arXiv subjects
Publications and source records attributed to Eung Jin Chun.
Lepton flavor violation in various sectors of the theory can bring important effects on neutrino masses and mixing through wave function renormalization. We examine general conditions for flavor structure of radiative corrections producing the atmospheric and solar neutrino mass splittings from degenerate mass patterns. Also obtained are the mixing angle relations consistent with the experimental results.
We point out that axino can be a natural candidate for sterile neutrino which would accommodate the LSND data with atmospheric and solar neutrino oscillations. It is shown that the so called 3+1 scheme can be easily realized when supersymmetry breaking is mediated by gauge interactions and also R-parity is properly broken. Among the currently possible solutions to the solar neutrino problem, only the large angle MSW oscillation is allowed in this scheme. The weak scale value of the Higgs $μ$ parameter and the required size of R-parity violation can be understood by means of spontaneously broken Peccei-Quinn symmetry.
Flaton models of Peccei-Quinn symmetry have good particle physics motivation, and are likely to cause thermal inflation leading to a well-defined cosmology. They can solve the $μ$ problem, and generate viable neutrino masses. Canonical flaton models predict an axion decay constant F_a of order 10^{10} GeV and generic flaton models give F_a of order 10^9 GeV as required by observation. The axion is a good candidate for cold dark matter in all cases, because its density is diluted by flaton decay if F_a is bigger than 10^{12} GeV. In addition to the dark matter axions, a population of relativistic axions is produced by flaton decay, which at nucleosynthesis is equivalent to some number δN_νof extra neutrino species. Focussing on the canonical model, containing three flaton particles and two flatinos, we evaluate all of the flaton-flatino-axion interactions and the corresponding axionic decay rates. They are compared with the dominant hadronic decay rates, for both DFSZ and KSVZ models. These formulas provide the basis for a precise calculation of the equivalent δN_νin terms of the parameters (masses and couplings). The KSVZ case is probably already ruled out by the existing bound δN_ν\lsim 1. The DFSZ case is allowed in a significant region of parameter space, and will provide a possible explanation for any future detection of nonzero $δN_ν$.
In an interesting class of models, non-renormalizable terms of the superpotential are responsible for the spontanteous breaking of Peccei-Quinn (PQ) symmetry as well as the generation of the $μ$ term. The flaton fields which break PQ symmetry are accompanied by flatinos, and the lightest flatino (the LSP) can be the stable, while the decay of the lightest neutralino (the NLSP) might be visible at colliders with a low axion scale. We examine the cosmology of these models, involving thermal inflation just after the PQ phase transition. The branching ratio of flatons into axions must be small so as not to interfere with nucleosynthesis, and flatons must not decay into the LSP or it will be over-abundant. We explore a simple model,with light flatons which can decay into $Z$ or $W$ bosons, or into a light Higgs ($h^0$) plus a $Z$ boson, to show that such features can be realized in a wide range of parameter space. The mass of the NLSP can be as low as $(m_{h^0}+m_Z)/2$, with an axion scale of order $10^{10}$ GeV and a final reheat temperature typically of order $10\GeV$. Then, the flatino LSP is a good dark matter candidate because the reheat temperature can be high enough to allow its production from the decay of the thermalized LSP, while low enough to prevent its overproduction from the decay of sfermions.
We analyze the effect of R-parity violation in the minimal supersymmetric standard model on the CP asymmetries in $b\to s γ$ decay. The direct and mixing-induced CP asymmetries arising from the lepton number violating couplings are strongly constrained by the current experimental limits on the corresponding couplings. Allowing a heavy neutrino ($m_{ν_τ}\sim10$ keV) and a moderate mass splitting of sfermions, the direct CP asymmetry around 15 % and the nearly maximal mixing-induced CP asymmetry ($\sim 100 %$) can be realized, depending on the R-parity conserving contributions to the radiative $b$ decay. With the baryon number violating couplings, only the mixing-induced CP asymmetry arises and it can be maximal provided there is a the similar sfermion mass splitting.
We examine some flavor changing processes such as rare leptonic decays of the long-lived neutral kaon, muon-electron conversion in nuclei and radiative muon decay which are induced by the combined effects of bilinear and trilinear R-parity violations. These processes are used to put strong constraints on certain products of the bilinear and trilinear couplings. We also discuss the constraints on R-parity violation from neutrino masses and compare them with the constraints from flavor changing decay processes. Large range of parameter space satisfying the constraints from neutrino masses can be excluded by the flavor changing processes considered in this paper, and also vice versa.
We bring the theoretical issue of whether two important cosmological demands, baryon asymmetry and degenerate neutrinos as hot dark matter, can be compatible in the context of the seesaw mechanism. To realize leptogenesis with almost degenerate Majorana neutrinos without severe fine-tuning of parameters, we propose the hybrid seesaw mechanism with a heavy Higgs triplet and right-handed neutrinos. Constructing a minimal hybrid seesaw model with SO(3) flavor symmetry for the neutrino sector, we show that the mass splittings for the atmospheric and solar neutrino oscillations which are consistent with the requirements for leptogenesis can naturally arise.
We analyze the electron and neutron electric dipole moments induced by R-parity violating interactions in supersymmetric models. It is pointed out that dominant contributions can come from one-loop diagrams involving both the bilinear and trilinear R-parity odd couplings, leading to somewhat severe constraints on the products of those couplings.
We provide, in the R-parity violating supersymmetric standard model, a comprehensive analysis for sneutrino minimization from the one-loop effective scalar potential, and also for one-loop renormalized neutrino masses and mixing by calculating the effective neutrino mass matrix in the weak basis. Applying our results to theories with gauge mediated supersymmetry breaking, we show how atmospheric and solar neutrino oscillations can be accommodated simultaneously in this framework. It is observed that the one-loop correction to sneutrino vacuum expectation values leads to a significant effect on the determination of the neutrino masses and mixing.
R-parity violation in the supersymmetric standard model could be the origin of neutrino masses and mixing accounting for the atmospheric and solar neutrino oscillations. More interestingly, this hypothesis may be tested in future colliders by detecting lepton number violating decays of the lightest supersymmetric particle. Here, we present a comprehensive analysis for the determination of sneutrino vacuum expectation values from the one-loop effective scalar potential, and also for the one-loop renormalization of neutrino masses and mixing. Applying our results to theories with gauge mediated supersymmetry breaking, we discuss the effects of the one-loop corrections and how the realistic neutrino mass matrices arise.
We propose a radiative origin of the two mass splittings of three degenerate Majorana neutrinos. It can be achieved by extending the standard model to have the usual effective dimension 5 operators generating SO(3)-invariant tree-level masses, and a charged scalar singlet coupling with the leptons preserving the U(1) subgroup of SO(3). The mass splittings for the atmospheric and solar neutrino oscillations then arise from one-loop corrections due to the charged scalar singlet coupling and the usual tau Yukawa coupling, respectively.
It is pointed out that important contribution to neutrino masses and mixing can come from flavour violating slepton exchange. For low and intermediate $\tanβ$ such effects can dominate over the usual tau Yukawa coupling effects included in the renormalization group evolution. The mixing angles satisfy then the relation different from the fixed point solution of the renormalization group equation, and the desired neutrino mass splitting can be generated.
We point out that the axino predicted as the supersymmetric partner of the axion is a good candidate for the recently proposed sterile neutrino cool dark matter. The axino mass falls into the right range in the context of gauge mediated supersymmetry breaking. A sizable mixing of the axino with active neutrinos arises when R-parity violation is allowed and the resulting neutrino masses and mixing accommodate the atmospheric and solar neutrino oscillations simultaneously.
R-parity and L violation in the MSSM would be the origin of the neutrino oscillation observed in Super-Kamiokande. A distinctive feature of this framework is that it can be tested in colliders by observing decay products of the destabilized LSP. We examine all the possible decay processes of the neutralino LSP assuming the bilinear contribution to neutrino masses dominates over the trilinear one which gives rise to the solar neutrino mass. We find that it is possible to probe neutrino oscillations through colliders in most of the R-parity conserving MSSM parameter space.
R-parity violating bilinear (soft) terms in the supersymmetric standard model would be the leading source for nonzero neutrino masses and mixing. We point out that the mixing between neutralinos (charginos) and neutrinos (charged leptons) driven by the bilinear terms take factorized forms, which may enable us to probe the neutrino mixing parameters in a collider. It is then shown that the Super-Kamiokande data on atmospheric neutrinos require all the baryon number violating couplings to be substantially suppressed: $λ''_{\rm any} <10^{-9}$.
When the strong CP problem is solved by spontaneous breaking of an anomalous global symmetry in theories with gauge-mediated supersymmetry breaking, the pseudo Goldstone fermion (the axino) is a good candidate of a light sterile neutrino. Its mixing with neutrinos relevant for current neutrino experiments can arise in the presence of R-parity violation. The realistic four neutrino mass matrix is obtained when the see-saw mechanism is brought in, and an ansatz for the right-handed neutrino mass is constructed.
We provide a simple solution to the $μ$ and strong CP problems in the context of gauge mediated supersymmetry breaking. The generic appearance of R symmetry in dynamical supersymmetry breaking is used to implement Peccei-Quinn symmetry. Acceptable $μ$ and $B$ terms as well as the large symmetry breaking scale are induced in the presence of nonrenormalizable interactions. Cosmological consequences of this scheme turn out to yield constraints on the PQ symmetry breaking scale and the number of the messenger/heavy quarks. Complexity in introducing non-R Peccei-Quinn symmetry is contrasted with the case of R symmetry.
We study the neutrino mass matrix in supersymmetric models in which the quark and charged lepton mass hierarchies and also the suppression of baryon or lepton number violating couplings are all explained by horizontal $U(1)_X$ symmetry. It is found that the neutrino masses and mixing angles suggested by recent atmospheric and solar neutrino experiments arise naturally in this framework which fits in best with gauge-mediated supersymmetry breaking with large $\tanβ$. This framework highly favors the small angle MSW oscillation of solar neutrinos, and determine the order of magnitudes of all the neutrino mixing angles and mass hierarchies.