Boris Kayser
We explain why the see-saw picture and leptogenesis make it particularly interesting to find out whether neutrinos are their own antiparticles, and whether their oscillations violate CP.
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It is shown that we cannot put Majorana neutrinos in the standard Dirac theory without violation of the gauge invariance. Experiments on $ν_l \to l (l = e, μ, τ)$ transitions do not confirm this supposition. It means that on neutrino oscillation experiments, the Majorana neutrino oscillations cannot be observed.
We explain why it is so hard to determine whether neutrinos are Majorana or Dirac particles as long as the only neutrinos we study are ultra-relativistic. We then show how non-relativistic neutrinos could help, and focus on the angular distributions in the decays of an as-yet-to-be-discovered heavy neutrino $N$. We find that these angular distributions could very well tell us whether neutrinos are Majorana or Dirac particles.
In answering the difficult questions on neutrinos asked by Sphinx I argue that search for proton decay is the most important experiment in coming 5-10 years. I also emphasize the crucial importance of the neutrinoless double beta decay with sensitivity of <m_{νe}> \sim 0.01 eV level as the unique feasible way of directly detecting neutrinos of atmospheric mass scale in laboratories. I point out that, if observed at this level, it means not only that neutrinos are Majorana particle but also that they must obey an inverted mass hierarchy.
We know that neutrino mass and mixing provide a window to physics beyond the Standard Model. Now this window is open, at least partly. And the questions are: what do we see, which kind of new physics, and how far "beyond"? I summarize the present knowledge of neutrino mass and mixing, and then formulate the main open questions. Following the bottom-up approach, properties of the neutrino mass matrix are considered. Then different possible ways to uncover the underlying physics are discussed. Some results along the line of: see-saw, GUT and SUSY GUT are reviewed.
The experimental discovery that neutrinos almost certainly have masses and mix raises a number of fundamental questions about the neutrinos. We discuss what is presently known about the answers to these questions, and how we can learn more.
To describe neutrino oscillations in the sense of quantum mechanics and quantum field theory, we propose to use an off-diagonal neutrino-Higgs (mass) interaction, as discussed originally in a family gauge theory and in the extended Standard Model. For neutrino oscillations which take place presumably between point-like Dirac particles, the proposed description would be unique in the quantum mechanics sense. This may help us to resolve a few outstanding puzzles - the question of why there are only three generations, the question of why the masses of neutrinos are so tiny, the question of why ne…
We argue that the evidence for neutrino mass is quite compelling. This mass raises a number of questions, which we enumerate, about neutrinos. Then we focus on one of these questions---the issue of the possible neutrino mass spectra. In particular, we explain that one can have a four-neutrino spectrum which does not require significant sterile-neutrino involvement in either the atmospheric or solar neutrino oscillations.
It is noted that the theory of neutrino oscillations can be constructed only in the framework of the particle physics theory, where is a mass shell conception and then transitions (oscillations) between neutrinos with equal masses are real and between neutrinos with different masses are virtual. It is necessary to solve the question: which type of neutrino transitions (oscillations) is realized in nature? There can be three types of neutrino transitions (oscillations). At present it is considered that Dirac and Majorana neutrino oscillations can be realized. It is shown that we cannot put Majo…
There are four puzzling questions about by the magnitudes of neutrino mixings and mass splittings. A brief sketch is given of the various kinds of models of neutrino masses and how they answer these questions. Special attention is given to so-called "lopsided" models.
As an introduction to NuFact '99, the ICFA/ECFA Workshop on Neutrino Factories Based on Muon Storage Rings, I place the issues of neutrino properties and neutrino oscillations in the broader context of fermion flavor.
In this talk I review the present bounds on the tau neutrino, concentrating on the possibility of bringing the mass bound below an MeV.
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。
The possible sources of one-photon radiation as background for quasi-elastic reaction nu_mu+n to mu^-+p are considered. The ones are relevant in experiments on determination of oscillation parameters at low neutrino energies (E_nu^lab~1 GeV). The estimation for the cross section of reaction nu_mu+n to mu^-+p+gamma is given at E_nu^lab=0.7 GeV as 0.65% from the corresponding cross section of quasi-elastic reaction.
We define the ratio R = (No. of observed electron events)/ (No. of expected muon events - No. of observed muon events) as a measure for relative importance of $ν_μ\to ν_e$ and $ν_μ\to ν_τ$ oscillations which will be measurable in coming long-baseline neutrino experiments. We then argue that if neutrino oscillation is observed with 0.02 < R < 0.87 it implies the rejection of the neutrino dark matter hypothesis. Our argument is valid if neutrinos come with only three flavors without steriles and if they have a hierarchical mass pattern.
Thanks to compelling evidence that neutrinos can change flavor, we now know that they have nonzero masses, and that leptons mix. In these lectures, we explain the physics of neutrino flavor change, both in vacuum and in matter. Then, we describe what the flavor-change data have taught us about neutrinos. Finally, we consider some of the questions raised by the discovery of neutrino mass, explaining why these questions are so interesting, and how they might be answered experimentally,
We give a review about the Minimal Supersymmetric Standard Model with three right-handed neutrinos (MSSM3RHN). We, first introduce the minimal set of fields to built this model in their superfields formalism. After it, we build the lagrangian of the model in the superspace formalism and also introduce the soft terms to break SUSY. We show how to get masses to the neutrinos and sneutrinos in this model.
It is by now established that neutrinos mix, have (different) non-zero masses, and therefore oscillate. The oscillation parameters themselves, however, are not all well-known. An open problem is that of the neutrino mass hierarchy. We study the possibility of determining the neutrino mass hierarchy with atmospheric neutrinos using an iron calorimeter detector capable of charge identification such as the proposed MONOLITH and ICAL/INO detectors. We find that such detectors are sensitive to the sign of the mass-squared difference, δ_{32} = m_3^2 - m_2^2, provided the as-yet unknown mixing angle …
Why are different mass states coherent? What is the correct formula for the oscillation phase? How can textbook formulas for oscillations in time describe experiments which never measure time? How can we treat the different velocities and different transit times of different mass eigenstates and avoid incorrect factors of two? How can textbook forumulas which describe coherence between energy states be justified when Stodolsky's theorem states there is no coherence between different energies? Is covariant relativistic quantum field theory necessary to describe neutrino oscillations? How import…
The discovery of neutrino oscillations invites many fundamental physics questions that have yet to be answered. Two of these questions are simple, easy to state, and essential: What are the values of the neutrino masses? Are neutrinos Majorana fermions? The reason we don't know the answer to those questions is that it is difficult to measure neutrino properties outside of the ultrarelativistic regime. We discuss the physics of $eγ\to eν\barν$ near threshold, where one has access to nonrelativistic neutrinos and only nonrelativistic neutrinos. Near threshold, $eγ\to eν\barν$ is a rich phenomeno…
The recent data describing the evidence for neutrino oscillations by Super Kamiokande implies that two neutrinos are very strongly mixed. We ask the question: can approximate maximal neutrino mixing be natural in unified (GUT or string) models? We attempt to answer this question in as much generality as possible. Without specifying a particular model, we are able to show that a gauged family symmetry can naturally provide the required maximal mixing between mu and tau neutrinos. The second and third family neutrino mass eigenstates are almost degenerate with masses of order 0.2 eV.
Suppose the geometrical explaination to the weak CP phase in quark sector is also valid for neutrinos, the mixing and CP violation in neutrino system are discussed. We find a larger $J_{CP}$ than $3\times 10^{-3}$ implys the large-mixing solution for solar neutrino problem. In case of bi-maximal mixing, we predict relative large CP violation with $J_{CP}$ larger than $10^{-3}$ in neutrino system, except the third mixing angle approachs to 0 or $π/2$ very closely.
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…
In this paper, we first calculate the realistic Earth matter effects in the detection of type II supernova neutrinos at the Daya Bay reactor neutrino experiment which is currently under construction. It is found that the Earth matter effects depend on the neutrino incident angle $θ$, the neutrino mass hierarchy $Δm_{31}^{2}$, the crossing probability at the high resonance region inside the supernova, $P_{H}$, the neutrino temperature, $T_α$, and the pinching parameter in the neutrino spectrum, $η_α$. We also take into account the collective effects due to neutrino-neutrino interactions inside …
Emergence of neutrino physics is fueled by the recent growth in quality and quantity of experimental data, yet, there are still open questions. How much can the determination of mixing parameters be improved? Can we improve bounds on theta_13 before experiments designed specifically for this parameter start? How well can we determine or limit sterile fraction of neutrino flux from sun and sterile mixing angle? We examine the impact of outcome from new measurements in the context of providing answers to these questions
Searches for Dark Matter suggest that it couples to ordinary matter only very weakly and possibly only through the Higgs or other scalar bosons. On the other hand, neutrinos might not couple to the Higgs boson directly, but only through a loop of Dark Matter particles, which would naturally explain the small neutrino masses. We demonstrate that current experimental constraints on such a ``scotogenic'' scenario allow to make the linear dependence of the lightest neutrino mass on the dark sector-Higgs coupling explicit, so that a measurement by the KATRIN experiment would directly determine its …
About Matter Effects on Neutrino Mixing Matrix Phases
本文指出中微子在物质中传播时，常用的仅含1个相位的PMNS矩阵无法正确对角化中微子系统，通过数值计算和解析估计验证该结论，并讨论了可探测该效应的场景。
In this talk I review what we know and don't know about neutrinos, neutrino masses and lepton mixing. I also discuss the importance of the discovery that neutrinos have nonzero masses, and illustrate how little is currently known about the physics behind them.
Inverting the type-I seesaw formula, we reconstruct the mass matrix of the heavy right-handed neutrinos $N_i$. We analyze how the data on neutrino oscillations affect the structure of this matrix. Under the assumption of hierarchical Dirac-type neutrino masses $m_{Di}$, we compute the mixing angles among $N_i$, their masses $M_i$ and the lepton asymmetries $ε_i$ generated in their decays. Unless special cancellations take place, one finds $M_i\propto m_{Di}^2$ and the generated baryon-to-photon ratio $η_B$ is much smaller than the observed value. We show that successful baryogenesis via leptog…
We summarize what has been learned about the neutrino mass spectrum and neutrino mixing, identify interesting open questions that can be answered by accelerator neutrino facilities of the future, and discuss the importance and physics of answering them.
The question of whether neutrino masses are Dirac or Majorana is one of the most important, and most difficult, questions remaining in the neutrino sector. Searches for neutrinoless double beta-decay may help to resolve this question, but are also sensitive to new, higher dimension Delta L=2 operators. In this paper we place two phenomenological constraints on these operators at dimension d<=11. First, we require that the operators obey the quark flavor symmetries of the Standard Model, with any violation of the symmetries being due to Yukawa interactions, a scheme known as Minimal Flavor Viol…
Massive neutrinos are a generic prediction of SO(10), and models of unification cry for supersymmetry. Since we have a rather detailed information on neutrino and charged fermion masses, the real question is: how/whether it is possible to build a SO(10) supersymmetric model, that correctly incorporates fermion masses. We show that a simple construction is possible in the context of a minimal theory. We concentrate on the two heaviest generations, discuss the predictions of the model, and briefly comment on open questions.
Several relevant issues in computing neutrino emissivity in Urca processes in color superconducting quark matter are addressed. These include: (1) The constraint on $u$ quark abundance is given from electric neutrality and the triangle relation among Fermi momenta for participants. (2) The phase space defined by Fermi momentum reduction of quarks is discussed in QCD and NJL model. (3) Fermi effective model of weak interaction is reviewed with special focus on its form in Nambu-Gorkov basis.
The presence of several clone solutions in the simultaneous measurement of ($θ_{13},δ$) has been widely discussed in literature. Here, after a pedagogical introduction on why these clones arise, we discuss how the clones location in the ($θ_{13},δ$) plane change as a function of the physical input pair ($\barθ_{13},\barδ$). We compare the clone flow of a set of possible future neutrino experiments: the CERN SuperBeam, BetaBeam and Neutrino Factory proposals. We show that the combination of these specific BetaBeam and SuperBeam could not help in solving the degeneracies. The combination of one …
This article summarises a talk given at the 2014 Palermo workshop on Astrophysics. It covers a short review on the neutrino physics status and the potential physics opportunities of future experiments. During the last year our knowledge on the neutrino oscillation parameter $\sin^2θ_{13}$ improved dramatically, and the large value opened the way to oscillation experiments sensitive to possible CP-violation. The first high-energetic neutrinos in the TeV range were detected in the IceCube experiment, while the Planck collaboration set further limits on the number of active neutrinos from cosmolo…
The discoveries and open questions in neutrino physics, as reported at Neutrino 2002 and more recently, are reviewed from a theoretical perspective.
In this talk the answer to the question: what neutrinos have to do with QCD, the present theory of strong interactions? is presented. The answer is positive as some strong arguments on this assertion that are presented bring out.
Neutrino proton elastic scattering and polarized deep inelastic spin sum rules provide complementary information about the spin structure of the proton. We outline the two approaches and what they may teach us about the transition from current to constituent quarks in QCD.
Double beta decay is indispensable to solve the question of the neutrino mass matrix together with neutrino oscillation experiments. The most sensitive experiment since eight years - the Heidelberg-Moscow experiment in Gran-Sasso - already now, with the experimental limit of < m_ν> < 0.26 eV excludes degenerate neutrino mass scenarios allowing neutrinos as hot dark matter in the universe for the small angle MSW solution of the solar neutrino problem. It probes cosmological models including hot dark matter already now on the level of future satellite experiments MAP and PLANCK. It further probe…
The major steps in the development of our knowledge about neutrinos are reviewed. The basics of neutrino oscillation formalism is presented. Neutrino oscillations in the framework of three-neutrino mixing are considered. The evidence for neutrino oscillations is discussed.
We discuss various issues concerning the interactions of nuclei with neutrinos of low impinging energies (i.e. having several tens of MeV to a few hundred MeV) of interest for particle physics, nuclear physics and astrophysics. We focus, in particular, on open questions as well as possible strategies to obtain more experimental information. The option of a low-energy beta-beam facility is extensively discussed. We also mention its potential concerning the neutrino magnetic moment.
Questions of flavor physics and neutrino mass from a flipped hypercharge
本文提出将标准模型超荷 $U(1)_Y$ 扩展为依赖代结构的 $U(1)_X\otimes U(1)_N$，通过反常消除解释三代费米子并预言右手中微子，从而自然产生中微子质量并解释多种味反常。
Two schemes of mixing of four massive neutrinos with two close neutrino masses separated by a gap of Delta m^2 about 1 eV^2 can accommodate solar, atmospheric and LSND neutrino oscillation data. It is shown that long-baseline nu(e)->nu(x) and nu(mu)->nu(e) transitions are strongly suppressed in these schemes. The scheme of mixing of three massive neutrinos with a mass hierarchy that can describe solar and atmospheric data is also discussed. It is shown that in this scheme the effective Majorana mass that characterizes the matrix element of neutrinoless double-beta decay is smaller than about 1…
The Majorana versus Dirac nature of neutrinos remains an open question. This is due, in part, to the fact that virtually all the experimentally accessible neutrinos are ultra-relativistic. Noting that Majorana neutrinos can behave quite differently from Dirac ones when they are non-relativistic, we show that, at leading order, the angular distribution of the daughters in the decay of a heavy neutrino into a lighter one and a self-conjugate boson is isotropic in the parent's rest frame if the neutrinos are Majorana, independent of the parent's polarization. If the neutrinos are Dirac fermions, …
Measurements of cosmic neutrinos have a reach potential for providing an insight into fundamental neutrino properties. For this a precise knowledge about an astrophysical environment of cosmic neutrinos propagation is needed. However this is not always possible, and the lack of information can bring about theoretical uncertainties in our physical interpretation of the results of experiments on cosmic neutrino fluxes. We formulate an approach that allows one to quantify the uncertainties using the apparatus of quantum measurement theory. We consider high-energy Dirac neutrinos emitted by some d…
We investigate what one can hope to learn about the parameters that describe the neutrino fluxes emitted by the explosion of a galactic supernova using the observations of a megaton-size Water-Cherenkov detector. We calculate the allowed regions that can be obtained by fitting these parameters to a simulated observation of events by such a detector. All four available detection channels (inverse beta decay, charge and neutral current on oxygen and elastic scattering on electrons) are included in the fit and we use a ten dimensional parameters space. Nine parameters describe the initial neutrin…
Two of the most important and pressing questions in cosmology and particle physics are: (1) What is the nature of cold dark matter? and (2) Will near-future experiments on neutrinoless double beta decay be able to ascertain that the neutrino is a Majorana particle, i.e. its own antiparticle? We show that these two seemingly unrelated issues are intimately connected if neutrinos acquire mass only because of their interactions with dark matter.
We consider the supernova shock effects, the Mikheyev-Smirnov-Wolfenstein (MSW) effects, the collective effects, and the Earth matter effects in the detection of type II supernova neutrinos on the Earth. It is found that the event number of supernova neutrinos depends on the neutrino mass hierarchy, the neutrino mixing angle $θ_{13}$, and neutrino masses. Therefore, we propose possible methods to identify the mass hierarchy and acquire information about $θ_{13}$ and neutrino masses by detecting supernova neutrinos. We apply these methods to some current neutrino experiments.
Non-relativistic neutrinos and the question of Dirac vs. Majorana neutrino nature
本文详细探讨了在非相对论性条件下区分狄拉克型与马约拉纳型中微子的可行性，分析了β衰变、遗迹中微子及散射等过程中的探测可能。
I report on recent theoretical results about neutrino mixing and oscillations. I show that in Quantum Field Theory, mixing transformations are not trivial and the vacuum for the mixed fields has a condensate structure. This fact has phenomenological consequences on neutrino oscillations: the oscillation formula turns out to have an additional oscillating piece and energy dependent amplitudes. The usual Pontecorvo formula is recovered in the relativistic limit. I report also about preliminary results on the presence of a topological (Berry) phase for oscillating neutrinos.
We discuss the question of CP-violation in the effective Hamiltonian approach in models of leptogenesis through heavy right handed neutrino decays. We first formulate the problem in four component notation and then point out that before the heavy neutrinos have decayed away, the universe becomes CP-asymmetric in the heavy neutrinos. However, the lepton asymmetry generated after they completely decay are independent of this asymmetry.
Neutrino properties from muonium-antimuonium mixing
本文通过计算μ子素-反μ子素混合振幅，在最小扩展标准模型中研究狄拉克与马约拉纳中微子的可区分性，发现放宽PMNS幺正性无法增强混合，而赝狄拉克情形在正质量排序下可显著增强混合，为MACE实验提供理论依据。
Neutrino Theory Overview
本文概述了中微子物理中的开放性问题，并提出通过多领域协同方法来探索未来实验前景。
New and more precise measurements of neutrino cross sections have renewed the interest in a better understanding of electroweak interactions on nucleons and nuclei. This effort is crucial to achieve the precision goals of the neutrino oscillation program, making new discoveries, like the CP violation in the leptonic sector, possible. We review the recent progress in the physics of neutrino cross sections, putting emphasis on the open questions that arise in the comparison with new experimental data. Following an overview of recent neutrino experiments and future plans, we present some details …
A specific model of parity-conserving lepton substructure is considered. We show that a positive-definite contribution to the muon $(g-2)/2$ at the possible level of about $4\times 10^{-9}$, can be related to a significant increase in the interaction cross section for cosmic-ray neutrinos with energies above about $10^{19}$ eV. The additional cross section at $\sim 10^{20}$ eV is calculated to be $\sim 10^{-29}$ cm$^2$, which is about 100 times the standard weak-interaction cross section. The model involves an extremely massive, neutral lepton, with $m_L\cong 2\times 10^6$ GeV fixed by the new…
In the era of precision neutrino physics, we study the influence of matter NSI on the question of neutrino mass ordering and its resolution. At long baseline experiments, since matter effects play a crucial role in addressing this very important question, it is timely to investigate how sub-leading effects due to NSI may affect and drastically alter inferences pertaining to this question. We demonstrate that the sensitivity to mass ordering gets significantly impacted due to NSI effects for various long baseline experiments including the upcoming long baseline experiment, Deep Underground Neut…
This proceeding explores some of the questions that connect the LHC and neutrino experiments: What is the origin of mass? What is the meaning of flavor? Is there direct evidence of new forces or particles? The neutrino program investigating these questions is large and diverse. The strategy here, to narrow the discussion, is to focus on relatively new ideas for experiments that may be less known within the LHC community.
Two simple exercises are solved, which educators can use to awake interest of their students in subtleties of the CERN Neutrino beam to Grand Sasso (CNGS) experiment. The first one is about the statistical error of the average departure time of neutrinos from CERN. The second one about a hypothetical bias in the departure times.
If the published event rates of the chlorine and Kamiokande solar neutrino experiments are correct, then the energy spectrum of neutrinos produced by the decay of $^8$B in the sun must be different from the energy spectrum determined from laboratory nuclear physics measurements. This change in the energy spectrum requires physics beyond the standard electroweak model. In addition, the GALLEX and SAGE experiments, which currently have large statistical uncertainties, differ from the predictions of the standard solar model by $2 σ$ and $3 σ$, respectively.
We present some thoughts on how to interpret the gravitionally induced neutrino oscillation phases presented by us in our 1996 Gravity Research Foundation Essay.
The only experimentally observed phenomenon that lies outside the standard model of the electroweak interaction is neutrino oscillations. A way to try to unify the extensive neutrino oscillation data is to add a phenomenological mass term to the Lagrangian that is not diagonal in the flavor basis. The goal is then to understand the world's data in terms of the parameters of the mixing matrix and the differences between the squares of the masses of the neutrinos. An outstanding question is what is the correct ordering of the masses, the hierarchy question. We point out a broken symmetry relevan…
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