513 research outputs found
Trying to understand confinement in the Schroedinger picture
We study the gauge-invariant gaussian ansatz for the vacuum wave functional
and show that it potentially possesses many desirable features of the
Yang--Mills theory, like asymptotic freedom, mass generation through the
transmutation of dimensions and a linear potential between static quarks. We
point out that these (and other) features can be studied in a systematic way by
combining perturbative and 1/n expansions. Contrary to the euclidean approach,
confinement can be easily formulated and easily built in, if not derived, in
the variational Schroedinger approach.Comment: 21 pages, 1 figure. Lecture given at the 4th St.Petersburg Winter
School in Theoretical Physics, Feb. 22-28, 199
Radio Galaxy Zoo: discovery of a poor cluster through a giant wide-angle tail radio galaxy
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2016 J. K. Banfield, H. Andernach, A. D. Kapińska, L. Rudnick, M. J. Hardcastle, G. Cotter, S. Vaughan, T. W. Jones, I. Heywood, J. D. Wing, O. I. Wong, T. Matorny, I. A. Terentev, Á. R. López-Sánchez, R. P. Norris, N. Seymour, S. S. Shabala, and K. W. Willett. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. The version of record is available on line at doi: 10.1093/mnras/stw1067We have discovered a previously unreported poor cluster of galaxies (RGZ-CL J0823.2+0333) through an unusual giant wide-angle tail radio galaxy found in the Radio Galaxy Zoo project. We obtained a spectroscopic redshift of for the E0-type host galaxy, 2MASX J08231289+0333016, leading to M and a GHz radio luminosity density of W Hz. These radio and optical luminosities are typical for wide-angle tailed radio galaxies near the borderline between Fanaroff-Riley (FR) classes I and II. The projected largest angular size of arcmin corresponds to kpc and the full length of the source along the curved jets/trails is Mpc in projection. X-ray data from the XMM-Newton archive yield an upper limit on the X-ray luminosity of the thermal emission surrounding RGZ J082312.9+033301,at erg s for assumed intra-cluster medium temperatures of keV. Our analysis of the environment surrounding RGZ J082312.9+033301 indicates that RGZ J082312.9+033301 lies within a poor cluster. The observed radio morphology suggests that (a) the host galaxy is moving at a significant velocity with respect to an ambient medium like that of at least a poor cluster, and that (b) the source may have had two ignition events of the active galactic nucleus with yrs in between. This reinforces the idea that an association between RGZ J082312.9+033301, and the newly discovered poor cluster exists.Peer reviewe
Study of below 1 GeV using Integral Equation Approach
The scattering of is studied using the axial
anomaly, elastic unitarity, analyticity and crossing symmetry. Using the
technique to derive the Roy's equation, an integral equation for the P-wave
amplitude is obtained in terms of the strong P-wave pion pion phase shifts. Its
solution is obtained numerically by an iteration procedure using the starting
point as the solution of the integral equation of the Muskelshsvilli-Omnes
type. It is, however, ambiguous and depends sensitively on the second
derivative of the P-wave amplitude at which cannot directly be
measured.Comment: 26 pages, 10 figure
BG Ind: the nearest doubly eclipsing, compact hierarchical quadruple system
BG Ind is a well-studied, bright, nearby binary consisting of a pair of F stars in a 1.46-d orbit. We have discovered in the TESS light curve for TIC 229804573 (aka BG Ind), a second eclipsing binary in the system with a 0.53-d period. Our subsequent analyses of the recent TESS and archival ground-based photometric and radial velocity (RV) data reveal that the two binaries are gravitationally bound in a 721-d period, moderately eccentric orbit. We present the results of a joint spectro-photodynamical analysis of the eclipse timing variation curves of both binaries based on TESS and ground-based archival data, the TESS light curve, archival RV data, and the spectral energy distribution, coupled with the use of PARSEC stellar isochrones. We confirm prior studies of BG Ind that found that the brighter binary A consists of slightly evolved F-type stars with refined masses of 1.32 and 1.43 M-circle dot, and radii of 1.59 and 2.34 R-circle dot. The previously unknown binary B has two less massive stars of 0.69 and 0.64 M-circle dot and radii of 0.64 and 0.61 R-circle dot. Based on a number of different arguments that we discuss, we conclude that the three orbital planes are likely aligned to within 17 degrees
Measurement of the pi^+ meson polarizabilities via the gamma p->gamma pi^+ n reaction
An experiment on the radiative pi^+ meson photoproduction from the proton
(gamma p->gamma pi^+ n) was carried out at the Mainz Microtron MAMI in the
kinematic region 537 MeV <E_{gamma}<817 MeV,
140^o<theta_{gamma-gamma'}^cm<180^o. The pi^+ meson polarizabilities have been
determined from a comparison of the data with the predictions of two different
theoretical models, the first one being based on an effective pole model with
pseudoscalar coupling while the second one is based on diagrams describing both
resonant and nonresonant contributions. The validity of the models has been
verified by comparing the predictions with the present experimental data in the
kinematic region where the pion polarizability contribution is negligible
(s_1<5 mu^2) and where the difference between the predictions of the two models
does not exceed 3%. In the region, where the pion polarizability contribution
is substantial (5<s_1/mu^2<15, -12<t/mu^2<-2), the difference
(alpha-beta)_{pi^+} of the electric (alpha) and the magnetic (beta)
polarizabilities has been determined. As a result we find:
(alpha-beta)_{pi^+}=(11.6\pm 1.5_{stat}\pm 3.0_{syst}\pm 0.5_{mod})x10^-4fm^3.
This result is at variance with recent calculations in the framework of chiral
perturbation theory.Comment: 34 pages, 12 figures, final version to appear in Eur. Phys. J. A;
typos have been correcte
The Random Transiter - EPIC 249706694/HD 139139
We have identified a star, EPIC 249706694 (HD 139139), that was observed
during K2 Campaign 15 with the Kepler extended mission that appears to exhibit
28 transit-like events over the course of the 87-day observation. The unusual
aspect of these dips, all but two of which have depths of ppm, is
that they exhibit no periodicity, and their arrival times could just as well
have been produced by a random number generator. We show that no more than four
of the events can be part of a periodic sequence. We have done a number of data
quality tests to ascertain that these dips are of astrophysical origin, and
while we cannot be absolutely certain that this is so, they have all the
hallmarks of astrophysical variability on one of two possible host stars (a
likely bound pair) in the photometric aperture. We explore a number of ideas
for the origin of these dips, including actual planet transits due to multiple
or dust emitting planets, anomalously large TTVs, S- and P-type transits in
binary systems, a collection of dust-emitting asteroids, `dipper-star'
activity, and short-lived starspots. All transit scenarios that we have been
able to conjure up appear to fail, while the intrinsic stellar variability
hypothesis would be novel and untested.Comment: 12 pages, 6 figures, and 7 tables; Accepted for publication in MNRA
The LOFAR Two-Metre Sky Survey (LoTSS): VI. Optical identifications for the second data release
The second data release of the LOFAR Two-Metre Sky Survey (LoTSS) covers 27%
of the northern sky, with a total area of deg. The high
angular resolution of LOFAR with Dutch baselines (6 arcsec) allows us to carry
out optical identifications of a large fraction of the detected radio sources
without further radio followup; however, the process is made more challenging
by the many extended radio sources found in LOFAR images as a result of its
excellent sensitivity to extended structure. In this paper we present source
associations and identifications for sources in the second data release based
on optical and near-infrared data, using a combination of a likelihood-ratio
cross-match method developed for our first data release, our citizen science
project Radio Galaxy Zoo: LOFAR, and new approaches to algorithmic optical
identification, together with extensive visual inspection by astronomers. We
also present spectroscopic or photometric redshifts for a large fraction of the
optical identifications. In total 4,116,934 radio sources lie in the area with
good optical data, of which 85% have an optical or infrared identification and
58% have a good redshift estimate. We demonstrate the quality of the dataset by
comparing it with earlier optically identified radio surveys. This is by far
the largest ever optically identified radio catalogue, and will permit robust
statistical studies of star-forming and radio-loud active galaxies.Comment: 29 pages. Accepted by A&A; data products available at
https://lofar-surveys.org/dr2_release.htm
TIC 168789840: A Sextuply Eclipsing Sextuple Star System
We report the discovery of a sextuply eclipsing sextuple star system from TESS data, TIC 168789840, also known as TYC 7037-89-1, the first known sextuple system consisting of three eclipsing binaries. The target was observed in Sectors 4 and 5 during Cycle 1, with lightcurves extracted from TESS Full Frame Image data. It was also previously observed by the WASP survey and ASAS-SN. The system consists of three gravitationally bound eclipsing binaries in a hierarchical structure of an inner quadruple system with an outer binary subsystem. Follow-up observations from several different observatories were conducted as a means of determining additional parameters. The system was resolved by speckle interferometry with a 0farcs42 separation between the inner quadruple and outer binary, inferring an estimated outer period of ~2 kyr. It was determined that the fainter of the two resolved components is an 8.217 day eclipsing binary, which orbits the inner quadruple that contains two eclipsing binaries with periods of 1.570 days and 1.306 days. Markov Chain Monte Carlo (MCMC) analysis of the stellar parameters has shown that the three binaries of TIC 168789840 are triplets, as each binary is quite similar to the others in terms of mass, radius, and Teff. As a consequence of its rare composition, structure, and orientation, this object can provide important new insight into the formation, dynamics, and evolution of multiple star systems. Future observations could reveal if the intermediate and outer orbital planes are all aligned with the planes of the three inner eclipsing binaries
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