28 research outputs found
QCD determination of the axial-vector coupling of the nucleon at finite temperature
A thermal QCD Finite Energy Sum Rule (FESR) is used to obtain the temperature
dependence of the axial-vector coupling of the nucleon, . We find
that is essentially independent of , in the very wide range , where is the critical temperature. While
at T=0 is -independent, it develops a dependence at
finite temperature. We then obtain the mean square radius associated with
and find that it diverges at , thus signalling quark
deconfinement. As a byproduct, we study the temperature dependence of the
Goldberger-Treiman relation.Comment: 8 pages and 3 figure
Electromagnetic pion form factor at finite temperature
The electromagnetic form factor of the pion in the space-like region, and at
finite temperature, , is obtained from a QCD Finite Energy
Sum Rule. The form factor decreases with increasing T, and vanishes at some
critical temperature, where the pion radius diverges. This divergence may be
interpreted as a signal for quark deconfinement.Comment: LATEX File. UCT-TP-215/94. One figure available on request. To be
published in Phys. Lett.
Axial anomaly, vector meson dominance and at finite temperature
A thermal Finite Energy QCD Sum Rule is used to determine the temperature
behaviour of the strong coupling. This coupling decreases
with increasing and vanishes at the critical temperature, a likely signal
for quark deconfinement. This is then used in the Vector Meson Dominance (VMD)
expression for the amplitude, which is also found to
vanish at the critical temperature, as expected. This result supports the
validity of VMD at . However, if VMD would not hold at finite
temperature, then there is no prediction for the
amplitude.Comment: 8 pages, no figure
Thermal Pions at Finite Isospin Chemical Potential
The density corrections, in terms of the isospin chemical potential ,
to the mass of the pions are studied in the framework of the SU(2) low energy
effective chiral lagrangian. The pion decay constant is
also analized. As a function of temperature for , the mass remains
quite stable, starting to grow for very high values of , confirming previous
results. However, there are interesting corrections to the mass when both
effects (temperature and chemical potential) are simultaneously present. At
zero temperature the should condensate when . This is not longer valid anymore at finite . The mass of the
acquires also a non trivial dependence on due to the finite
temperature.Comment: 13 pages, 5 figure
Vector Meson Dominance and at Finite Temperature from QCD Sum Rules
A Finite Energy QCD sum rule at non-zero temperature is used to determine the
- and the T-dependence of the vertex function in the
space-like region. A comparison with an independent QCD determination of the
electromagnetic pion form factor at indicates that Vector
Meson Dominance holds to a very good approximation at finite temperature. At
the same time, analytical evidence for deconfinement is obtained from the
result that vanishes at the critical temperature
, independently of . Also, by extrapolating the form
factor to , it is found that the pion radius increases with increasing
, and it diverges at .Comment: 7 pages, Latex, 3 figures to be delivered from the authors by
request, to appear in Phys. Lett.
QCD sum rules and thermal properties of Charmonium in the vector channel
The thermal evolution of the hadronic parameters of charmonium in the vector
channel, i.e. the J/psi resonance mass, coupling (leptonic decay constant),
total width, and continuum threshold is analyzed in the framework of thermal
Hilbert moment QCD sum rules. The continuum threshold , as in other
hadronic channels, decreases with increasing temperature until the PQCD
threshold s_0 = 4, m_Q^2 is reached at T \simeq 1.22T_c (m_Q is the charm quark
mass) and the J/psi mass is essentially constant in a wide range of
temperatures. The other hadronic parameters behave in a very different way from
those of light-light and heavy-light quark systems. The total width grows with
temperature up to T \simeq 1.04T_c beyond which it decreases sharply with
increasing T. The resonance coupling is also initially constant beginning to
increase monotonically around T \simeq T_c. This behavior strongly suggests
that the J/psi resonance might survive beyond the critical temperature for
deconfinement, in agreement with lattice QCD results.Comment: 4 pages, two figures, contribution to QCD 10, Montpellier 28th
June-2nd July 201
The Meson and the Thermal Behavior of an Effective Hadronic Coupling Constant
Vector Meson Dominance ideas together with a Finite Energy QCD sum rule
allows for the determination of the - and the - dependence of the
effective hadronic coupling constant in the space-like
region. It turns out that vanishes at the critical
temperature , independently of . A comparison with a previous
independent QCD determination of the electromagnetic pion form factor at finite
temperature supports the validity of Vector Meson Dominance at finite
temperature. We find also thet the pion radius increases with , having a
divergent behavior at .Comment: 4 pages, Latex.One figure, to be requested by from the author
Electromagnetic and Scalar Pion form factor in the Kroll-Lee-Zumino model
The renormalizable Abelian quantum field theory model of Kroll, Lee, and
Zumino is used at the one loop level to compute vertex corrections to the
tree-level, Vector Meson Dominance (VMD) electromagnetic pion form factor.
These corrections, together with the one-loop vacuum polarization contribution,
imply a resulting electromagnetic pion form factor in excellent agreement with
data in the whole range of accessible momentum transfers in the space-like
region. The time-like form factor, which reproduces the Gounaris-Sakurai
formula at and near the rho-meson peak, is unaffected by the vertex correction
at order . The KLZ model is also used to compute the scalar
radius of the pion at the one loop level, finding . This value implies for the low energy constant of chiral perturbation
theory .Comment: four pages, two figure
Vector Meson Dominance, Axial Anomaly and the Thermal behavior of
By using a thermal Finite Energy QCD Sum Rule, we are able to establish the
temperature dependence of the strong coupling. It
turns out that this coupling decreases as a function of temperature, vanishing
at the critical temperature. This corresponds to a possible deconfining
phenomenological signal. This result, together with the Vector Meson Dominance
(VMD) expression for the amplitude , allows us to
establish that this amplitude also vanishes at the critical temperature, in
agreement with previous independent analysis. This results supports, once
again, the validity of VMD at finite temperature. Several posssible scenarios
are discussed. However, if VMD would not hold at finite temperature, then we
will not be able to find a prediction for the thermal behavior of the amplitude.Comment: Talk given at the QCD Euroconference, Montpellier July 2000 5 page
Testing spatial noncommutativiy via the Aharonov-Bohm effect
The possibility of detecting noncommutative space relics is analyzed using
the Aharonov-Bohm effect. We show that, if space is noncommutative, the
holonomy receives non-trivial kinematical corrections that will produce a
diffraction pattern even when the magnetic flux is quantized. The scattering
problem is also formulated, and the differential cross section is calculated.
Our results can be extrapolated to high energy physics and the bound is found. If this bound holds, then noncommutative
effects could be explored in scattering experiments measuring differential
cross sections for small angles. The bound state Aharonov- Bohm effect is also
discussed.Comment: 16 pp, Revtex 4, 2 fig, new references added. To appear in PR