147 research outputs found
A Constraint on Yukawa-Coupling Unification from Lepton-Flavor Violating Processes
We present a new constraint on a lepton mixing matrix from lepton-flavor
violating (LFV) processes in supersymmetric standard models with massive
neutrinos. Here, we assume Yukawa-coupling unification , in which -neutrino Yukawa coupling is unified into
top-quark Yukawa coupling at the unification scale GeV. We show that the present experimental bound on decay already gives a stringent limit on the lepton mixing (typically
for ). Therefore, many existing neutrino-mass
models are strongly constrained. Future improvement of bounds on LFV processes
will provide a more significant impact on the models with the Yukawa-coupling
unification. We also stress that a precise measurement of a neutrino mixing
in future neutrino experiments would be very important, since
the observation of non-zero , together with negative
experimental results for the LFV processes, have a robust potential to exclude
a large class of SUSY standard models with the Yukawa-coupling unification.Comment: 12 pages, 3 figure
Laser Irradiated Enhancement of the Atomic Electron Capture Rate in search of New Physics
Electron capture processes are important in the search for new physics. In
this context, a high capture rate is desired. We investigate the possibility of
enhancing the electron capture rate by irradiating laser beam to ''atom''. The
possibility of such enhancement can be understood as a consequence of an
enhancement of the electron wave function at the origin, , through an
increased effective mass of the electron. We find that an order of magnitude
enhancement can be realized by using a laser with intensity on the order of
W/mm and a photon energy on the order of eV.Comment: 14 pages, 7 figures, editing and typos corrected, title change
Disordered ground states in a quantum frustrated spin chain with side chains
We study a frustrated mixed spin chain with side chains, where the spin
species and the exchange interactions are spatially varied. A nonlinear sigma
model method is formulated for this model, and a phase diagram with two
disordered spin-gap phases is obtained for typical cases. Among them we examine
the case with a main chain consisting of an alternating array of spin-1 and
spin-1/2 sites and side chains each of a single spin-1/2 site in great detail.
Based on numerical, perturbational, and variational approaches, we propose a
singlet cluster solid picture for each phase, where the ground state is
expressed as a tensor product of local singlet states.Comment: 12 pages, 13 figures (included
Investigation of the Two-Particle-Self-Consistent Theory for the Single-Impurity Anderson Model and an Extension to the Case of Strong Correlation
The two-particle-self-consistent theory is applied to the single-impurity
Anderson model. It is found that it cannot reproduce the small energy scale in
the strong correlation limit. A modified scheme to overcome this difficulty is
proposed by introducing an appropriate vertex correction explicitly. Using the
same vertex correction, the self-energy is investigated, and it is found that
under certain assumptions it reproduces the result of the modified perturbation
theory which interpolates the weak and the strong correlation limits.Comment: 5 pages, 7 figures, submitted to J. Phys. Soc. Jp
Oscillation enhanced search for new interaction with neutrinos
We discuss the measurement of new physics in long baseline neutrino
oscillation experiments. Through the neutrino oscillation, the probability to
detect the new physics effects such as flavor violation is enhanced by the
interference with the weak interaction. We carefully explain the situations
that the interference can take place. Assuming a neutrino factory and an
upgraded conventional beam, we estimate the feasibility to observe new physics
numerically and point out that we can search new interactions using some
channels, for example , in these experiments. We also
discuss several models which induce the effective interactions interfering with
the weak interaction, and show that some new physics effects are large enough
to be observed in the oscillation enhanced way.Comment: 25 pages, 20 figure
Chiral Symmetry Breaking in Brane Models
We discuss the chiral symmetry breaking in general intersecting Dq/Dp brane
models consisting of N_c Dq-branes and a single Dp-brane with an s-dimensional
intersection. There exists a QCD-like theory localized at the intersection and
the Dq/Dp model gives a holographic description of it. The rotational symmetry
of directions transverse to both of the Dq and Dp-branes can be identified with
a chiral symmetry, which is non-Abelian for certain cases. The asymptotic
distance between the Dq-branes and the Dp-brane corresponds to a quark mass. By
studying the probe Dp-brane dynamics in a Dq-brane background in the near
horizon and large N_c limit we find that the chiral symmetry is spontaneously
broken and there appear (pseudo-)Nambu-Goldstone bosons. We also discuss the
models at finite temperature.Comment: 29pages, 14figures. v2: a reference added. v3: 27pages, 12figures,
two references added, discussions on s=q configurations are corrected. v4:
minor change in Sec.
The energy spectrum of all-particle cosmic rays around the knee region observed with the Tibet-III air-shower array
We have already reported the first result on the all-particle spectrum around
the knee region based on data from 2000 November to 2001 October observed by
the Tibet-III air-shower array. In this paper, we present an updated result
using data set collected in the period from 2000 November through 2004 October
in a wide range over 3 decades between eV and eV, in which
the position of the knee is clearly seen at around 4 PeV. The spectral index is
-2.68 0.02(stat.) below 1PeV, while it is -3.12 0.01(stat.) above 4
PeV in the case of QGSJET+HD model, and various systematic errors are under
study now.Comment: 12 pages, 7 figures, accepted by Advances in space researc
Standard(-like) Model from an SO(12) Grand Unified Theory in six-dimensions with extra-space
We analyze a gauge-Higgs unification model which is based on a gauge theory
defined on a six-dimensional spacetime with an extra-space. We impose a
symmetry condition for a gauge field and non-trivial boundary conditions of the
. We provide the scheme for constructing a four-dimensional theory from
the six-dimensional gauge theory under these conditions. We then construct a
concrete model based on an SO(12) gauge theory with fermions which lie in a 32
representation of SO(12), under the scheme. This model leads to a
Standard-Model(-like) gauge theory which has gauge symmetry SU(3)
SU(2) U(1)( U(1)) and one generation of SM
fermions, in four-dimensions. The Higgs sector of the model is also analyzed,
and it is shown that the electroweak symmetry breaking and the prediction of
W-boson and Higgs-boson masses are obtained.Comment: 18 page
Extension of the Cosmic-Ray Energy Spectrum Beyond the Predicted Greisen-Zatsepin-Kuz'min Cutoff
The cosmic-ray energy spectrum above 10^{18.5} eV is reported using the
updated data set of the Akeno Giant Air Shower Array (AGASA) from February 1990
to October 1997. The energy spectrum extends beyond 10^{20} eV and the energy
gap between the highest energy event and the others is being filled up with
recently observed events. The spectral shape suggests the absence of the 2.7 K
cutoff in the energy spectrum or a possible presence of a new component beyond
the 2.7 K cutoff.Comment: to be published in PRL, 3 figures, REVTEX forma
Magnetization plateaus in antiferromagnetic-(ferromagnetic)_{n} polymerized S=1/2 XXZ chains
The plateau-non-plateau transition in the
antiferromagnetic-(ferromagnetic) polymerized XXZ chains under
the magnetic field is investigated. The universality class of this transition
belongs to the Brezinskii-Kosterlitz-Thouless (BKT) type. The critical points
are determined by level spectroscopy analysis of the numerical diagonalization
data for where is the size of a unit cell.
It is found that the critical strength of ferromagnetic coupling decreases with
for small but increases for larger enough . It is also found that
the plateau for large is wide enough for moderate values of exchange
coupling so that it should be easily observed experimentally. This is in
contrast to the plateaus for chains which are narrow for a wide range
of exchange coupling even away from the critical point
- …