9,860 research outputs found
Neutrino Oscillation and Charged Lepton-Flavor Violation in the Supersymmetric Standard Models
The neutrino experiment results suggest that the neutrinos have finite masses
and the lepton-flavor symmetries are violating in nature. In the supersymmetric
models, the charged lepton-flavor violating processes, such as mu -> e gamma
and tau -> mu gamma, may have the branching ratios accessible to the future
experiments, depending on origins of the neutrino masses and the SUSY breaking.
In this paper we discuss the branching ratios in the supergravity scenario
using the current solar and atmospheric neutrino experimental data.Comment: 12 pages. Talk given at the Workshop on High Intensity Muon Sources
(HIMUS99), Tsukuba, Japan, 1-4 Dec 199
Signatures of shape phase transitions in odd-mass nuclei
Quantum phase transitions between competing ground-state shapes of atomic
nuclei with an odd number of protons or neutrons are investigated in a
microscopic framework based on nuclear energy density functional theory and the
particle-plus-boson-core coupling scheme. The boson-core Hamiltonian, as well
as the single-particle energies and occupation probabilities of the unpaired
nucleon, are completely determined by constrained self-consistent mean-field
calculations for a specific choice of the energy density functional and paring
interaction, and only the strength parameters of the particle-core coupling are
adjusted to reproduce selected spectroscopic properties of the odd-mass system.
We apply this method to odd-A Eu and Sm isotopes with neutron number , and explore the influence of the single unpaired fermion on the occurrence
of a shape phase transition. Collective wave functions of low-energy states are
used to compute quantities that can be related to quantum order parameters:
deformations, excitation energies, E2 transition rates and separation energies,
and their evolution with the control parameter (neutron number) is analysed.Comment: 15 pages, 13 figures; Accepted for publication in Phys. Rev.
Shape-phase transitions in odd-mass -soft nuclei with mass
Quantum phase transitions between competing equilibrium shapes of nuclei with
an odd number of nucleons are explored using a microscopic framework of nuclear
energy density functionals and a particle-boson core coupling model. The boson
Hamiltonian for the even-even core nucleus, as well as the spherical
single-particle energies and occupation probabilities of unpaired nucleons, are
completely determined by a constrained self-consistent mean-field calculation
for a specific choice of the energy density functional and pairing interaction.
Only the strength parameters of the particle-core coupling have to be adjusted
to reproduce a few empirical low-energy spectroscopic properties of the
corresponding odd-mass system. The model is applied to the odd-A Ba, Xe, La and
Cs isotopes with mass , for which the corresponding even-even Ba
and Xe nuclei present a typical case of -soft nuclear potential. The
theoretical results reproduce the experimental low-energy excitation spectra
and electromagnetic properties, and confirm that a phase transition between
nearly spherical and -soft nuclear shapes occurs also in the odd-A
systems.Comment: 13 pages, 15 figures, 9 table
Microscopic analysis of the octupole phase transition in Th isotopes
A shape phase transition between stable octupole deformation and octupole
vibrations in Th nuclei is analyzed in a microscopic framework based on nuclear
density functional theory. The relativistic functional DD-PC1 is used to
calculate axially-symmetric quadrupole-octupole constrained energy surfaces.
Observables related to order parameters are computed using an interacting-boson
Hamiltonian, with parameters determined by mapping the microscopic energy
surfaces to the expectation value of the Hamiltonian in the boson condensate.
The systematics of constrained energy surfaces and low-energy excitation
spectra point to the occurrence of a phase transition between octupole-deformed
shapes and shapes characterized by octupole-soft potentials.Comment: 6 pages, 5 figures, accepted for publication in Physical Review C,
Rapid Communicatio
Berezinskii-Kosterlitz-Thouless transitions in the six-state clock model
Classical 2D clock model is known to have a critical phase with
Berezinskii-Kosterlitz-Thouless(BKT) transitions. These transitions have
logarithmic corrections which make numerical analysis difficult. In order to
resolve this difficulty, one of the authors has proposed the method called
level spectroscopy, which is based on the conformal field theory. We extend
this method to the multi-degenerated case. As an example, we study the
classical 2D 6-clock model which can be mapped to the quantum self-dual 1D
6-clock model. Additionally, we confirm that the self-dual point has a precise
numerical agreement with the analytical result, and we argue the degeneracy of
the excitation states at the self-dual point from the effective field
theoretical point of view.Comment: 18pages, 7figure
Microscopic description of octupole shape-phase transitions in light actinides and rare-earth nuclei
A systematic analysis of low-lying quadrupole and octupole collective states
is presented, based on the microscopic energy density functional framework. By
mapping the deformation constrained self-consistent axially symmetric
mean-field energy surfaces onto the equivalent Hamiltonian of the
interacting boson model (IBM), that is, onto the energy expectation value in
the boson condensate state, the Hamiltonian parameters are determined. The
study is based on the global relativistic energy density functional DD-PC1. The
resulting IBM Hamiltonian is used to calculate excitation spectra and
transition rates for the positive- and negative-parity collective states in
four isotopic chains characteristic for two regions of octupole deformation and
collectivity: Th, Ra, Sm and Ba. Consistent with the empirical trend, the
microscopic calculation based on the systematics of -
energy maps, the resulting low-lying negative-parity bands and transition rates
show evidence of a shape transition between stable octupole deformation and
octupole vibrations characteristic for -soft potentials.Comment: 18 pages, 18 figures, 1 tabl
Theory of resonant inelastic x-ray scattering at the K edge in LaCuO - Multiple scattering effects -
We develop a theory of resonant inelastic x-ray scattering (RIXS) at the
edge in LaCuO on the basis of the Keldysh Green's function formalism.
In our previous analysis (Phys. Rev. B 71, 035110 (2005)), the scattering by
the core-hole potential was treated within the Born approximation, and a
crude-model density of states was used for the band. We improve the
analysis by taking account of the multiple scattering in Cu3d-O bands and
by using a realistic DOS obtained from a band calculation. The multiple
scattering effect is evaluated with the use of the time representation
developed by Nozi\`eres and De Dominicis. It is found that the multiple
scattering effect makes the -edge peak in the absorption coefficient shift
to the lower energy region as a function of photon energy, that is, the photon
energy required to excite the electron to the -edge peak reduces. It is
also found that the multiple-scattering effect does not change the two-peak
structure in the RIXS spectra but modifies slightly the shape as a function of
energy loss. These findings suggests that the multiple scattering effect could
mainly be included into a renormalization of the core-level energy and partly
justify the Born approximation, leading to a future application to the RIXS in
three-dimensional systems.Comment: revised version with extended discussion, 24 pages, 12 figures,
accepted for PR
Evidence for the Multiverse in the Standard Model and Beyond
In any theory it is unnatural if the observed parameters lie very close to
special values that determine the existence of complex structures necessary for
observers. A naturalness probability, P, is introduced to numerically evaluate
the unnaturalness. If P is small in all known theories, there is an observer
naturalness problem. In addition to the well-known case of the cosmological
constant, we argue that nuclear stability and electroweak symmetry breaking
(EWSB) represent significant observer naturalness problems. The naturalness
probability associated with nuclear stability is conservatively estimated as
P_nuc < 10^{-(3-2)}, and for simple EWSB theories P_EWSB < 10^{-(2-1)}. This
pattern of unnaturalness in three different arenas, cosmology, nuclear physics,
and EWSB, provides evidence for the multiverse. In the nuclear case the problem
is largely solved even with a flat multiverse distribution, and with nontrivial
distributions it is possible to understand both the proximity to neutron
stability and the values of m_e and m_d - m_u in terms of the electromagnetic
contribution to the proton mass. It is reasonable that multiverse distributions
are strong functions of Lagrangian parameters due to their dependence on
various factors. In any EWSB theory, strongly varying distributions typically
lead to a little or large hierarchy, and in certain multiverses the size of the
little hierarchy is enhanced by a loop factor. Since the correct theory of EWSB
is unknown, our estimate for P_EWSB is theoretical. The LHC will determine
P_EWSB more robustly, which may remove or strengthen the observer naturalness
problem of EWSB. For each of the three arenas, the discovery of a natural
theory would eliminate the evidence for the multiverse; but in the absence of
such a theory, the multiverse provides a provisional understanding of the data.Comment: 79 pages, 23 figure
Topological delocalization of two-dimensional massless Dirac fermions
The beta function of a two-dimensional massless Dirac Hamiltonian subject to
a random scalar potential, which e.g., underlies the theoretical description of
graphene, is computed numerically. Although it belongs to, from a symmetry
standpoint, the two-dimensional symplectic class, the beta function
monotonically increases with decreasing . We also provide an argument based
on the spectral flows under twisting boundary conditions, which shows that none
of states of the massless Dirac Hamiltonian can be localized.Comment: 4 pages, 2 figure
Magnetization Plateau of an S=1 Frustrated Spin Ladder
We study the magnetization plateau at 1/4 of the saturation magnetization of
the S=1 antiferromagnetic spin ladder both analytically and numerically, with
the aim of explaining recent experimental results on BIP-TENO by Goto et al. We
propose two mechanisms for the plateau formation and clarify the plateau phase
diagram on the plane of the coupling constants between spins
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