2,305 research outputs found
Chaoticity and Dissipation of Nuclear Collective Motion in a Classical Model
We analyze the behavior of a gas of classical particles moving in a
two-dimensional "nuclear" billiard whose multipole-deformed walls undergo
periodic shape oscillations. We demonstrate that a single particle Hamiltonian
containing coupling terms between the particles' motion and the collective
coordinate induces a chaotic dynamics for any multipolarity, independently on
the geometry of the billiard. The absence of coupling terms allows us to
recover qualitatively the "wall formula" predictions. We also discuss the
dissipative behavior of the wall motion and its relation with the
order-to-chaos transition in the dynamics of the microscopic degrees of
freedom.Comment: LateX, 11 pages, 7 figures available on request, to appear in the
Proceedings of XXXIV Winter Meeting on Nuclear Physics, Bormio 22-27 January,
199
Pairing correlations of cold fermionic gases at overflow from a narrow to a wide harmonic trap
Within the context of Hartree-Fock-Bogoliubov theory, we study the behavior
of superfluid Fermi systems when they pass from a small to a large container.
Such systems can be now realized thanks to recent progress in experimental
techniques. It will allow to better understand pairing properties at overflow
and in general in rapidly varying external potentials
Energy-level quantization in YBa2Cu3O7-x phase-slip nanowires
Significant progress has been made in the development of superconducting
quantum circuits, however new quantum devices that have longer decoherence
times at higher temperatures are urgently required for quantum technologies.
Superconducting nanowires with quantum phase slips are promising candidates for
use in novel devices that operate on quantum principles. Here, we demonstrate
ultra-thin YBa2Cu3O7-x nanowires with phase-slip dynamics and study their
switching-current statistics at temperatures below 20 K. We apply theoretical
models that were developed for Josephson junctions and show that our results
provide strong evidence for energy-level quantization in the nanowires. The
crossover temperature to the quantum regime is 12-13 K, while the lifetime in
the excited state exceeds 20 ms at 5.4 K. Both values are at least one order of
magnitude higher than those in conventional Josephson junctions based on
low-temperature superconductors. We also show how the absorption of a single
photon changes the phase-slip and quantum state of a nanowire, which is
important for the development of single-photon detectors with high operating
temperature and superior temporal resolution. Our findings pave the way for a
new class of superconducting nanowire devices for quantum sensing and
computing
Bose-Fermi Pair Correlations in Attractively Interacting Bose-Fermi Atomic Mixtures
We study static properties of attractively interacting Bose-Fermi mixtures of
uniform atomic gases at zero temperature. Using Green's function formalism we
calculate boson-fermion scattering amplitude and fermion self-energy in the
medium to lowest order of the hole line expansion. We study ground state energy
and pressure as functions of the scattering length for a few values of the
boson-fermion mass ratio and the number ratio . We find that
the attractive contribution to energy is greatly enhanced for small values of
the mass ratio. We study the role of the Bose-Fermi pair correlations in the
mixture by calculating the pole of the boson-fermion scattering amplitude in
the medium. The pole shows a standard quasiparticle dispersion for a Bose-Fermi
pair, for . For small values of the mass ratio, on the other
hand, a Bose-Fermi pair with a finite center-of-mass momentum experiences a
strong attraction, implying large medium effects. In addition, we also study
the fermion dispersion relation. We find two dispersion branches with the
possibility of the avoided crossings. This strongly depends on the number rario
.Comment: 14 pages, 27 figure
Dynamics of few-body states in a medium
Strongly interacting matter such as nuclear or quark matter leads to few-body
bound states and correlations of the constituents. As a consequence quantum
chromodynamics has a rich phase structure with spontaneous symmetry breaking,
superconductivity, condensates of different kinds. All this appears in many
astrophysical scenarios. Among them is the formation of hadrns during the early
stage of the Universe, the structure of a neutron star, the formation of nuclei
during a supernova explosion. Some of these extreme conditions can be simulated
in heavy ion colliders. To treat such a hot and dense system we use the Green
function formalism of many-body theory. It turns out that a systematic Dyson
expansion of the Green functions leads to modified few-body equations that are
capable to describe phase transitions, condensates, cluster formation and more.
These equations include self energy corrections and Pauli blocking. We apply
this method to nonrelativistic and relativistic matter. The latter one is
treated on the light front. Because of the medium and the inevitable truncation
of space, the few-body dynamics and states depend on the thermodynamic
parameters of the medium.Comment: 3 pages, 2 figures, talk presented at the 19th European Conference on
Few-Body System
Continued fraction approximation for the nuclear matter response function
We use a continued fraction approximation to calculate the RPA response
function of nuclear matter. The convergence of the approximation is assessed by
comparing with the numerically exact response function obtained with a typical
effective finite-range interaction used in nuclear physics. It is shown that
just the first order term of the expansion can give reliable results at
densities up to the saturation density value
Screening Effects in Superfluid Nuclear and Neutron Matter within Brueckner Theory
Effects of medium polarization are studied for pairing in neutron and
nuclear matter. The screening potential is calculated in the RPA limit,
suitably renormalized to cure the low density mechanical instability of nuclear
matter. The selfenergy corrections are consistently included resulting in a
strong depletion of the Fermi surface. All medium effects are calculated based
on the Brueckner theory. The gap is determined from the generalized gap
equation. The selfenergy corrections always lead to a quenching of the gap,
which is enhanced by the screening effect of the pairing potential in neutron
matter, whereas it is almost completely compensated by the antiscreening effect
in nuclear matter.Comment: 8 pages, 6 Postscript figure
Cooper pair sizes in 11Li and in superfluid nuclei: a puzzle?
We point out a strong influence of the pairing force on the size of the two
neutron Cooper pair in Li, and to a lesser extent also in He. It
seems that these are quite unique situations, since Cooper pair sizes of stable
superfluid nuclei are very little influenced by the intensity of pairing, as
recently reported. We explore the difference between Li and heavier
superfulid nuclei, and discuss reasons for the exceptional situation in
Li.Comment: 9 pages. To be published in J. of Phys. G special issue on Open
Problems in Nuclear Structure (OPeNST
Light clusters in nuclear matter of finite temperature
We investigate properties and the distribution of light nuclei (A<4) in
symmetric nuclear matter of finite temperature within a microscopic framework.
For this purpose we have solved few-body Alt-Grassberger-Sandhas type equations
for quasi-nucleons that include self-energy corrections and Pauli blocking in a
systematic way. In a statistical model we find a significant influence in the
composition of nuclear matter if medium effects are included in the microscopic
calculation of nuclei. If multiplicities are frozen out at a certain time (or
volume), we expect significant consequences for the formation of light
fragments in a heavy ion collision. As a consequence of the systematic
inclusion of medium effects the ordering of multiplicities becomes opposite to
the law of mass action of ideal components. This is necessary to explain the
large abundance of -particles in a heavy ion collision that are
otherwise largely suppressed in an ideal equilibrium scenario.Comment: 9 pages, 9 figures, epja-style file
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