3,395 research outputs found
Stress Tensor of the Hydrogen Molecular Ion
The electronic stress tensor of the hydrogen molecule ion H_2^+ is
investigated for the ground state (sigma_g 1s) and the first excited state
(sigma_u^* 1s) using their exact wave functions. A map of its largest
eigenvalue and corresponding eigenvector is shown to be closely related to the
nature of chemical bonding. For the ground state, we also show the spatial
distribution of interaction energy density to describe in which part of the
molecule stabilization and destabilization take place.Comment: 9 pages, 4 figure
Revisiting the Constraint on the Helium Abundance from CMB
We revisit the constraint on the primordial helium mass fraction Yp from
observations of cosmic microwave background (CMB) alone. By minimizing chi
square of recent CMB experiments over 6 other cosmological parameters, we
obtained rather weak constraints as 0.17 < Yp < 0.52 at 1 sigma C.L. for a
particular data set. We also study the future constraint on cosmological
parameters when we take account of the prediction of the standard big bang
nucleosynthesis (BBN) theory as a prior on the helium mass fraction where Yp
can be fixed for a given energy density of baryon. We discuss the implications
of the prediction of the standard BBN on the analysis of CMB.Comment: 15 pages, 5 figures, published versio
The Dwarf Nova Outbursts of Nova Her 1960 (=V446 Her)
V446 Her is the best example of an old nova which has developed dwarf nova
eruptions in the post-nova state. We report on observed properties of the
long-term light curve of V446 Her, using photometry over 19 years. Yearly
averages of the outburst magnitudes shows a decline of ~0.013 mag/yr,
consistent with the decline of other post-novae that do not have dwarf nova
outbursts. Previous suggestions of bimodal distributions of the amplitudes and
widths of the outbursts are confirmed. The outbursts occur at a mean spacing of
18 days but the range of spacings is large (13-30 days). From simulations of
dwarf nova outbursts it has been predicted that the outburst spacing in V446
Her will increase as M-dot from the red dwarf companion slowly falls following
the nova; however the large intrinsic scatter in the spacings serves to hide
any evidence of this effect. We do find a systematic change in the outburst
pattern in which the brighter, wider type of outbursts disappeared after late
2003, and this phenomenon is suggested to be due to falling M-dot following the
nova.Comment: To appear at the Astronomical Journal; 7 pages, 1 table, 11 figure
Cluster formations in deformed states for Si and S
We study cluster formation in strongly deformed states for Si and
S using a macroscopic-microscopic model. The study is based on
calculated total-energy surfaces, which are the sums of deformation-dependent
macroscopic-microscopic potential-energy surfaces and rotational-energy
contributions. We analyze the angular-momentum-dependent total-energy surfaces
and identify the normal- and super-deformed states in Si and S,
respectively. We show that at sufficiently high angular momenta strongly
deformed minima appear. The corresponding microscopic density distributions
show cluster structure that closely resemble the O+C and
O+O configurations. At still higher deformations, beyond the
minima, valleys develop in the calculated surfaces. These valleys lead to mass
divisions that correspond to the target-projectile configurations for which
molecular resonance states have been observed. We discuss the relation between
the one-body deformed minima and the two-body molecular-resonance states.Comment: 6 pages, 7 figure
Search for three alpha states around an O core in Si
We investigate the existence of weakly coupled gas-like states comprised of
three particles around an O core in Si. We calculate the
excited states in Si using the multi-configuration mixing method based
on the O + 3 cluster model. We also include the O +
C and Mg + basis wave functions prepared by the
generator coordinate method. To identify the gas-like states, we calculate the
isoscalar monopole transition strengths and the overlap of the obtained states
with the geometrical cluster wave function and the
Tohsaki-Horiuchi-Schuck-R\"{o}pke (THSR) wave function. The results show that
the obtained fourth and twelfth states significantly overlap with the THSR wave
function. These two states clearly coexist with the O + C cluster
states, emerging at similar energies. The calculated isoscalar monopole
strengths between those two states are significantly large, indicating that the
states are members of the excitation mode. Furthermore, the calculated
root-mean-squared (RMS) radii for these states also suggest that a layer of
gas-like three particles could exist around the surface of the
O core, which can be described as a "two-dimensional gas" in the
intermediate state before the Hoyle-like three states emerge.Comment: 5 pages, 3 figure
The oscillation effects on thermalization of the neutrinos in the universe with low reheating temperature
We study how the oscillations of the neutrinos affect their thermalization
process during the reheating period with temperature O(1) MeV in the early
universe. We follow the evolution of the neutrino density matrices and
investigate how the predictions of big bang nucleosynthesis vary with the
reheating temperature. For the reheating temperature of several MeV, we find
that including the oscillations makes different predictions, especially for
He abundance. Also, the effects on the lower bound of the reheating
temperature from cosmological observations are discussed.Comment: 24 pages, 8 figures; references and explanatory comments added,
conclusion unchange
Dineutron-dineutron correlation in He
Background: The four-neutron correlation has been attracting much attention
for decades. In addition to the study on the tetra-neutron system, it is
worthwhile to investigate the correlation in bound systems.
Purpose: The He nucleus is a system where four neutrons are weakly bound
around the He core. The dineutron () correlation has been long
discussed in various weakly-bound neutron-rich nuclei such as He and
Li, whereas the He nucleus gives us an opportunity to investigate
the - type four-neutron correlation.
Methods: We introduce a microscopic model and describe the
ground-state structure of He. The mixing of the two- component in the
ground state is examined. The ground-state wave function is verified by
investigating various observables including high-energy scattering cross
sections.
Results: Our model reasonably reproduces the available experimental data, the
binding energy, charge radius, total reaction cross section, and proton-nucleus
elastic scattering cross section data. We find that the significant mixing of
the two- cluster configurations around He in the ground state of
He: The ground state has a squared overlap of about 45% with a
-He- configuration with the He- distance of 3 fm and
opening angle of 80.
Conclusion: The ground state of He contains a certain amount of the
two- cluster component, indicating the strong nuclear deformation, which
was experimentally observed recently.Comment: 8 pages, 6 figure
The Hubble constant and dark energy from cosmological distance measures
We study how the determination of the Hubble constant from cosmological
distance measures is affected by models of dark energy and vice versa. For this
purpose, constraints on the Hubble constant and dark energy are investigated
using the cosmological observations of cosmic microwave background, baryon
acoustic oscillations and type Ia suprenovae. When one investigates dark
energy, the Hubble constant is often a nuisance parameter, thus it is usually
marginalized over. On the other hand, when one focuses on the Hubble constant,
simple dark energy models such as a cosmological constant and a constant
equation of state are usually assumed. Since we do not know the nature of dark
energy yet, it is interesting to investigate the Hubble constant assuming some
types of dark energy and see to what extent the constraint on the Hubble
constant is affected by the assumption concerning dark energy. We show that the
constraint on the Hubble constant is not affected much by the assumption for
dark energy. We furthermore show that this holds true even if we remove the
assumption that the universe is flat. We also discuss how the prior on the
Hubble constant affects the constraints on dark energy and/or the curvature of
the universe.Comment: 45 pages, 15 figure
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