5,276 research outputs found
Binomial level densities
It is shown that nuclear level densities in a finite space are described by a
continuous binomial function, determined by the first three moments of the
Hamiltonian, and the dimensionality of the underlying vector space.
Experimental values for Mn, Fe, and Ni are very well
reproduced by the binomial form, which turns out to be almost perfectly
approximated by Bethe's formula with backshift. A proof is given that binomial
densities reproduce the low moments of Hamiltonians of any rank: A strong form
of the famous central limit result of Mon and French. Conditions under which
the proof may be extended to the full spectrum are examined.Comment: 4 pages 2 figures Second version (previous not totally superseeded
Particle-Number Reprojection in the Shell Model Monte Carlo Method: Application to Nuclear Level Densities
We introduce a particle-number reprojection method in the shell model Monte
Carlo that enables the calculation of observables for a series of nuclei using
a Monte Carlo sampling for a single nucleus. The method is used to calculate
nuclear level densities in the complete -shell using a good-sign
Hamiltonian. Level densities of odd-A and odd-odd nuclei are reliably extracted
despite an additional sign problem. Both the mass and the dependence of
the experimental level densities are well described without any adjustable
parameters. The single-particle level density parameter is found to vary
smoothly with mass. The odd-even staggering observed in the calculated
backshift parameter follows the experimental data more closely than do
empirical formulae.Comment: 14 pages, 4 eps figures included, RevTe
Total and Parity-Projected Level Densities of Iron-Region Nuclei in the Auxiliary Fields Monte Carlo Shell Model
We use the auxiliary-fields Monte Carlo method for the shell model in the
complete -shell to calculate level densities. We introduce
parity projection techniques which enable us to calculate the parity dependence
of the level density. Results are presented for Fe, where the calculated
total level density is found to be in remarkable agreement with the
experimental level density. The parity-projected densities are well described
by a backshifted Bethe formula, but with significant dependence of the
single-particle level-density and backshift parameters on parity. We compare
our exact results with those of the thermal Hartree-Fock approximation.Comment: 14 pages, 3 Postscript figures included, RevTe
Parity Dependence of Nuclear Level Densities
A simple formula for the ratio of the number of odd- and even-parity states
as a function of temperature is derived. This formula is used to calculate the
ratio of level densities of opposite parities as a function of excitation
energy. We test the formula with quantum Monte Carlo shell model calculations
in the -shell. The formula describes well the transition from low
excitation energies where a single parity dominates to high excitations where
the two densities are equal.Comment: 14 pages, 4 eps figures included, RevTe
SiO Maser Survey of the Large-Amplitude Variables in the Galactic Center
We have surveyed ~400 known large-amplitude variables within 15' of the
galactic center in the SiO J=1--0 v=1 and 2 maser lines at 43 GHz, resulting in
179 detections. SiO lines were also detected from 16 other resulting in 180
detections. SiO lines were also detected from 16 other sources, which are
located within 20" (the telescope half beamwidth) of the program objects. The
detection rate of 48 percent is comparable to that obtained in Bulge IRAS
source surveys. Among the SiO detections, five stars have radial velocities
greater than 200 km/s. The SiO detection rate increases steeply with the period
of light variation, particularly for stars with P>500 d, where it exceeds 80%.
We found that, at a given period, the SiO detection rate is approximately three
times that for OH. These facts suggest that the large-amplitude variables in
the Nuclear Disk region are AGB stars similar in their overall properties to
the inner and outer Bulge IRAS/SiO sources. From the set of radial velocity
data, the mass distribution within 30 pc of the galactic center is derived by a
new method which is based on the collisionless Boltzmann equation integrated
along the line of sight. The mass within 30 pc is about 6.4 [\pm 0.7] \times
10^7 M_{\odot} and the mass of the central black hole is 2.7 [\pm 1.3] \times
10^6 M_{\odot}. Consideration of the line-of-sight velocity of each star and
its potential energy leads to the conclusion that the five high-velocity stars
come from galactocentric distances as high as 300 pc. The high-velocity
subsample of stars with negative radial velocities exhibits a tendency to have
brighter K magnitudes than the subsample of stars with positive velocities. The
origin of these high-velocity stars is discussed.Comment: Hires. figures are available as No.604 of NRO report at
http://www.nro.nao.ac.jp/library/report/list.html . PASJ 56 (april 28 issue)
in pres
Canonical and Microcanonical Distributions for Fermi Systems
Recursion relations are presented that allow exact calculation of canonical
and microcanonical partition functions of degenerate Fermi systems, assuming no
explicit two-body interactions. Calculations of the level density, sorted by
angular momentum, are presented for Ni-56 are presented. The issue of treating
unbound states is also addressed.Comment: 5 pages, 5 figure
SiO Maser Survey of IRAS Sources in the Inner Galactic Disk
We have surveyed 401 color selected IRAS sources in the Galactic disk in the
SiO J=1--0 v= 1 and 2 maser lines at 43 GHz, resulting in 254 (239 new)
detections. The observed sources lie mostly in a strip of the inner Galactic
disk with boundaries -10<l<40 deg and |b|<3 deg. This survey provides radial
velocities of inner-disk stars for which optical measurements cannot be made
due to interstellar extinction. The SiO -- diagram in the area lv$ map does, indicating a slight difference of stellar
type between SiO and OH emitting stars. After identifying all of the SiO
detected sources in the 2MASS near-infrared catalog, we computed their
luminosity distances based on the infrared fluxes. We then mapped these objects
onto the first quadrant of the Galactic plane. Combining the distances with the
SiO radial-velocities, we obtained a pattern speed for SiO maser sources,
Omega_P=21 (+- 13) km s^{-1} kpc^{-1}, between the distances 1 and 5.5 kpc,
without the use of any dynamical models. The increase of the pattern speed
toward the Galactic center (up to 60 km s^{-1} kpc^{-1} between the distances,
5.5 and 7 kpc) suggests the presence of two pattern speeds in the Galaxy.Comment: 38 page 9 figures, high res. eps files are available as NRO report
No. 608 (http://www.nro.nao.ac.jp/library/report/list.html). PASJ 56 No. 4 in
pres
Detections of SiO Masers from the Large-Amplitude Variables in the Galactic Nuclear Disk
We have surveyed known large-amplitude variables within 15' of the Galactic
center in the SiO J=1-0 v=1 and 2 maser lines at 43 GHz, resulting in 79
detections and 58 non-detections. The detection rate of 58 percent is
comparable to that obtained in Bulge IRAS source surveys. SiO lines were also
detected from four other sources near the program objects. The SiO detection
rate increases steeply with the period, particularly for stars with P>500 d,
where it exceeds 80%. We found at a given period that the SiO detection rate is
approximately double that for OH. These facts suggest that the large-amplitude
variables in the Nuclear Disk region are AGB stars similar in their overall
properties to the inner and outer bulge IRAS/SiO sources.Comment: 5 pages, 2 figures, 1 Table. PASJ 54, No 2 April 25 issue in pres
Quantum number projection at finite temperature via thermofield dynamics
Applying the thermo field dynamics, we reformulate exact quantum number
projection in the finite-temperature Hartree-Fock-Bogoliubov theory. Explicit
formulae are derived for the simultaneous projection of particle number and
angular momentum, in parallel to the zero-temperature case. We also propose a
practical method for the variation-after-projection calculation, by
approximating entropy without conflict with the Peierls inequality. The quantum
number projection in the finite-temperature mean-field theory will be useful to
study effects of quantum fluctuations associated with the conservation laws on
thermal properties of nuclei.Comment: 27 pages, using revtex4, to be published in PR
Physics Opportunities with the FCC-hh Injectors
In this chapter we explore a few examples of physics opportunities using the
existing chain of accelerators at CERN, including potential upgrades. In this
context the LHC ring is also considered as a part of the injector system. The
objective is to find examples that constitute sensitive probes of New Physics
that ideally cannot be done elsewhere or can be done significantly better at
theCERN accelerator complex. Some of these physics opportunities may require a
more flexible injector complex with additional functionality than that just
needed to inject protons into the FCC-hh at the right energy, intensity and
bunch structure. Therefore it is timely to discuss these options concurrently
with the conceptual design of the FCC-hh injector system.Comment: 13 pages, chapter 5 in Physics at the FCC-hh, a 100 TeV pp collide
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