420 research outputs found
UNDERSTANDING THE SCALAR MESON NONET
It is shown that one can fit the available data on the a0(980), f0(980),
f0(1300) and K*0(1430) mesons as a distorted 0++ qq bar nonet using very few
(5-6) parameters and an improved version of the unitarized quark model. This
includes all light two-pseudoscalar thresholds, constraints from Adler zeroes,
flavour symmetric couplings, unitarity and physically acceptable analyticity.
The parameters include a bare uu bar or dd bar mass, an over-all coupling
constant, a cutoff and a strange quark mass of 100 MeV, which is in accord with
expectations from the quark model.
It is found that in particular for the a0(980) and f0(980) the KK bar
component in the wave function is large, i.e., for a large fraction of the time
the qq bar state is transformed into a virtual KK bar pair. This KK bar
component, together with a similar component of eta' pi for the a0(980) , and
eta eta, eta eta' and eta' eta' components for the f0(980), causes the
substantial shift to a lower mass than what is naively expected from the qq bar
component alone.
Mass, width and mixing parameters, including sheet and pole positions, of the
four resonances are given, with a detailed pedagogical discussion of their
meaning.Comment: 35 pages in plain latex (ZPC in press), 10 figures obtainable from
the author ([email protected]) with regular mail or as a large PS
fil
Does A Narrow Tetraquark State Exist?
The existence of a shallow or virtual tetraquark state, ,
is discussed. Using the putative masses for the doubly charmed baryons
() from SELEX, the mass of the state is estimated
to be about , only slightly above the threshold. The
experimental signatures for various masses are also
discussed.Comment: LaTeX, 16 page
Estimating sigma-meson couplings from D \to 3\pi decays
Using recent experimental evidence from E791 on the sigma meson in D \to 3\pi
decays, we study the relevant couplings in D \to \sigma \pi and \sigma \to \pi\
pi within the accepted theoretical framework for non leptonic D decays. We also
review the linear sigma model, finding that it gives a description which is
consistent with the experimental data.Comment: 6 pages, no figures. Final version accepted for publication as a
Brief Report in Physical Review
On Deusons or Deuteronlike Meson-Meson Bound States
The systematics of deuteronlike two-meson bound states, {\it deusons}, is
discussed. Previous arguments that many of the present non- states are
such states are elaborated including, in particular, the tensor potential. For
pseudoscalar states the important observation is made that the centrifugal
barrier from the P-wave can be overcome by the and terms of the
tensor potential. In the heavy meson sector one-pion exchange alone is strong
enough to form at least deuteron-like and composites
bound by approximately 50 MeV, while and states are
expected near the threshold.Comment: Invited talk at the Hadron93 International Conf. on Hadron
Spectroscopy, Como, Italy 22.-25.6. 1993. 5 pages in LATEX HU-SEFT R 1993-13
Measuring rates of present-day relative sea-level rise in low-elevation coastal zones: a critical evaluation
Although tide gauges are the primary source of data used to
calculate multi-decadal- to century-scale rates of relative sea-level change,
we question the usefulness of tide-gauge data in rapidly subsiding
low-elevation coastal zones (LECZs). Tide gauges measure relative sea-level
rise (RSLR) with respect to the base of associated benchmarks. Focusing on
coastal Louisiana, the largest LECZ in the United States, we find that these
benchmarks (n=35) are anchored an average of 21.5 m below the land
surface. Because at least 60 % of subsidence occurs in the top 5 m of
the sediment column in this area, tide gauges in coastal Louisiana do not
capture the primary contributor to RSLR. Similarly, global navigation
satellite system (GNSS) stations (n=10) are anchored an average of
> 14.3 m below the land surface and therefore also do not
capture shallow subsidence. As a result, tide gauges and GNSS stations in
coastal Louisiana, and likely in LECZs worldwide, systematically
underestimate rates of RSLR as experienced at the land surface. We present an
alternative approach that explicitly measures RSLR in LECZs with respect to
the land surface and eliminates the need for tide-gauge data in this context.
Shallow subsidence is measured by rod surface-elevation table–marker horizons
(RSET-MHs) and added to measurements of deep subsidence from GNSS data, plus
sea-level rise from satellite altimetry. We show that for an LECZ the size of
coastal Louisiana (25 000–30 000 km2), about 40 RSET-MH instruments
suffice to collect useful data. Rates of RSLR obtained from this approach are
substantially higher than rates as inferred from tide-gauge data. We
therefore conclude that LECZs may be at higher risk of flooding within a
shorter time horizon than previously assumed.</p
X(3872): Hadronic Molecules in Effective Field Theory
We consider the implications from the possibility that the recently observed
state X(3872) is a meson-antimeson molecule. We write an effective Lagrangian
consistent with the heavy-quark and chiral symmetries needed to describe
X(3872). We claim that if X(3872) is a molecular bound state of D^*0 and
anti-D^0 mesons, the heavy-quark symmetry requires the existence of the
molecular bound state X_b of B^*0 and anti-B^0 with the mass of 10604 MeV.Comment: 12 pages, 1 figure, 1 table, RevTe
BB Intermeson Potentials in the Quark Model
In this paper we derive quark model results for scattering amplitudes and
equivalent low energy potentials for heavy meson pairs, in which each meson
contains a heavy quark. This "BB" system is an attractive theoretical
laboratory for the study of the nuclear force between color singlets; the
hadronic system is relatively simple, and there are lattice gauge theory (LGT)
results for V_BB(r) which may be compared to phenomenological models. We find
that the quark model potential (after lattice smearing) has qualitative
similarities to the LGT potential in the two B*B* channels in which direct
comparison is possible, although there is evidence of a difference in length
scales. The quark model prediction of equal magnitude but opposite sign for I=0
and I=1 potentials also appears similar to LGT results at intermediate r. There
may however be a discrepancy between the LGT and quark model I=1 BB potentials.
A numerical study of the two-meson Schrodinger equations in the (bqbar)(bqbar)
and (cqbar)(cqbar) sectors with the quark model potentials finds a single
"molecule", in the I=0 BB* sector. Binding in other channels might occur if the
quark model forces are augmented by pion exchange.Comment: 30 pages, 5 figures, revtex and epsfig. Submitted to Phys. Rev.
Unquenching the Quark Model and Screened Potentials
The low-lying spectrum of the quark model is shown to be robust under the
effects of `unquenching'. In contrast, the use of screened potentials is shown
to be of limited use in models of hadrons. Applications to unquenching the
lattice Wilson loop potential and to glueball mixing in the adiabatic hybrid
spectrum are also presented.Comment: 6 pages, 3 ps figures, revtex. Version to appear in J. Phys.
A new Perspective on the Scalar meson Puzzle, from Spontaneous Chiral Symmetry Breaking Beyond BCS
We introduce coupled channels of Bethe-Salpeter mesons both in the boundstate
equation for mesons and in the mass gap equation for chiral symmetry.
Consistency is insured by the Ward Identities for axial currents, which
preserve the Goldstone boson nature of the pion and prevents a systematic shift
of the hadron spectrum. We study the decay of a scalar meson coupled to a pair
of pseudoscalars. We also show that coupled channels reduce the breaking of
chiral symmetry, with the same Feynman diagrams that appear in the coupling of
a scalar meson to a pair of pseudoscalar mesons. Exact calculations are
performed in a particular confining quark model, where we find that the
groundstate meson is the f_0(980) with a partial decay
width of 40MeV. We also find a 30% reduction of the chiral condensate due to
coupled channels.Comment: 17 pages, Revtex, 8 eps figures, and several eps diagrams in
equation
Conformal Phase Transition and Fate of the Hidden Local Symmetry in Large N_f QCD
It is observed that the Hidden Local Symmetry (HLS) for the vector mesons in
the ordinary QCD with smaller N_f plays the role of the "Higgsed magnetic gauge
symmetry" for the Seiberg duality in the SUSY QCD. For large N_f where the
conformal phase transition with chiral restoration and deconfinement is
expected to take place, we find that the HLS model also exhibits the chiral
restoration by the loop corrections (including the quadratic divergence) in a
manner similar to that in the CP^{N-1} model, provided that the bare HLS
Lagrangian respects the Georgi's vector limit at a certain N_f (\approx 7).Comment: 4 Pages (RevTeX), 3 PS figures are included Minor corrections are
made for the introductory part. This is the version to appear in Physical
Review Letter
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