Search

Evaluation of a wide variety of Feynman diagrams with multi-loop integrals and physical parameters and its comparison with high energy experiments are expected to investigate new physics beyond the Standard Model. We have been developing a direct computation method of multi-loop integrals of Feynman diagrams. One of features of our method is that we adopt the double exponential rule for numerical integrations which enables us to evaluate loop integrals with boundary singularities. Another feature is that in order to accelerate the numerical integrations with multi-precision calculations, we develop an accelerator system with Field Programmable Gate Array boards on which processing elements with dedicated logic for quadruple/hexuple/octuple precision arithmetic operations are implemented. In addition, we also develop a programming interface designed for easy use of the system. The development is continued for practical use of the system. We present the current development of our system, and the numerical results of higher-loop diagrams performed using our system., Comment: 7 pages, 4 figures, in proceedings of the 18th International Workshop on Advanced Computing and Analysis Techniques in Physics Research (ACAT 2017)

The kd-tree is a fundamental tool in computer science. Among others, an application of the kd-tree search (oct-tree method) to fast evaluation of particle interactions and neighbor search is highly important since computational complexity of these problems are reduced from O(N^2) with a brute force method to O(N log N) with the tree method where N is a number of particles. In this paper, we present a parallel implementation of the tree method running on a graphic processor unit (GPU). We successfully run a simulation of structure formation in the universe very efficiently. On our system, which costs roughly $900, the run with N ~ 2.87x10^6 particles took 5.79 hours and executed 1.2x10^13 force evaluations in total. We obtained the sustained computing speed of 21.8 Gflops and the cost per Gflops of 41.6/Gflops that is two and half times better than the previous record in 2006., Comment: Poster paper to be appeared in SC09

We present a novel approach to accelerate astrophysical hydrodynamical simulations. In astrophysical many-body simulations, GRAPE (GRAvity piPE) system has been widely used by many researchers. However, in the GRAPE systems, its function is completely fixed because specially developed LSI is used as a computing engine. Instead of using such LSI, we are developing a special purpose computing system using Field Programmable Gate Array (FPGA) chips as the computing engine. Together with our developed programming system, we have implemented computing pipelines for the Smoothed Particle Hydrodynamics (SPH) method on our PROGRAPE-3 system. The SPH pipelines running on PROGRAPE-3 system have the peak speed of 85 GFLOPS and in a realistic setup, the SPH calculation using one PROGRAPE-3 board is 5-10 times faster than the calculation on the host computer. Our results clearly shows for the first time that we can accelerate the speed of the SPH simulations of a simple astrophysical phenomena using considerable computing power offered by the hardware., Comment: 27 pages, 13 figures, submitted to PASJ

In the current most plausible Cold Dark Matter (CDM) cosmology, larger clumps increase their mass by the progressive merger of smaller clumps. During the evolution, a several merger events, e.g., many minor and a few major merger events, strongly affect the morphology of galaxies as assumed in semi-analytic models. With our physically most detailed high resolution SPH models, we try to tackle the origin of the galaxy morphology. We compute the evolution of 50 over-density peaks in SCDM cosmology and analyzed the obtained properties of the model. We have obtained many different types of star formation history. As a preliminary result, we found the relation between the morphology of the model galaxies and their star formation history. Also we present the global star formation history and metal enrichment history as a function of the redshift, which are obtained by the summing the whole results., Comment: 3 pages, 2 figures, to appear in the proceeding of IAU Symp. 208 "Astrophysical Supercomputing using Particle Simulations"

Among the major uncertainties involved in the Chandrasekhar mass models for Type Ia supernovae are the companion star of the accreting white dwarf (or the accretion rate that determines the carbon ignition density) and the flame speed after ignition. We present nucleosynthesis results from relatively slow deflagration (1.5 - 3 % of the sound speed) to constrain the rate of accretion from the companion star. Because of electron capture, a significant amount of neutron-rich species such as ^{54}Cr, ^{50}Ti, ^{58}Fe, ^{62}Ni, etc. are synthesized in the central region. To avoid the too large ratios of ^{54}Cr/^{56}Fe and ^{50}Ti/^{56}Fe, the central density of the white dwarf at thermonuclear runaway must be as low as \ltsim 2 \e9 \gmc. Such a low central density can be realized by the accretion as fast as $\dot M \gtsim 1 \times 10^{-7} M_\odot yr^{-1}$. These rapidly accreting white dwarfs might correspond to the super-soft X-ray sources., Comment: 10 page LaTeX, 7 PostScript figures, to appear in Nuclear Physics A, Vol. A621 (1997)

Rayleigh-Taylor (R-T) instabilities in the explosion of SN 1993J are investigated by means of two-dimensional hydrodynamical simulations. It is found that the extent of mixing is sensitive to the progenitor's core mass and the envelope mass. Because the helium core mass (3 - 4 \ms) is smaller than that of SN 1987A, R-T instabilities at the He/C+O interfaces develop to induce a large scale mixing in the helium core, while the instability is relatively weak at the H/He interface due to the small envelope mass. The predicted abundance distribution, in particular the amount of the \ni~ mixing, is compared with those required in the theoretical light curves and the late time optical spectra. This enables us to specify the progenitor of SN 1993J in some detail., Comment: 20 pages, LaTeX (AASTeX), to appear in ApJ