264 research outputs found
Effective potential for composite operators and for an auxiliary scalar field in a Nambu-Jona-Lasinio model
We derive the effective potentials for composite operators in a
Nambu-Jona-Lasinio (NJL) model at zero and finite temperature and show that in
each case they are equivalent to the corresponding effective potentials based
on an auxiliary scalar field. The both effective potentials could lead to the
same possible spontaneous breaking and restoration of symmetries including
chiral symmetry if the momentum cutoff in the loop integrals is large enough,
and can be transformed to each other when the Schwinger-Dyson (SD) equation of
the dynamical fermion mass from the fermion-antifermion vacuum (or thermal)
condensates is used. The results also generally indicate that two effective
potentials with the same single order parameter but rather different
mathematical expressions can still be considered physically equivalent if the
SD equation corresponding to the extreme value conditions of the two potentials
have the same form.Comment: 7 pages, no figur
P-matrix and J-matrix approaches. Coulomb asymptotics in the harmonic oscillator representation of scattering theory
The relation between the R- and P-matrix approaches and the harmonic
oscillator representation of the quantum scattering theory (J-matrix method) is
discussed. We construct a discrete analogue of the P-matrix that is shown to be
equivalent to the usual P-matrix in the quasiclassical limit. A definition of
the natural channel radius is introduced. As a result, it is shown to be
possible to use well-developed technique of R- and P-matrix theory for
calculation of resonant states characteristics, scattering phase shifts, etc.,
in the approaches based on harmonic oscillator expansions, e.g., in nuclear
shell-model calculations. P-matrix is used also for formulation of the method
of treating Coulomb asymptotics in the scattering theory in oscillator
representation.Comment: Revtex, 57 pages including 15 figures; to be published in Annals of
Physic
Anomalous specific heat jump in the heavy fermion superconductor CeCoIn
We study the anomalously large specific heat jump and its systematic change
with pressure in CeCoIn superconductor. Starting with the general free
energy functional of the superconductor for a coupled electron boson system, we
derived the analytic result of the specific heat jump of the strong coupling
superconductivity occurring in the coupled electron boson system. Then using
the two component spin-fermion model we calculate the specific heat coefficient
both for the normal and superconducting states and show a good
agreement with the experiment of CeCoIn. Our result also clearly
demonstrated that the specific heat coefficient of a coupled electron
boson system can be freely interpreted as a renormalization either of the
electronic or of the bosonic degrees of freedom.Comment: 5 pages, 2 figure
Mechanical Properties of Dissimilar A356/SAPH440 Lap Joints by the Friction Stir Spot Welding and Self-Piercing Riveting
Aluminum alloy A356-T6 and automotive steel sheet SAPH440 were joined using friction stir spot welding and self-piercing riveting. The maximum tensile shear strength values in weld joints were approximately 3.5 kN at a rotation speed of 500 rpm and plunge depth of 1.0 mm. It was confirmed that the intermetallic compound layer of weld joints below 9.23 m did not exceed the permissible thickness 10 m of Al–Fe joints. The self-piercing riveting joints exhibited maximum tensile- shear strength of 7.9 kN, which was higher than that of the weld joints. However, during the riveting process, cracking appeared in the joint on the aluminum side, which was caused by lack of ductility of cast aluminum. In addition, it was observed that the cracks on the aluminum side were getting larger, as the radius of the lower mold increased.Алюминиевый сплав А356-Т6 и автомобильную листовую сталь SAPH440 соединяли с помощью точечной ротационной сварки трением и самопробивной клепки. Максимальный предел прочности на сдвиг при растяжении для сварных соединений составлял примерно 3,5 кН при скорости вращения 500 об/мин и глубине проникновения 1,0 мм. Доказано, что слой интерметаллидов сварных соединений толщиной менее 9,23 мкм не превышал допустимый уровень в 10 мкм для соединений Al–Fe. Клепаные соединения имели предел прочности 7,9 кН в отличие от сварных соединений. Однако при клепке на алюминии появлялись трещины ввиду низкой пластичности литого материала, при этом трещины подрастали по мере увеличения радиуса нижней формы
Three-Body Halos. II. from Two- to Three-Body Asymptotics
The large distance behavior of weakly bound three-body systems is
investigated. The Schr\"{o}dinger equation and the Faddeev equations are
reformulated by an expansion in eigenfunctions of the angular part of a
corresponding operator. The resulting coupled set of effective radial equations
are then derived. Both two- and three-body asymptotic behavior are possible and
their relative importance is studied for systems where subsystems may be bound.
The system of two nucleons outside a core is studied numerically in detail and
the character of possible halo structure is pointed out and investigated.Comment: 16 pages, compressed and uuencoded PosrScript file, IFA-94/3
Coboson formalism for Cooper pairs used to derive Richardson's equations
We propose a many-body formalism for Cooper pairs which has similarities to
the one we recently developed for composite boson excitons (coboson in short).
Its Shiva diagram representation evidences that Cooper pairs differ from
single pairs through electron exchange only: no direct coupling exists due
to the very peculiar form of the BCS potential. As a first application, we here
use this formalism to derive Richardson's equations for the exact eigenstates
of Cooper pairs. This gives hints on why the dependence of the
-pair ground state energy we recently obtained by solving Richardson's
equations analytically in the low density limit, stays valid up to the dense
regime, no higher order dependence exists even under large overlap, a
surprising result hard to accept at first. We also briefly question the BCS
wave function ansatz compared to Richardson's exact form, in the light of our
understanding of coboson many-body effects
Spin-dependent effective interactions for halo nuclei
We discuss the spin-dependence of the effective two-body interactions
appropriate for three-body computations. The only reasonable choice seems to be
the fine and hyperfine interactions known for atomic electrons interacting with
the nucleus. One exception is the nucleon-nucleon interaction imposing a
different type of symmetry. We use the two-neutron halo nucleus 11Li as
illustration. We demonstrate that models with the wrong spin-dependence are
basically without predictive power. The Pauli forbidden core and valence states
must be consistently treated.Comment: TeX file, 6 pages, 3 postscript figure
Sufficient Covariate, Propensity Variable and Doubly Robust Estimation
Statistical causal inference from observational studies often requires
adjustment for a possibly multi-dimensional variable, where dimension reduction
is crucial. The propensity score, first introduced by Rosenbaum and Rubin, is a
popular approach to such reduction. We address causal inference within Dawid's
decision-theoretic framework, where it is essential to pay attention to
sufficient covariates and their properties. We examine the role of a propensity
variable in a normal linear model. We investigate both population-based and
sample-based linear regressions, with adjustments for a multivariate covariate
and for a propensity variable. In addition, we study the augmented inverse
probability weighted estimator, involving a combination of a response model and
a propensity model. In a linear regression with homoscedasticity, a propensity
variable is proved to provide the same estimated causal effect as multivariate
adjustment. An estimated propensity variable may, but need not, yield better
precision than the true propensity variable. The augmented inverse probability
weighted estimator is doubly robust and can improve precision if the propensity
model is correctly specified
Two-proton overlap functions in the Jastrow correlation method and cross section of the OC reaction
Using the relationship between the two-particle overlap functions (TOF's) and
the two-body density matrix (TDM), the TOF's for the
OC reaction are calculated on the
basis of a TDM obtained within the Jastrow correlation method. The main
contributions of the removal of and pairs from O
are considered in the calculation of the cross section of the
OC reaction using the Jastrow TOF's
which include short-range correlations (SRC). The results are compared with the
cross sections calculated with different theoretical treatments of the TOF's.Comment: 10 pages, 8 figures, ReVTeX
Pseudogap formation of four-layer BaRuO and its electrodynamic response changes
We investiaged the optical properties of four-layer BaRuO, which shows
a fermi-liquid-like behavior at low temperature. Its optical conductivity
spectra clearly displayed the formation of a pseudogap and the development of a
coherent peak with decreasing temperature. Temperature-dependences of the
density and the scattering rate of the coherent component were
also derived. As the temperature decreases, both and decrease for
four-layer BaRuO. These electrodynamic responses were compared with those
of nine-layer BaRuO, which also shows a pseudogap formation but has an
insulator-like state at low temperature. It was found that the relative rates
of change of both and determine either metallic or insulator-like
responses in the ruthenates. The optical properties of the four-layer ruthenate
were also compared with those of other pseudogap systems, such as high
cuprates and heavy electron systems.Comment: 7 figures. submitted to Phys. Rev.
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