arXiv subjects

Hidenori Takahashi

Publications and source records attributed to Hidenori Takahashi.

49 records · Page 3Linked to original sources

arXiv2008

Si and Fe depletion in Galactic star-forming regions observed by the Spitzer Space Telescope

We report the results of the mid-infrared spectroscopy of 14 Galactic star-forming regions with the high-resolution modules of the Infrared Spectrograph (IRS) on board the Spitzer Space Telescope. We detected [SiII] 35um, [FeII] 26um, and [FeIII] 23um as well as [SIII] 33um and H2 S(0) 28um emission lines. Using the intensity of [NII] 122um or 205um and [OI] 146um or 63um reported by previous observations in four regions, we derived the ionic abundance Si+/N+ and Fe+/N+ in the ionized gas and Si+/O0 and Fe+/O0 in the photodissociation gas. For all the targets, we derived the ionic abundance of Si+/S2+ and Fe2+/S2+ for the ionized gas. Based on photodissociation and HII region models the gas-phase Si and Fe abundance are suggested to be 3-100% and <8% of the solar abundance, respectively, for the ionized gas and 16-100% and 2-22% of the solar abundance, respectively, for the photodissociation region gas. Since the [FeII] 26um and [FeIII] 23um emissions are weak, the high sensitivity of the IRS enables to derive the gas-phase Fe abundance widely in star-forming regions. The derived gas-phase Si abundance is much larger than that in cool interstellar clouds and that of Fe. The present study indicates that 3-100% of Si atoms and <22% of Fe atoms are included in dust grains which are destroyed easily in HII regions, probably by the UV radiation. We discuss possible mechanisms to account for the observed trend; mantles which are photodesorbed by UV photons, organometallic complexes, or small grains.

astro-ph↗

arXiv2007

Bosons after Symmetry Breaking in Quantum Field Theory

We present a unified description of the spontaneous symmetry breaking and its associated bosons in fermion field theory. There is no Goldstone boson in the fermion field theory models of Nambu-Jona-Lasinio, Thirring and QCD$_2$ after the chiral symmetry is spontaneously broken in the new vacuum. The defect of the Goldstone theorem is clarified, and the "massless boson" predicted by the theorem is virtual and corresponds to just a $free$ massless fermion and antifermion pair. Further, we discuss the exact spectrum of the Thirring model by the Bethe ansatz solutions, and the analytical expressions of all the physical observables enable us to understand the essence of the spontaneous symmetry breaking in depth. Also, we examine the boson spectrum in QCD$_2$, and show that bosons always have a finite mass for $SU(N_c)$ colors. The problem of the light cone prescription in QCD$_2$ is discussed, and it is shown that the trivial light cone vacuum is responsible for the wrong prediction of the boson mass.

hep-th↗

arXiv2007

The Far-Infrared Surveyor (FIS) for AKARI

The Far-Infrared Surveyor (FIS) is one of two focal plane instruments on the AKARI satellite. FIS has four photometric bands at 65, 90, 140, and 160 um, and uses two kinds of array detectors. The FIS arrays and optics are designed to sweep the sky with high spatial resolution and redundancy. The actual scan width is more than eight arcmin, and the pixel pitch is matches the diffraction limit of the telescope. Derived point spread functions (PSFs) from observations of asteroids are similar to the optical model. Significant excesses, however, are clearly seen around tails of the PSFs, whose contributions are about 30% of the total power. All FIS functions are operating well in orbit, and its performance meets the laboratory characterizations, except for the two longer wavelength bands, which are not performing as well as characterized. Furthermore, the FIS has a spectroscopic capability using a Fourier transform spectrometer (FTS). Because the FTS takes advantage of the optics and detectors of the photometer, it can simultaneously make a spectral map. This paper summarizes the in-flight technical and operational performance of the FIS.

astro-ph↗

arXiv2006

Hofstadter Butterfly Diagram in Noncommutative Space

We study an energy spectrum of electron moving under the constant magnetic field in two dimensional noncommutative space. It take place with the gauge invariant way. The Hofstadter butterfly diagram of the noncommutative space is calculated in terms of the lattice model which is derived by the Bopp's shift for space and by the Peierls substitution for external magnetic field. We also find the fractal structure in new diagram. Although the global features of the new diagram are similar to the diagram of the commutative space, the detail structure is different from it.

hep-th↗

arXiv2005

Parity Violation in Chiral Symmetry Breaking and Neutrino

I consider parity violation of the chiral symmetry broken vacuum. It is shown that the parity of the true vacuum in the chiral symmetry breaking model is violated. I propose new mechanism of massive neutrino, which the neutrinos have mass in terms of the chiral symmetry breaking. In this mechanism, it may give us new understanding why almost neutrinos have left chirality. Further, NJL model is proposed as alternative phenomenological model of neutrinos.

hep-ph↗

arXiv2005

Glueball mass spectra for supergravity duals of noncommutative gauge theories

We derive the glueball masses in noncommutative super Yang--Mills theories in four dimensions via the dual supergravity description. The spectrum of glueball masses is discrete due to the noncommutativity and the glueball masses are proportional to the noncommutativity parameter with dimension of length. The mass spectrum in the WKB approximation closely agrees with the mass spectrum in finite temperature Yang--Mills theory.

hep-th↗

arXiv2004

Spontaneous spin current near the interface between unconventional superconductors and ferromagnets

We study theoretically the proximity effect between ferromagnets (F) and superconductors (S) with broken time-reversal symmetry (${\cal T}$). A chiral $(p_x\pm ip_y)$-wave, and a $d_{x^2-y^2}$-wave superconductor, the latter of which can form ${\cal T}$-breaking surface state, i.e., $(d_{x^2-y^2} \pm is)$-state, are considered for the S side. The spatial variations of the superconducting order parameters and the magnetization are determined by solving the Bogoliubov de Gennes equation. In the case of a chiral $(p_x\pm ip_y)$-wave superconductor, a spontaneous spin current flows along the interface, but not in the case of a $d_{x^2-y^2}$-wave superconductor. For F/S$(p_x+ip_y)$/F trilayer system, total spin current can be finite while total charge current vanishes, if the magnetization of two F layers are antiparallel.

cond-mat.supr-con↗

arXiv2003

Comment on "The massive Thirring model from XYZ spin chain" by Kolanovic et al

It is shown that the continuum limit of the spin 1/2 Heisenberg XYZ model is far from sufficient for the site number of 16. Therefore, the energy spectrum of the XYZ model obtained by Kolanovic et al. has nothing to do with the massive Thirring model, but it shows only the spectrum of the finite size effects.

hep-th↗

arXiv2003

No Goldstone boson in NJL and Thirring models

We present an intuitive picture of the chiral symmetry breaking in the NJL and Thirring models. For the current current interaction model with the massless fermion, the vacuum is realized with the chiral symmetry broken phase, and the fermion acquires the induced mass. With this finite fermion mass, we calculate the boson mass, and find that the boson is always massive, and there exists no Goldstone boson in the Nambu-Jona-Lasinio (NJL) model.

hep-th↗

arXiv2002

Spontaneous spin current near the interface between ferromagnets and unconventional superconductors

Proximity effects between ferromagnets (F) and superconductors (S) with broken time-reversal symmetry (T) are studied theoretically. For the S side we consider a chiral (p_x \pm ip_y)-wave, and a d_{x^2-y^2}-wave superconductor, the latter of which can form T-breaking surface state, i.e., (d_{x^2-y^2} \pm is)-state. The Bogoliubov de Gennes equation which describes the spatial variations of the superconducting order parameter and the magnetization is derived and solved numerically. It is found that a spontaneous spin current flows along the interface between the (p_x \pm ip_y)-wave superconductor and the ferromagnet. On the contrary, in the case of a [110] interface of the d_{x^2-y^2}-wave SC, the surface state has a (d \pm p_x \pm p_y)-wave (or (d_{x^2-y^2} \pm is)-wave) symmetry, and thus no (only charge) spontaneous current arises.

cond-mat.str-el↗

arXiv2002

D1/D5 system and Wilson Loops in (Non-)commutative Gauge Theories

We study the behavior of the Wilson loop in the (5+1)-dimensional supersymmetric Yang-Mills theory with the presence of the solitonic object. Using the dual string description of the Yang-Mills theory that is given by the D1/D5 system, we estimate the Wilson loops both in the temporal and spatial cases. For the case of the temporal loop, we obtain the velocity dependent potential. For the spatial loop, we find that the area law is emerged due to the effect of the D1-branes. Further, we consider D1/D5 system in the presence of the constant B field. It is found that the Wilson loop obeys the area law for the effect of the noncommutativity.

hep-th↗

arXiv1997

Finite size corrections in massive Thirring model

We calculate for the first time the finite size corrections in the massive Thirring model. This is done by numerically solving the equations of periodic boundary conditions of the Bethe ansatz solution. It is found that the corresponding central charge extracted from the $1/L$ term is around 0.4 for the coupling constant of ${g_0}=-{π\over 4} $ and decreases down to zero when ${g_0}=-{π\over{3}}$. This is quite different from the predicted central charge of the sine-Gordon model.

hep-th↗

arXiv1996

Bound states of 1+1 dimensional field theories

We discuss the bound states of the massive Thirring model. Here, the periodic boundary condition equations for the Bethe ansatz solutions are numerically solved. It is found that the massive Thirring model has only one bound state and the bound state spectrum as the function of the coupling constant agrees with that of infinite momentum frame prescription by Fujita and Ogura. Boson boson states (2p$-$2h states) appear only as the continuum spectrum without making any bound states. Further, the finite size correction to the vacuum energy is estimated. The evaluated central charge is found to be close to unity.

hep-th↗