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The Overlap-Dirac Operator: Topology and Chiral Symmetry Breaking
We review the spectral flow techniques for computing the index of the overlap Dirac operator including results relevant for SUSY Yang-Mills theories. We describe properties of the overlap Dirac operator, and methods to implement it numerically. We use the results from the spectral flow to illuminate the difficulties in numerical calculations involving domain wall and overlap fermions
Noncompact chiral U(1) gauge theories on the lattice
A new, adiabatic phase choice is adopted for the overlap in the case of an
infinite volume, noncompact abelian chiral gauge theory. This gauge choice
obeys the same symmetries as the Brillouin-Wigner (BW) phase choice, and, in
addition, produces a Wess-Zumino functional that is linear in the gauge
variables on the lattice. As a result, there are no gauge violations on the
trivial orbit in all theories, consistent and covariant anomalies are simply
related and Berry's curvature now appears as a Schwinger term. The adiabatic
phase choice can be further improved to produce a perfect phase choice, with a
lattice Wess-Zumino functional that is just as simple as the one in continuum.
When perturbative anomalies cancel, gauge invariance in the fermionic sector is
fully restored. The lattice effective action describing an anomalous abelian
gauge theory has an explicit form, close to one analyzed in the past in a
perturbative continuum framework.Comment: 35 pages, one figure, plain TeX; minor typos corrected; to appear in
PR
Globalization and pollution: tele-connecting local primary PM2.5 emissions to global consumption
Globalization pushes production and consumption to geographically diverse locations and generates a variety of sizeable opportunities and challenges. The distribution and associated effects of short-lived primary fine particulate matter (PM2.5), a representative of local pollution, are significantly affected by the consumption through global supply chain. Tele-connection is used here to represent the link between production and consumption activity at large distances. In this study, we develop a global consumption-based primary PM2.5 emission inventory to track primary PM2.5 emissions embodied in the supply chain and evaluate the extent to which local PM2.5 emissions are triggered by international trade. We further adopt consumption-based accounting and identify the global original source that produced the emissions. We find that anthropogenic PM2.5 emissions from industrial sectors accounted for 24 Tg globally in 2007; approximately 30% (7.2 Tg) of these emissions were embodied in export of products principally from Brazil, South Africa, India and China (3.8 Tg) to developed countries. Large differences (up to 10 times) in the embodied emissions intensity between net importers and exporters greatly increased total global PM2.5 emissions. Tele-connecting production and consumption activity provides valuable insights with respect to mitigating long-range transboundary air pollution and prompts concerted efforts aiming at more environmentally conscious globalization
Super Yang-Mills on the lattice with domain wall fermions
The dynamical N=1, SU(2) Super Yang-Mills theory is studied on the lattice
using a new lattice fermion regulator, domain wall fermions. This formulation
even at non-zero lattice spacing does not require fine-tuning, has improved
chiral properties and can produce topological zero-mode phenomena. Numerical
simulations of the full theory on lattices with the topology of a torus
indicate the formation of a gluino condensate which is sustained at the chiral
limit. The condensate is non-zero even for small volume and small supersymmetry
breaking mass where zero mode effects due to gauge fields with fractional
topological charge appear to play a role.Comment: LaTeX, 35 pages, 11 eps figures. A few changes in sec. 5.3, figure 11
added. To appear in Phys. Rev.
Topology and chiral symmetry breaking in SU(N) gauge theories
We study the low-lying eigenmodes of the lattice overlap Dirac operator for
SU(N) gauge theories with N=2,3,4 and 5 colours. We define a fermionic
topological charge from the zero-modes of this operator and show that, as N
grows, any disagreement with the topological charge obtained by cooling the
fields, becomes rapidly less likely. By examining the fields where there is a
disagreement, we are able to show that the Dirac operator does not resolve
instantons below a critical size of about rho = 2.5 a, but resolves the larger,
more physical instantons. We investigate the local chirality of the near-zero
modes and how it changes as we go to larger N. We observe that the local
chirality of these modes, which is prominent for SU(2) and SU(3), becomes
rapidly weaker for larger N and is consistent with disappearing entirely in the
limit of N -> infinity. We find that this is not due to the observed
disappearance of small instantons at larger N.Comment: 41 pages, 12 figures, RevTe
Relationship between electrophilicity index, Hammett constant and nucleus-independent chemical shift
Inter-relationships between the electrophilicity index (Ω), Hammett constant (óp @#@) and nucleusindependent chemical shift (NICS (1) - NICS value one ångstrom above the ring centre) have been investigated for a series of meta- and para-substituted benzoic acids. Good linear relationships between Hammett constant vs electrophilicity and Hammett constant vs NICS (1) values have been observed. However, the variation of NICS (1) against CO shows only a low correlation coefficient
Dimensional Reduction of Fermions in Brane Worlds of the Gross-Neveu Model
We study the dimensional reduction of fermions, both in the symmetric and in
the broken phase of the 3-d Gross-Neveu model at large N. In particular, in the
broken phase we construct an exact solution for a stable brane world consisting
of a domain wall and an anti-wall. A left-handed 2-d fermion localized on the
domain wall and a right-handed fermion localized on the anti-wall communicate
with each other through the 3-d bulk. In this way they are bound together to
form a Dirac fermion of mass m. As a consequence of asymptotic freedom of the
2-d Gross-Neveu model, the 2-d correlation length \xi = 1/m increases
exponentially with the brane separation. Hence, from the low-energy point of
view of a 2-d observer, the separation of the branes appears very small and the
world becomes indistinguishable from a 2-d space-time. Our toy model provides a
mechanism for brane stabilization: branes made of fermions may be stable due to
their baryon asymmetry. Ironically, our brane world is stable only if it has an
extreme baryon asymmetry with all states in this ``world'' being completely
filled.Comment: 26 pages, 7 figure
Gauging the mass of metals in the gas phase of galaxies from the Local Universe to the Epoch of Reionization
The chemical enrichment of dust and metals are vital processes in
constraining the star formation history of the universe. Previously, the dust
masses of high-redshift star-forming galaxies have been determined through
their far-infrared continuum, however, equivalent, and potentially simpler,
approaches to determining the metal masses have yet to be explored at . Here, we present a new method of inferring the metal mass in the
interstellar medium (ISM) of galaxies out to , using the
far-infrared [CII]m emission line as a proxy. We calibrated the
[CII]-to- conversion factor based on a benchmark observational
sample at , in addition to gamma-ray burst sightlines at and
cosmological hydrodynamical simulations of galaxies at and
. We found a universal scaling across redshifts of with a 0.4 dex scatter,
which is constant over more than two orders of magnitude in metallicity. We
applied this scaling to recent surveys for [CII] in galaxies at
and determined the fraction of metals retained in the gas-phase ISM, , as a function of redshift showing that an increasing
fraction of metals reside in the ISM of galaxies at higher redshifts. We place
further constraints on the cosmic metal mass density in the ISM () at and , yielding () and
(). These results are consistent with the expected metal
yields from the integrated star formation history at the respective redshifts.
This suggests that the majority of metals produced at are confined
to the ISM of galaxies.Comment: Accepted in A&A, abstract abridge
First results from DesertSTAR: a 7-pixel 345-GHz heterodyne array receiver for the Heinrich Hertz Telescope
We present the first astronomical results from DesertSTAR, a 7 pixel heterodyne array receiver designed for operation in the astrophysically rich 345 GHz atmospheric window. DesertSTAR was constructed for the 10m Heinrich Hertz Telescope located at 3150m elevation on Mt. Graham, Arizona. This receiver promises to increase mapping speed at the HHT by a factor of ~15 over the facility's existing single beam, dual polarization receiver. DesertSTAR uses tunerless, single-ended waveguide SIS mixers to achieve uncorrected receiver noise temperatures of ~60K. The instantaneous bandwidth is 2 GHz, with a 5 GHz Intermediate Frequency, offering 1600 km/s of velocity coverage. Cryogenic isolators are employed between the mixers and low noise amplifiers to assure a flat IF passband. The system uses a Joule-Thompson closed-cycle refrigerator with 180W capacity at 70K and 1.8W capacity at 4K. A novel reflective phase grating is used for Local Oscillator multiplexing, while a simple Mylar beamsplitter is used as an LO diplexer. Optics include only polyethelene mixer lenses and a single, cold, flat mirror, maximizing simplicity for high efficiency and easy optical alignment. The computer controlled bias system provides low noise bias for the SIS junctions, magnets and LNAs through a modular and hardware independent GUI interface, and allows remote operation and monitoring. We present measurements of receiver noise, beam quality, efficiency and stability in addition to astronomical observations obtained during engineering runs at the HHT
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