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We correct a factor in the Lagrangian, a sign of a coupling constant and 3-body decay rate. The factor of the second term in the interaction Lagrangian, (2), should be multiplied by 2,

We study the decay process of an unstable quantum system, especially the deviation from the exponential decay law. We show that the exponential period no longer exists in the case of the s-wave decay with small Q value, where the Q value is the difference between the energy of the initially prepared state and the minimum energy of the continuous eigenstates in the system. We also derive the quantitative condition that this kind of decay process takes place and discuss what kind of system is suitable to observe the decay.

We study the stau lifetime in a scenario with the LSP taken to be a neutralino and the NLSP being a stau, based on the minimal supersymmetric Standard Model. The mass difference between the LSP and NLSP, $\delta m$, must satisfy $\delta m/m_{\tilde{\chi}} \sim$ a few % or less for coannihilation to occur, where $m_{\tilde{\chi}}$ is the neutralino mass. We calculate the stau lifetime from the decay modes $\tilde{\tau}\to \tilde{\chi}\tau$, $\tilde{\chi}\nu_\tau\pi$, and $\tilde{\chi}\nu_\tau\mu(e)\nu_{\mu(e)}$ and discuss its dependence on various parameters. We find that the lifetime is in the range $10^{-22}$--$10^{16}$ sec for $10^{-2} \le \delta m \le 10$ GeV. We also discuss the connection with lepton flavor violation if there is mixing between sleptons.Comment: 15 pages, 5 figure

Modification of standard big-bang nucleosynthesis is considered in the minimal supersymmetric standard model to resolve the excessive theoretical prediction of the abundance of primordial lithium 7. We focus on the stau as a next-lightest superparticle, which is long lived due to its small mass difference with the lightest superparticle. It provides a number of additional decay processes of 7 Li and 7 Be. A particularly important process is the internal conversion in the stau-nucleus bound state, which destroys the 7 Li and 7 Be effectively. We show that the modification can lead to a prediction consistent with the observed abundance of 7 Li.

A scenario of the big-bang nucleosynthesis is analyzed within the minimal supersymmetric standard model, which is consistent with a stau-neutralino coannihilation scenario to explain the relic abundance of dark matter. We find that we can account for the possible discrepancy of the abundance of 7 Li between the observation and the prediction of the big-bang nucleosynthesis by taking the mass of the neutralino as 300 GeV and the mass difference between the stau and the neutralino as (100 -120) MeV. We can therefore simultaneously explain the abundance of the dark matter and that of 7 Li by these values of parameters. The lifetime of staus in this scenario is predicted to be O(100 -1000) sec.

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We investigate the gauge-Higgs unification models within the scheme of the coset space dimensional reduction, beginning with a gauge theory in a fourteen-dimensional spacetime where extra-dimensional space has the structure of a ten-dimensional compact coset space. We found seventeen phenomenologically acceptable models through an exhaustive search for the candidates of the coset spaces, the gauge group in fourteen dimension, and fermion representation. Of the seventeen, ten models led to SO(10)(×U (1)) GUT-like models after dimensional reduction, three models led to SU (5) × U (1) GUT-like models, and four toThe combinations of the coset space, the gauge group in the fourteen-dimensional spacetime, and the representation of the fermion contents of such models are listed. §1. IntroductionThe Standard Model (SM) has described the interactions of the elementary particles successfully. In this model, the Higgs scalar plays an essential role in the mechanism of spontaneous breaking of the gauge symmetry from SU (3) C ×SU (2) L ×U (1) Y down to SU (3) C × U (1) em , giving masses to the elementary particles. Nevertheless, the Higgs particle itself is still undiscovered. Not only is it the last frontier of the SM, it will also provide the key clue to the physics beyond the SM, since the SM does not address even the most fundamental nature of the Higgs particle, such as its mass and the self-coupling constants.The gauge-Higgs unification is one of attractive approaches to the physics beyond the SM in this regard 1)-3) (for recent approaches, see Refs. 4)-19)). In this approach, the Higgs sector is embraced into the gauge interactions in the spacetime with dimensions larger than four, where the extra-dimensional space is compactified to a small scale to reproduce the four-dimensional spacetime. The scalar particles originate from the extra-dimensional components of the gauge field and part of the fundamental properties of Higgs scalar is determined from the gauge interactions.We consider this approach in the framework of coset space dimensional reduction (CSDR) 20) (for recent approaches, see Refs. 21)-23)). This framework introduces a compact extra-dimensional space which has the structure of a coset of Lie groups, and identifies the gauge transformation as the translation within the extra-dimensional space. This identification determines both the gauge symmetry and the particle contents of the four-dimensional theory.