M. Agostini, G. Benato, S. Dell'Oro, S. Pirro, F. Vissani
We discuss the impact of the cosmological measurements on the predictions of the Majorana mass of the neutrinos, the parameter probed by neutrinoless double-beta decay experiments. Using a minimal set of assumptions, we quantify the probabilities of discovering neutrinoless double-beta decay and introduce a new graphical representation that could be of interest for the community.
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Majorana CP Violation Insights from Decaying Neutrinos
通过分析中微子衰变对Majorana相位的影响，研究其在中微子振荡概率中的表现及CP反常效应。
We analyze the power of the Tevatron dataset to exclude or discover fourth generation neutrinos. In a general framework, one can have mixed left- and right-handed neutrinos, with Dirac and Majorana neutrinos as extreme cases. We demonstrate that a single Tevatron experiment can make powerful statements across the entire mixing space, extending LEP's mass limits of 60-80 GeV up to 150-175 GeV, depending on the mixing.
We study the conditions under which the Majorana phase of the two flavor neutrino mixing matrix appears in the oscillation probabilities and causes $CP$ violation. We find that the Majorana phase remains in the neutrino evolution equation if the neutrino decay eigenstates are not aligned with the mass eigenstates. We show that, in general, two kinds of $CP$ violation are possible: one due to the Majorana phase and the other due to the phase of the off-diagonal element of the neutrino decay matrix. We find that the $CP$ violating terms in the oscillation probabilities are also sensitive to neut…
In three generations or more, we derive the oscillation probabilities of both Dirac and Majorana neutrinos relativistically by using the Dirac equation. We present various oscillation probabilities for including wrong-helicity neutrinos, right-handed neutrinos, and anti-neutrinos. We summarize the relations between these probabilities. As neutrinos have finite mass, there are two components for each chirality corresponding to positive and negative helicities. We show that the probability is different for each component even if neutrinos have the same chirality. The probabilities derived by the…
Exploring the nature of neutrinos in a dissipative environment
本文在开放量子系统框架下研究耗散环境对长基线中微子振荡的影响，发现跃迁概率可容纳马约拉纳相位，并评估了T2K、ESSnuSB、NOvA、T2HKK和DUNE区分狄拉克与马约拉纳中微子的灵敏度。
We show that, for Majorana neutrinos propagating in a constant magnetic field, the flavour survival probabilities for left-handed neutrinos is the same as for right-handed neutrinos, i.e., $P^M (ν_{αL}\toν_{αL}) = P^M (ν_{αR}\toν_{αR})$, where $α= e, μ, τ$, whereas in the Dirac case the corresponding probabilities $P^D (ν_{αL}\toν_{αL})$ and $P^D (\barν_{αR}\to\barν_{αR})$ are in general different. This might lead to a novel way to search for the nature of neutrinos. We also discuss how this relation for Majorana neutrinos gets modified when the magnetic field is not constant. However, if matt…
Statistical Framework for Discovery Sensitivity and Majorana Mass Estimation in \(^{136}\)Xe Neutrinoless Double Beta Decay
针对\(^{136}\)Xe无中微子双β衰变实验，开发了一个结合泊松似然与背景建模的统计框架，评估能量分辨率、ROI宽度、本底指数和曝光量对发现灵敏度的影响，并估计马约拉纳质量上限。
We analyze in some detail the course of Theoretical Physics held by Ettore Majorana at the University of Naples in 1938, just before his mysterious disappearance. In particular we present the recently discovered "Moreno Paper", where all the lecture notes are reported. Six of these lectures are not present in the collection of the original manuscripts conserved at the Domus Galilaeana in Pisa, consisting of only ten lectures.
A form of mixing matrix for three active and three sterile, conventional Majorana neutrinos is proposed. Its Majorana lefthanded part arises from the popular bimaximal mixing matrix for three active neutrinos that works satisfactorily in solar and atmospheric experiments if the LSND effect is ignored. One of three sterile neutrinos, effective in the Majorana righthanded and Dirac parts of the proposed mixing matrix, is responsible for the possible LSND effect by inducing one of three extra neutrino mass states to exist actively. The corresponding form of neutrino mass matrix is derived. Also, …
It is firmly believed that a signal of neutrinoless double beta decay can unquestionably confirm the Majorana nature of neutrinos. However we notice that a Majorana neutrino mass induced after some neutrinoless double beta decay processes can be accidentally cancelled by another Majorana neutrino mass induced before any neutrinoless double beta decay processes. This realistic cancellation can simultaneously allow an observable neutrinoless double beta decay and a vanishing Majorana neutrino mass. In consequence a future discovery of neutrinoless double beta decay cannot fully rule out the poss…
Discriminating Majorana and Dirac heavy neutrinos at lepton colliders
本研究针对未来轻子对撞机可能发现的100GeV-10TeV重中性轻子，提出结合轻子电荷与运动学变量的多变量分析方法，可在几乎全发现范围以95%置信水平区分其狄拉克或马约拉纳属性，并探讨了不同对撞机的味结构研究互补性。
We analyze both chirality-changing and chirality-preserving transitions of Dirac-Majorana neutrinos. In vacuum, the first ones are suppressed with respect to the others due to helicity conservation and the interactions with a (``normal'') medium practically does not affect the expressions of the probabilities for these transitions, even if the amplitudes of oscillations slightly change. For usual situations involving relativistic neutrinos we find no resonant enhancement for all flavour-conserving transitions. However, for very light neutrinos propagating in superdense media, the pattern of os…
We study the discovery potential for detecting new neutral heavy Majorana leptons as suggested by some extentions of the Standard Model in recently proposed electron-proton colliders. Since 1998-1999 the option of an electron-proton collider for the Very Large Hadron Collider at Fermilab operating with the proton booster has been considered. We study the reaction $e^{-}p \longrightarrow e^{+}+ jets$ and present estimates for the signal and Standard Model background including hadronization.
For some theoretical and experimental considerations, the relatively light Majorana neutrinos at the GeV scale have been attracting some interest. In this article we consider a scenario with only one Majorana neutrino $N$, negligible mixing with the active neutrinos $ν_{L}$, where the Majorana neutrino interactions could be described in a model independent approach based on an effective theory. Under such a framework, we particularly study the feasibility of observing the $N$ with mass in the range 0$-$30 GeV via the process $e^+ e^- \to νN \toγ+ \slashed E$ in the future Belle-II and ILC expe…
The process $e^- γ\to e^+ W_R^- W_R^-$ is studied in the framework of the Left-Right symmetric model. It is shown that this reaction and $e^- γ\to l^+ W_R^- W_R^-$ for the arbitrary final lepton are likely to be discovered for CLIC collider option. For relatively light doubly charged Higgs boson its mass does not have much influence on the discovery potential, while for heavier values the probability of the reaction increases.
The Majorana nature of massive neutrinos will be crucially probed in the next-generation experiments of the neutrinoless double-beta ($0ν2β$) decay. The effective mass term of this process, $\langle m\rangle^{}_{ee}$, may be contaminated by new physics. So how to interpret a discovery or null result of the $0ν2β$ decay in the foreseeable future is highly nontrivial. In this paper we introduce a novel three-dimensional description of $|\langle m\rangle_{ee}^{}|$, which allows us to see its sensitivity to the lightest neutrino mass and two Majorana phases in a transparent way. We take a look at …
Unification of Neutrino-Neutrino and Neutrino-Antineutrino Oscillations
本文在两代Majorana中微子框架内利用相对论方程统一导出三类振荡概率，证明Majorana相位源于手征性变化而非轻子数破坏，验证了幺正性守恒，并发现中微子-反中微子振荡概率不存在零距离效应与直接CP破坏。
We discuss the process $e^-e^- \to W^- W^-$ mediated by heavy Majorana neutrino exchange in the t- and u channel. In our model the cross section for this reaction is a function of the masses (m_N) of the heavy Majorana neutrinos and mixing parameters (U_{eN}) originating from mixing between the ordinary left-handed standard model neutrinos and additional singlet right-handed neutrino fields. Taking into account the standard model background and contraints from low energy measurements, we present discovery limits in the (m_N,U_{eN}^2) plane. We also discuss how to measure in principle the CP vi…
We derive the neutrino oscillation probabilities including sterile neutrinos by using the Dirac equation. If neutrinos have both the Dirac and the Majorana mass terms, left-handed neutrino $ν_L$ and right-handed anti-neutrino $ν_R^c$ enter the same multiplet and can transfer each other. Sterile neutrinos have been introduced by hand as the fourth generation neutrino in many papers, however, we can understand sterile neutrinos naturally in the framework of three generations. We also point out that the oscillations into sterile neutrinos strongly suggest the existence of both the Dirac and the M…
We analyze the implications of neutrino masses for the magnitude of neutrino magnetic moments. By considering electroweak radiative corrections to the neutrino mass, we derive model-independent naturalness upper bounds on neutrino magnetic moments, generated by physics above the electroweak scale. For Majorana neutrinos, these bounds are weaker than present experimental limits if $μ_ν$ if generated by new physics at $\sim$ 1 TeV, and surpass current experimental sensitivity only for new physics scales $>$ 10 -- 100 TeV. The discovery of a neutrino magnetic moment near present limits would thus…
We analyze the implications of neutrino masses for the magnitude of neutrino magnetic moments. By considering electroweak radiative corrections to the neutrino mass, we derive model-independent naturalness upper bounds on neutrino magnetic moments, $μ_ν$, generated by physics above the electroweak scale. For Dirac neutrinos, the bound is several orders of magnitude more stringent than present experimental limits. However, for Majorana neutrinos the magnetic moment contribution to the mass is Yukawa suppressed. The bounds we derive for magnetic moments of Majorana neutrinos are weaker than pres…
We investigate the possibility of detecting Majorana neutrinos at the Large Hadron-electron Collider (LHeC), an electron-proton collision mode at CERN. We study the $l_j^{+} + 3 jets$ ($l_j\equiv e ,μ,τ$) final states which are, due to leptonic number violation, a clear signature for intermediate Majorana neutrino contributions. Such signals are not possible if the heavy neutrinos have Dirac nature. The interactions between Majorana neutrinos and the Standard Model (SM) particles are obtained from an effective lagrangian approach. We present our results for the total cross section as a functio…
Landau-Zener-Stückelberg-Majorana dynamics of magnetized quarkonia
研究时间依赖磁场中粲偶素的能级交叉动力学，通过多通道Landau-Zener哈密顿量分析线性扫描、高斯衰减和脉冲下的占据概率，揭示非绝热效应（Landau-Zener跃迁和Stückelberg干涉）的影响。
We investigate the possibility of detecting Majorana neutrinos at the $e^+e^-$ Next Linear Collider (NLC). We study the $l_j^{\mp} l_k^{\mp} + jets$ ($l_j\equiv e ,μ,τ$) final states which are, due to leptonic number violation, a clear signature for intermediate Majorana neutrino contributions. Such signals (final leptons of the same-sign) are not possible if the heavy neutrinos have Dirac nature. The interactions between Majorana neutrinos and the Standard Model (SM) particles are obtained from an effective Lagrangian approach. As for the background, we considered the SM reaction $e^+ e^- \ri…
We discuss same-sign dilepton production mediated by Majorana neutrinos in high-energy proton-proton collisions $pp\ra \ell^+ \ell^{\prime +}X$ for $\ell,~ \ell^\prime = e,~ μ,~ τ$ at the LHC energy $\sqrt{s}=14$ TeV. Assuming one heavy Majorana neutrino of mass $m_N$, we present discovery limits in the $(m_{N},|U_{\ell N}U_{\ell^\prime N}|)$ plane where $U_{\ell N}$ are the mixing parameters. Taking into account the present limits from low energy experiments, we show that at LHC one has sensitivity to heavy Majorana neutrinos up to a mass $m_{N}\leq 2$ -- 5 TeV in the dilepton channels $μμ,~ …
Majorana CP-violating phases and NSI effects in Neutrino Decay
本文在两味中微子振荡背景下，研究了NSI与Majorana相位对中微子衰变的影响，发现精确测量振荡概率及其差值可明确区分并识别Majorana相位的存在。
We show that discovery of baryon number violation in two processes with at least one obeying the selection rule Δ(B-L) = \pm 2 can determine the Majorana character of neutrinos. Thus observing p \to e^+ π^0 and n \to e^- π^0 decays, or p \to e^+ π^0 and n-nbar oscillations, or n \to e^- π^+ and n-nbar oscillations would establish that neutrinos are Majorana particles. We discuss this in a model-independent effective operator approach.
From a phenomenological point of view, we study active-active and active-sterile flavour-changing (and flavour-conserving) oscillations of Dirac-Majorana neutrinos both in vacuum and in matter. The general expressions for the transition probabilities in vacuum are reported. We then investigate some interesting consequences following from particular simple forms of the neutrino mass matrices, and for the envisaged scenarios we discuss in detail neutrino propagation in matter. Special emphasis is given to the problem of occurrence of resonant enhancement of active-active and active-sterile neutr…
Within a mirror type assignment for the excited composite fermions the neutrino mass term is built up from a Dirac mass, $m_*$, which gives the mass of charged lepton component of the $SU(2)$, right-handed, doublet, and a Majorana mass, $m_L$, for the left-handed component (singlet) of the excited neutrino. The mass matrix is diagonalized leading to two Majorana mass eigenstates. The active neutrino field $ν^*_R$ is thus a superposition of the two mass eigenstates with mixing coefficients which depend on the ratio $m_L/m_*$. We discuss the prospects of discovery of these physical states at the…
In this study we explore the LHC's Run II potential to the discovery of heavy Majorana neutrinos, with luminosities between $30$ and $3000$ fb$^{-1}$ in the $l^{\pm}l^{\pm}j~j$ final state. Given that there exist many models for neutrino mass generation, even within the Type I seesaw framework, we use a simplified model approach and study two simple extensions to the Standard Model, one with a single heavy Majorana neutrino, singlet under the Standard Model gauge group, and a limiting case of the left-right symmetric model. We then extend the analysis to a future hadron collider running at $10…
We discuss same-sign dilepton production mediated by Majorana neutrinos in high-energy proton-proton collisions $pp\ra \ell^+ \ell^{\prime +}X$ for $\ell,~ \ell^\prime = e,~ μ,~ τ$ at the LHC energy $\sqrt{s}=14$ TeV, and in the rare decays of $K$, $D$, $D_s$, and $B$ mesons of the type $M^{+}\ra M^{\prime -}\ell ^{+}\ell ^{\prime+}$. For the $pp$ reaction, assuming one heavy Majorana neutrino of mass $m_N$, we present discovery limits in the $(m_{N},|U_{\ell N}U_{\ell^\prime N}|)$ plane where $U_{\ell N}$ are the mixing parameters. Taking into account the present limits from low energy experi…
We show that Majorana particles belong to the Wigner class of fermions in which the charge conjugation and the parity operators commute, rather than anticommute. Rigorously speaking, Majorana spinors do not satisfy the Dirac equation [a result originally due to M. Kirchbach, which we re-render here]. Instead, they satisfy a different wave equation, which we derive. This allows us to reconcile Stückelberg-Feynman interpretation with the Majorana construct. We present several new properties of neutral particle spinors and argue that discovery of Majorana particles constitutes dawn of a new era i…
The existence of a neutrino magnetic moment implies contributions to the neutrino mass via radiative corrections. We derive model-independent "naturalness" upper bounds on the magnetic moments of Dirac and Majorana neutrinos, generated by physics above the electroweak scale. For Dirac neutrinos, the bound is several orders of magnitude more stringent than present experimental limits. However, for Majorana neutrinos the magnetic moment bounds are weaker than present experimental limits if $μ_ν$ is generated by new physics at ~ 1 TeV, and surpass current experimental sensitivity only for new phy…
The probability for chiral oscillation of Majorana neutrino in Quantum Field Theory
本文通过量子场论推导了Majorana中微子手性振荡的概率，并利用Bogoliubov变换解释了轻子数随时间变化的机制。
Vector Boson Fusion Signatures of Superheavy Majorana Neutrinos at Muon Colliders
本研究评估了未来μ子对撞机通过矢量玻色子融合探测超重马约拉纳中微子的能力，证明其可探测质量高达100 TeV、混合角小至0.001的中微子，为下一代对撞机提供动机。
Wave packet description of Majorana neutrino oscillations in a magnetic field
研究了Majorana中微子在磁场中的振荡行为，推导了考虑退相干效应的振荡概率表达式，并分析了相干长度与频率关系。
Solar Flares as a Probe of Neutrino Nature: Distinguishing Dirac and Majorana via Resonant Spin-Flavor Precession
利用太阳耀斑中微子共振自旋-味预旋现象，区分狄拉克与马约拉纳中微子本质。
The Bayesian discovery probability of future experiments searching for neutrinoless double-$β$ decay is evaluated under the popular assumption that neutrinos are their own antiparticles. A Bayesian global fit is performed to construct a probability distribution for the effective Majorana mass, the observable of interest for these experiments. This probability distribution is then combined with the sensitivity of each experiment derived from a heuristic counting analysis. The discovery probability is found to be higher than previously considered, but strongly depends on whether the neutrino mas…
Distinguishing between Dirac and Majorana neutrinos using temporal correlations
本文首次在两味中微子PT对称非厄米哈密顿量框架下利用Leggett-Garg不等式的时间关联区分狄拉克与马约拉纳中微子，并展示优化参数下K4和K3的差异分别可达约15%和10%。
We present a search strategy for both Dirac and Majorana sterile neutrinos from the purely leptonic decays of $W^\pm \to e^\pm e^\pm μ^\mp ν$ and $μ^\pm μ^\pm e^\mp ν$ at the 14 TeV LHC. The discovery and exclusion limits for sterile neutrinos are shown using both the Cut-and-Count (CC) and Multi-Variate Analysis (MVA) methods. We also discriminate between Dirac and Majorana sterile neutrinos by exploiting a set of kinematic observables which differ between the Dirac and Majorana cases. We find that the MVA method, compared to the more common CC method, can greatly enhance the discovery and di…
We evaluate the LHC discovery potential for the fourth family Standard Model neutrinos in the process $pp\to Z/h\toν_{4}{\barν_{4}}\to WμWμ$. We show that, depending on their masses, the simultaneous discovery of both the Higgs boson and the heavy neutrinos is probable at early stages of LHC operation. Results are presented for both Majorana and Dirac type fourth family neutrinos.
The production of Like-Sign-Di-leptons (LSD), in the high energy lepton number violating ($ΔL = +2$) reaction, p p --> 2jets + l+l+ (l=e,μ,τ) of interest for the experiments to be performed at the forthcoming Large Hadron Collider (LHC), is investigated in detail, taking up a composite model scenario in which the exchanged virtual composite neutrino is assumed to be a Majorana particle that couples to the light leptons via the $SU(2)\times U(1)$ gauge bosons through a magnetic type coupling ($σ_{μν}$). An helicity projection method is used to evaluate exactly the tree-level amplitudes of the c…
The Daya Bay Collaboration (An et al) has recently proclaimed discovery of non-zero reactor angle, $θ_{13}$, $\sin^{2}2θ_{13}$=0.092$\pm$0.016(stat)$\pm$0.005(syst), at $5.2σ$ which is in conformity with the earlier observations of Abe et al, Adamson et al and Kerret et al last year. The discovery has immense implication for exploring CP-violation in the leptonic sector. In the present work, we examine CP-violation in Majorana neutrino mass matrix, in the basis where charged lepton mass matrix is diagonal, in which the ratio of elements are equal, also, termed as Strong Scaling Ans$\ddot{a}$tz…
The neutrinophilic two-Higgs-doublet model ($ν$2HDM) provides a natural way to generate tiny neutrino mass from interactions with the new doublet scalar $Φ_ν$ ($H^\pm,~H,~A$) and singlet neutrinos $N_R$ of TeV scale. In this paper, we perform detailed simulations for the lepton number violating (LNV) signatures at LHC arising from cascade decays of the new scalars and neutrinos with the mass order $m_{N_R}<m_{Φ_ν}$. Under constraints from lepton flavor violating processes and direct collider searches, their decay properties are explored and lead to three types of LNV signatures: $2\ell^\pm 4j+…
Massive neutrinos are guaranteed to have nonzero electromagnetic moments and, since there are at least three neutrino species, these dipole moments define a matrix. Here, we estimate the current upper bounds on all independent neutrino electromagnetic moments, concentrating on Earth-bound experiments and measurements with solar neutrinos, including the very recent results reported by XENONnT. We make no simplifying assumptions and compare the hypotheses that neutrinos are Majorana fermions or Dirac fermions. In particular, we fully explore constraints in the Dirac-neutrino parameter space. Maj…
If the massive neutrinos are the Majorana particles, how to pin down the Majorana CP-violating phases will eventually become an unavoidable question relevant to the future neutrino experiments. We argue that a study of neutrino-antineutrino oscillations will greatly help in this regard, although the issue remains purely academic at present. In this work we first derive the probabilities and CP-violating asymmetries of neutrino-antineutrino oscillations in the three-flavor framework, and then illustrate their properties in two special cases: the normal neutrino mass hierarchy with m_1 = 0 and t…
Three-flavour neutrino oscillations in a magnetic field
本文研究了磁场中三味中微子的Dirac和Majorana振荡，揭示了振荡频率的复杂相互作用及对中微子通量的影响。
We investigate the LHC discovery potential for electroweak scale heavy neutrino singlets (seesaw I), scalar triplets (seesaw II) and fermion triplets (seesaw III). For seesaw I we consider a heavy Majorana neutrino coupling to the electron or muon. For seesaw II we concentrate on the likely scenario where the new scalars decay to two leptons. For seesaw III we restrict ourselves to heavy Majorana fermion triplets decaying to light leptons plus gauge or Higgs bosons, which are dominant except for unnaturally small mixings. The possible signals are classified in terms of the charged lepton multi…
It is often said that neutrino mass is a window to a new physics beyond the standard model (SM). This is certainly true if neutrinos are Majorana particles since the SM with Majorana neutrino mass is not a complete theory. The classical text-book test of neutrino Majorana mass, the neutrino-less double beta decay depends on the completion, and thus cannot probe neutrino mass. As pointed out already more than twenty five years ago, the colliders such as Tevatron or LHC offer a hope of probing directly the origin of neutrino Majorana mass through lepton number violating production of like sign l…
After discovery of the Higgs boson at CERN the Standard Model acquired a status of the theory of the elementary particles in the electroweak range (up to about 300 GeV). What general conclusions can be inferred from the Standard Model? It looks that the Standard Model teaches us that in the framework of such general principles as local gauge symmetry, unification of weak and electromagnetic interactions and Brout-Englert-Higgs spontaneous breaking of the electroweak symmetry nature chooses the simplest possibilities. Two-component left-handed massless neutrino fields play crucial role in the d…
Neutrinoless double beta decay data together with information on the absolute neutrino masses obtained from the future KATRIN experiment and/or astrophysical measurements give a chance to find CP violation in the lepton sector with Majorana neutrinos. We derive and discuss necessary conditions which make discovery of such CP violation possible for the future neutrino oscillation and mass measurements data.
Right-Handed Neutrino Masses from the Electroweak Scale
本文提出右手中微子Majorana质量源于电弱对称性破缺，在双Higgs二重态有效理论中通过跷跷板机制生成轻中微子质量及低于电弱标度的右手中微子，并探讨其在Higgs扇区、无中微子双β衰变等方面的唯象与理论性质。
Towards experimental confirmations of the type-I seesaw mechanism, we explore a prospect of discovering the heavy Majorana right-handed neutrinos (RHNs) from a resonant production of a new massive gauge boson ($Z^{\prime}$) and its subsequent decay into a pair of RHNs ($Z^{\prime}\to NN$) at the future LHC. Recent simulation studies have shown that the discovery of the RHNs through this process is promising in the future. However, the current LHC data very severely constrains the production cross section of the $Z^{\prime}$ boson into a dilepton final states, $pp \to Z^{\prime}\to \ell^{+}\ell…
Heavy sterile neutrinos with masses below $M_W$ can induce trilepton events at the 14 TeV LHC through purely leptonic $W$ decays of $W^\pm \to e^\pm e^\pm μ^\mp ν$ and $μ^\pm μ^\pm e^\mp ν$ where the heavy neutrino will be in an intermediate state on its mass shell. Discovery and exclusion limits for the heavy neutrinos are found using both Cut-and-Count (CC) and a Multi-Variate Analysis (MVA) methods in this study. We also show that it is possible to discriminate between a Dirac and a Majorana heavy neutrino, even when lepton number conservation cannot be directly tested due to unobservabilit…
If massive neutrinos are Majorana particles, then the lepton number should be violated in nature and neutrino-antineutrino oscillations $ν^{}_α\leftrightarrow \overlineν^{}_β$ (for $α, β= e, μ, τ$) will definitely take place. In the present paper, we study the properties of CP violation in neutrino-antineutrino oscillations with the non-unitary leptonic flavor mixing matrix, which is actually a natural prediction in the canonical seesaw model due to the mixing between light and heavy Majorana neutrinos. The oscillation probabilities $P(ν^{}_α\to \overlineν^{}_β)$ and $P(\overlineν^{}_α\to ν^{}…
After discovery of the Higgs boson at CERN the Standard Model acquired a status of the full, correct theory of the elementary particles in the electroweak range. What general conclusions can be inferred from the SM? I am suggesting here that in the framework of such general principles as local gauge symmetry, unification of the weak and electromagnetic interactions and Brout-Englert-Higgs spontaneous breaking of the electroweak symmetry nature chooses the simplest possibilities. It is very plausible that massless left-handed neutrinos (simplest, most economical possibility) play crucial role i…
Vector boson fusion processes become increasingly more important at higher collider energies and for probing larger mass scales due to collinear logarithmic enhancements of the cross section. In this context, we revisit the production of a hypothetic heavy Majorana neutrino $(N)$ at hadron colliders. Particular attention is paid to the fusion process $Wγ\rightarrow N\ell^{\pm}$. We systematically categorize the contributions from an initial state photon in the elastic, inelastic, and deeply inelastic channels. Comparing with the leading channel via the Drell-Yan production $q \bar{q}'\rightarr…
Quasi-Dirac neutrinos are obtained when the Lagrangian density of a neutrino mass model contains both Dirac and Majorana mass terms, and the Majorana terms are sufficiently small. This type of neutrinos introduces new mixing angles and mass splittings into the Hamiltonian, which will modify the standard neutrino oscillation probabilities. In this paper, we focus on the case where the new mass splittings are too small to be measured, but new angles and phases are present. We perform a sensitivity study for this scenario for the upcoming experiments DUNE and JUNO, finding that they will improve …
Neutrino theory: open questions and future opportunities
该报告围绕中微子质量起源问题，梳理了高/低标度跷跷板、辐射等马约拉纳中微子质量产生机制及其可检验性，指出明确质量起源是远期目标，同时展望了可推动进展的实验方向。
I discuss, in a semi-pedagogical way, our current understanding of neutrino physics. I present a brief history of how the neutrino came to be ``invented'' and observed, and discuss the evidence that led to the recent discovery that neutrinos change flavor. I then spend some time presenting mass-induced neutrino flavor change (neutrino oscillation), and how it pieces all the neutrino puzzles except for the LSND anomaly, which is also briefly discussed. I conclude by highlighting the importance of determining the nature of the neutrinos, i.e., are they Dirac or Majorana fermions.
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