2,529 research outputs found
Quasiparticle light elements and quantum condensates in nuclear matter
Nuclei in dense matter are influenced by the medium. In the cluster mean
field approximation, an effective Schr\"odinger equation for the -particle
cluster is obtained accounting for the effects of the surrounding medium, such
as self-energy and Pauli blocking. Similar to the single-baryon states (free
neutrons and protons), the light elements (, internal quantum
state ) are treated as quasiparticles with energies that depend on the center of mass momentum , the temperature
, and the total densities of neutrons and protons, respectively.
We consider the composition and thermodynamic properties of nuclear matter at
low densities. At low temperatures, quartetting is expected to occur.
Consequences for different physical properties of nuclear matter and finite
nuclei are discussed.Comment: 5 pages, 1 figure, 2 table
The Nucleon Spectral Function at Finite Temperature and the Onset of Superfluidity in Nuclear Matter
Nucleon selfenergies and spectral functions are calculated at the saturation
density of symmetric nuclear matter at finite temperatures. In particular, the
behaviour of these quantities at temperatures above and close to the critical
temperature for the superfluid phase transition in nuclear matter is discussed.
It is shown how the singularity in the thermodynamic T-matrix at the critical
temperature for superfluidity (Thouless criterion) reflects in the selfenergy
and correspondingly in the spectral function. The real part of the on-shell
selfenergy (optical potential) shows an anomalous behaviour for momenta near
the Fermi momentum and temperatures close to the critical temperature related
to the pairing singularity in the imaginary part. For comparison the selfenergy
derived from the K-matrix of Brueckner theory is also calculated. It is found,
that there is no pairing singularity in the imaginary part of the selfenergy in
this case, which is due to the neglect of hole-hole scattering in the K-matrix.
From the selfenergy the spectral function and the occupation numbers for finite
temperatures are calculated.Comment: LaTex, 23 pages, 21 PostScript figures included (uuencoded), uses
prc.sty, aps.sty, revtex.sty, psfig.sty (last included
Critical Enhancement of the In-medium Nucleon-Nucleon Cross Section at low Temperatures
The in-medium nucleon-nucleon cross section is calculated starting from the
thermodynamic T-matrix at finite temperatures. The corresponding
Bethe-Salpeter-equation is solved using a separable representation of the Paris
nucleon-nucleon-potential. The energy-dependent in-medium N-N cross section at
a given density shows a strong temperature dependence. Especially at low
temperatures and low total momenta, the in-medium cross section is strongly
modified by in-medium effects. In particular, with decreasing temperature an
enhancement near the Fermi energy is observed. This enhancement can be
discussed as a precursor of the superfluid phase transition in nuclear matter.Comment: 10 pages with 4 figures (available on request from the authors),
MPG-VT-UR 34/94 accepted for publication in Phys. Rev.
Spontaneous breaking of rotational symmetry in superconductors
We show that homogeneous superconductors with broken spin/isospin symmetry
lower their energy via a transition to a novel superconducting state where the
Fermi-surfaces are deformed to a quasi-ellipsoidal form at zero total momentum
of Cooper pairs. In this state, the gain in the condensation energy of the
pairs dominates over the loss in the kinetic energy caused by the lowest order
(quadrupole) deformation of Fermi-surfaces from the spherically symmetric form.
There are two energy minima in general, corresponding to the deformations of
the Fermi-spheres into either prolate or oblate forms. The phase transition
from spherically symmetric state to the superconducting state with broken
rotational symmetry is of the first order.Comment: 5 pages, including 3 figures, published versio
Pairing properties of nucleonic matter employing dressed nucleons
A survey of pairing properties of nucleonic matter is presented that includes
the off-shell propagation associated with short-range and tensor correlations.
For this purpose, the gap equation has been solved in its most general form
employing the complete energy and momentum dependence of the normal self-energy
contributions. The latter correlations include the self-consistent calculation
of the nucleon self-energy that is generated by the summation of ladder
diagrams. This treatment preserves the conservation of particle number unlike
approaches in which the self-energy is based on the Brueckner-Hartree-Fock
approximation. A huge reduction in the strength as well as temperature and
density range of - pairing is obtained for nuclear matter as
compared to the standard BCS treatment. Similar dramatic results pertain to
pairing of neutrons in neutron matter.Comment: 15 pages, 10 figure
Spatially inhomogeneous condensate in asymmetric nuclear matter
We study the isospin singlet pairing in asymmetric nuclear matter with
nonzero total momentum of the condensate Cooper pairs. The quasiparticle
excitation spectrum is fourfold split compared to the usual BCS spectrum of the
symmetric, homogeneous matter. A twofold splitting of the spectrum into
separate branches is due to the finite momentum of the condensate, the isospin
asymmetry, or the finite quasiparticle lifetime. The coupling of the isospin
singlet and triplet paired states leads to further twofold splitting of each of
these branches. We solve the gap equation numerically in the isospin singlet
channel in the case where the pairing in the isospin triplet channel is
neglected and find nontrivial solutions with finite total momentum of the
pairs. The corresponding phase assumes a periodic spatial structure which
carries a isospin density wave at constant total number of particles. The phase
transition from the BCS to the inhomogeneous superconducting phase is found to
be first order and occurs when the density asymmetry is increased above 0.25.
The transition from the inhomogeneous superconducting to the unpaired normal
state is second order. The maximal values of the critical total momentum (in
units of the Fermi momentum) and the critical density asymmetry at which
condensate disappears are and . The possible
spatial forms of the ground state of the inhomogeneous superconducting phase
are briefly discussed.Comment: 13 pages, including 3 figues, uses RevTeX; minor corrections, PRC in
pres
A Self-Consistent Solution to the Nuclear Many-Body Problem at Finite Temperature
The properties of symmetric nuclear matter are investigated within the
Green's functions approach. We have implemented an iterative procedure allowing
for a self-consistent evaluation of the single-particle and two-particle
propagators. The in-medium scattering equation is solved for a realistic
(non-separable) nucleon-nucleon interaction including both particle-particle
and hole-hole propagation. The corresponding two-particle propagator is
constructed explicitely from the single-particle spectral functions. Results
are obtained for finite temperatures and an extrapolation to T=0 is presented.Comment: 11 pages 5 figure
Corrections to Tribimaximal Mixing from Nondegenerate Phases
We propose a seesaw scenario that possible corrections to the tribimaximal
pattern of lepton mixing are due to the small phase splitting of the
right-handed neutrino mass matrix. we show that the small deviations can be
expressed analytically in terms of two splitting parameters( and
) in the leading order. The solar mixing angle favors a
relatively smaller value compared to zero order value (), and the
Dirac type CP phase chooses a nearly maximal one. The two Majorana
type CP phases and turn out to be a nearly linear dependence.
Also a normal hierarchy neutrino mass spectrum is favored due to the stability
of perturbation calculations.Comment: 19 pages 6 figures, Accepted by Mod. Phy. Lett.
Des critères de dimensionnement des ouvrages de gestion des eaux pluviales à la source pour répondre aux exigences en termes de pollution et de débit
Colloque avec actes et comité de lecture. Internationale.International audienc
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