1,543 research outputs found
Neutral weak currents in nucleon superfluid Fermi liquids: Larkin-Migdal and Leggett approaches
Neutrino emission in processes of breaking and formation of nucleon Cooper
pairs is calculated in the framework of the Larkin-Migdal and the Leggett
approaches to the description of superfluid Fermi liquids at finite
temperatures. We explain peculiarities of both approaches and explicitly
demonstrate that they lead to the same expression for the emissivity in pair
breaking and formation processes.Comment: 24 pages, 3 figure
A description of the f2(1270), rho3(1690), f4(2050), rho5(2350) and f6(2510) resonances as multi-rho(770) states
In a previous work regarding the interaction of two resonances,
the () resonance was obtained dynamically as a
two- molecule with a very strong binding energy, 135~MeV per
particle. In the present work we use the interaction in spin 2 and
isospin 0 channel to show that the resonances (),
(), () and ()
are basically molecules of increasing number of particles. We use
the fixed center approximation of the Faddeev equations to write the multi-body
interaction in terms of the two-body scattering amplitudes. We find the masses
of the states very close to the experimental values and we get an increasing
value of the binding energy per as the number of mesons is
increased.Comment: 17 pages, 6 figure
Solutions of the dispersion equation in the region of overlapping of zero-sound and particle-hole modes
In this paper the solutions of the zero-sound dispersion equation in the
random phase approximation (RPA) are considered. The calculation of the damped
zero-sound modes \omega_s(k) (complex frequency of excitation) in the nuclear
matter is presented. The method is based on the analytical structure of the
polarization operators \Pi(\omega,k). The solutions of two dispersion equations
with \Pi(\omega,k) and with Re(\Pi(\omega,k)) are compared. It is shown that in
the first case we obtain one-valued smooth solutions without "thumb-like"
forms. Considering the giant resonances in the nuclei as zero-sound excitations
we compare the experimental energy and escape width of the giant dipole
resonance (GDR) in the nucleus A with \omega_s(k) taken at a definite wave
vector k=k_A.Comment: 14 pages, 5 figures; revised versio
VTOL in ground effect flows for closely spaced jets
Results of a series of in ground effect twin jet tests are presented along with flow models for closely spaced jets to help predict pressure and upwash forces on simulated aircraft surfaces. The isolated twin jet tests revealed unstable fountains over a range of spacings and jet heights, regions of below ambient pressure on the ground, and negative pressure differential in the upwash flow field. A separate computer code was developed for vertically oriented, incompressible jets. This model more accurately reflects fountain behavior without fully formed wall jets, and adequately predicts ground isobars, upwash dynamic pressure decay, and fountain lift force variation with height above ground
Possibility of s-wave pion condensates in neutron stars revisited
We examine possibilities of pion condensation with zero momentum (s-wave
condensation) in neutron stars by using the pion-nucleus optical potential U
and the relativistic mean field (RMF) models. We use low-density
phenomenological optical potentials parameterized to fit deeply bound pionic
atoms or pion-nucleus elastic scatterings. Proton fraction (Y_p) and electron
chemical potential (mu_e) in neutron star matter are evaluated in RMF models.
We find that the s-wave pion condensation hardly takes place in neutron stars
and especially has no chance if hyperons appear in neutron star matter and/or
b_1 parameter in U has density dependence.Comment: 4 pages, 3 figures, REVTe
Difficulties in Inducing a Gauge Theory at Large N
It is argued that the recently proposed Kazakov-Migdal model of induced gauge
theory, at large , involves only the zero area Wilson loops that are
effectively trees in the gauge action induced by the scalars. This retains only
a constant part of the gauge action excluding plaquettes or anything like them
and the gauge variables drop out.Comment: 6 pages, Latex, AZPH-TH/93-01, COLO-HEP/30
Diquark and Pion Condensation in Random Matrix Models for two-color QCD
We introduce a random matrix model with the symmetries of QCD with two colors
at nonzero isospin and baryon chemical potentials and temperature. We analyze
its phase diagram and find phases with condensation of pion and diquark states
in addition to the phases with spontaneously broken chiral symmetries. In the
limit of small chemical potentials and quark masses, we reproduce the mean
field results obtained from chiral Lagrangians. As in the case of QCD with
three colors, the presence of two chemical potentials breaks the flavor
symmetry and leads to phases that are characterized by different behaviors of
the chiral condensates for each flavor. In particular, the phase diagram we
obtain is similar to QCD with three colors and three flavors of quarks of equal
masses at zero baryon chemical potential and nonzero isospin and strange
chemical potentials. A tricritical point of the superfluid transitions found in
lattice calculations and from an analysis in terms of chiral Lagrangians does
not appear in the random matrix model. Remarkably, at fixed isospin chemical
potential, for the regions outside of the superfluid phases, the phase diagram
in the temperature - baryon chemical potential plane for two colors and three
colors are qualitatively the same.Comment: 19 pages, 7 figures, RevTeX
Renormalization Group Approach to Strong-Coupled Superconductors
We develop an asymptotically exact renormalization group (RG) approach that
treats electron-electron and electron-phonon interactions on equal footing. The
approach allows an unbiased study of the instabilities of Fermi liquids without
the assumption of a broken symmetry. We apply our method to the problem of
strongly coupled superconductors and find the temperature T* below which the
high-temperature Fermi liquid state becomes unstable towards Cooper pairing. We
show that T* is the same as the critical temperature Tc obtained in
Eliashberg's strong coupling theory starting from the low-temperature
superconducting phase. We also show that Migdal's theorem is implicit in our
approach. Finally, our results lead to a novel way to calculate numerically,
from microscopic parameters, the transition temperature of superconductors.Comment: 6 pages, 3 figures, expanded presentation, final versio
Zero sound in triplet-correlated superfluid neutron matter
The linear response of a superfluid neutron liquid onto external vector field
is studied for the case of ^{3}P_{2}-\,^{3}F_{2} pairing. The consideration
is limited to the case when the wave-length of the perturbation is large as
compared to the coherence length in the superfluid matter and the transferred
energy is small in comparison with the gap amplitude. The obtained results are
used to analyse the collisionless phonon-like excitations of the condensate of
superfluid neutrons. In particular, we analyze the case of neutron condensation
into the state with which is conventionally considered as the
preferable one in the bulk matter of neutron stars. Zero sound (if it exists)
is found to be anisotropic and undergoes strong decrement below some
temperature threshold depending substantially on the intensity of Fermi-liquid
interactions.Comment: 16 pages, 2 figure
Renormalization-Group Approach to Spin-Wave Theory of Quantum Heisenberg Ferromagnet
The renormalization-group method is used to analyze the low-temperature
behaviour of a two-dimentional, spin- quantum Heisenberg ferromagnet. A set
of recursion equations is derived in an one-loop approximation. The
low-temperature asymptotics of the correlation length and the uniform
susceptibility are obtained. For small spins () the results are
essentially different from those in the spin-wave theory.Comment: 9 pages, RevTex 3.0 fil
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