156 research outputs found
Approximate particle number projection for finite range density dependent forces
The Lipkin-Nogami method is generalized to deal with finite range density
dependent forces. New expressions are derived and realistic calculations with
the Gogny force are performed for the nuclei Er and Er. The
sharp phase transition predicted by the mean field approximation is washed out
by the Lipkin-Nogami approach; a much better agreement with the experimental
data is reached with the new approach than with the Hartree-Fock_Bogoliubov
one, specially at high spins.Comment: 5 pages, RevTeX 3.0, 3 postscript figures included using uufiles.
Submitted to Phys. Rev. Let
Pulse length and amplitude dependent resistive switching mechanisms in Pt-Pr₀̣₆₇Ca₀̣₃₃MnO₃-Pt sandwich structures
Superdeformed rotational bands in the Mercury region; A Cranked Skyrme-Hartree-Fock-Bogoliubov study
A study of rotational properties of the ground superdeformed bands in \Hg{0},
\Hg{2}, \Hg{4}, and \Pb{4} is presented. We use the cranked
Hartree-Fock-Bogoliubov method with the {\skm} parametrization of the Skyrme
force in the particle-hole channel and a seniority interaction in the pairing
channel. An approximate particle number projection is performed by means of the
Lipkin-Nogami prescription. We analyze the proton and neutron quasiparticle
routhians in connection with the present information on about thirty presently
observed superdeformed bands in nuclei close neighbours of \Hg{2}.Comment: 26 LaTeX pages, 14 uuencoded postscript figures included, Preprint
IPN-TH 93-6
Cranked Relativistic Hartree-Bogoliubov Theory: Formalism and Application to the Superdeformed Bands in the region
Cranked Relativistic Hartree-Bogoliubov theory without and with approximate
particle number projection by means of the Lipkin-Nogami method is presented in
detail as an extension of Relativistic Mean Field theory with pairing
correlations to the rotating frame. Pairing correlations are taken into account
by a finite range two-body force of Gogny type. The applicability of this
theory to the description of rotating nuclei is studied in detail on the
example of superdeformed bands in even-even nuclei of the mass
region. Different aspects such as the importance of pairing and particle number
projection, the dependence of the results on the parametrization of the RMF
Lagrangian and Gogny force etc. are investigated in detail. It is shown that
without any adjustment of new parameters the best description of experimental
data is obtained by using the well established parameter sets NL1 for the
Lagrangian and D1S for the pairing force. Contrary to previous studies at spin
zero it is found that the increase of the strength of the Gogny force is not
necessary in the framework of Relativistic Hartree-Bogoliubov theory provided
that particle number projection is performed.Comment: 34 pages, 24 figures, 3 tables, uses Revtex and epsf.sty, submitted
to Nuclear Physics
The nuclear energy density functional formalism
The present document focuses on the theoretical foundations of the nuclear
energy density functional (EDF) method. As such, it does not aim at reviewing
the status of the field, at covering all possible ramifications of the approach
or at presenting recent achievements and applications. The objective is to
provide a modern account of the nuclear EDF formalism that is at variance with
traditional presentations that rely, at one point or another, on a {\it
Hamiltonian-based} picture. The latter is not general enough to encompass what
the nuclear EDF method represents as of today. Specifically, the traditional
Hamiltonian-based picture does not allow one to grasp the difficulties
associated with the fact that currently available parametrizations of the
energy kernel at play in the method do not derive from a genuine
Hamilton operator, would the latter be effective. The method is formulated from
the outset through the most general multi-reference, i.e. beyond mean-field,
implementation such that the single-reference, i.e. "mean-field", derives as a
particular case. As such, a key point of the presentation provided here is to
demonstrate that the multi-reference EDF method can indeed be formulated in a
{\it mathematically} meaningful fashion even if does {\it not} derive
from a genuine Hamilton operator. In particular, the restoration of symmetries
can be entirely formulated without making {\it any} reference to a projected
state, i.e. within a genuine EDF framework. However, and as is illustrated in
the present document, a mathematically meaningful formulation does not
guarantee that the formalism is sound from a {\it physical} standpoint. The
price at which the latter can be enforced as well in the future is eventually
alluded to.Comment: 64 pages, 8 figures, submitted to Euroschool Lecture Notes in Physics
Vol.IV, Christoph Scheidenberger and Marek Pfutzner editor
Foundations of self-consistent particle-rotor models and of self-consistent cranking models
The Kerman-Klein formulation of the equations of motion for a nuclear shell
model and its associated variational principle are reviewed briefly. It is then
applied to the derivation of the self-consistent particle-rotor model and of
the self-consistent cranking model, for both axially symmetric and triaxial
nuclei. Two derivations of the particle-rotor model are given. One of these is
of a form that lends itself to an expansion of the result in powers of the
ratio of single-particle angular momentum to collective angular momentum, that
is essentual to reach the cranking limit. The derivation also requires a
distinct, angular-momentum violating, step. The structure of the result implies
the possibility of tilted-axis cranking for the axial case and full
three-dimensional cranking for the triaxial one. The final equations remain
number conserving. In an appendix, the Kerman-Klein method is developed in more
detail, and the outlines of several algorithms for obtaining solutions of the
associated non-linear formalism are suggested.Comment: 29 page
Solution of the Skyrme-Hartree-Fock-Bogolyubov equations in the Cartesian deformed harmonic-oscillator basis. (VI) HFODD (v2.38j): a new version of the program
We describe the new version (v2.38j) of the code HFODD which solves the
nuclear Skyrme-Hartree-Fock or Skyrme-Hartree-Fock-Bogolyubov problem by using
the Cartesian deformed harmonic-oscillator basis. In the new version, we have
implemented: (i) projection on good angular momentum (for the Hartree-Fock
states), (ii) calculation of the GCM kernels, (iii) calculation of matrix
elements of the Yukawa interaction, (iv) the BCS solutions for state-dependent
pairing gaps, (v) the HFB solutions for broken simplex symmetry, (vi)
calculation of Bohr deformation parameters, (vii) constraints on the Schiff
moments and scalar multipole moments, (viii) the D2h transformations and
rotations of wave functions, (ix) quasiparticle blocking for the HFB solutions
in odd and odd-odd nuclei, (x) the Broyden method to accelerate the
convergence, (xi) the Lipkin-Nogami method to treat pairing correlations, (xii)
the exact Coulomb exchange term, (xiii) several utility options, and we have
corrected two insignificant errors.Comment: 45 LaTeX pages, 4 figures, submitted to Computer Physics
Communication
A re-interpretation of the concept of mass and of the relativistic mass-energy relation
For over a century the definitions of mass and derivations of its relation
with energy continue to be elaborated, demonstrating that the concept of mass
is still not satisfactorily understood. The aim of this study is to show that,
starting from the properties of Minkowski spacetime and from the principle of
least action, energy expresses the property of inertia of a body. This implies
that inertial mass can only be the object of a definition - the so called
mass-energy relation - aimed at measuring energy in different units, more
suitable to describe the huge amount of it enclosed in what we call the
"rest-energy" of a body. Likewise, the concept of gravitational mass becomes
unnecessary, being replaceable by energy, thus making the weak equivalence
principle intrinsically verified. In dealing with mass, a new unit of
measurement is foretold for it, which relies on the de Broglie frequency of
atoms, the value of which can today be measured with an accuracy of a few parts
in 10^9
PHANGS-JWST First Results: A combined HST and JWST analysis of the nuclear star cluster in NGC 628
We combine archival HST and new JWST imaging data, covering the ultraviolet
to mid-infrared regime, to morphologically analyze the nuclear star cluster
(NSC) of NGC 628, a grand-design spiral galaxy. The cluster is located in a 200
pc x 400 pc cavity, lacking both dust and gas. We find roughly constant values
for the effective radius (r_eff ~ 5 pc) and ellipticity ({\epsilon} ~ 0.05),
while the S\'ersic index (n) and position angle (PA) drop from n ~ 3 to ~ 2 and
PA ~ 130{\deg} to 90{\deg}, respectively. In the mid-infrared, r_eff ~ 12pc,
{\epsilon} ~ 0.4, and n ~ 1-1.5, with the same PA ~ 90{\deg}. The NSC has a
stellar mass of log10 (M_nsc / M_Sun) = 7.06 +- 0.31, as derived through B-V,
confirmed when using multi-wavelength data, and in agreement with the
literature value. Fitting the spectral energy distribution, excluding the
mid-infrared data, yields a main stellar population's age of (8 +- 3) Gyr with
a metallicity of Z = 0.012 +- 0.006. There is no indication of any significant
star formation over the last few Gyr. Whether gas and dust were dynamically
kept out or evacuated from the central cavity remains unclear. The best-fit
suggests an excess of flux in the mid-infrared bands, with further indications
that the center of the mid-infrared structure is displaced with respect to the
optical center of the NSC. We discuss five potential scenarios, none of them
fully explaining both the observed photometry and structure.Comment: 26 pages, 10 figures, 6 tables. Accepted for publication by ApJ
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