8,415 research outputs found
Studies on X(4260) and X(4660) particles
Studies on the X(4260) and X(4660) resonant states in an effective lagrangian
approach are reviewed. Using a Breit--Wigner propagator to describe their
propagation, we find that the X(4260) has a sizable coupling to the
channel, while other couplings are found to be negligible.
Besides, it couples much stronger to than to : As an approximate result for
X(4660), we obtain that the ratio of
. Finally, taking X(3872) as an example, we also point out a possible way to
extend the previous method to a more general one in the effective lagrangian
approach.Comment: Talk given by H. Q. Zheng at "Xth Quark Confinement and the Hadron
Spectrum", October 8-12, 2012, TUM Campus Garching, Munich, Germany. 6 pages,
3 figures, 3 table
New insights into the and other charm scalar mesons
Through the scattering of light-pseudoscalar mesons () off
charmed mesons (), we study the state and other
relevant charm scalar mesons in a unitarized chiral effective field theory
approach. We investigate the charm scalar meson poles with different
strangeness () and isospin () quantum numbers as well as their
corresponding residues, which provide the coupling strengths of the charm
scalar mesons. Both the light-quark mass and dependences of the pole
positions of the and the poles with are
analyzed in detail in this work. Interestingly we observe quite similar pion
mass trajectories for the resonance pole at around 2.1 GeV with
to those of the given in the literature. When increasing the values
of we find that a bound state and a virtual state in the
channel asymmetrically approach the threshold for , and they meet
at this threshold at . When , the bound and virtual states move
into the complex plane on the second Riemann sheet and become a symmetric pair
of resonance poles. For large enough values of , neither the
pole nor the poles with tend to fall down to
the real axis, indicating that they do not behave like a standard
quark-antiquark meson at large .Comment: 26 pages, published version in PR
New Insights on Low Energy Scattering Amplitudes
The - and - wave phase shifts of low-energy pion-nucleon scatterings
are analysed using Peking University representation, in which they are
decomposed into various terms contributing either from poles or branch cuts. We
estimate the left-hand cut contributions with the help of tree-level
perturbative amplitudes derived in relativistic baryon chiral perturbation
theory up to . It is found that in and
channels, contributions from known resonances and cuts are far from enough to
saturate experimental phase shift data -- strongly indicating contributions
from low lying poles undiscovered before, and we fully explore possible physics
behind. On the other side, no serious disagreements are observed in the other
channels.Comment: slightly chnaged version, a few more figures added. Physical
conclusions unchange
Analyses of pion-nucleon elastic scattering amplitudes up to in extended-on-mass-shell subtraction scheme
We extend the analysis of elastic pion-nucleon scattering up to
level using extended-on-mass-shell subtraction scheme within the framework of
covariant baryon chiral perturbation theory. Numerical fits to partial wave
phase shift data up to GeV are performed to pin down the free
low energy constants. A good description to the existing phase shift data is
achieved. We find a good convergence for the chiral series at ,
considerably improved with respect to the -level analyses found in
previous literature. Also, the leading order contribution from explicit
resonance and partially-included loop
contribution are included to describe phase shift data up to
GeV. As phenomenological applications, we investigate chiral correction to the
Goldberger-Treiman relation % and find that it converges rapidly,
and the correction is found to be very small: . We also
get a reasonable prediction of pion-nucleon sigma term up to
by performing fits including both the pion-nucleon partial wave phase
shift data and the lattice QCD data. We report that MeV
from the fit without , and MeV from the
fit with explicit .Comment: The final version published in Phys.Rev. D 87, 054019 (2013
A unified formulation of one-loop tensor integrals for finite volume effects
A unified formulation of one-loop tensor integrals is proposed for
systematical calculations of finite volume corrections. It is shown that
decomposition of the one-loop tensor integrals into a series of tensors
accompanied by tensor coefficients is feasible, if a unit space-like four
vector , originating from the discretization effects at finite volume,
is introduced. A generic formula has been derived for numerical computations of
all the involved tensor coefficients. For the vanishing external three-momenta,
we also investigate the feasibility of the conventional Passarino-Veltmann
reduction of the tensor integrals in a finite volume. Our formulation can be
easily used to realize the automation of the calculations of finite volume
corrections to any interesting quantities at one-loop level. Besides, it
provides finite volume result in a unique and concise form, which is suited
for, e.g., carrying out precision determination of physical observable from
modern lattice QCD data.Comment: Version accepted for publication in JHEP; 38 pages, 5 figures, 2
table
Positivity constraints on the low-energy constants of the chiral pion-nucleon Lagrangian
Positivity constraints on the pion-nucleon scattering amplitude are derived
in this article with the help of general S-matrix arguments, such as
analyticity, crossing symmetry and unitarity, in the upper part of Mandelstam
triangle, R. Scanning inside the region R, the most stringent bounds on the
chiral low energy constants of the pion-nucleon Lagrangian are determined. When
just considering the central values of the fit results from covariant baryon
chiral perturbation theory using extended-on-mass-shell scheme, it is found
that these bounds are well respected numerically both at O(p^3) and O(p^4)
level. Nevertheless, when taking the errors into account, only the O(p^4)
bounds are obeyed in the full error interval, while the bounds on O(p^3) fits
are slightly violated. If one disregards loop contributions, the bounds always
fail in certain regions of R. Thus, at a given chiral order these terms are not
numerically negligible and one needs to consider all possible contributions,
i.e., both tree-level and loop diagrams. We have provided the constraints for
special points in R where the bounds are nearly optimal in terms of just a few
chiral couplings, which can be easily implemented and employed to constrain
future analyses. Some issues about calculations with an explicit Delta(1232)
resonance are also discussed.Comment: 15 pages, 13 eps figures, 2 table
Renormalization of the three-boson system with short-range interactions revisited
We consider renormalization of the three-body scattering problem in
low-energy effective field theory of self-interacting scalar particles by
applying time-ordered perturbation theory to the manifestly Lorentz-invariant
formulation. The obtained leading-order equation is perturbatively
renormalizable and non-perturbatively finite and does not require a three-body
counter term in contrast to its non-relativistic approximation.Comment: 6 pages, 4 figure
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