733 research outputs found
Can the X(3872) be a 1^{++} four-quark state?
We use QCD spectral sum rules to test the nature of the meson X(3872),
assumed to be an exotic four-quark (c\bar{c}q\bar{q}) state with J^{PC}=1^{++}.
For definiteness, we work with the current proposed recently by Maiani et al
[1], at leading order in \alpha_s, consider the contributions of higher
dimension condensates and keep terms which are linear in the light quark mass
m_q. We find M_X=(3925+- 127) MeV which is compatible, within the errors, with
he experimental candidate X(3872), while the SU(3) breaking-terms lead to an
unusual mass-splitting M_{X^{s}}-M_X=- (61+-30) MeV. The mass-difference
between the neutral states due to isospin violation of about (2.6-3.9) MeV is
much smaller than the value (8+-3) MeV proposed in [1]. For the b-quark, we
predict M_{X_b}= (10144+-106) MeV for the X_b(b\bar{b}q \bar{q}), which is much
below the {\bar B}B* threshold in contrast to the {\bar B}B* molecule
prediction [2], and for the X_b^s(b\bar{b}s \bar{s}), a mass-splitting
M_{X^s_{b}}-M_{X_b}=-(121+-182) MeV. Our analysis also indicates that the
mass-splitting between the ground state and the radial excitation of about
(225~250) MeV is much smaller than in the case of ordinary mesons and is
(within the errors) flavour-independent. We also extract the decay constants,
analogous to f_\pi, of such mesons, which are useful for further studies of
their leptonic and hadronic decay widths. The uncertainties of our estimates
are mainly due to the ones from the c and b quark masses.Comment: 16 pages, 10 figures. Version to appear in Phys. Rev.
Pentaquark decay is suppressed by chirality conservation
It is shown, that if the pentaquark baryon can be
represented by the local quark current , its decay is forbidden in the limit of chirality conservation. The
decay width is proportional to , where , is quark condensate, and,
therefore, is strongly suppressed. Also the polarization operator of the
pentaquark current with isospin 1 is calculated using the operator product
expansion and estimation for it mass is obtained .Comment: 4 pages, 1 fig, typos correcte
Time Scale for Rapid Draining of a Surficial Lake Into the Greenland Ice Sheet
A 2008 report by Das et al. documented the rapid drainage during summer 2006 of a supraglacial lake, of approximately 44×10^6 m^3, into the Greenland ice sheet over a time scale moderately longer than 1 hr. The lake had been instrumented to record the time-dependent fall of water level and the uplift of the ice nearby. Liquid water, denser than ice, was presumed to have descended through the sheet along a crevasse system and spread along the bed as a hydraulic facture. The event led two of the present authors to initiate modeling studies on such natural hydraulic fractures. Building on results of those studies, we attempt to better explain the time evolution of such a drainage event. We find that the estimated time has a strong dependence on how much a pre-existing crack/crevasse system, acting as a feeder channel to the bed, has opened by slow creep prior to the time at which a basal hydraulic fracture nucleates. We quantify the process and identify appropriate parameter ranges, particularly of the average temperature of the ice beneath the lake (important for the slow creep opening of the crevasse). We show that average ice temperatures 5–7 °C below melting allow such rapid drainage on a time scale which agrees well with the 2006 observations
J/psi couplings to charmed resonances and to pi
We present an evaluation of the strong couplings JD^(*)D^(*) and
JD^(*)D^(*)pi by an effective field theory of quarks and mesons. These
couplings are necessary to calculate pi+J/psi --> D^(*)+barD^(*) cross
sections, an important background to the J/psi suppression signal in the
quark-gluon plasma. We write down the general effective lagrangian and compute
the relevant couplings in the soft pion limit and beyond.Comment: 11 pages, 4 figures, 2 reference added and minor comments, style
changed to RevTe
- …