1,543 research outputs found

    Neutral weak currents in nucleon superfluid Fermi liquids: Larkin-Migdal and Leggett approaches

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    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

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    In a previous work regarding the interaction of two ρ(770)\rho(770) resonances, the f2(1270)f_2(1270) (JPC=2++J^{PC}=2^{++}) resonance was obtained dynamically as a two-ρ\rho molecule with a very strong binding energy, 135~MeV per ρ\rho particle. In the present work we use the ρρ\rho\rho interaction in spin 2 and isospin 0 channel to show that the resonances ρ3(1690)\rho_3(1690) (33^{--}), f4(2050)f_4(2050) (4++4^{++}), ρ5(2350)\rho_5(2350) (55^{--}) and f6(2510)f_6(2510) (6++6^{++}) are basically molecules of increasing number of ρ(770)\rho(770) 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 ρ\rho as the number of ρ\rho 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

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    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

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    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

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    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

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    It is argued that the recently proposed Kazakov-Migdal model of induced gauge theory, at large NN, 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

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    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

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    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

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    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 mj=0m_{j}=0 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

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    The renormalization-group method is used to analyze the low-temperature behaviour of a two-dimentional, spin-ss 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 (s=1/2,1s= 1/2,1) the results are essentially different from those in the spin-wave theory.Comment: 9 pages, RevTex 3.0 fil
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