97 research outputs found
Chiral Dynamics of Low-Energy Kaon-Baryon Interactions with Explicit Resonance
The processes involving low energy and interactions (where
or ) are studied in the framework of heavy baryon chiral
perturbation theory with the (1405) resonance appearing as an
independent field.
The leading and next-to-leading terms in the chiral expansion are taken into
account. We show that an approach which explicitly includes the (1405)
resonance as an elementary quantum field gives reasonable descriptions of both
the threshold branching ratios and the energy dependence of total cross
sections.Comment: 16 pages, 6 figure
New silica-based low-loss optical fibre
A new type of silica-based optical fibre has been made from relatively cheap and abundant materials. The attenuation is very low over the entire range from the near ultraviolet to the gallium-arsenide-laser wavelength. The minimum loss of 2.7 dB/km occurs at 0.83µm
Measurements of spin rotation parameter A in pion-proton elastic scattering at 1.62 GeV/c
The ITEP-PNPI collaboration presents the results of the measurements of the
spin rotation parameter A in the elastic scattering of positive and negative
pions on protons at P_beam = 1.62 GeV/c. The setup included a
longitudinally-polarized proton target with superconductive magnet, multiwire
spark chambers and a carbon polarimeter with thick filter. Results are compared
to the predictions of partial wave analyses. The experiment was performed at
the ITEP proton synchrotron, Moscow.Comment: 7 pages, 3 figures. To be published in Phys. Lett.
Negative Kaons in Dense Baryonic Matter
Kaon polarization operator in dense baryonic matter of arbitrary isotopic
composition is calculated including s- and p-wave kaon-baryon interactions. The
regular part of the polarization operator is extracted from the realistic
kaon-nucleon interaction based on the chiral and 1/N_c expansion. Contributions
of the Lambda(1116), Sigma(1195), Sigma*(1385) resonances are taken explicitly
into account in the pole and regular terms with inclusion of mean-field
potentials. The baryon-baryon correlations are incorporated and fluctuation
contributions are estimated. Results are applied for K- in neutron star matter.
Within our model a second-order phase transition to the s-wave K- condensate
state occurs at rho_c \gsim 4 \rho_0 once the baryon-baryon correlations are
included. We show that the second-order phase transition to the p-wave
condensate state may occur at densities in
dependence on the parameter choice. We demonstrate that a first-order phase
transition to a proton-enriched (approximately isospin-symmetric) nucleon
matter with a p-wave K- condensate can occur at smaller densities, \rho\lsim 2
\rho_0. The transition is accompanied by the suppression of hyperon
concentrations.Comment: 41 pages, 24 figures, revtex4 styl
Cross-Correlation of the Cosmic Microwave Background with the 2MASS Galaxy Survey: Signatures of Dark Energy, Hot Gas, and Point Sources
We cross-correlate the Cosmic Microwave Background (CMB) temperature
anisotropies observed by the Wilkinson Microwave Anisotropy Probe (WMAP) with
the projected distribution of extended sources in the Two Micron All Sky Survey
(2MASS). By modelling the theoretical expectation for this signal, we extract
the signatures of dark energy (Integrated Sachs-Wolfe effect;ISW), hot gas
(thermal Sunyaev-Zeldovich effect;thermal SZ), and microwave point sources in
the cross-correlation. Our strongest signal is the thermal SZ, at the 3.1-3.7
\sigma level, which is consistent with the theoretical prediction based on
observations of X-ray clusters. We also see the ISW signal at the 2.5 \sigma
level, which is consistent with the expected value for the concordance LCDM
cosmology, and is an independent signature of the presence of dark energy in
the universe. Finally, we see the signature of microwave point sources at the
2.7 \sigma level.Comment: 35 pages (preprint format), 8 figures. In addition to minor revisions
based on referee's comments, after correcting for a bug in the code, the SZ
detection is consistent with the X-ray observations. Accepeted for
publication in Physical Review
Flavor SU(3) breaking effects in the chiral unitary model for meson-baryon scatterings
We examine flavor SU(3) breaking effects on meson-baryon scattering
amplitudes in the chiral unitary model. It turns out that the SU(3) breaking,
which appears in the leading quark mass term in the chiral expansion, can not
explain the channel dependence of the subtraction parameters of the model,
which are crucial to reproduce the observed scattering amplitudes and resonance
properties.Comment: RevTeX4, 4 pages, 3 figures, 2 table
The Five Factor Model of personality and evaluation of drug consumption risk
The problem of evaluating an individual's risk of drug consumption and misuse
is highly important. An online survey methodology was employed to collect data
including Big Five personality traits (NEO-FFI-R), impulsivity (BIS-11),
sensation seeking (ImpSS), and demographic information. The data set contained
information on the consumption of 18 central nervous system psychoactive drugs.
Correlation analysis demonstrated the existence of groups of drugs with
strongly correlated consumption patterns. Three correlation pleiades were
identified, named by the central drug in the pleiade: ecstasy, heroin, and
benzodiazepines pleiades. An exhaustive search was performed to select the most
effective subset of input features and data mining methods to classify users
and non-users for each drug and pleiad. A number of classification methods were
employed (decision tree, random forest, -nearest neighbors, linear
discriminant analysis, Gaussian mixture, probability density function
estimation, logistic regression and na{\"i}ve Bayes) and the most effective
classifier was selected for each drug. The quality of classification was
surprisingly high with sensitivity and specificity (evaluated by leave-one-out
cross-validation) being greater than 70\% for almost all classification tasks.
The best results with sensitivity and specificity being greater than 75\% were
achieved for cannabis, crack, ecstasy, legal highs, LSD, and volatile substance
abuse (VSA).Comment: Significantly extended report with 67 pages, 27 tables, 21 figure
New Physics and CP Violation in Hyperon Nonleptonic Decays
The sum of the CP-violating asymmetries A(Lambda_-^0) and A(Xi_-^-) in
hyperon nonleptonic decays is presently being measured by the E871 experiment.
We evaluate contributions to the asymmetries induced by chromomagnetic-penguin
operators, whose coefficients can be enhanced in certain models of new physics.
Incorporating recent information on the strong phases in Xi->Lambda pi decay,
we show that new-physics contributions to the two asymmetries can be
comparable. We explore how the upcoming results of E871 may constrain the
coefficients of the operators. We find that its preliminary measurement is
already better than the epsilon parameter of K-Kbar mixing in bounding the
parity-conserving contributions.Comment: 12 pages, 2 figure
How not to describe a species: lessons from a tangle of anacondas (Boidae: Eunectes Wagler, 1830)
A recent revision of the anacondas (Serpentes: Boidae: Eunectes), with the description of a new species of green anaconda, generated extensive publicity, but also provoked considerable controversy due to inadequacies of the evidence used and errors in nomenclature. We here use the case of this problematic publication to: (i) highlight common issues affecting species delimitations, especially an over-reliance on mitochondrial DNA data, and reiterate best practices; (ii) reanalyse the data available for anacondas to establish the true current state of knowledge and to highlight lines of further research; and (iii) analyse the nomenclatural history and status of the genus. While our analysis reveals significant morphological variation in both green and yellow anacondas, denser sampling and an analysis of informative nuclear markers are required for meaningful species delimitation in Eunectes. Tracing the history of name-bearing types establishes Trinidad as the type locality for Boa murina Linnaeus, 1758 and allows identification of the extant lectotype for the species. Finally, we emphasize the responsibility of both journals and authors to ensure that published taxonomic work meets the burden of evidence required to substantiate new species descriptions and that species are named in compliance with the rules of zoological nomenclature
Helicity Amplitudes of the Lambda(1670) and two Lambda(1405) as dynamically generated resonances
We determine the helicity amplitudes A_1/2 and radiative decay widths in the
transition Lambda(1670) to gamma Y (Y=Lambda or Sigma^0). The Lambda(1670) is
treated as a dynamically generated resonance in meson-baryon chiral dynamics.
We obtain the radiative decay widths of the Lambda(1670) to gamma Lambda as 3
\pm 2 keV and to gamma Sigma^0 as 120 \pm 50 keV. Also, the Q^2 dependence of
the helicity amplitudes A_1/2 is calculated. We find that the K Xi component in
the Lambda(1670) structure, mainly responsible for the dynamical generation of
this resonance, is also responsible for the significant suppression of the
decay ratio Gamma_{gamma Lambda}/Gamma_{gamma Sigma^0}. A measurement of the
ratio would, thus, provide direct access to the nature of the Lambda(1670). To
compare the result for the Lambda(1670), we calculate the helicity amplitudes
A_1/2 for the two states of the Lambda(1405). Also, the analytic continuation
of Feynman parameterized integrals of more complicated loop amplitudes to the
complex plane is developed which allows for an internally consistent evaluation
of A_1/2.Comment: 15 pages, 8 figure
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