8,865 research outputs found
The Five-Loop Four-Point Amplitude of N=4 super-Yang-Mills Theory
Using the method of maximal cuts, we construct the complete D-dimensional
integrand of the five-loop four-point amplitude of N = 4 super-Yang-Mills
theory, including nonplanar contributions. In the critical dimension where this
amplitude becomes ultraviolet divergent, we present a compact explicit
expression for the nonvanishing ultraviolet divergence in terms of three vacuum
integrals. This construction provides a crucial step towards obtaining the
corresponding amplitude of N = 8 supergravity useful for resolving the general
ultraviolet behavior of supergravity theories.Comment: 5 pages, 4 figures, RevTex. Ancillary file included. v2 minor
corrections, corrected references and overall phase in eq. (5), matching
journal versio
Galaxy clustering with photometric surveys using PDF redshift information
Photometric surveys produce large-area maps of the galaxy distribution, but
with less accurate redshift information than is obtained from spectroscopic
methods. Modern photometric redshift (photo-z) algorithms use galaxy
magnitudes, or colors, that are obtained through multi-band imaging to produce
a probability density function (PDF) for each galaxy in the map. We used
simulated data to study the effect of using different photo-z estimators to
assign galaxies to redshift bins in order to compare their effects on angular
clustering and galaxy bias measurements. We found that if we use the entire
PDF, rather than a single-point (mean or mode) estimate, the deviations are
less biased, especially when using narrow redshift bins. When the redshift bin
widths are , the use of the entire PDF reduces the typical
measurement bias from 5%, when using single point estimates, to 3%.Comment: Matches the MNRAS published version. 19 pages, 19 Figure
Consumption and habits : evidence from panel data
The purpose of this paper is to test for the presence of habit formation in consumption decisions using household panel data. We use the test proposed by Meghir and Weber (1996) and estimate the within -period marginal rate of substitution between commodities, which is robust to the presence of liquidity constraints. To that end, we use a Spanish panel data set in which households are observed up to eight consecutive quarters. This temporal dimension is crucial, since it allows us to take into account time invariant unobserved heterogeneity across households ("fixed effects") and, therefore, to investigate if the relationship between current and past consumption reflects habits or heterogeneity. Our results conf irm the importance of accounting for fixed effects when analyzing intertemporal consumption decisions allowing for time non-separabilities. Once fixed effects are controlled for and a proper set of instruments is used, the results yield supporting evidence of habit formation in the demand system of food at home, transport and services
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