3,800 research outputs found
Measuring the quark condensate from the decays tau -> 3 pi + nu(tau)
The possibility of detecting the S-wave of the decays tau -> 3 pi + nu(tau)
in the threshold region is explored, with emphasis on the sensitivity to the
size of the quark antiquark condensate .Comment: contribution to QCD99, 4 pages, Latex, using espcrc2.sty (included),
2 PS figur
An example of resonance saturation at one loop
We argue that the large-Nc expansion of QCD can be used to treat a Lagrangian
of resonances in a perturbative way. As an illustration of this we compute the
L_10 coupling of the Chiral Lagrangian by integrating out resonance fields at
one loop. Given a Lagrangian and a renormalization scheme, this is how in
principle one can answer in a concrete and unambiguous manner questions such as
at what scale resonance saturation takes place.Comment: 9 pages, 5 figures. Enlarged discussion, results unchanged. To be
published in Phys. Rev.
Retention capacity of random surfaces
We introduce a "water retention" model for liquids captured on a random
surface with open boundaries, and investigate it for both continuous and
discrete surface heights 0, 1, ... n-1, on a square lattice with a square
boundary. The model is found to have several intriguing features, including a
non-monotonic dependence of the retention on the number of levels in the
discrete case: for many n, the retention is counterintuitively greater than
that of an n+1-level system. The behavior is explained using percolation
theory, by mapping it to a 2-level system with variable probability. Results in
1-dimension are also found.Comment: 5 page
Geometric approach to condensates in holographic QCD
An SU(Nf)xSU(Nf) Yang-Mills theory on an extra-dimensional interval is
considered, with appropriate symmetry-breaking boundary conditions on the IR
brane. UV-brane to UV-brane correlators at high energies are compared with the
OPE of two-point functions of QCD quark currents. Condensates correspond to
departure from AdS of the (different) metrics felt by vector and axial
combinations, away from the UV brane. Their effect on hadronic observables is
studied: the extracted condensates agree with the signs and orders of magnitude
expected from QCD.Comment: References added: published version plus misprints correction
Fluctuations of g-factors in metal nanoparticles: Effects of electron-electron interaction and spin-orbit scattering
We investigate the combined effect of spin-orbit scattering and
electron-electron interactions on the probability distribution of -factors
of metal nanoparticles. Using random matrix theory, we find that even a
relatively small interaction strength %(ratio of exchange constant and mean
level %spacing \spacing ) significantly increases -factor
fluctuations for not-too-strong spin-orbit scattering (ratio of spin-orbit rate
and single-electron level spacing 1/\tau_{\rm so} \spacing \lesssim 1), and
leads to the possibility to observe -factors larger than two.Comment: RevTex, 2 figures inserte
Contributions of order to form factors and unitarity of the CKM matrix
The form factors for the semileptonic decay are computed to
order in generalized chiral perturbation theory. The main difference
with the standard expressions consists in contributions quadratic in
quark masses, which are described by a single divergence-free low-energy
constant, . A new simultaneous analysis is presented for the CKM matrix
element , the ratio , decay rates and the
scalar form factor slope . This framework easily accommodates the
precise value for deduced from superallowed nuclear -decays
Chiral two-loop pion-pion scattering parameters from crossing-symmetric constraints
Constraints on the parameters in the one- and two-loop pion-pion scattering
amplitudes of standard chiral perturbation theory are obtained from explicitly
crossing-symmetric sum rules. These constraints are based on a matching of the
chiral amplitudes and the physical amplitudes at the symmetry point of the
Mandelstam plane. The integrals over absorptive parts appearing in the sum
rules are decomposed into crossing-symmetric low- and high-energy components
and the chiral parameters are finally related to high-energy absorptive parts.
A first application uses a simple model of these absorptive parts. The
sensitivity of the results to the choice of the energy separating high and low
energies is examined with care. Weak dependence on this energy is obtained as
long as it stays below ~560 MeV. Reliable predictions are obtained for three
two-loop parameters.Comment: 23 pages, 4 figures in .eps files, Latex (RevTex), our version of
RevTex runs under Latex2.09, submitted to Phys. Rev. D,minor typographical
corrections including the number at the end of the abstract, two sentences
added at the end of Section 5 in answer to a referee's remar
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