1,913 research outputs found
Perturbative renormalization of the first moment of structure functions for domain-wall QCD
Using the domain-wall formulation of lattice fermions, we have computed the
one-loop renormalization factors of one-link operators which measure the first
nontrivial moment of the unpolarized, polarized and transversity structure
functions, in the flavor nonsinglet sector. The knowledge of these factors is
necessary in order to extract physical numbers from domain-wall Monte Carlo
simulations of parton distributions.
We have automated the perturbative calculations by developing suitable FORM
codes. The results show that in many instances the total renormalization
factors are almost equal to one, and that hence the corresponding operators
are, for the appropriate values of the Dirac mass and the coupling ,
practically unrenormalized.Comment: REVTeX 4, 12 pages, 1 figure; changes in the final paragraphs of
sections 1 and 5 concerning comparisons with previous results, plus
correction of minor typos; final version, accepted for publication in
Physical Review
A lattice calculation of the pion form factor with Ginsparg-Wilson-type fermions
Results for Monte Carlo calculations of the electromagnetic vector and scalar
form factors of the pion in a quenched simulation are presented. We work with
two different lattice volumes up to a spatial size of 2.4 fm at a lattice
spacing of 0.148 fm. The pion form factors in the space-like region are
determined for pion masses down to 340 MeV.Comment: REVTeX 4, 8 pages, 9 figures, 4 tables; final versio
Progress towards a lattice determination of (moments of) nucleon structure functions
Using unimproved and non-perturbatively O(a) improved Wilson fermions,
results are given for the three lowest moments of unpolarised nucleon structure
functions. Renormalisation, chiral extrapolation and the continuum limit of the
matrix elements are briefly discussed. The simulations are performed for both
quenched and two flavours of unquenched fermions. No obvious sign of deviation
from linearity in the chiral extrapolations are found. (This is most clearly
seen in our quenched unimproved data, which extends to lighter quark mass.)
Possible quenching effects also seem to be small. The lowest moment thus
remains too large, so it seems to be necessary to reach smaller quark masses in
numerical simulations.Comment: 3 pages, Latex, 4 figures, Talk presented at
Lattice2001(matrixelement
Perturbative Renormalization of Improved Lattice Operators
We derive bases of improved operators for all bilinear quark currents up to
spin two (including the operators measuring the first moment of DIS Structure
Functions), and compute their one-loop renormalization constants for arbitrary
coefficients of the improvement terms. We have thus control over O(a)
corrections, and for a suitable choice of improvement coefficients we are only
left with errors of O(a^2).Comment: 4 pages, LaTeX + 1 eps file + epscrc2.sty (included). Talk given to
the Lattice 97 International Symposium, 22-26 July 1997, Edinburgh, UK. Minor
changes in notatio
3-point functions from twisted mass lattice QCD at small quark masses
We show at the example of the matrix element between pion states of a
twist-2, non-singlet operator that Wilson twisted mass fermions allow to
compute this phenomenologically relevant quantitiy at small pseudo scalar
masses of O(270 MeV). In the quenched approximation, we investigate the scaling
behaviour of this observable that is derived from a 3-point function by
applying two definitions of the critical mass and find a scaling compatible
with the expected O(a^2) behaviour in both cases. A combined continuum
extrapolations allows to obtain reliable results at small pion masses, which
previously could not be explored by lattice QCD simulations.Comment: 6 pages, 2 figures, talk presented at Lattice 200
Data security issues in cloud scenarios
The amount of data created, stored, and processed has enormously increased in the last years. Today, millions of devices are connected to the Internet and generate a huge amount of (personal) data that need to be stored and processed using scalable, efficient, and reliable computing infrastructures. Cloud computing technology can be used to respond to these needs. Although cloud computing brings many benefits to users and companies, security concerns about the cloud still represent the major impediment for its wide adoption.
We briefly survey the main challenges related to the storage and processing of data in the cloud. In particular, we focus on the problem of protecting data in storage, supporting fine-grained access, selectively sharing data, protecting query privacy, and verifying the integrity of computations
Renormalization of minimally doubled fermions
We investigate the renormalization properties of minimally doubled fermions,
at one loop in perturbation theory. Our study is based on the two particular
realizations of Borici-Creutz and Karsten-Wilczek. A common feature of both
formulations is the breaking of hyper-cubic symmetry, which requires that the
lattice actions are supplemented by suitable counterterms. We show that three
counterterms are required in each case and determine their coefficients to one
loop in perturbation theory. For both actions we compute the vacuum
polarization of the gluon. It is shown that no power divergences appear and
that all contributions which arise from the breaking of Lorentz symmetry are
cancelled by the counterterms. We also derive the conserved vector and
axial-vector currents for Karsten-Wilczek fermions. Like in the case of the
previously studied Borici-Creutz action, one obtains simple expressions,
involving only nearest-neighbour sites. We suggest methods how to fix the
coefficients of the counterterms non-perturbatively and discuss the
implications of our findings for practical simulations.Comment: 23 pages, 1 figur
- …