2,089 research outputs found
Many Body Theory for Quartets, Trions, and Pairs in Low Density Multi-Component Fermi-Systems
A selfconsistent many body approach for the description of gases with
quartets, trions, and pairs is presented. Applications to 3D Fermi systems at
low density are discussed
Occupation numbers in Self Consistent RPA
A method is proposed which allows to calculate within the SCRPA theory the
occupation numbers via the single particle Green function. This scheme complies
with the Hugenholtz van Hove theorem. In an application to the Lipkin model it
is found that this prescription gives consistently better results than two
other commonly used approximations: lowest order boson expansion and the number
operator method.Comment: 25 pages, 10 figures, submitted to Nucl. Phys.
The proteasome biogenesis regulator Rpn4 cooperates with the unfolded protein response to promote ER stress resistance
Misfolded proteins in the endoplasmic reticulum (ER) activate the unfolded protein response (U PR), which enhances protein folding to restore homeostasis. Additional pathways respond to ER stress, but how they help counteract protein misfolding is incompletely understood. Here, we develop a titratable system for the induction of ER stress in yeast to enable a genetic screen for factors that augment stress resistance independently of the UPR. We identify the proteasome biogenesis regulator Rpn4 and show that it cooperates with the UPR. Rpn4 abundance increases during ER stress, first by a post-transcriptional, then by a transcriptional mechanism. Induction of RPN4 transcription is triggered by cytosolic mislocalization of secretory proteins, is mediated by multiple signaling pathways and accelerates clearance of misfolded proteins from the cytosol. Thus, Rpn4 and the UPR are complementary elements of a modular cross-compartment response to ER stress
Isospin singlet (pn) pairing and quartetting contribution to the binding energy of nuclei
Isospin singlet (pn) pairing as well as quartetting in nuclei is expected to
arise near the symmetry line . Empirical values can be deduced from the
nuclear binding energies applying special filters. Within the local density
approximation, theoretical estimates for finite nuclei are obtained from
results for the condensation energy of asymmetric nuclear matter. It is shown
that the isospin singlet condensation energy drops down abruptly for |N-Z|~4
for medium nuclei in the region A=40. Furthermore, alpha-like quartetting and
the influence of excitations are discussed.Comment: 19 pages, 19 figures, submitted to PR
Random Phase Approximation and Extensions Applied to a Bosonic Field Theory
An application of a self-consistent version of RPA to quantum field theory
with broken symmetry is presented. Although our approach can be applied to any
bosonic field theory, we specifically study the theory in 1+1
dimensions. We show that standard RPA approach leads to an instability which
can be removed when going to a superior version,i.e. the renormalized RPA. We
present a method based on the so-called charging formula of the many electron
problem to calculate the correlation energy and the RPA effective potential.Comment: 30 pages, LaTeX file, 10 figures included, final version accepted in
EPJ
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
Deuteron formation in nuclear matter
We investigate deuteron formation in nuclear matter at finite temperatures
within a systematic quantum statistical approach. We consider formation through
three-body collisions relevant already at rather moderate densities because of
the strong correlations. The three-body in-medium reaction rates driven by the
break-up cross section are calculated using exact three-body equations
(Alt-Grassberger-Sandhas type) that have been suitably modified to consistently
include the energy shift and the Pauli blocking. Important quantities are the
lifetime of deuteron fluctuations and the chemical relaxation time. We find
that the respective times differ substantially while using in-medium or
isolated cross sections. We expect implications for the description of heavy
ion collisions in particular for the formation of light charged particles at
low to intermediate energies.Comment: 19 pages, 5 figure
Medium polarization in asymmetric nuclear matter
The influence of the core polarization on the effective nuclear interaction
of asymmetric nuclear matter is calculated in the framework of the induced
interaction theory. The strong isospin dependence of the density and spin
density fluctuations is studied along with the interplay between the neutron
and proton core polarizations. Moving from symmetric nuclear matter to pure
neutron matter the crossover of the induced interaction from attractive to
repulsive in the spin singlet state is determined as a function of the isospin
imbalance.The density range in which it occurs is also determined. For the spin
triplet state the induced interaction turns out to be always repulsive. The
implications of the results for the neutron star superfluid phases are shortly
discussed.Comment: 6 pages, 4 figure
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