3,975 research outputs found
Comparative study of hyperon-nucleon interactions of quark model and chiral effective field theory by low-momentum equivalent interactions and matrices
Hyperon-nucleons interactions constructed by two frameworks, the
Kyoto-Niigata SU quark model and the chiral effective field theory, are
compared by investigating equivalent interactions in a low-momentum space and
in addition by calculating hyperon single-particle potentials in the
lowest-order Brueckner theory in symmetric nuclear matter. Two descriptions are
shown to give similar matrix elements in most channels after renormalizing high
momentum components. Although the range of the interaction is
different in two potentials, the single-particle potential in nuclear
matter is very similar. The -nucleus and -nucleus potentials are
also found to be similar. These predictions are to be confronted with
forthcoming experimental data.Comment: 8 pages, 7 figures. To appear in Phys. Rev.
Inverse Spin Hall Effect Driven by Spin Motive Force
The spin Hall effect is a phenomenon that an electric field induces a spin
Hall current. In this Letter, we examine the inverse effect that, in a
ferromagnetic conductor, a charge Hall current is induced by a spin motive
force, or a spin-dependent effective ` electric' field ,
arising from the time variation of magnetization texture. By considering
skew-scattering and side-jump processes due to spin-orbit interaction at
impurities, we obtain the Hall current density as , where is the local spin direction and
is the spin Hall conductivity. The Hall angle due to the spin
motive force is enhanced by a factor of compared to the conventional
anomalous Hall effect due to the ordinary electric field, where is the spin
polarization of the current. The Hall voltage is estimated for a field-driven
domain wall oscillation in a ferromagnetic nanowire.Comment: 4 pages, 3 figures, the title has been change
Current-driven resonant excitation of magnetic vortex
A magnetic vortex core in a ferromagnetic circular nanodot has a resonance
frequency originating from the confinement of the vortex core. By the
micromagnetic simulation including the spin-transfer torque, we show that the
vortex core can be resonantly excited by an AC (spin-polarized) current through
the dot and that the resonance frequency can be tuned by the dot shape. The
resistance measurement under the AC current successfully detects the resonance
at the frequency consistent with the simulation.Comment: 16 pages, 4 figure
Millimeter Interferometric Investigations of the Energy Sources of Three Ultraluminous Infrared Galaxies, UGC 5101, Mrk 273, and IRAS 17208-0014, based on HCN to HCO+ Ratios
We present interferometric observations of three ultraluminous infrared
galaxies (ULIRGs; UGC 5101, Mrk 273, and IRAS 17208-0014) in the 3-mm
wavelength range, using the Nobeyama Millimeter Array. Both the HCN (J=1-0) and
HCO+ (J=1-0) molecular lines were observed simultaneously. HCN emission was
clearly detected at the nuclear positions of these ULIRGs, and HCO+ emission
was detected at the nuclear positions of UGC 5101 and IRAS 17208-0014. The HCN
to HCO+ brightness-temperature ratios toward the nuclei of the three ULIRGs
were derived and compared with those of lower luminosity galaxies known to be
dominated by active galactic nuclei (AGNs) or starbursts. In UGC 5101 and Mrk
273, where there is evidence for obscured AGNs from previous observations at
other wavelengths, we found high HCN/HCO+ ratios (>1.8) that are in the range
found for AGN-dominated galaxies. In IRAS 17208-0014, where the presence of a
powerful obscured AGN has been unclear, the ratio (1.7) is in between the
observed values for starburst- and AGN-dominated galaxies. The high HCN/HCO+
brightness-temperature ratios in UGC 5101 and Mrk 273 could be the consequence
of an HCN abundance enhancement, which is expected from chemical effects of the
central X-ray emitting AGN on the surrounding dense molecular gas. Our proposed
millimeter interferometric method based on HCN/HCO+ ratios may be an effective
tool for unveiling elusive buried AGNs at the cores of ULIRGs, especially
because of the negligible dust extinction at these wavelengths.Comment: 15 pages (emulateapj.sty), 8 figures (figures 1-5 resolution
reduced), Accepted for publication in Astronomical Journal, A PDF file with
high resolution is availble at
http://optik2.mtk.nao.ac.jp/~imanishi/Paper/HCN/HCN.pd
Dense Molecular Gas and the Role of Star Formation in the Host Galaxies of Quasi-Stellar Objects
New millimeter-wave CO and HCN observations of the host galaxies of
infrared-excess Palomar Green quasi-stellar objects (PG QSOs) previously
detected in CO are presented. These observations are designed to assess the
validity of using the infrared luminosity to estimate star formation rates of
luminous AGN by determining the relative significance of dust-heating by young,
massive stars and active galactic nuclei (AGN) in QSO hosts and IRAS galaxies
with warm, AGN-like infrared colors. The HCN data show the PG QSO host IZw1 and
most of the warm IRAS galaxies to have high L_IR / L'_HCN (>1600) relative to
the cool IRAS galaxy population for which the median L_IR / L'_HCN ~
890(+440,-470). If the assumption is made that the infrared emission from cool
IRAS galaxies is reprocessed light from embedded star-forming regions, then
high values of L_IR / L'_HCN are likely the result of dust heating by the AGN.
Further, if the median ratio of L'_HCN / L'_CO ~ 0.06 observed for Seyfert
galaxies and IZw1 is applied to the PG QSOs not detected in HCN, then the
derived L_IR / L'_HCN correspond to a stellar contribution to the production of
L_IR of ~ 7-39%, and star formation rates ~ 2-37 M_sun/yr are derived for the
QSO hosts. Alternatively, if the far-infrared is adopted as the star formation
component of the total infrared in cool galaxies, the stellar contributions in
QSO hosts to their L_FIR are up to 35% higher than the percentages derived for
L_IR. This raises the possibility that the L_FIR in several of the PG QSO
hosts, including IZw1, could be due entirely to dust heated by young, massive
stars. Finally, there is no evidence that the global HCN emission is enhanced
relative to CO in galaxies hosting luminous AGN.Comment: LaTex, 31 pages, including 9 postscript figures, AJ, in press
(December 2006
Theory of Anomalous Hall Effect in a Heavy fermion System with a Strong Anisotropic Crystal Field
In a heavy fermion system, there exists the anomalous Hall effect caused by
localized -orbital freedom, in addition to the normal Hall effect due to the
Lorentz force. In 1994, we found that the Hall coefficient caused by the
anomalous Hall effect () is predominant and the relation ( is the electrical resistivity) holds at low
temperatures in many compounds. In this work, we study the system where the
magnetic susceptibility is highly anisotropic due to the strong crystalline
electric field on -orbitals. Interestingly, we find that is
nearly isotropic in general. This tendency is frequently observed
experimentally, which has casted suspicion that the anomalous Hall effect may
be irrelevant in real materials. Our theory corresponds to corrections and
generalizations of the pioneering work on ferromagnetic metals by Karplus and
Luttinger.Comment: 4 pages, revtex, to be published in J. Phys. Soc. Jpn. (No.8
Near-infrared and Millimeter Constraints on the Nuclear Energy Source of the Infrared Luminous Galaxy NGC 4418
We present near-infrared and millimeter investigations of the nucleus of the
infrared luminous galaxy NGC 4418, which previous observations suggest
possesses a powerful buried AGN. We found the following main results: (1) The
infrared K-band spectrum shows CO absorption features at 2.3-2.4 micron owing
to stars and very strong H2 emission lines. The luminosity ratios of H2
emission lines are suggestive of a thermal origin, and the equivalent width of
the H2 1-0 S(1) line is the second largest observed to date in an external
galaxy, after the well-studied strong H2-emitting galaxy NGC 6240. (2) The
infrared L-band spectrum shows a clear polycyclic aromatic hydrocarbon (PAH)
emission feature at 3.3 micron, which is usually found in star-forming
galaxies. The estimated star-formation luminosity from the observed PAH
emission can account for only a small fraction of the infrared luminosity. (3)
Millimeter interferometric observations of the nucleus reveal a high HCN (1-0)
to HCO+ (1-0) luminosity ratio of 1.8, as has been previously found in pure
AGNs. (4) The measurements of HCN (1-0) luminosity using a single-dish
millimeter telescope show that the HCN (1-0) to infrared luminosity ratio is
slightly larger than the average, but within the scattered range, for other
infrared luminous galaxies. All of these results can be explained by the
scenario in which, in addition to energetically-insignificant, weakly-obscured
star-formation at the surface of the nucleus, a powerful X-ray emitting AGN
deeply buried in dust and high density molecular gas is present.Comment: 31 pages, 9 figures, Accepted for publication in Astronomical Journal
(2004 November issue
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