark matter satisfies the Boltzmann distribution. The onset of Fermi-Dirac or Bose-Einstein degeneracy obtains disagreement with observations and we determine, with 99% confidence, that the mass of dark matter particles is mh> 16 eV if fermions, or mh> 45 eV if bosons. We measure the root-mean-square velocity of dark matter particles in the spiral galaxies. This observable is of cosmological origin and allows us to obtain the root-mean-square velocity of dark matter particles in the early universe when perturbations were still linear. Extrapolating to the past we obtain the expansion parameter at which dark matter particles become non-relativistic: ahNR=[4.17&plusmn;0.34(STAT)&plusmn;2.50(SYST)]×10&minus;6. Knowing we then obtain the dark matter particle mass mh=69.0&plusmn;4.2(stat)&plusmn;31.0(syst)eV, and the ratio of dark matter-to-photon temperature Th/T=0.389&plusmn;0.008(stat)&plusmn;0.058(syst) after e+e&minus;annihilation while dark matter remains ultra-relativistic. We repeat these measurements with ten galaxies with masses that span three orders of magnitude, and angular momenta that span five orders of magnitude, and obtain fairly consistent results. We conclude that dark matter was once in thermal equilibrium with the (pre?) Standard Model particles (hence the observed Boltzmann distribution) and then decoupled from the Standard Model and from self-annihilation at temperatures above m&mu;. These results disfavor models with freeze-out or freeze-in. We also measure the primordial amplitude of vector modes, and constrain the baryon-dark matter cross-section: . Finally, we consider sterile Majorana neutrinos as a dark matter candidate.

A Study of Dark Matter with Spiral Galaxy Rotation Curves. Part II

In Part II of this study of spiral galaxy rotation curves we apply corrections and estimate all identified systematic uncertainties. We arrive at a detailed, precise, and self-consistent picture of dark matter.

Massive and massless neutrinos on unbalanced seesaws

The observation of neutrino oscillations requires new physics beyond the standard model （SM）. A SM-like gauge theory with p lepton families can be extended by introducing q heavy right-handed Majorana neutrinos but preserving its SU（2）L × U（1）Y gauge symmetry. The overall neutrino mass matrix M turns out to be a symmetric （p＋q） × （p＋q） matrix. Given p 〉 q, the rank of M is in general equal to 2q, corresponding to 2q non-zero mass eigenvalues. The existence of （p-q） massless left-handed Majorana neutrinos is an exact consequence of the model, independent of the usual approximation made in deriving the Type-I seesaw relation between the effective p x p light Majorana neutrino mass matrix Mv and the q × q heavy Majorana neutrino mass matrix MR. In other words, the numbers of massive left- and right-handed neutrinos are fairly matched. A good example to illustrate this ＂seesaw fair play rule＂ is the minimal seesaw model with p = 3 and q = 2, in which one massless neutrino sits on the unbalanced seesaw.

无中微子双贝塔衰变:新物理探索和宇宙学观测

近二十多年来,太阳、大气、反应堆和加速器的中微子振荡实验提供了大量确凿的证据表明中微子有质量。然而,粒子物理学标准模型却预言中微子质量为零。这意味着中微子质量的产生必然要求引入超出标准模型的新物理。文章将介绍无中微子双贝塔衰变对新物理探索和宇宙学观测的重要影响,尤其是该稀有衰变过程的实验观测在突破粒子物理学和宇宙学标准模型的前沿研究中扮演的独一无二的角色。

Towards the meV limit of the effective neutrino mass in neutrinoless double-beta decays

We emphasize that it is extremely important for future neutrinoless double-beta(0νββ)decay experiments to reach the sensitivity to the effective neutrino mass|mββ|≈1 meV.With such a sensitivity,it is highly possible to discover the signals of 0νββ decays.If no signal is observed at this sensitivity level,then either neutrinos are Dirac particles or stringent constraints can be placed on their Majorana masses.In this paper,assuming the sensitivity of|mββ|≈1 meV for future 0νββ decay experiments and the precisions on neutrion oscillation parameters after the JUNO experiment,we fully explore the constrained regions of the lightest neutrino mass m1 and two Majorana-type CP-violating phases{ρ,σ}.Several important conclusions in the case of normal neutrino mass ordering can be made.First,the lightest neutrino mass is severely constrained to a narrow range m1∈[0.7,8]meV,which together with the precision measurements of neutrino mass-squared differences from oscillation experiments completely determines the neutrino mass spectrum m2∈[8.6,11.7]meV ing phases is limited to ρ∈[130°,230°],which cannot be obtained from any other realistic experiments.Third,the sum of three neutrino masses is found to beΣ≡m1+m2+m3∈[59.2,72.6]meV,while the effective neutrino mass for beta decays turns out to be mβ≡(|Ue1|2m1^2+|Ue2|2m2^2+|Ue3|2m3^2)1/2∈[8.9,12.6]meV.These observations clearly set up the roadmap for future non-oscillation neutrino experiments aiming to solve the fundamental problems in neutrino physics.

Lepton number violation in D meson decay

The lepton number violation （LNV） process can be induced by introducing a fourth generation heavy Majorana neutrino, which is coupled to the charged leptons of the Standard Model （SM）. There have been many previous studies on the leptonic number violating decay processes with this mechanism. We follow the trend to study the process： D→Kllπ with the same-sign dilepton final states. We restrict ourselves to certain neutrino mass regions, in which the heavy neutrino could be on-shell and the dominant contribution to the branching fraction comes from the resonance enhanced effect. Applying the narrow width approximation （NWA）, we found that the upper limit for the branching fractions for D^0 → K^- 1＋1＋π- are generally at the order of 10-12 to 10-9, if we take the most stringent upper limit bound currently available in the literature for the mixing matrix elements. We also provide the constraints, which is competitive compared to the LNV B decays, on the mixing matrix element ｜VeN ｜^2 based on the upper limit of D^0→K^-e＋e＋π- estimated from the Monte-Carlo （MC） study at BESⅢ. Although the constraints are worse than the ones from （0vββ） decay in the literature, the future experiment at the charm factory may yield more stringent constraints.

揭开中微子和反中微子的马约拉纳神秘面纱——无中微子双贝塔衰变低温晶体量热器实验

中微子可能的马约拉纳粒子属性超出了目前标准模型的范畴,是粒子物理与核物理研究领域最重要的科学问题之一。无中微子双贝塔衰变(0vββ)实验是能够确定中微子马约拉纳属性的唯一途径。0vββ的发现可以揭示中微子绝对质量、轻子数破缺、物质—反物质不对称等一系列自然奥秘,是当今粒子物理与核物理研究的前沿课题。在探索无中微子双贝塔衰变的可选择实验方案中,低温晶体量热器具有高能量分辨率、高运行稳定性和低辐射本底的技术优势,成为新一代0vββ实验最具竞争力的探测器技术之一。文章首先介绍无中微子双贝塔衰变的研究历史,之后介绍低温晶体量热器及其最先进的代表——CUORE实验,最后展望关于我国锦屏地下实验室开展低温晶体量热器0vββ实验研究的前景。

中微子质量起源与宇宙的原初反物质消失之谜

粒子物理学的标准模型建立于20世纪60~70年代,它在随后的半个多世纪经受住了无数次科学实验的检验,成为人类描述与理解各种强、弱和电磁相互作用现象最成功的理论工具.但是该模型也存在一些缺陷,比如它刻意回避了中微子质量及其起源的问题,也无法解答为什么可观测宇宙中不存在原初反物质但却存在大量暗物质的问题.

无中微子双贝塔衰变:寻找马约拉纳中微子之路

无中微子双贝塔衰变是目前粒子物理与核物理学家积极寻找的一种极其稀有的原子核衰变模式。它的发现将验证中微子是否是其本身的反粒子,也就是通常指的马约拉纳费米子。同时这一物理过程破坏轻子数守恒,也可以为宇宙初期的正反物质不对称性提供重要的条件。鉴于其极重要的物理意义,国际上多个实验组利用不同的探测器技术,在多种不同的目标同位素中寻找这一突破粒子物理标准模型的稀有衰变。目前主流实验还未发现确定的无中微子双贝塔衰变信号,但对其半衰期的限制已经达到了10^(26)年量级。国内近期也开展了一系列预研实验,期望在未来几年内可以确定一到两个切实可行的实验方案,开展吨级实验。