19,998 research outputs found
Quantum imaging of spin states in optical lattices
We investigate imaging of the spatial spin distribution of atoms in optical
lattices using non-resonant light scattering. We demonstrate how scattering
spatially correlated light from the atoms can result in spin state images with
enhanced spatial resolution. Furthermore, we show how using spatially
correlated light can lead to direct measurement of the spatial correlations of
the atomic spin distribution
On higher derivative corrections to Wess-Zumino and Tachyonic actions in type II super string theory
We evaluate in detail the string scattering amplitude to compute different
interactions of two massless scalars, one tachyon and one closed string
Ramond-Ramond field in type II super string theory. In particular we find two
scalar field and two tachyon couplings to all orders of up to
on-shell ambiguity. We then obtain the momentum expansion of this amplitude and
apply this infinite number of couplings to actually check that the infinite
number of tachyon poles of S-matrix element of this amplitude for the
case (where is the spatial dimension of a D-brane and is the rank
of a Ramond-Ramond field strength) to all orders of is precisely
equal to the infinite number of tachyon poles of the field theory. In addition
to confirming the couplings of closed string Ramond-Ramond field to the
world-volume gauge field and scalar fields including commutators, we also
propose an extension of the Wess-Zumino action which naturally reproduces these
new couplings in field theory such that they could be confirmed with direct
S-matrix computations. Finally we show that the infinite number of massless
poles and contact terms of this amplitude for the case can be
reproduced by Chern-Simons, higher derivative corrections of the Wess-Zumino
and symmetrized trace tachyon DBI actions.Comment: 51 pages, some refs and comments added, typos are removed. Almost all
ambiguities in BPS and non-BPS effective actions have been addresse
An Approach to Ecosystem-Based Fishery Management
Marine scientists and policymakers are encouraging ecosystem-based fishery management (EBFM), but there is limited guidance on how to operationalize the concept. We adapt financial portfolio theory as a method for EBFM that accounts for species interdependencies, uncertainty, and sustainability constraints. Illustrating our method with routinely collected data available from the Chesapeake Bay, we demonstrate the gains from taking into account species variances and covariances in setting species total allowable catches. We find over the period from 1962–2003 that managers could have increased the revenues from fishing and reduced the variance by employing ecosystem frontiers in setting catch levels.ecosystem-based fishery management, portfolio, trophic modeling, precaution
Averaged null energy condition violation in a conformally flat spacetime
We show that the averaged null energy condition can be violated by a
conformally coupled scalar field in a conformally flat spacetime in 3+1
dimensions. The violation is dependent on the quantum state and can be made as
large as desired. It does not arise from the presence of anomalies, although
anomalous violations are also possible. Since all geodesics in conformally flat
spacetimes are achronal, the achronal averaged null energy condition is
likewise violated.Comment: 11 page
On the evolutionary behaviour of BL Lac objects
We present a new well defined sample of BL Lac objects selected from the
ROSAT All-Sky Survey (RASS). The sample consists of 39 objects with 35 forming
a flux limited sample down to f_X = 8 x 10^{-13} cgs, redshifts are known for
33 objects (and 31 of the complete sample). X-ray spectral properties were
determined for each object individually with the RASS data. The luminosity
function of RASS selected BL Lac objects is compatible with results provided by
objects selected with the Einstein observatory, but the RASS selected sample
contains objects with luminosities at least tenfold higher. Our analysis
confirms the negative evolution for X-ray selected BL Lac objects found in a
sample by the Einstein observatory, the parameterization provides similar
results. A subdivision of the sample into halves according to the X-ray to
optical flux ratio yielded unexpected results. The extremely X-ray dominated
objects have higher redshifts and X-ray luminosities and only this subgroup
shows clear signs of strong negative evolution. The evolutionary behaviour of
objects with an intermediate spectral energy distribution between X-ray and
radio dominated is compatible with no evolution at all. Consequences for
unified schemes of X-ray and radio selected BL Lac objects are discussed.We
suggest that the intermediate BL Lac objects are the basic BL Lac population.
The distinction between the two subgroups can be explained if extreme X-ray
dominated BL Lac objects are observed in a state of enhanced X-ray activity.Comment: 14 pages incl. 8 figures, accepted by A&
Reverse geometric engineering of singularities
One can geometrically engineer supersymmetric field theories theories by
placing D-branes at or near singularities. The opposite process is described,
where one can reconstruct the singularities from quiver theories. The
description is in terms of a noncommutative quiver algebra which is constructed
from the quiver diagram and the superpotential. The center of this
noncommutative algebra is a commutative algebra, which is the ring of
holomorphic functions on a variety V. If certain algebraic conditions are met,
then the reverse geometric engineering produces V as the geometry that D-branes
probe. It is also argued that the identification of V is invariant under
Seiberg dualities.Comment: 17 pages, Latex. v2: updates reference
The Physical Properties of LBGs at z>5: Outflows and the "pre-enrichment problem"
We discuss the properties of Lyman Break galaxies (LBGs) at z>5 as determined
from disparate fields covering approximately 500 sq. arcmin. While the broad
characteristics of the LBG population has been discussed extensively in the
literature, such as luminosity functions and clustering amplitude, we focus on
the detailed physical properties of the sources in this large survey (>100 with
spectroscopic redshifts). Specifically, we discuss ensemble mass estimates,
stellar mass surface densities, core phase space densities, star-formation
intensities, characteristics of their stellar populations, etc as obtained from
multi-wavelength data (rest-frame UV through optical) for a subsample of these
galaxies. In particular, we focus on evidence that these galaxies drive
vigorous outflows and speculate that this population may solve the so-called
``pre-enrichment problem''. The general picture that emerges from these studies
is that these galaxies, observed about 1 Gyr after the Big Bang, have
properties consistent with being the progenitors of the densest stellar systems
in the local Universe -- the centers of old bulges and early type galaxies.Comment: 4 pages, to appear in "Pathways Through an Eclectic Universe", J. H.
Knappen, T. J. Mahoney, and A. Vazedekis (Eds.), ASP Conf. Ser., 200
Hawking radiation, Unruh radiation and the equivalence principle
We compare the response function of an Unruh-DeWitt detector for different
space-times and different vacua and show that there is a {\it detailed}
violation of the equivalence principle. In particular comparing the response of
an accelerating detector to a detector at rest in a Schwarzschild space-time we
find that both detectors register thermal radiation, but for a given,
equivalent acceleration the fixed detector in the Schwarzschild space-time
measures a higher temperature. This allows one to locally distinguish the two
cases. As one approaches the horizon the two temperatures have the same limit
so that the equivalence principle is restored at the horizon.Comment: 9 pages. Added references and added discussion. To be published in
PR
Domain Walls on Singularities
We describe domain walls that live on and singularities. The
walls are BPS if the singularity is resolved and non--BPS if it is deformed and
fibered. We show that these domain walls may interpolate between vacua that
support monopoles and/or vortices.Comment: 16 pages in phyzzx.te
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