9,264 research outputs found
Chiral-Odd and Spin-Dependent Quark Fragmentation Functions and their Applications
We define a number of quark fragmentation functions for spin-0, -1/2 and -1
hadrons, and classify them according to their twist, spin and chirality. As an
example of their applications, we use them to analyze semi-inclusive
deep-inelastic scattering on a transversely polarized nucleon.Comment: 19 pages in Plain TeX, MIT CTP #221
CMB Likelihood Functions for Beginners and Experts
Although the broad outlines of the appropriate pipeline for cosmological
likelihood analysis with CMB data has been known for several years, only
recently have we had to contend with the full, large-scale, computationally
challenging problem involving both highly-correlated noise and extremely large
datasets (). In this talk we concentrate on the beginning and end of
this process. First, we discuss estimating the noise covariance from the data
itself in a rigorous and unbiased way; this is essentially an iterated
minimum-variance mapmaking approach. We also discuss the unbiased determination
of cosmological parameters from estimates of the power spectrum or experimental
bandpowers.Comment: Long-delayed submission. In AIP Conference Proceedings "3K Cosmology"
held in Rome, Oct 5-10, 1998, edited by Luciano Maiani, Francesco Melchiorri
and Nicola Vittorio, 343-347, New York, American Institute of Physics 199
Streaming velocities as a dynamical estimator of Omega
It is well known that estimating the pairwise velocity of galaxies, v_{12},
from the redshift space galaxy correlation function is difficult because this
method is highly sensitive to the assumed model of the pairwise velocity
dispersion. Here we propose an alternative method to estimate v_{12} directly
from peculiar velocity samples, which contain redshift-independent distances as
well as galaxy redshifts. In contrast to other dynamical measures which
determine beta = sigma_8 x Omega^{0.6}, our method can provide an estimate of
(sigma_8)^2 x Omega^{0.6} for a range of sigma_8 (here Omega is the
cosmological mass density parameter while sigma_8 is the standard normalization
parameter for the spectrum of matter density fluctuations). We demonstrate how
to measure this quantity from realistic catalogues.Comment: 8 pages of text, 4 figures Subject headings: Cosmology: theory -
observation - peculiar velocities: large scale flows Last name of one of the
authors was misspelled. It is now corrected. Otherwise the manuscript is
identical to its original versio
Evidence for a low-density Universe from the relative velocities of galaxies
The motions of galaxies can be used to constrain the cosmological density
parameter Omega and the clustering amplitude of matter on large scales. The
mean relative velocity of galaxy pairs, estimated from the Mark III survey,
indicates that Omega = 0.35 +0.35/-0.25. If the clustering of galaxies is
unbiased on large scales, Omega = 0.35 +/- 0.15, so that an unbiased
Einstein-de Sitter model (Omega = 1) is inconsistent with the data.Comment: 12 pages, 2 figures, to appear in the Jan.7 issue of ``Science''; In
the original version, the title appeared twice. This problem has now been
corrected. No other changes were mad
Measuring Omega with Galaxy Streaming Velocities
The mean pairwise velocity of galaxies has traditionally been estimated from
the redshift space galaxy correlation function. This method is notorious for
being highly sensitive to the assumed model of the pairwise velocity
dispersion. Here we propose an alternative method to estimate the streaming
velocity directly from peculiar velocity samples, which contain
redshift-independent distances as well as galaxy redshifts. This method can
provide an estimate of for a range of where
is the cosmological density parameter, while is the
standard normalization for the power spectrum of density fluctuations. We
demonstrate how to measure this quantity from realistic catalogues and identify
the main sources of bias and errorsComment: Proceedings of New Worlds in Astroparticle Physics, 6 pages, 2
figure
Simultaneous Estimation of Noise and Signal in Cosmic Microwave Background Experiments
To correctly analyse data sets from current microwave detection technology, one is forced to estimate the sky signal and experimental noise simultaneously. Given a time-ordered data set we propose a formalism and method for estimating the signal and associated errors without prior knowledge of the noise power spectrum. We derive the method using a Bayesian formalism and relate it to the standard methods; in particular we show how this leads to a change in the estimate of the noise covariance matrix of the sky signal. We study the convergence and accuracy of the method on two mock observational strategies and discuss its application to a currently-favoured calibration procedure
The Drell-Yan process and Deep Inelastic Scattering from the lattice
We report on measurements of the h_1 structure function, relevant to
calculating cross-sections for the Drell-Yan process. This is a quantity which
can not be measured in Deep Inelastic Scattering, it gives additional
information on the spin carried by the valence quarks, as well as insights on
how relativistic the quarks are.Comment: 3 pages, Latex, 3 figures, espcrc2.sty included, Talk presented at
LATTICE96(phenomenology
Emergent Chiral Symmetry: Parity and Time Reversal Doubles
There are numerous examples of approximately degenerate states of opposite
parity in molecular physics. Theory indicates that these doubles can occur in
molecules that are reflection-asymmetric. Such parity doubles occur in nuclear
physics as well, among nuclei with odd A 219-229. We have also suggested
elsewhere that such doubles occur in particle physics for baryons made up of
`cbu' and `cbd' quarks. In this article, we discuss the theoretical foundations
of these doubles in detail, demonstrating their emergence as a surprisingly
subtle consequence of the Born-Oppenheimer approximation, and emphasizing their
bundle-theoretic and topological underpinnings. Starting with certain ``low
energy'' effective theories in which classical symmetries like parity and time
reversal are anomalously broken on quantization, we show how these symmetries
can be restored by judicious inclusion of ``high-energy'' degrees of freedom.
This mechanism of restoring the symmetry naturally leads to the aforementioned
doublet structure. A novel by-product of this mechanism is the emergence of an
approximate symmetry (corresponding to the approximate degeneracy of the
doubles) at low energies which is not evident in the full Hamiltonian. We also
discuss the implications of this mechanism for Skyrmion physics, monopoles,
anomalies and quantum gravity.Comment: 32 pages, latex. minor changes in presentation and reference
Attractive Casimir Forces in a Closed Geometry
We study the Casimir force acting on a conducting piston with arbitrary cross
section. We find the exact solution for a rectangular cross section and the
first three terms in the asymptotic expansion for small height to width ratio
when the cross section is arbitrary. Though weakened by the presence of the
walls, the Casimir force turns out to be always attractive. Claims of repulsive
Casimir forces for related configurations, like the cube, are invalidated by
cutoff dependence.Comment: An updated version to coincide with the one published December 2005
in PRL. 4 pages, 2 figure
Power-law weighted networks from local attachments
This letter introduces a mechanism for constructing, through a process of
distributed decision-making, substrates for the study of collective dynamics on
extended power-law weighted networks with both a desired scaling exponent and a
fixed clustering coefficient. The analytical results show that the connectivity
distribution converges to the scaling behavior often found in social and
engineering systems. To illustrate the approach of the proposed framework we
generate network substrates that resemble steady state properties of the
empirical citation distributions of (i) publications indexed by the Institute
for Scientific Information from 1981 to 1997; (ii) patents granted by the U.S.
Patent and Trademark Office from 1975 to 1999; and (iii) opinions written by
the Supreme Court and the cases they cite from 1754 to 2002.Comment: 18 pages, 3 figures; Proceedings of the IEEE Conference on Decision
and Control and the European Control Conference, Orlando, FL, Dec. 2011;
Added references; We modified the model in order to take into account
extended power-law distributions which better fit to the citations data sets;
Added proofs of theorems; Shorten version; Updated plo
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