9,916 research outputs found
Chiral Gauge Theory on Lattice with Domain Wall Fermions
We investigate a U(1) lattice chiral gauge theory with domain wall fermions
and compact gauge fixing. In the reduced model limit, our perturbative and
numerical investigations show that there exist no extra mirror chiral modes.
The longitudinal gauge degrees of freedom have no effect on the free domain
wall fermion spectrum consisting of opposite chiral modes at the domain wall
and at the anti-domain wall which have an exponentially damped overlap.Comment: 16 pages revtex, 5 postscript figures, PRD versio
The Phase Diagram and Spectrum of Gauge-Fixed Abelian Lattice Gauge Theory
We consider a lattice discretization of a covariantly gauge-fixed abelian
gauge theory. The gauge fixing is part of the action defining the theory, and
we study the phase diagram in detail. As there is no BRST symmetry on the
lattice, counterterms are needed, and we construct those explicitly. We show
that the proper adjustment of these counterterms drives the theory to a new
type of phase transition, at which we recover a continuum theory of (free)
photons. We present both numerical and (one-loop) perturbative results, and
show that they are in good agreement near this phase transition. Since
perturbation theory plays an important role, it is important to choose a
discretization of the gauge-fixing action such that lattice perturbation theory
is valid. Indeed, we find numerical evidence that lattice actions not
satisfying this requirement do not lead to the desired continuum limit. While
we do not consider fermions here, we argue that our results, in combination
with previous work, provide very strong evidence that this new phase transition
can be used to define abelian lattice chiral gauge theories.Comment: 42 pages, 30 figure
Effects of CMB temperature uncertainties on cosmological parameter estimation
We estimate the effect of the experimental uncertainty in the measurement of
the temperature of the cosmic microwave background (CMB) on the extraction of
cosmological parameters from future CMB surveys. We find that even for an ideal
experiment limited only by cosmic variance up to l = 2500 for both the
temperature and polarisation measurements, the projected cosmological parameter
errors are remarkably robust against the uncertainty of 1 mK in the FIRAS
instrument's CMB temperature monopole measurement. The maximum degradation in
sensitivity is 20%, for the baryon density estimate, relative to the case in
which the monopole is known infinitely well. While this degradation is
acceptable, we note that reducing the uncertainty in the current temperature
measurement by a factor of five will bring it down to the per cent level. We
also estimate the effect of the uncertainty in the dipole temperature
measurement. Assuming the overall calibration of the data to be dominated by
the dipole error of 0.2% from FIRAS, the sensitivity degradation is
insignificant and does not exceed 10% in any parameter direction.Comment: 12 pages, 2 figures, uses iopart.cls, v2: added discussion of CMB
dipole uncertainty, version accepted by JCA
Active motions of Brownian particles in a generalized energy-depot model
We present a generalized energy-depot model in which the conversion rate of
the internal energy into motion can be dependent on the position and the
velocity of a particle. When the conversion rate is a general function of the
velocity, the active particle exhibits diverse patterns of motion including a
braking mechanism and a stepping motion. The phase trajectories of the motion
are investigated in a systematic way. With a particular form of the conversion
rate dependent on the position and velocity, the particle shows a spontaneous
oscillation characterizing a negative stiffness. These types of active
behaviors are compared with the similar phenomena observed in biology such as
the stepping motion of molecular motors and the amplification in hearing
mechanism. Hence, our model can provide a generic understanding of the active
motion related to the energy conversion and also a new control mechanism for
nano-robots. We also investigate the noise effect, especially on the stepping
motion and observe the random walk-like behavior as expected.Comment: to appear in New J. Phy
Chiral Fermions on the Lattice through Gauge Fixing -- Perturbation Theory
We study the gauge-fixing approach to the construction of lattice chiral
gauge theories in one-loop weak-coupling perturbation theory. We show how
infrared properties of the gauge degrees of freedom determine the nature of the
continuous phase transition at which we take the continuum limit. The fermion
self-energy and the vacuum polarization are calculated, and confirm that, in
the abelian case, this approach can be used to put chiral gauge theories on the
lattice in four dimensions. We comment on the generalization to the nonabelian
case.Comment: 31 pages, 5 figures, two refs. adde
The first VLBI image of an Infrared-Faint Radio Source
Context: To investigate the joint evolution of active galactic nuclei and
star formation in the Universe. Aims: In the 1.4 GHz survey with the Australia
Telescope Compact Array of the Chandra Deep Field South and the European Large
Area ISO Survey - S1 we have identified a class of objects which are strong in
the radio but have no detectable infrared and optical counterparts. This class
has been called Infrared-Faint Radio Sources, or IFRS. 53 sources out of 2002
have been classified as IFRS. It is not known what these objects are. Methods:
To address the many possible explanations as to what the nature of these
objects is we have observed four sources with the Australian Long Baseline
Array. Results: We have detected and imaged one of the four sources observed.
Assuming that the source is at a high redshift, we find its properties in
agreement with properties of Compact Steep Spectrum sources. However, due to
the lack of optical and infrared data the constraints are not particularly
strong.Comment: Accepted for publication in Astronomy and Astrophysics, 5 pages,
needs aa.cl
Improving Phase Change Memory Performance with Data Content Aware Access
A prominent characteristic of write operation in Phase-Change Memory (PCM) is
that its latency and energy are sensitive to the data to be written as well as
the content that is overwritten. We observe that overwriting unknown memory
content can incur significantly higher latency and energy compared to
overwriting known all-zeros or all-ones content. This is because all-zeros or
all-ones content is overwritten by programming the PCM cells only in one
direction, i.e., using either SET or RESET operations, not both. In this paper,
we propose data content aware PCM writes (DATACON), a new mechanism that
reduces the latency and energy of PCM writes by redirecting these requests to
overwrite memory locations containing all-zeros or all-ones. DATACON operates
in three steps. First, it estimates how much a PCM write access would benefit
from overwriting known content (e.g., all-zeros, or all-ones) by
comprehensively considering the number of set bits in the data to be written,
and the energy-latency trade-offs for SET and RESET operations in PCM. Second,
it translates the write address to a physical address within memory that
contains the best type of content to overwrite, and records this translation in
a table for future accesses. We exploit data access locality in workloads to
minimize the address translation overhead. Third, it re-initializes unused
memory locations with known all-zeros or all-ones content in a manner that does
not interfere with regular read and write accesses. DATACON overwrites unknown
content only when it is absolutely necessary to do so. We evaluate DATACON with
workloads from state-of-the-art machine learning applications, SPEC CPU2017,
and NAS Parallel Benchmarks. Results demonstrate that DATACON significantly
improves system performance and memory system energy consumption compared to
the best of performance-oriented state-of-the-art techniques.Comment: 18 pages, 21 figures, accepted at ACM SIGPLAN International Symposium
on Memory Management (ISMM
A further study of the possible scaling region of lattice chiral fermions
In the possible scaling region for an SU(2) lattice chiral fermion advocated
in {\it Nucl. Phys.} B486 (1997) 282, no hard spontaneous symmetry breaking
occurs and doublers are gauge-invariantly decoupled via mixing with composite
three-fermion-states that are formed by local multifermion interactions.
However the strong coupling expansion breaks down due to no ``static limit''
for the low-energy limit (). In both neutral and charged channels, we
further analyze relevant truncated Green functions of three-fermion-operators
by the strong coupling expansion and analytical continuation of these Green
functions in the momentum space. It is shown that in the low-energy limit,
these relevant truncated Green functions of three-fermion-states with the
``wrong'' chiralities positively vanish due to the generalized form factors
(the wave-function renormalizations) of these composite three-fermion-states
vanishing as O((pa)^4) for . This strongly implies that the composite
three-fermion-states with ``wrong'' chirality are ``decoupled'' in this limit
and the low-energy spectrum is chiral, as a consequence, chiral gauge
symmetries can be exactly preserved.Comment: A few typing-errors, in particular in Eq.50, have been correcte
Full QCD simulation on CP-PACS
A status report is made of an on-going full QCD study on the CP-PACS aiming
at a comparative analysis of the effects of improving gauge and quark actions
on hadronic quantities and static quark potential. Simulations are made for
four action combinations, the plaquette or an RG-improved action for gluons and
the Wilson or SW-clover action for quarks, at -1.3GeV and
-0.9. Results demonstrate clearly that the clover
term markedly reduces discretization errors for hadron spectrum, while adding
six-link terms to the plaquette action leads to much better rotational symmetry
in the potential. These results extend experience with quenched simulations to
full QCD.Comment: Talk presented by K. Kanaya at the International Workshop on
``LATTICE QCD ON PARALLEL COMPUTERS'', 10-15 March 1997, Center for
Computational Physics, University of Tsukub
Analysis of the Fusion Hindrance in Mass-symmetric Heavy Ion Reactions
The fusion hindrance, which is also denominated by the term extra-push, is
studied on mass-symmetric systems by the use of the liquid drop model with the
two-center parameterization. Following the idea that the fusion hindrance
exists only if the liquid drop barrier (saddle point) is located at the inner
side of the contact point after overcoming the outer Coulomb barrier, the
reactions in which two barriers are overlapped with each other are determined.
It is shown that there are many systems where the fusion hindrance does not
exist for the atomic number of projectile or target nucleus , while
for , all of the mass-symmetric reactions are fusion-hindered.Comment: 6 pages, 4 figures. to be published in Sci. in China
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