3,879 research outputs found
The effect of using local mean versus constant reference salinity to estimate Arctic Ocean freshwater content changes
Changes of high-latitude freshwater content (FWC) play an important role in shaping the variability of polar oceans. FWC is defined as depth-integrated departure of salinity from a reference salinity Sref divided by this Sref . A constant Sref is often used for high-latitude FWC estimates. Here it is argued that for analyzing FWC spatiotemporal changes the use of local mean Sref is a better choice. Analysis of 2007 FWC anomalies in the 25–75 m layer demonstrated, for example, that the choice of Sref = 34.8 (which is often used in climate studies) leads to FWC spatial anomalies exaggerated, on average, by ~0.6 m, which is a substantial fraction of total spatial FWC changes. The problem is aggravated in areas where the difference between the local Sref and Sref = 34.8 is greater. Thus, it is concluded that using climatological mean salinities as Sref provides superior estimates of spatiotemporal Arctic Ocean FWC changes.Changes of high-latitude freshwater content (FWC) play an important role in shaping the variability of polar oceans. FWC is defined as depth-integrated departure of salinity from a reference salinity Sref divided by this Sref . A constant Sref is often used for high-latitude FWC estimates. Here it is argued that for analyzing FWC spatiotemporal changes the use of local mean Sref is a better choice. Analysis of 2007 FWC anomalies in the 25–75 m layer demonstrated, for example, that the choice of Sref = 34.8 (which is often used in climate studies) leads to FWC spatial anomalies exaggerated, on average, by ~0.6 m, which is a substantial fraction of total spatial FWC changes. The problem is aggravated in areas where the difference between the local Sref and Sref = 34.8 is greater. Thus, it is concluded that using climatological mean salinities as Sref provides superior estimates of spatiotemporal Arctic Ocean FWC changes
K*-couplings for the antidecuplet excitation
We estimate the coupling of the K* vector meson to the N-->Theta+ transition
employing unitary symmetry, vector meson dominance, and results from the GRAAL
Collaboration for eta photoproduction off the neutron. Our small numerical
value for the coupling constant is consistent with the non-observation of the
Theta+ in recent CLAS searches for its photoproduction. We also estimate the
K*-coupling for the N-->Sigma* excitation, with Sigma* being the Sigma-like
antidecuplet partner of the Theta+-baryon.Comment: 9 pages, 1 figure. Minor changes in text and abstract, references
added; version to appear in Phys. Rev.
Extraction of radiative decay width for the non-strange partner of Theta^+
Using the results of the GRAAL collaboration on the \eta photoproduction from
the neutron target, we attempt to extract the partial radiative width of the
possible new nucleon resonance N^*(1675). The obtained estimates support this
resonance to be a very attractive candidate for the non-strange member of the
exotic antidecuplet of baryons -- a partner of the \Theta^+ pentaquark. Our
phenomenological value for the transition magnetic moment \mu(n^* n), appears
to be in good agreement with predictions of the Chiral Quark Soliton Model.Comment: 4 pages, v2 corresponds to the journal publicatio
New LHCb pentaquarks as hadrocharmonium states
New LHCb Collaboration results on pentaquarks with hidden charm [1] are
discussed. These results fit nicely in the hadrocharmonium pentaquark scenario
[2,3]. In the new data the old LHCb pentaquark splits into two
states and . We interpret these two almost degenerate
hadrocharmonium states with and as a result of
hyperfine splitting between hadrocharmonium states predicted in [2]. It arises
due to QCD multipole interaction between color-singlet hadrocharmonium
constituents. We improve the theoretical estimate of hyperfine splitting [2,3]
that is compatible with the experimental data. The new state finds
a natural explanation as a bound state of and a nucleon, with
, and binding energy 42 MeV. As a bound state of a spin-zero
meson and a nucleon, hadrocharmonium pentaquark does not experience
hyperfine splitting. We find a series of hadrocharmonium states in the vicinity
of the wide pentaquark that can explain its apparently large decay
width. We compare the hadrocharmonium and molecular pentaquark scenarios and
discuss their relative advantages and drawbacks.Comment: 10 page
Pentaquarks with hidden charm as hadroquarkonia
We consider hidden charm pentaquarks as hadroquarkonium states in a QCD
inspired approach. Pentaquarks arise naturally as bound states of quarkonia
excitations and ordinary baryons. The LHCb pentaquark is
interpreted as a -nucleon bound state with spin-parity . The
partial decay width MeV is calculated
and turned out to be in agreement with the experimental data for .
The pentaquark is predicted to be a member of one of the two almost
degenerate hidden-charm baryon octets with spin-parities .
The masses and decay widths of the octet pentaquarks are calculated. The widths
are small and comparable with the width of the pentaquark, and the
masses of the octet pentaquarks satisfy the Gell-Mann-Okubo relation.
Interpretation of pentaquarks as loosely bound and
deuteronlike states is also considered. We determine
quantum numbers of these bound states and calculate their masses in the
one-pion exchange scenario. The hadroquarkonium and molecular approaches to
exotic hadrons are compared and the relative advantages and drawbacks of each
approach are discussed.Comment: 33 pages, 2 figures, 3, tables; Minor changes, 2 references added;
Version published in Eur. Phys. J.
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