769 research outputs found
Functional Integral in terms of the Field Strength: An Approach to Chiral Symmetry Breaking
The chiral symmetry breaking in the 4-dimensional QED with the chirally
invariant four-fermion interaction is discussed by using a novel path integral
expression in terms of the field-strength tensor. In the local potential
approximation, we find that the chiral symmetry is spontaneously broken for any
nonzero gauge and four-fermion couplings on the tree level of an auxiliary
field . The present approach allows us to easily include higher orders
of the gauge coupling so that the effective potential up to the sixth order is
obtained.Comment: 18 pages, 2 figure
Nambu-Jona-Lasinio Model Coupled to Constant Electromagnetic Fields in D-Dimension
Critical dynamics of the Nambu-Jona-Lasinio model, coupled to a constant
electromagnetic field in D=2, 3, and 4, is reconsidered from a viewpoint of
infrared behavior and vacuum instability. The latter is associated with
constant electric fields and cannot be avoidable in the nonperturbative
framework obtained through the proper time method. As for magnetic fields, an
infrared cut-off is essential to investigate the critical phenomena. The result
reconfirms the fact that the critical coupling in D=3 and 4 goes to zero even
under an infinitesimal magnetic field. There also shows that a non-vanishing
causes instability. A perturbation with
respect to external fields is adopted to investigate critical quantities, but
the resultant asymptotic expansion excellently matches with the exact value.Comment: 27 pages, 17 figure files, LaTe
Large-angle scattering and quasi-elastic barrier distributions
We study in detail the barrier distributions extracted from large-angle
quasi-elastic scattering of heavy ions at energies near the Coulomb barrier.
Using a closed-form expression for scattering from a single barrier, we compare
the quasi-elastic barrier distribution with the corresponding test function for
fusion. We examine the isocentrifugal approximation in coupled-channels
calculations of quasi-elastic scattering and find that for backward angles, it
works well, justifying the concept of a barrier distribution for scattering
processes. This method offers an interesting tool for investigating unstable
nuclei. We illustrate this for the Mg + Pb reaction, where the
quadrupole collectivity of the neutron-rich Mg remains to be clarified
experimentally.Comment: 26 pages, 10 eps figure
Role of non-collective excitations in heavy-ion fusion reactions and quasi-elastic scattering around the Coulomb barrier
Despite the supposed simplicity of double-closed shell nuclei, conventional
coupled-channels calculations, that include all of the known collective states
of the target and projectile, give a poor fit to the fusion cross section for
the O + Pb system. The discrepancies are highlighted through the
experimental barrier distribution and logarithmic derivative, that are both
well defined by the precise experimental fusion data available. In order to
broaden our search for possible causes for this anomaly, we revisit this system
and include in our calculations a large number of non-collective states of the
target, whose spin, parity, excitation energy and deformation paramter are
known from high-precision proton inelastic-scattering measurements. Although
the new coupled-channels calculations modify the barrier distribution, the
disagreemnt with experiment remains both for fusion and for quasi-elastic (QE)
scattering. We find that the Q-value distributions for large-angle QE
scattering become rapidly more important as the incident energy increases,
reflecting the trend of the experimental data. The mass-number dependence of
the non-collective excitations is discussed.Comment: 8 pages, 7 figure
Time-Dependent Generator Coordinate Method for Many-Particle Tunneling
It has been known that the time-dependent Hartree-Fock (TDHF) method, or the
time-dependent density functional theory (TDDFT), fails to describe many-body
quantum tunneling. We overcome this problem by superposing a few time-dependent
Slater determinants with the time-dependent generator coordinate method
(TDGCM). We apply this method to scattering of two particles in one
dimension, and demonstrate that the TDGCM method yields a finite tunneling
probability even at energies below the Coulomb barrier, at which the tunneling
probability is exactly zero in the TDHF. This is the first case in which a
many-particle tunneling is simulated with a microscopic real-time approach.Comment: 9 pages, 4 figure
Time-dependent generator coordinate method for many-particle tunneling
It has been known that the time-dependent Hartree-Fock (TDHF) method, or the time-dependent density functional theory (TDDFT), fails to describe many-body quantum tunneling. We overcome this problem by superposing a few time-dependent Slater determinants with the time-dependent generator coordinate method (TDGCM). We apply this method to scattering of two α particles in one dimension, and demonstrate that the TDGCM method yields a finite tunneling probability even at energies below the Coulomb barrier, at which the tunneling probability is exactly zero in the TDHF. This is the first case in which a many-particle tunneling is simulated with a microscopic real-time approach
Direct observation of the proliferation of ferroelectric loop domains and vortex-antivortex pairs
We discovered "stripe" patterns of trimerization-ferroelectric domains in
hexagonal REMnO3 (RE=Ho, ---, Lu) crystals (grown below ferroelectric
transition temperatures (Tc), reaching up to 1435 oC), in contrast with the
vortex patterns in YMnO3. These stripe patterns roughen with the appearance of
numerous loop domains through thermal annealing just below Tc, but the stripe
domain patterns turn to vortex-antivortex domain patterns through a freezing
process when crystals cross Tc even though the phase transition appears not to
be Kosterlitz-Thouless-type. The experimental systematics are compared with the
results of our six-state clock model simulation and also the Kibble-Zurek
Mechanism for trapped topological defects
Can apparent superluminal neutrino speeds be explained as a quantum weak measurement?
Probably not.Comment: 10 pages, 1 figur
- …