7,805 research outputs found
Regge trajectories and quarkonium spectrum from a first principle Salpeter equation
We compute the heavy-heavy, light-light and light-heavy quarkonium spectrum
starting from a first principle Salpeter equation obtained in a preceding
paper. We neglect spin-orbit structures and exclude from our treatment the
light pseudoscalar states which in principle would require the use of the full
Bethe-Salpeter equation due to the chiral symmetry breaking problem. For the
rest we find an overall good agreement with the experimental data. In
particular for the light-light case we find straight Regge trajectories with
the right slope and intercepts. The strong coupling constant , the
string tension occurring in the potential and the heavy quark masses
are taken from the heavy quarkonium semirelativistic fit with only a small
rearrangement. The light quark masses are set equal to baricentral value of the
current quark masses as reported by the particle data group. For what concerns
the light-light and the light-heavy systems the calculation is essentially
parameter free.Comment: 18 pages, 3 figures, revtex.st
The Dirac operator spectrum: a perturbative approach
By computing the Dirac operator spectrum by means of Numerical Stochastic
Perturbation Theory, we aim at throwing some light on the widely accepted
picture for the mechanism which is behind the Bank-Casher relation. The latter
relates the chiral condensate to an accumulation of eigenvalues in the low end
of the spectrum. This can be in turn ascribed to the usual mechanism of
repulsion among eigenvalues which is typical of quantum interactions. First
results appear to confirm that NSPT can indeed enable us to inspect a huge
reshuffling of eigenvalues due to quantum repulsion.Comment: 8 pages, 6 figures; talk presented at the 27th International
Symposium on Lattice Field Theory (Lattice 2009), Beijing, China, 26-31 Jul
200
High-loop perturbative renormalization constants for Lattice QCD (III): three-loop quark currents for Iwasaki gauge action and n_f=4 Wilson fermions
This is the third of a series of papers on three-loop computation of
renormalization constants for Lattice QCD. Our main point of interest are
results for the regularization defined by Iwasaki gauge action and n_f=4 Wilson
fermions. Our results for quark bilinears renormalized according to the RI'-MOM
scheme can be compared to non-perturbative results. The latter are available
for Twisted Mass QCD: being defined in the chiral limit, renormalization
constants must be the same. We also address more general problems. In
particular, we discuss a few methodological issues connected to summing the
perturbative series such as the effectiveness of Boosted Perturbation Theory
and the disentanglement of irrelevant and finite volume contributions.
Discussing these issues we consider ont only the new results of this paper, but
also those for the regularization defined by tree-level Symanzik improved gauge
action and n_f=2 Wilson fermions, which we presented in a recent paper of ours.
We finally comment to which extent the techniques we put at work in the NSPT
context can provide a fresher look into the lattice version of the RI'-MOM
scheme.Comment: 20 pages, 4 figures, pdflatex The Section on different ways of
summing the series has been updated: a few extra informations have been
provided and a clearer notation has been introduce
Nanostructuring of glass micro-nanowires
In the past decade, glass fiber tapers with micron or sub-micron diameter have attracted much attention and found a wide range of applications in optics [1] including mode filtering, supercontinuum generation, high-Q resonators and resonant sensing, optical trapping and optical propulsion. Nanofabrication can add new application opportunities, like Fabry-Perot resonators, Scanning near-field optical microscopy (SNOM) probe and surface plasmon resonators
Effective field theories for baryons with two- and three-heavy quarks
Baryons made of two or three heavy quarks can be described in the modern
language of non-relativistic effective field theories. These, besides allowing
a rigorous treatment of the systems, provide new insight in the nature of the
three-body interaction in QCD.Comment: 7 pages, 1 figure; published versio
High loop renormalization constants for Wilson fermions/Symanzik improved gauge action
We present the current status of our computation of quark bilinear
renormalization constants for Wilson fermions and Symanzik improved gauge
action. Computations are performed in Numerical Stochastic Perturbation Theory.
Volumes range from 10^4 to 32^4. Renormalization conditions are those of the
RI'-MOM scheme, imposed at different values of the physical scale. Having
measurements available at several momenta, irrelevant effects are taken into
account by means of hypercubic symmetric Taylor expansions. Finite volumes
effects are assessed repeating the computations at different lattice sizes. In
this way we can extrapolate our results to the continuum limit, in infinite
volume.Comment: 8 pages, 3 figures, talk presented at the 27th International
Symposium on Lattice Field Theory (Lattice 2009), Beijing, China, 26-31 Jul
200
Heavy Quarkonium in a weakly-coupled quark-gluon plasma below the melting temperature
We calculate the heavy quarkonium energy levels and decay widths in a
quark-gluon plasma, whose temperature T and screening mass m_D satisfy the
hierarchy m alpha_s >> T >> m alpha_s^2 >> m_D (m being the heavy-quark mass),
at order m alpha_s^5. We first sequentially integrate out the scales m, m
alpha_s and T, and, next, we carry out the calculations in the resulting
effective theory using techniques of integration by regions. A collinear region
is identified, which contributes at this order. We also discuss the
implications of our results concerning heavy quarkonium suppression in heavy
ion collisions.Comment: 25 pages, 2 figure
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