4,620 research outputs found
Alpha-cluster structure and density wave in oblate nuclei
Pentagon and triangle shapes in Si-28 and C-12 are discussed in relation with
nuclear density wave. In the antisymmetrized molecular dynamics calculations,
the band in Si-28 and the band in C-12 are described by
the pentagon and triangle shapes, respectively. These negative-parity bands can
be interpreted as the parity partners of the ground bands and they
are constructed from the parity-asymmetric-intrinsic states. The pentagon and
the triangle shapes originate in 7alpha and 3alpha cluster structures,
respectively. In a mean-field picture, they are described also by the static
one-dimensional density wave at the edge of the oblate states. In analysis with
ideal alpha cluster models using Brink-Bloch cluster wave functions and that
with a simplified model, we show that the static edge density wave for the
pentagon and triangle shapes can be understood by spontaneous breaking of axial
symmetry, i.e., the instability of the oblate states with respect to the edge
density wave. The density wave is enhanced in the Z=N nuclei due to the
proton-neutron coherent density waves, while it is suppressed in Z\ne N nuclei.Comment: 23 pages, 8 figure
Strong Evidence that the Galactic Bulge is Shining in Gamma Rays
There is growing evidence that the Galactic Center Excess identified in the
-LAT gamma-ray data arises from a population of faint
astrophysical sources. We provide compelling supporting evidence by showing
that the morphology of the excess traces the stellar over-density of the
Galactic bulge. By adopting a template of the bulge stars obtained from a
triaxial 3D fit to the diffuse near-infrared emission, we show that it is
detected at high significance. The significance deteriorates when either the
position or the orientation of the template is artificially shifted, supporting
the correlation of the gamma-ray data with the Galactic bulge. In deriving
these results, we have used more sophisticated templates at low-latitudes for
the bubbles compared to previous work and the
three-dimensional Inverse Compton (IC) maps recently released by the team. Our results provide strong constraints on Millisecond Pulsar
(MSP) formation scenarios proposed to explain the excess. We find that an
scenario, in which some of the relevant binaries
are and the rest are formed , is
preferred over a primordial-only formation scenario at confidence
level. Our detailed morphological analysis also disfavors models of the
disrupted globular clusters scenario that predict a spherically symmetric
distribution of MSPs in the Galactic bulge. For the first time, we report
evidence of a high energy tail in the nuclear bulge spectrum that could be the
result of IC emission from electrons and positrons injected by a population of
MSPs and star formation activity from the same site.Comment: 21 pages, 13 figures, V2: Minor changes to match submitted version,
V3: matches JCAP published versio
Analysis of previous microscopic calculations for second state in C in terms of 3-alpha particle Bose-condensed state
The wave function of the second state of C which was obtained
long time ago by solving the microscopic 3 problem is shown to be
almost completely equivalent to the wave function of the 3 condensed
state which has been proposed recently by the present authors. This equivalence
of the wave functions is shown to hold in two cases where different effective
two-nucleon forces are adopted. This finding gives strong support for
interpreting the second state of C which is the key state for the
synthesis of C in stars ('Hoyle' state), and which is one of the typical
mysterious states in light nuclei, as a gas-like structure of three
particles, Bose-condensed into an identical s-wave function.Comment: revtex, 5 pages, 2 figures, submitted to Phys. Rev.
Improved Limits on Sterile Neutrino Dark Matter using Full-Sky Fermi Gamma-Ray Burst Monitor Data
A sterile neutrino of ~keV mass is a well motivated dark matter candidate.
Its decay generates an X-ray line that offers a unique target for X-ray
telescopes. For the first time, we use the Gamma-ray Burst Monitor (GBM)
onboard the Fermi Gamma-Ray Space Telescope to search for sterile neutrino
decay lines; our analysis covers the energy range 10-25 keV (sterile neutrino
mass 20-50 keV), which is inaccessible to X-ray and gamma-ray satellites such
as Chandra, Suzaku, XMM-Newton, and INTEGRAL. The extremely wide field of view
of the GBM enables a large fraction of the Milky Way dark matter halo to be
probed. After implementing careful data cuts, we obtain ~53 days of full sky
observational data. We observe an excess of photons towards the Galactic
Center, as expected from astrophysical emission. We search for sterile neutrino
decay lines in the energy spectrum, and find no significant signal. From this,
we obtain upper limits on the sterile neutrino mixing angle as a function of
mass. In the sterile neutrino mass range 25-40 keV, we improve upon previous
upper limits by approximately an order of magnitude. Better understanding of
detector and astrophysical backgrounds, as well as detector response, will
further improve the sensitivity of a search with the GBM.Comment: 16 pages, 11 figures, references added, discussion expanded, some
typos fixed, matches the published versio
Removal of forbidden states in a three- system
The ground and excited 0 states of C are investigated in a
3 macroscopic model using the deep potential of Buck, Friedrich and
Wheatley. The elimination of forbidden states is performed either by
constructing the allowed state space explicitly or by using the orthogonalizing
pseudopotential. The well-known enigmatic behavior of the latter approach is
resolved. It is safe to define the forbidden states referring to the underlying
microscopic model.Comment: 18pages, 2figure
nature of the superdeformed band of and the evolution of the molecular structure
The relation between the superdeformed band of and molecular bands is studied by the deformed-base
antisymmetrized molecular dynamics with the Gogny D1S force. It is found that
the obtained superdeformed band members of have considerable
amount of the component. Above the superdeformed
band, we have obtained two excited rotational bands which have more prominent
character of the molecular band. These three
rotational bands are regarded as a series of
molecular bands which were predicted by using the unique
- optical potentil. As the excitation energy and principal
quantum number of the relative motion increase, the cluster structure becomes more prominent but at the same time, the band
members are fragmented into several states
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