383 research outputs found
Pion propagation in the linear sigma model at finite temperature
We construct effective one-loop vertices and propagators in the linear sigma
model at finite temperature, satisfying the chiral Ward identities and thus
respecting chiral symmetry, treating the pion momentum, pion mass and
temperature as small compared to the sigma mass. We use these objects to
compute the two-loop pion self-energy. We find that the perturbative behavior
of physical quantities, such as the temperature dependence of the pion mass, is
well defined in this kinematical regime in terms of the parameter
m_pi^2/4pi^2f_pi^2 and show that an expansion in terms of this reproduces the
dispersion curve obtained by means of chiral perturbation theory at leading
order. The temperature dependence of the pion mass is such that the first and
second order corrections in the above parameter have the same sign. We also
study pion damping both in the elastic and inelastic channels to this order and
compute the mean free path and mean collision time for a pion traveling in the
medium before forming a sigma resonance and find a very good agreement with the
result from chiral perturbation theory when using a value for the sigma mass of
600 MeV.Comment: 18 pages, 11 figures, uses RevTeX and epsfig. Expanded conclusions,
added references. To appear in Phys. Rev.
Angular distributions in states near threshold
A resonance X(3872), first observed in the decays , has been seen
to decay to . The mass spectrum peaks near
its kinematic upper limit, prompting speculation that the dipion system may be
in a . The decay also has been observed.
The reaction has been studied.
Consequently, angular distributions in decays of
states near threshold are of interest, and results are presented.Comment: 10 pages, no figures. To be submitted to Phys. Rev.
Analysis of preliminary data on reaction
We perform the analysis of the preliminary data on reaction simultaneously with the data on
scattering and reactions and
. It is found that the meson mass
MeV and .Comment: 8 pages, revtex, 3 ps files of figures, minor change
Structure of Light Scalar Mesons from D_s and D^0 Non-Leptonic Decays
Non-leptonic D meson decays may provide a reliable testbed for the multiquark
interpretation of light scalar mesons. In this letter we consider D_s decay and
show that a 4-quark f_0(980) meson could induce a decay pattern, which is
forbidden for a q-qbar constituent structure. Experimental tests to probe such
possibilities are within reach in the near future.Comment: 11 pages, 3 figures, minor changes. To appear in Phys. Lett.
A Study in Depth of f0(1370)
Claims have been made that f0(1370) does not exist. The five primary sets of
data requiring its existence are refitted. Major dispersive effects due to the
opening of the 4pi threshold are included for the first time; the sigma -> 4pi
amplitude plays a strong role. Crystal Barrel data on pbar-p -> 3pizero at rest
require f0(1370) signals of at least 32 and 33 standard deviations in 1S0 and
3P1 annihilation respectively. Furthermore, they agree within 5 MeV for mass
and width. Data on pbar-p -> eta-eta-pizero agree and require at least a 19
standard deviation contribution. This alone is sufficient to demonstrate the
existence of f0(1370). BES II data for J/Psi -> phi-pi-pi contain a visible
f0(1370) signal > 8 standard devations. In all cases, a resonant phase
variation is required. The possibility of a second pole in the sigma amplitude
due to the opening of the 4pi channel is excluded. Cern-Munich data for pi-pi
elastic scattering are fitted well with the inclusion of some mixing between
sigma, f0(1370) and f0(1500). The pi-pi widths for f2(1565), rho3(1690),
rho3(1990) and f4(2040) are determined.Comment: 25 pages, 22 figures. Typos corrected in Eqs 2 and 7. Introduction
rewritten. Conclusions unchange
Large Nc and Chiral Dynamics
We study the dependence on the number of colors of the leading pi pi
scattering amplitude in chiral dynamics. We demonstrate the existence of a
critical number of colors for and above which the low energy pi pi scattering
amplitude computed from the simple sum of the current algebra and vector meson
terms is crossing symmetric and unitary at leading order in a truncated and
regularized 1/Nc expansion. The critical number of colors turns out to be Nc=6
and is insensitive to the explicit breaking of chiral symmetry.
Below this critical value, an additional state is needed to enforce the
unitarity bound; it is a broad one, most likely of "four quark" nature.Comment: RevTeX4, 6 fig., 5 page
Structure of the axial-vector meson and the strong coupling constant with the light-cone QCD sum rules
In this article, we take the point of view that the charmed axial-vector
meson is the conventional meson and calculate the
strong coupling constant in the framework of the light-cone
QCD sum rules approach. The numerical values of strong coupling constants
and are very large, and support the
hadronic dressing mechanism. Just like the scalar mesons and
, the scalar meson and axial-vector meson
may have small kernels of the typical
meson size, the strong couplings to the hadronic channels (or the virtual
mesons loops) may result in smaller masses than the conventional
mesons in the constituent quark models, and enrich the pure states
with other components.Comment: 17 pages, 7 figures, revised version. In the first version, I take
the value in numerical calculation, in the
revised version, I take a small value , the
value of the strong coupling constant is also change
Inception of a global atlas of sea levels since the Last Glacial Maximum
Determining the rates, mechanisms, and geographic variability of relative sea-level (RSL) change following the Last Glacial Maximum (LGM) provides insight into the sensitivity of ice sheets to climate change, the response of the solid Earth and gravity field to ice-mass redistribution, and constrains statistical and physical models used to project future sea-level rise. To do so in a scientifically robust way requires standardized datasets that enable broad spatial comparisons that minimize bias. As part of a larger goal to develop a unified, spatially-comprehensive post-LGM global RSL database, in this special issue we provide a standardized global synthesis of regional RSL data that resulted from the first ‘Geographic variability of HOLocene relative SEA level (HOLSEA)’ meetings in Mt Hood, Oregon (2016) and St Lucia, South Africa (2017). The HOLSEA meetings brought together sea-level researchers to agree upon a consistent protocol to standardize, interpret, and incorporate realistic uncertainties of RSL data. This special issue provides RSL data from ten geographical regions including new databases from Atlantic Europe and the Russian Arctic and revised/expanded databases from Atlantic Canada, the British Isles, the Netherlands, the western Mediterranean, the Adriatic, Israel, Peninsular Malaysia, Southeast Asia, and the Indian Ocean. In total, the database derived from this special issue includes 5634 (5290 validated) index (n = 3202) and limiting points (n = 2088) that span from ∼20,000 years ago to present. Progress in improving the standardization of sea-level databases has also been accompanied by advancements in statistical and analytical methods used to infer spatial patterns and rates of RSL change from geological data that have a spatially and temporally sparse distribution and geochronological and elevational uncertainties. This special issue marks the inception of a unified, spatially-comprehensive post-LGM global RSL database
Hadronic Spectrum - Multiquark States
Many newly discovered mesons behave like \ccbar charmonium states in that
they preferentially decay into final states that contain a - and a
-quark, but do not fit expectations for any of the unfilled levels of
the conventional \ccbar spectrum. There is a growing suspicion that at least
some of these states are {\it exotic}, {\it i.e.} have a substructure that is
more complex than the quark-antiquark mesons of the classical constituent quark
model. Some of these candidate states have a non-zero electric charge and,
thus, a minimal quark content of \ccbar u\bar{d} or \ccbar d\bar{u}. In
addition, states with similar properties have been observed in the - and
-quark sectors. In this report, the experimental situation is briefly
reviewed.Comment: 8 pages, 9 figures, plenary talk at PANIC 2008, Nov. 9-14, 2008
Eilat, Israel. (Uses elsart1p.cls.
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