23,609 research outputs found
Power Spectrum Sensitivity and the Design of Epoch of Reionization Observatories
Recent theoretical developments for observing the Epoch of Reionization (EOR)
have concentrated on the power spectrum signature of redshifted 21 cm emission.
These studies have demonstrated the great potential of statistical EOR
observations, however, the sensitivity calculations for proposed low frequency
radio arrays have been highly approximate. The formalism developed for
interferometric measurements of the cosmic microwave background can be extended
to three dimensions to naturally incorporate the line-of-sight information
inherent in the EOR signal. In this paper we demonstrate how to accurately
calculate the EOR power spectrum sensitivity of an array, and develop scaling
relationships which can be used to guide the design of EOR observatories. The
implications for antenna distribution, antenna size, and correlator
requirements on the EOR sensitivity are detailed.Comment: 7 pages, 3 figures, submitted to Ap
Wilson Loops and Chiral Correlators on Squashed Sphere
We study chiral deformations of and supersymmetric
gauge theories obtained by turning on
interactions with the superfield. Using localization, we
compute the deformed gauge theory partition function and the
expectation value of circular Wilson loops on a squashed four-sphere. In
the case of the deformed theory, exact formulas for and
are derived in terms of an underlying interacting matrix model replacing
the free Gaussian model describing the theory. Using the AGT
correspondence, the -deformations are related to the insertions of
commuting integrals of motion in the four-point CFT correlator and chiral
correlators are expressed as -derivatives of the gauge theory partition
function on a finite -background. In the so called Nekrasov-Shatashvili
limit, the entire ring of chiral relations is extracted from the
-deformed Seiberg-Witten curve. As a byproduct of our analysis we
show that gauge theories on rational -backgrounds are dual to
CFT minimal models.Comment: 33 pages, 2 figure, in this version we have added two new references
and a detailed comparison with the results obtained in one of these tw
Technological Progress and the Distribution of Productivities across Sectors
This paper studies the impact of the process of technological change on the distribution of productivities and profits across sectors. We find that if technological progress affects high-tech and traditional sectors differently, the impact of changes in the determinants of economic growth may differ depending on which is the actual change. When an economy is growing faster due to an increase in the productivity of research or to a reduction of the taxes on capital accumulation, inequality will decrease. However, if faster growth is due to the presence of tax incentives to high technology sectors or to structural changes that allow a better absorption of externalities, inequality will increase.
Bubbling AdS3
In the light of the recent Lin, Lunin, Maldacena (LLM) results we investigate
1/2-BPS geometries in minimal (and next-to minimal) supergravity in D=6
dimensions. In the case of minimal supergravity, solutions are given by
fibrations of a two-torus T^2 specified by two harmonic functions. For a
rectangular torus the two functions are related by a non-linear equation with
rare solutions: AdS_3x S^3, the pp-wave and the multi-center string.
``Bubbling'', i.e. superpositions of droplets, is accommodated by allowing the
complex structure of the T^2 to vary over the base. The analysis is repeated in
the presence of a tensor multiplet and similar conclusions are reached with
generic solutions describing D1D5 (or their dual fundamental string-momentum)
systems. In this framework, the profile of the dual fundamental string-momentum
system is identified with the boundaries of the droplets in a two-dimensional
plane.Comment: 20 pages, 4 figures. v3: Minor corrections in section 2.
RG-flows and Open/Closed String Duality
We discuss the interpaly between IR and UV divergences in theories with open
and unoriented strings in view of the AdS/CFT correspondence. We start by
deriving general formulas for the computation of threshold corrections to gauge
couplings in generic configurations with open and unoriented strings. These
allow us to discuss the IR/UV correspondence between beta-function coefficients
and ``dilaton'' tadpoles for several brane configurations probed by D3-branes.
Finally we comment on the AdS supergravity descriptions of gauge theories that
are (super)conformal in the large N limit.Comment: Minor corrections. References added. Version to be published in
JHEP08(2000)035. 22 pages, Late
Anomalies & Tadpoles
We show that massless RR tadpoles in vacuum configurations with open and
unoriented strings are always related to anomalies. RR tadpoles arising from
sectors of the internal SCFT with non-vanishing Witten index are in one-to-one
correspondence with conventional irreducible anomalies. The anomalous content
of the remaining RR tadpoles can be disclosed by considering anomalous
amplitudes with higher numbers of external legs. We then provide an explicit
parametrization of the anomaly polynomial in terms of the boundary reflection
coefficients, i.e. one-point functions of massless RR fields on the disk. After
factorization of the reducible anomaly, we extract the relevant WZ couplings in
the effective lagrangians.Comment: 20 pages, Late
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