arXiv subjects

H. Kaneko

Publications and source records attributed to H. Kaneko.

12 recordsLinked to original sources

arXiv2020

The Molecular Mass function of the Local Universe

We construct the molecular mass function using the bivariate Kband-Mass Function of the Herschel Reference Survey, a volume-limited sample already widely studied at the entire electromagnetic spectrum. The molecular mass function is derived from the K-band and the gas mass cumulative distribution using a copula method described in detail in our previous papers. The H2 mass is relatively strong correlated with the K-band luminosity because of the tight relation between the stellar mass and the molecular gas mass within the sample with a scatter likely due to those galaxies which have lost their molecular content because of environmental effects or because of a larger gas consumption due to past star formation processes. The derived H2 Mass Function samples the molecular mass range from 4 10^6 to 10^10 solar masses, and when compared with theoretical models, it agrees well with the theoretical predictions at the lower end of the mass values, while at masses larger than 10^10 solar masses the HRS sample may miss galaxies with large content of molecular hydrogen and the outcomes are not conclusive. The value of the local density of the molecular gas mass inferred from our analysis is ~1.5x10^7 Mo Mpc^-3, and it is compared with the results at larger redshifts, confirming the lack of strong evolution of the molecular mass density between z=0 and z=4. This is the first Molecular Mass Function derived on a complete sample in the local Universe, which can be used as a reliable calibration at redshift $z$=0 for models aiming at predicting the evolution of the molecular mass density

astro-ph.GA↗

arXiv2019

Magnetization beyond the Ising limit of Ho$_2$Ti$_2$O$_7$

We report that the local Ising anisotropy in pyrochlore oxides - the crucial requirement for realizing the spin-ice state - can be broken by means of high magnetic fields. For the case of the well-established classical spin-ice compound Ho$_2$Ti$_2$O$_7$ the magnetization exceeds the angle-dependent saturation value of the Ising limit using ultra-high fields up to 120 T. However, even under such extreme magnetic fields full saturation cannot be achieved. Crystal-electric-field calculations reveal that a level crossing for two of the four ion positions leads to magnetization steps at 55 and 100 T. In addition, we show that by using a field sweep rate in the range of the spin-relaxation time the dynamics of the spin system can be probed. Exclusively at 25 ns/T a new peak of the susceptibility appears around 2 T. We argue, this signals the cross-over between spin-ice and polarized correlations.

cond-mat.str-el↗

arXiv2017

Imaging the Molecular Outflows of the Prototypical ULIRG NGC 6240 with ALMA

We present 0".97 $\times$ 0".53 (470 pc $\times$ 250 pc) resolution CO ($J$ = 2-1) observations toward the nearby luminous merging galaxy NGC 6240 with the Atacama Large Millimeter/submillimeter Array. We confirmed a strong CO concentration within the central 700 pc, which peaks between the double nuclei, surrounded by extended CO features along the optical dust lanes ($\sim$11 kpc). We found that the CO emission around the central a few kpc has extremely broad velocity wings with full width at zero intensity $\sim$ 2000 km s$^{-1}$, suggesting a possible signature of molecular outflow(s). In order to extract and visualize the high-velocity components in NGC 6240, we performed a multiple Gaussian fit to the CO datacube. The distribution of the broad CO components show four extremely large linewidth regions ($\sim$1000 km s$^{-1}$) located 1-2 kpc away from both nuclei. Spatial coincidence of the large linewidth regions with H$α$, near-IR H$_2$, and X-ray suggests that the broad CO (2-1) components are associated with nuclear outflows launched from the double nuclei.

astro-ph.GA↗

arXiv2012

The Schmidt-Kennicutt Law of Matched-Age Star Forming Regions; Pa-alpha Observations of the Early-Phase Interacting Galaxy Taffy I

In order to test a recent hypothesis that the dispersion in the Schmidt-Kennicutt law arises from variations in the evolutionary stage of star forming molecular clouds, we compared molecular gas and recent star formation in an early-phase merger galaxy pair, Taffy I (UGC\ 12915/UGC\ 12914, VV\ 254) which went through a direct collision 20 Myr ago and whose star forming regions are expected to have similar ages. Narrow-band Pa-alpha image is obtained using the ANIR near-infrared camera on the mini-TAO 1m telescope. The image enables us to derive accurate star formation rates within the galaxy directly. The total star formation rate, 22.2 M_sun/yr, was found to be much higher than previous estimates. Ages of individual star forming blobs estimated from equivalent widths indicate that most star forming regions are ~7 Myr old, except for a giant HII region at the bridge which is much younger. Comparison between star formation rates and molecular gas masses for the regions with the same age exhibits a surprisingly tight correlation, a slope of unity, and star formation efficiencies comparable to those of starburst galaxies. These results suggest that Taffy I has just evolved into a starburst system after the collision, and the star forming sites are at a similar stage in their evolution from natal molecular clouds except for the bridge region. The tight Schmidt-Kennicutt law supports the scenario that dispersion in the star formation law is in large part due to differences in evolutionary stage of star forming regions.

astro-ph.CO↗

arXiv2012

Vector- and Pseudoscalar-baryon coupled channel systems

In this manuscript, I will report the details of our recent work on the vector meson-baryon (VB) interaction, which we studied with the motivation of finding dynamical generation of resonances in the corresponding systems. We started our study by building a formalism based on the hidden local symmetry and calculating the leading order contributions to the scattering equations by summing the diagrams with: (a) a vector meson exchange in the t-channel (b) an octet baryon exchange in the s-, u-channels and (c) a contact interaction arising from the part of the vector meson-baryon Lagrangian which is related to the anomalous magnetic moment of the baryons. We find the contribution from all these sources, except the s-channel, to be important. The amplitudes obtained by solving the coupled channel Bethe-Salpeter equations for the systems with total strangeness zero, show generation of one isospin 3/2, spin 1/2 resonance and three isospin 1/2 resonances: two with spin 3/2 and one with spin 1/2. We identify these resonances with $Δ$ (1900) $S_{31}$, $N^*$(2080) $D_{13}$, $N^*$(1700) $D_{13}$, and $N^*$(2090) $S_{11}$, respectively. We have further extended our study by including pseudoscalar meson-baryon (PB) as the coupled channels of VB systems. For this, we obtain the PB $\rightarrow$ VB amplitudes by using the Kroll-Ruddermann term where, considering the vector meson dominance phenomena, the photon is replaced by a vector meson. The calculations done within this formalism reveal a very strong coupling of the VB channels to the low-lying resonances like $Λ$(1405) and $Λ$(1670), which can have important implications on certain reactions producing them. In addition to this, we find that the effect of coupling the higher mass states to the lighter channels is not restricted to increasing the width of those states, it can be far more strong.

nucl-th↗

arXiv2011

Coupling vector and pseudoscalar mesons to study baryon resonances

A study of meson-baryon systems with total strangeness -1 is made within a framework based on the chiral and hidden local symmetries. These systems consist of octet baryons, pseudoscalar and vector mesons. The pseudoscalar meson-baryon (PB) dynamics has been earlier found determinant for the existence of some strangeness -1 resonances, for example, $Λ(1405)$, $Λ(1670)$, etc. The motivation of the present work is to study the effect of coupling the closed vector meson-baryon (VB) channels to these resonances. To do this, we obtain the $PB \rightarrow PB$ and $VB \rightarrow VB$ amplitudes from the t-channel diagrams and the $PB \leftrightarrow VB$ amplitudes are calculated using the Kroll-Ruddermann term where, considering the vector meson dominance phenomena, the photon is replaced by a vector meson. The calculations done within this formalism reveal a very strong coupling of the VB channels to the $Λ(1405)$ and $Λ(1670)$. In the isospin 1 case, we find an evidence for a double pole structure of the $Σ(1480)$ which, like the isospin 0 resonances, is also found to couple strongly to the VB channels. The strong coupling of these low-lying resonances to the VB channels can have important implications on certain reactions producing them.

nucl-th↗

arXiv2011

Vector meson-Baryon dynamics and generation of resonances

The purpose of this work is to study vector meson-octet baryon interactions with the aim to find dynamical generation of resonances in such systems. For this, we consider s-, t-, u-channel diagrams along with a contact interaction originating from the hidden local symmetry Lagrangian. We find the contribution from all these sources, except the s-channel, to be important. The amplitudes obtained by solving coupled channel Bethe Salpeter equations for systems with total strangeness zero, show generation of one isospin 3/2, spin 1/2 resonance and three isospin 1/2 resonances: two with spin 3/2 and one with spin 1/2. We identify these resonances with $Δ(1900) S_{31}$, $N^* (2080) D_{13}$, $N^* (1700) D_{13}$, and $N^*(2090) S_{11}$, respectively.

hep-ph↗

arXiv2009

Potassium Abundances in Red Giants of Mildly to Very Metal-Poor Globular Clusters

A non-LTE analysis of K I resonance lines at 7664.91 and 7698.97 A was carried out for 15 red giants belonging to three globular clusters of different metallicity (M 4, M 13, and M 15) along with two reference early-K giants (rho Boo and alpha Boo), in order to check whether the K abundances are uniform within a cluster and to investigate the behavior of [K/Fe] ratio at the relevant metallicity range of -2.5 <[Fe/H] < -1. We confirmed that [K/H] (as well as [Fe/H]) is almost homogeneous within each cluster to a precision of < ~0.1 dex, though dubiously large deviations are exceptionally seen for two peculiar stars showing signs of considerably increased turbulence in the upper atmosphere. The resulting [K/Fe] ratios are mildly supersolar by a few tenths of dex for three clusters, tending to gradually increase from ~+0.1-0.2 at [Fe/H] ~-1 to ~+0.3 at [Fe/H] ~ -2.5. This result connects reasonably well with the [K/Fe] trend of disk stars (-1 < [Fe/H]) and that of extremely metal-poor stars (-4 <[Fe/H] < -2.5). That is, [K/Fe] appears to continue a gradual increase from [Fe/H]~0 toward a lower metallicity regime down to [Fe/H]~-3, where a broad maximum of [K/Fe]~+0.3-0.4 is attained, possibly followed by a slight downturn at [Fe/H]<~-3.

astro-ph.SR↗

arXiv2006

Multi-layer scintillation detector for the MOON double beta decay experiment: Scintillation photon responses studied by a prototype detector MOON-1

An ensemble of multi-layer scintillators is discussed as an option of the high-sensitivity detector Mo Observatory Of Neutrinos (MOON) for spectroscopic measurements of neutrino-less double beta decays. A prototype detector MOON-1, which consists of 6 layer plastic-scintillator plates, was built to study the sensitivity of the MOON-type detector. The scintillation photon collection and the energy resolution, which are key elements for the high-sensitivity experiments, are found to be 1835+/-30 photo-electrons for 976 keV electrons and sigma = 2.9+/-0.1% (dE/E = 6.8+/-0.3 % in FWHM) at the Qbb ~ 3 MeV region, respectively. The multi-layer plastic-scintillator structure with good energy resolution as well as good background suppression of beta-gamma rays is crucial for the MOON-type detector to achieve the inverted hierarchy neutrino mass sensitivity.

nucl-ex↗

arXiv2005

Fuzzy Spacetime with SU(3) Isometry in IIB Matrix Model

A group of fuzzy spacetime with SU(3) isometry is studied at the two loop level in IIB matrix model. It consists of spacetime from 4 to 6 dimensions, namely from CP2 to SU(3)/U(1)x U(1). The effective action scales in a universal manner in the large N limit as N and N^{4/3} on 4 and 6 dimensional manifolds respectively. The 4 dimensional spacetime CP2 possesses the smallest effective action in this class.

hep-th↗

arXiv2005

Stability of Fuzzy S^2 x S^2 x S^2 in IIB Type Matrix Models

We study the stability of fuzzy S^2 x S^2 x S^2 backgrounds in three different IIB type matrix models with respect to the change of the spins of each S^2 at the two loop level. We find that S^2 x S^2 x S^2 background is metastable and the effective action favors a single large S^2 in comparison to the remaining S^2 x S^2 in the models with Myers term. On the other hand, we find that a large S^2 x S^2 in comparison to the remaining S^2 is favored in IIB matrix model itself. We further study the stability of fuzzy S^2 x S^2 background in detail in IIB matrix model with respect to the scale factors of each S^2 as well. In this case, we find unstable directions which lower the effective action away from the most symmetric fuzzy S^2 x S^2 background.

hep-th↗

arXiv2003

The CDFII Time-Of-Flight Detector and Impact on Beauty Flavor Tagging

The new CDFII detector incorporates a Time-of-Flight detector (TOF), employing plastic scintillator bars and fine-mesh photomultipliers. Since August 2001 the TOF system has been fully instrumented and integrated into the CDFII data acquisition system. With a design goal of $100 ps$ resolution the TOF system will provide at least two standard deviations separation between $K^{\pm}$ and $π^{\pm}$ for momenta $p<1.6 GeV/c$, complementing low momentum particle identification by means of the specific ionization energy loss measured in the drift chamber. We describe the design of the TOF detector and discuss the current status of its calibration and initial performances. Finally we review the expected impact of the TOF detector in the flavor tagging of neutral $B_S$ meson.

hep-ex↗