2,046 research outputs found
A study of point discharge current observations in the thunderstorm environment at a tropical station during the year 1987 and 1988
The results of the measurements of point discharge current observations at Pune, India, during years 1987 and 1988 are presented by categorizing and studying their number of spells, polar current average durations, and current magnitudes in day-time and night-time conditions. While the results showed that the thunderstorm activity occupies far more day-time than the night-time the level of current magnitudes remains nearly the same in the two categories
Power Counting and Perturbative One Pion Exchange in Heavy Meson Molecules
We discuss the possible power counting schemes that can be applied in the
effective field theory description of heavy meson molecules, such as the
X(3872) or the recently discovered Zb(10610) and Zb(10650) states. We argue
that the effect of coupled channels is suppressed by at least two orders in the
effective field theory expansion, meaning that they can be safely ignored at
lowest order. The role of the one pion exchange potential between the heavy
mesons, and in particular the tensor force, is also analyzed. By using
techniques developed in atomic physics for handling power-law singular
potentials, which have been also successfully employed in nuclear physics, we
determine the range of center-of-mass momenta for which the tensor piece of the
one pion exchange potential is perturbative. In this momentum range, the one
pion exchange potential can be considered a subleading order correction,
leaving at lowest order a very simple effective field theory consisting only on
contact-range interactions.Comment: 21 pages, 1 figur
The Heavy Quark Spin Symmetry Partners of the X(3872)
We explore the consequences of heavy quark spin symmetry for the charmed
meson-antimeson system in a contact-range (or pionless) effective field theory.
As a trivial consequence, we theorize the existence of a heavy quark spin
symmetry partner of the X(3872), with , which we call X(4012) in
reference to its predicted mass. If we additionally assume that the X(3915) is
a heavy spin symmetry partner of the X(3872), we end up predicting a
total of six molecular states. We also discuss the error
induced by higher order effects such as finite heavy quark mass corrections,
pion exchanges and coupled channels, allowing us to estimate the expected
theoretical uncertainties in the position of these new states.Comment: 18 pages; final version accepted for publicatio
Pion Interactions in the X(3872)
We consider pion interactions in an effective field theory of the narrow
resonance X(3872), assuming it is a weakly bound molecule of the charm mesons
D^{0} \bar D^{*0} and D^{*0} \bar D^{0}. Since the hyperfine splitting of the
D^{0} and D^{*0} is only 7 MeV greater than the neutral pion mass, pions can be
produced near threshold and are non-relativistic. We show that pion exchange
can be treated in perturbation theory and calculate the next-to-leading-order
correction to the partial decay width \Gamma[X \to D^0 \bar D^{0} \pi^0].Comment: 26 pages, 11 figures, revtex4, to appear in Phys. Rev.
Axial Anomaly and Transition Form Factors
We investigate the properties of the amplitude induced by the anomaly. In a
relatively high energy region those amplitudes are constructed by the vector
meson poles and the anomaly terms, in which the anomaly terms can be
essentially evaluated by the triangle quark graph. We pay our attention to the
anomaly term and make intensive analysis of the existing experimental data,
i.e., the electromagnetic and transition form factors. Our
result shows that it is essential to use the constituent quark mass instead of
the current quark mass in evaluating the anomaly term from the triangle graph.Comment: LaTeX, 14 pages + 4 figures, (figures are included as uuencoded
files), KUNS-1210 HE(TH) 93/0
Rapid forgetting results from competition over time between items in visual working memory
Working memory is now established as a fundamental cognitive process across a range of species. Loss of information held in working memory has the potential to disrupt many aspects of cognitive function. However, despite its significance, the mechanisms underlying rapid forgetting remain unclear, with intense recent debate as to whether it is interference between stored items that leads to loss of information or simply temporal decay. Here we show that both factors are essential and interact in a highly specific manner. Although a single item can be maintained in memory with high fidelity, multiple items compete in working memory, progressively degrading each other’s representations as time passes. Specifically, interaction between items is associated with both worsening precision and increased reporting errors of object features over time. Importantly, during the period of maintenance, although items are no longer visible, maintenance resources can be selectively redeployed to protect the probability to recall the correct feature and the precision with which cued items can be recalled, as if it was the only item in memory. These findings reveal that the biased competition concept could be applied not only to perceptual processes but also to active maintenance of working memory representations over time
Chiral Lagrangian with Heavy Quark-Diquark Symmetry
We construct a chiral Lagrangian for doubly heavy baryons and heavy mesons
that is invariant under heavy quark-diquark symmetry at leading order and
includes the leading O(1/m_Q) symmetry violating operators. The theory is used
to predict the electromagnetic decay width of the J=3/2 member of the ground
state doubly heavy baryon doublet. Numerical estimates are provided for doubly
charm baryons. We also calculate chiral corrections to doubly heavy baryon
masses and strong decay widths of low lying excited doubly heavy baryons.Comment: 20 pages, no figure
Dynamical Polarizabilities of SU(3) Octet of Baryons
We present calculations and an analysis of the spin-independent dipole
electric and magnetic dynamical polarizabilities for the lowest in mass SU(3)
octet of baryons. These extensive calculations are made possible by the recent
implementation of semi-automatized calculations in Chiral Perturbation Theory
which allows evaluating dynamical spin-independent electromagnetic
polarizabilities from Compton scattering up to next-to-the-leading order. Our
results are in good agreement with calculations performed for nucleons found in
the literature. The dependencies for the range of photon energies up to 1 GeV,
covering the majority of the meson photo production channels, are analyzed. The
separate contributions into polarizabilities from the various baryon meson
clouds are studied.Comment: 10 pages, 7 figures, extended analysis of hyperon polarizabilitie
Production of the X(3872) in B Meson Decay by the Coalescence of Charm Mesons
If the recently-discovered charmonium state X(3872) is a loosely-bound S-wave
molecule of the charm mesons \bar D^0 D^{*0} or \bar D^{*0} D^0, it can be
produced in B meson decay by the coalescence of charm mesons. If this
coalescence mechanism dominates, the ratio of the differential rate for B^+ \to
\bar D^0 D^{*0} K^+ near the \bar D^0 D^{*0} threshold and the rate for B^+ \to
X K^+ is a function of the \bar D^0 D^{*0} invariant mass and hadron masses
only. The identification of the X(3872) as a \bar D^0 D^{*0}/\bar D^{*0} D^0
molecule can be confirmed by observing an enhancement in the \bar D^0 D^{*0}
invariant mass distribution near the threshold. An estimate of the branching
fraction for B^+ \to X K^+ is consistent with observations if X has quantum
numbers J^{PC} = 1^{++} and if J/\psi \pi^+ \pi^- is one of its major decay
modes.Comment: 4 pages, 3 figures, revtex
Dissecting Photometric Redshift for Active Galactic Nucleus Using XMM- and Chandra-COSMOS Samples
In this paper, we release accurate photometric redshifts for 1692 counterparts to Chandra sources in the central square degree of the Cosmic Evolution Survey (COSMOS) field. The availability of a large training set of spectroscopic redshifts that extends to faint magnitudes enabled photometric redshifts comparable to the highest quality results presently available for normal galaxies. We demonstrate that morphologically extended, faint X-ray sources without optical variability are more accurately described by a library of normal galaxies (corrected for emission lines) than by active galactic nucleus (AGN) dominated templates, even if these sources have AGN-like X-ray luminosities. Preselecting the library on the bases of the source properties allowed us to reach an accuracy σ_(Δz/(1+z(spec))~0.015 with a fraction of outliers of 5.8% for the entire Chandra-COSMOS sample. In addition, we release revised photometric redshifts for the 1735 optical counterparts of the XMM-detected sources over the entire 2 deg^2 of COSMOS. For 248 sources, our updated photometric redshift differs from the previous release by Δz > 0.2. These changes are predominantly due to the inclusion of newly available deep H-band photometry (H_(AB) = 24 mag). We illustrate once again the importance of a spectroscopic training sample and how an assumption about the nature of a source together, with the number and the depth of the available bands, influences the accuracy of the photometric redshifts determined for AGN. These considerations should be kept in mind when defining the observational strategies of upcoming large surveys targeting AGNs, such as eROSITA at X-ray energies and the Australian Square Kilometre Array Pathfinder Evolutionary Map of the Universe in the radio band
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