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T. Murakami

Publications and source records attributed to T. Murakami.

At least 91 records · Page 5Linked to original sources
arXiv2005

BRST symmetry of SU(2) Yang-Mills theory in Cho--Faddeev--Niemi decomposition

We determine the nilpotent BRST and anti-BRST transformations for the Cho--Faddeev-Niemi variables for the SU(2) Yang-Mills theory based on the new interpretation given in the previous paper of the Cho--Faddeev-Niemi decomposition. This gives a firm ground for performing the BRST quantization of the Yang--Mills theory written in terms of the Cho--Faddeev-Niemi variables. We propose also a modified version of the new Maximal Abelian gauge which could play an important role in the reduction to the original Yang-Mills theory.

hep-th↗
arXiv2005

The Reionization History and Early Metal Enrichment inferred from the Gamma-Ray Burst Rate

Based on the gamma-ray burst (GRB) event rate at redshifts of $4 \leq z \leq 12$, which is assessed by the spectral peak energy-to-luminosity relation recently found by Yonetoku et al., we observationally derive the star formation rate (SFR) for Pop III stars in a high redshift universe. As a result, we find that Pop III stars could form continuously at $4 \leq z \leq 12$. Using the derived Pop III SFR, we attempt to estimate the ultraviolet (UV) photon emission rate at $7 \leq z \leq 12$ in which redshift range no observational information has been hitherto obtained on ionizing radiation intensity. We find that the UV emissivity at $7 \leq z \leq 12$ can make a noticeable contribution to the early reionization. The maximal emissivity is higher than the level required to keep ionizing the intergalactic matter at $7 \leq z \leq 12$. However, if the escape fraction of ionizing photons from Pop III objects is smaller than 10%, then the IGM can be neutralized at some redshift, which may lead to the double reionization. As for the enrichment, the ejection of all metals synthesized in Pop III objects is marginally consistent with the IGM metallicity, although the confinement of metals in Pop III objects can reduce the enrichment significantly.

astro-ph↗
arXiv2004

phi photo-production from Li, C, Al, and Cu nuclei at Egamma=1.5 - 2.4 GeV

The photo-production of $ϕ$ mesons from Li, C, Al, and Cu at forward angles has been measured at $E_gamma$=1.5--2.4 GeV. The number of events for incoherent phi photo-production is found to have a target mass number dependence of $A^{0.72\pm 0.07}$ in the kinematical region of $|t|\le 0.6$ ${\rm GeV}^2/c^2$. The total cross section of the $ϕ$-nucleon interaction, $σ_{ϕN}$, has been estimated as $35^{+17}_{-11}$ mb using the $A$-dependence of the $ϕ$ photo-production yield and a Glauber-type multiple scattering theory. This value is much larger than $σ_{ϕN}$ in free space, suggesting that the $ϕ$ properties might change in the nuclear medium.

nucl-ex↗
arXiv2004

Wide band X-ray Imager (WXI) and Soft Gamma-ray Detector (SGD) for the NeXT Mission

The NeXT mission has been proposed to study high-energy non-thermal phenomena in the universe. The high-energy response of the super mirror will enable us to perform the first sensitive imaging observations up to 80 keV. The focal plane detector, which combines a fully depleted X-ray CCD and a pixellated CdTe detector, will provide spectra and images in the wide energy range from 0.5 keV to 80 keV. In the soft gamma-ray band up to ~1 MeV, a narrow field-of-view Compton gamma-ray telescope utilizing several tens of layers of thin Si or CdTe detector will provide precise spectra with much higher sensitivity than present instruments. The continuum sensitivity will reach several times 10^(-8) photons/s/keV/cm^(2) in the hard X-ray region and a few times10^(-7) photons/s/keV/cm^(2) in the soft gamma-ray region.

astro-ph↗
arXiv2003

GRB Formation Rates inferred from the Spectral Peak Energy - Luminosity Relation

We investigate the GRB formation rate based on the relation between the spectral peak energy ($E_{p}$) and the isotropic luminosity. The $E_{p}$--luminosity relation covers the energy range of 50 -- 2000 keV and the luminosity range of $10^{50}$--$10^{54} erg/s, respectively. We find that the relation is considerably tighter than similar relations suggested previously. Using $E_{p}$--luminosity relation, we estimate the luminosity and the redshift of 684 GRBs with the unknown distances and derive the GRB formation rate as a function of the redshift. For $0 \le z \le 2$, the GRB formation rate is well correlated with the star formation rate while it increases monotonously from $z\sim 2$ out to $z \sim 12$. This behavior is consistent with the results of previous works using the lag--luminosity relation or the variability--luminosity relation.

astro-ph↗
arXiv2003

The Data Acquisition System Based on PMC Bus

High energy physics experiments in KEK/Japan rush into over KHz trigger stage. Thus, we need a successor of the data acquisition(DAQ) system that replaces the CAMAC or FASTBUS systems. To meet these needs, we have developed a DAQ system which includes a crate, base-board modules, daughter cards for front-end A/D or T/D conversion, and back-end communication cards for data transfer and timing control. The size of the crate is for the 9U Euro-cards with the standard VME32 bus and extension connectors for power supply. The base-board comprises of a local bus with the sequencer connected to the front-end daughter cards via event buffering FIFOs, and the standard PMC (PCI mezzanine card) bus to be set a PMC processor unit to reduce data size from the front-end daughter cards. A data transfer module, which is connected to the event building system, and a trigger control unit, which communicates with the central timing controller are installed on the back-end communication card connected to the rear end of the base-board. We describe the design of this DAQ system and evaluate the performance of it.

physics.ins-det↗
arXiv2003

Development of a PCI Based Data Acquisition Platform for High Intensity Accelerator Experiments

Data logging at an upgraded KEKB accelerator or the J-PARC facility, currently under commission, requires a high density data acquisition platform with integrated data reduction CPUs. To follow market trends, we have developed a DAQ platform based on the PCI bus, a choice which permits a fast DAQ and a long expected lifetime of the system. The platform is a 9U-VME motherboard consisting of four slots for signal digitization modules, readout FIFOs for data buffering, and three PMC slots, on one of which resides a data reduction CPU. We have performed long term and thermal stability tests. The readout speed on the platform has been measured up to 125 MB/s in DMA mode.

hep-ex↗
arXiv2003

An Analysis of Mutual Communication between Qubits by Capacitive Coupling

A behavior of a two qubit system coupled by the electric capacitance has been studied quantum mechanically. We found that the interaction is essentially the same as the one for the dipole-dipole interaction; i.e., qubit-qubit coupling of the NMR quantum gate. Therefore a quantum gate could be constructed by the same operation sequence for the NMR device if the coupling is small enough. The result gives an information to the effort of development of the devices assuming capacitive coupling between qubits.

quant-ph↗
arXiv2002

The Quiescent Counterpart of the Soft Gamma-ray Repeater SGR 0526-66

It is now commonly believed that Soft gamma-ray repeaters (SGRs) and Anomalous X-ray pulsars (AXPs) are magnetars -- neutron stars powered by their magnetic fields. However, what differentiates these two seemingly dissimilar objects is, at present, unknown. We present Chandra observations of RX J052600.3-660433, the quiescent X-ray counterpart of SGR 0526-66. Restricting to a period range around 8-s, the period noted in the afterglow of the burst of 5 March 1979, we find evidence for a similar periodicity in two epochs of data, obtained 20 months apart, implying a period derivative of $6.6(5)e-11$ s/s which is similar to the period derivatives of the magnetars. The spectrum is best fitted by a combination of a black body and a power law. However, the photon index of the power law component, $Γ\sim 3$ -- intermediate to those of AXPs and SGRs. This continuum of $Γ$ leads us to suggest that the underlying physical parameter which differentiates SGRs from AXPs is manifested in the power law component. Two decades ago, SGR 0526-66 was a classical SGR whereas now it behaves like an AXP. Thus it is possible that the same object cycles between SGR and AXP state. We speculate that the main difference between AXPs and SGRs is the geometry of the $B$-fields and this geometry is time dependent. [Abstract truncated]

astro-ph↗
arXiv2002

Renormalizing a BRST-invariant composite operator of mass dimension 2 in Yang-Mills theory

We discuss the renormalization of a BRST and anti-BRST invariant composite operator of mass dimension 2 in Yang-Mills theory with the general BRST and anti-BRST invariant gauge fixing term of the Lorentz type. The interest of this study stems from a recent claim that the non-vanishing vacuum condensate of the composite operator in question can be an origin of mass gap and quark confinement in any manifestly covariant gauge, as proposed by one of the authors. First, we obtain the renormalization group flow of the Yang-Mills theory. Next, we show the multiplicative renormalizability of the composite operator and that the BRST and anti-BRST invariance of the bare composite operator is preserved under the renormalization. Third, we perform the operator product expansion of the gluon and ghost propagators and obtain the Wilson coefficient corresponding to the vacuum condensate of mass dimension 2. Finally, we discuss the connection of this work with the previous works and argue the physical implications of the obtained results.

hep-th↗
arXiv2001

The Isoscalar Giant Dipole Resonance in 208Pb and the Nuclear incompressibility

The isoscalar giant dipole resonance (ISGDR) has been investigated in 208Pb using inelastic scattering of 400 MeV alpha particles at forward angles, including 0deg. Using the superior capabilities of the Grand Raiden spectrometer, it has been possible to obtain spectra devoid of any "instrumental" background. The ISGDR strength distribution has been extracted from a multipole-composition of the observed spectra. The implication of these results on the experimental value of nuclear incompressibility are discussed.

nucl-ex↗
arXiv2001

Non-Equilibrium Ionization States of GRB Environments

Iron spectral features are thought to be the best tracer of a progenitor of gamma-ray bursts (GRBs). The detections of spectral features such as an iron line and/or a Radiative Recombination edge and Continuum (RRC) were reported in four X-ray afterglows of GRBs. However their properties were different each other burst by burst. For example, Chandra observation of GRB 991216 reported both the strong H-like iron line together with its RRC. On the contrary, Yoshida et al. (2001) report only a detection of the strong RRC in GRB 970828 with ASCA. Since it is difficult to produce the strong RRC, we have to consider special condition for the line and/or the RRC forming region. In this paper, we point out a possibility of a ``non-equilibrium ionization state'' for the line and the RRC forming region.

astro-ph↗
arXiv2001

A Possible Emission Feature in an X-ray Afterglow of GRB970828 as a Radiative Recombination Edge

A gamma-ray burst of 28 August 1997 was localized by the All-Sky Monitor on the Rossi XTE satellite and its coordinates were promptly disseminated. An ASCA followup started 1.17 days after the burst as a Target of Opportunity Observation and detected an X-ray afterglow. The spectral data displayed a hump around ~5 keV and an absorption column of 7.1 x 10^21 cm^{-2}. This hump structure is likely a recombination edge of iron in the vicinity of the source, taking account of the redshift z = 0.9578 found for the likely host galaxy of the associated radio flare. Radiative Recombination edge and Continuum model can interpret the spectrum from highly ionized plasma in a non equilibrium ionization state. The absorption could be also due to the medium presumably in the vicinity of the GRB.

astro-ph↗
arXiv2001

HST Observations of SGR 0526-66: New Constraints on Accretion and Magnetar Models

Soft Gamma-ray Repeaters (SGRs) are among the most enigmatic sources known today. Exhibiting huge X- and Gamma-ray bursts and flares, as well as soft quiescent X-ray emission, their energy source remains a mystery. Just as mysterious are the Anomalous X-ray pulsars (AXPs), which share many of the same characteristics. Thanks to recent Chandra observations, SGR 0526-66, the first SGR, now appears to be a transition object bridging the two classes, and therefore observations of it have implications for both SGRs and AXPs. The two most popular current models for their persistent emission are accretion of a fossil disk or decay of an enormous (~10^15 G) magnetic field in a magnetar. We show how deep optical observations of SGR 0526-66, the only SGR with small enough optical extinction for meaningful observations, show no evidence of an optical counterpart. These observation place strong new constraints on both accretion disk and magnetar models, and suggest that the spectral energy distribution may peak in the hard-UV. Almost all accretion disks are excluded by the optical data, and a magnetar would require a ~10^15-10^16 G field.

astro-ph↗
arXiv2000

Observation of $ρ/ ω$ Meson Modification in Nuclear Matter

We have measured invariant mass spectra of electron-positron pairs in the target rapidity region of 12GeV p+A reactions. We have observed a significant difference in the mass spectra below the $ω$ meson between p+C and p+Cu interactions. The difference is interpreted as a signature of the $ρ/ω$ modification at normal nuclear-matter density.

nucl-ex↗
arXiv2000

Observation of X-ray lines from a Gamma-Ray Burst (GRB991216): Evidence of Moving Ejecta from the Progenitor

We report on the discovery of two emission features observed in the X-ray spectrum of the afterglow of the gamma-ray burst (GRB) of 16 Dec. 1999 by the Chandra X-Ray Observatory. These features are identified with the Ly$_α$ line and the narrow recombination continuum by hydrogenic ions of iron at a redshift $z=1.00\pm0.02$, providing an unambiguous measurement of the distance of a GRB. Line width and intensity imply that the progenitor of the GRB was a massive star system that ejected, before the GRB event, $\approx 0.01 \Ms$ of iron at a velocity $\approx 0.1 c$, probably by a supernova explosion.

astro-ph↗
arXiv1999

ASCA Observation of the quiescent X-ray counterpart to SGR1627-41

We present a 2 - 10 keV ASCA observation of the field around the soft gamma repeater SGR1627-41. A quiescent X-ray source was detected in this observation whose position was consistent both with that of a recently discovered BeppoSAX X-ray source and with the Interplanetary Network localization for this SGR. In 2 - 10 keV X-rays, the spectrum of the X-ray source may be fit equally well by a power law, blackbody, or bremsstrahlung function, with unabsorbed flux ~5 x 10^-12 erg cm^-2 s^-1. We do not confirm a continuation of a fading trend in the flux, and we find no evidence for periodicity, both noted in the earlier BeppoSAXobservations.

astro-ph↗