2,518 research outputs found
Effective Superpotentials for SO/Sp with Flavor from Matrix Models
We study matrix models related to gauge theories with flavors. We
give the effective superpotentials for gauge theories with arbitrary tree level
superpotential up to first instanton level. For quartic tree level
superpotential we obtained exact one-cut solution. We also derive
Seiberg-Witten curve for these gauge theories from matrix model argument.Comment: 17pp,2 figures, v2;refs added and to appear in MPL
Oblique Ion Two-Stream Instability in the Foot Region of a Collisionless Shock
Electrostatic behavior of a collisionless plasma in the foot region of high
Mach number perpendicular shocks is investigated through the two-dimensional
linear analysis and electrostatic particle-in-cell (PIC) simulation. The
simulations are double periodic and taken as a proxy for the situation in the
foot. The linear analysis for relatively cold unmagnetized plasmas with a
reflected proton beam shows that obliquely propagating Buneman instability is
strongly excited. We also found that when the electron temperature is much
higher than the proton temperature, the most unstable mode is the highly
obliquely propagating ion two-stream instability excited through the resonance
between ion plasma oscillations of the background protons and of the beam
protons, rather than the ion acoustic instability that is dominant for parallel
propagation. To investigate nonlinear behavior of the ion two-stream
instability, we have made PIC simulations for the shock foot region in which
the initial state satisfies the Buneman instability condition. In the first
phase, electrostatic waves grow two-dimensionally by the Buneman instability to
heat electrons. In the second phase, highly oblique ion two-stream instability
grows to heat mainly ions. This result is in contrast to previous studies based
on one-dimensional simulations, for which ion acoustic instability further
heats electrons. The present result implies that overheating problem of
electrons for shocks in supernova remnants is resolved by considering ion
two-stream instability propagating highly obliquely to the shock normal and
that multi-dimensional analysis is crucial to understand the particle heating
and acceleration processes in shocks.Comment: 20 pages, 9 figures, accepted for publication in Ap
A Simple Measurement of Turbulence in Cores of Galaxy Clusters
Using a simple model, we study the effects of turbulence on the motion of
bubbles produced by AGN jet activities in the core of a galaxy cluster. We
focus on the turbulence with scales larger then the size of the bubbles. We
show that for a bubble pair with an age of ~10^8 yr, the projected angle
between the two vectors from the cluster center to the two bubbles should be ~>
90 degree and the ratio of their projected distances from the cluster center
should be ~< 2.5, if the velocity and scale of the turbulence are ~250 km s^-1
and ~20 kpc, respectively. The positions of the bubbles observed in the Perseus
cluster suggest that the turbulent velocity is ~>100 km s^-1 for the cluster.Comment: Accepted for publication in ApJ
Absence of Electron Surfing Acceleration in a Two-Dimensional Simulation
Electron acceleration in high Mach number perpendicular shocks is
investigated through two-dimensional electrostatic particle-in-cell (PIC)
simulation. We simulate the shock foot region by modeling particles that
consist of three components such as incident protons and electrons and
reflected protons in the initial state which satisfies the Buneman instability
condition. In contrast to previous one-dimensional simulations in which strong
surfing acceleration is realized, we find that surfing acceleration does not
occur in two-dimensional simulation. This is because excited electrostatic
potentials have a two-dimensional structure that makes electron trapping
impossible. Thus, the surfing acceleration does not work either in itself or as
an injection mechanism for the diffusive shock acceleration. We briefly discuss
implications of the present results on the electron heating and acceleration by
shocks in supernova remnants.Comment: 12 pages, 4 figures, accepted for publication in ApJ
Effective theories of gauge-Higgs unification models in warped spacetime
We derive four-dimensional (4D) effective theories of the gauge-Higgs
unification models in the warped spacetime. The effective action can be
expressed in a simple form by neglecting subleading corrections to the wave
functions. We have shown in our previous works that some Higgs couplings to the
other fields are suppressed by factors that depend on from the
values in the standard model. Here is the Wilson line phase
along the fifth dimension, which characterizes the electroweak symmetry
breaking. The effective action derived here explicitly shows a nonlinear
structure of the Higgs sector, which clarifies the origins of those suppression
factors.Comment: 36 pages, 1 figur
Strong Turbulence in the Cool Cores of Galaxy Clusters: Can Tsunamis Solve the Cooling Flow Problem?
Based on high-resolution two-dimensional hydrodynamic simulations, we show
that the bulk gas motions in a cluster of galaxies, which are naturally
expected during the process of hierarchical structure formation of the
universe, have a serous impact on the core. We found that the bulk gas motions
represented by acoustic-gravity waves create local but strong turbulence, which
reproduces the complicated X-ray structures recently observed in cluster cores.
Moreover, if the wave amplitude is large enough, they can suppress the
radiative cooling of the cores. Contrary to the previous studies, the heating
is operated by the turbulence, not weak shocks. The turbulence could be
detected in near-future space X-ray missions such as ASTRO-E2.Comment: Movies are available at http://th.nao.ac.jp/tsunami/index.ht
Quantitative Estimates of Environmental Effects on the Star Formation Rate of Disk Galaxies in Clusters of Galaxies
A simple model is constructed to evaluate the change of star formation rate
of a disk galaxy due to environmental effects in clusters of galaxies. Three
effects, (1) tidal force from the potential well of the cluster, (2) increase
of external pressure when the galaxy plows into the intracluster medium, (3)
high-speed encounters between galaxies, are investigated. General analysis
indicates that the star formation rate increases significantly when the
pressure of molecular clouds rises above in yr. The tidal force from the potential well of the cluster increases
pressures of molecular clouds in a disk galaxy infalling towards the cluster
center. Before the galaxy reaches the cluster center, the star formation rate
reaches a maximum. The peak is three to four times larger than the initial
value. If this is the main mechanism of the Butcher-Oemler effect, blue
galaxies are expected to be located within kpc from the center of
the cluster. However this prediction is inconsistent with the recent
observations. The increase of external pressure when the galaxy plows into the
intracluster medium does not change star formation rate of a disk galaxy
significantly. The velocity perturbation induced by a single high-speed
encounter between galaxies is too small to affect star formation rate of a disk
galaxy, while successive high-speed encounters (galaxy harassment) trigger star
formation activity because of the accumulation of gas in the galaxy center.
Therefore, the galaxy harassment remains as the candidate for a mechanism of
the Butcher-Oemler effect.Comment: 12 pages, 13 figures. To be published in Ap
Open String on Symmetric Product
We develop some basic properties of the open string on the symmetric product
which is supposed to describe the open string field theory in discrete
lightcone quantization (DLCQ). After preparing the consistency conditions of
the twisted boundary conditions for Annulus/M\"obius/Klein Bottle amplitudes in
generic non-abelian orbifold, we classify the most general solutions of the
constraints when the discrete group is . We calculate the corresponding
orbifold amplitudes from two viewpoints -- from the boundary state formalism
and from the trace over the open string Hilbert space. It is shown that the
topology of the world sheet for the short string and that of the long string in
general do not coincide. For example the annulus sector for the short string
contains all the sectors (torus, annulus, Klein bottle, M\"obius strip) of the
long strings. The boundary/cross-cap states of the short strings are classified
into three categories in terms of the long string, the ordinary boundary and
the cross-cap states, and the ``joint'' state which describes the connection of
two short strings. We show that the sum of the all possible boundary conditions
is equal to the exponential of the sum of the irreducible amplitude -- one body
amplitude of long open (closed) strings. This is typical structure of DLCQ
partition function. We examined that the tadpole cancellation condition in our
language and derived the well-known gauge group .Comment: 56 pages, 11 figures, Late
Ground state of an distorted diamond chain - model of
We study the ground state of the model Hamiltonian of the trimerized
quantum Heisenberg chain in which
the non-magnetic ground state is observed recently. This model consists of
stacked trimers and has three kinds of coupling constants between spins; the
intra-trimer coupling constant and the inter-trimer coupling constants
and . All of these constants are assumed to be antiferromagnetic. By
use of the analytical method and physical considerations, we show that there
are three phases on the plane (, ), the dimer phase, the spin fluid phase
and the ferrimagnetic phase. The dimer phase is caused by the frustration
effect. In the dimer phase, there exists the excitation gap between the
two-fold degenerate ground state and the first excited state, which explains
the non-magnetic ground state observed in . We also obtain the phase diagram on the
plane from the numerical diagonalization data for finite systems by use of the
Lanczos algorithm.Comment: LaTeX2e, 15 pages, 21 eps figures, typos corrected, slightly detailed
explanation adde
THE EFFECTS OF A MARATHON RACE ON RUNNING ECONOMY AND LEG MUSCULAR STRENGTH AND POWER
INTRODUCTION: Previous studies have reported that running economy as well as leg muscular strength and power decrease after a marathon race(Nicol et al., 1991 ; Chevrolet et al. 1993). However, the relationship between the change in running economy and the change in muscular strength and power is still unclear. Therefore, the purpose of this study was to examine the effects of a marathon race on running economy, as well as leg muscular strength and power. Relationships among race performance, decrease in running economy and decrease in leg muscular strength and power were also investigated.
METHODS: Thirteen healthy males performed treadmill running (200 m/min., 3 min.), isometric knee extension (3s), counter-movement-jump and 5-series-jumps 3-1 day(s) before (PRE) and immediately after (POST) participating in either the 1996 or 1997 "Tsukuba marathon race (42.195 km) ".
RESULTS:
1) Mean race time of the marathon was 2 hours 57 minutes 39 seconds. Average running speed during the latter half of the race was significantly lower than the former half .
2) In comparison to PRE, oxygen consumption during treadmill running in POST increased significantly while maximal strength of isometric knee extension, jumping height of counter-movement-jump and jumping height of 5-series-jumps decreased significantly .
3) There were no relationships between percent change ((Post-Pre)/Pre x 100) in oxygen consumption during treadmill running and percent change in leg muscular strength and power.
4) There was a significant correlation between percent change ((Latter- Former)/Former x 100) in running speed during the race and percent change in jumping height of counter-movement-jump (r=0.541). However, no significant relationship was observed between percent change in running speed and percent change in running economy.
CONCLUSION: Running a marathon race decreases both running economy and muscular strength and power but these seem to be caused by different mechanisms. The decrease in leg muscular strength and power during the marathon race seems have been an influence on the decrease in running speed during the latter half of the race.
REFERENCES
Chevrolet et al. (1993) Med. Sci. Sports Exerc. 25:501-507.
Nicol et al. (1991) Scand. J. Sports Med. 1:195-204
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