15 research outputs found
On baryon resonances and chiral symmetry
We study J^P=(3/2)^- baryon resonances as generated by chiral coupled-channel
dynamics. Parameter free results are obtained in terms of the Weinberg-Tomozawa
term predicting the leading s-wave interaction strength of Goldstone bosons
with baryon-decuplet states. In the 'heavy' SU(3) limit with m_\pi = m_K \sim
500 MeV the resonances turn into bound states forming a decuplet and octet
representation of the SU(3) group. Using physical masses the mass splitting are
remarkably close to the empirical pattern.Comment: revised version: includes two additional references, gives improved
discussions and eliminted some misprint
Chiral restoration from pionic atoms?
We evaluate widths and shifts of pionic atoms using a theoretical
microscopical potential in which the pion decay constant is changed by
an in--medium density dependent one (), predicted by different
partial Chiral restoration calculations. We show that the results obtained for
shifts and widths are worse than if this modification were not implemented. On
the other hand, we argue that in microscopic many body approaches for the pion
selfenergy, based on effective Lagrangians, the mechanisms responsible for the
change of in the medium should be automatically incorporated.
Therefore, the replacement of by in the many body
derivation of the microscopic potential would be inappropriate.Comment: 10 pages, new comments and references adde
Testing Chiral Dynamics in Pionic Atoms
The energy dependence of chirally expanded pi N isoscalar and isovector
amplitudes b_0(E) and b_1(E) respectively, for zero-momentum off shell pions
near threshold, is used to impose the minimal substitution requirement E -> E -
V_c on the properly constructed pion optical potential within a large-scale fit
to 100 pionic-atom data across the periodic table which also include the
recently established `deeply bound' pionic atoms of Pb and Sn. This fit cannot
be reconciled with the well known free-space values of the pi N threshold
amplitudes. In contrast, introducing the empirically known energy dependence
for on-shell pions leads to a better fit and to satisfactory values for the pi
N threshold amplitudes. The difference between these two approaches is briefly
discussed.Comment: 10 pages, 3 figures, submitted to PLB. Discussion section rewritten,
omitting an erroneous equation. Results and conclusions unchanged Accepted by
PL
Quark mass dependence of s-wave baryon resonances
We study the quark mass dependence of J(P) = 1/2(-) s-wave baryon resonances. Parameter free results are obtained in terms of the leading order chiral Lagrangian. In the 'heavy' SU(3) limit with m(pi) = M-K similar or equal to 500 MeV the resonances turn into bound states forming two octets plus a singlet representations of the SU(3) group. A contrasted result is obtained in the 'light' SU(3) limit with m(pi) = m(K) similar or equal to 140 MeV for which no resonances exist. Using physical quark masses our analysis suggests to assign to the S = -2 resonances Xi(1690) and Xi(1620) the quantum numbers J(P) = 1/2(-)
On meson resonances and chiral symmetry
We study meson resonances with quantum numbers J^P=1^+ in terms of the chiral
SU(3) Lagrangian. At leading order a parameter-free prediction is obtained for
the scattering of Goldstone bosons off vector mesons with J^P=1^- once we
insist on approximate crossing symmetry of the unitarized scattering amplitude.
A resonance spectrum arises that is remarkably close to the empirical pattern.
In particular, we find that the strangeness-zero resonances h_1(1380), f_(1285)
and b_1(1235) are formed due to strong K \bar K_\mu and \bar K K_\mu channels.
This leads to large coupling constants of those resonances to the latter
states.Comment: 29 pages, 6 figures, more detailed discussions are give
bound states in nuclei
The energies and widths of bound states of the meson in different
nuclei are obtained using the results for its selfenergy in a nuclear medium,
which is evaluated in a selfconsistent manner using techniques of unitarized
chiral perturbation theory. We find bound states in all studied nuclei (from
on) and the half widths obtained are larger than the separation of
the levels, what makes the experimental observation of peaks unlikely. We have
paid a special attention to the region of nuclei where only the state
appears and the binding energies are of the order of magnitude of the half
width, which would magnify the chances that some broad peak could be observed.
This is found in the region of with a binding energy around 12.6
MeV and half width of 16.7 MeV. In heavy nuclei like there are
many bound states which would be difficult to disentangle and the deepest state
has a binding energy about 21 MeV and half width around 16 MeV. Such an
overlapping accumulation of states could be seen as an extension of the
continuum of strength into the bound region in production
experiments.Comment: 9 pages, Latex, 2 Figure
The Polyakov loop and the heat kernel expansion at finite temperature
The lower order terms of the heat kernel expansion at coincident points are
computed in the context of finite temperature quantum field theory for flat
space-time and in the presence of general gauge and scalar fields which may be
non Abelian and non stationary. The computation is carried out in the imaginary
time formalism and the result is fully consistent with invariance under
topologically large and small gauge transformations. The Polyakov loop is shown
to play a fundamental role.Comment: 4 pages, REVTEX, no figure
Open-charm meson resonances with negative strangeness
We study heavy-light meson resonances with quantum numbers J^P=0^+ and
J^P=1^+ in terms of the non-linear chiral SU(3) Lagrangian. Adjusting the free
parameters that arise at subleading order to reproduce the mass of the D(2420)
resonance as well as the new states established recently by the BABAR, CLEO and
BELLE collaborations we obtain refined masses for the anti-triplet and sextet
states. Bound states of antikaons at the D(1867) and D(2008) mesons are
predicted at 2352 MeV (J^P=0^+) and 2416 MeV (J^P=1^+). In addition we
anticipate a narrow scalar state of mass 2389 MeV with (I,S)=(1/2,0)Comment: 12 pages, 3 figure
Multipole response of doped He drops
The multipole response of He drops doped with very attractive
impurities, such as a Xe atom or an SF molecule, has been investigated in
the framework of the Finite Range Density Functional Theory and the Random
Phase Approximation. We show that volume ( = 0) and surface ( = 1, 2)
modes become more fragmented, as compared with the results obtained for pure
He drops. In addition, the dipole mean energy goes smoothly to zero
when increases, indicating that for large values these impurities are
delocalized in the bulk of the drop.Comment: 8 pages, 7 figures, to appear in J. Chem. Phy
Antikaon production in A+A collisions at SIS energies within an off-shell G-matrix approach
The production and propagation of antikaons -- described by dynamical
spectral functions as evaluated from a coupled channel
-matrix approach -- is studied for nucleus-nucleus collisions at SIS
energies in comparison to the conventional quasi-particle limit and the
available experimental data using off-shell transport theory. We find that the
spectra for and at 1.8 AGeV
remain underestimated in the -matrix approach as in the on-shell
quasi-particle approximation whereas the preliminary spectra for at
1.5 AGeV are well described in both limits. This also holds
approximately for the rapidity distributions in semi-central collisions
of at 1.93 AGeV. However, in all limits considered there is no
convincing description of all spectra simultaneously. Our off-shell transport
calculations, furthermore, demonstrate that the strongest in-medium effects
should be found for low antikaon momenta in the center-of-mass frame, since the
deceleration of the antikaons in the attractive Coulomb and nuclear potentials
and the propagation to the on-shell mass induces a net shift and squeezing of
the spectra to the low momentum regime.Comment: 44 pages, including 18 eps figures, to be published in Nucl. Phys.