108 research outputs found
Chiral perturbation theory with Wilson-type fermions including effects: degenerate case
We have derived the quark mass dependence of , and
, using the chiral perturbation theory which includes the effect
associated with the explicit chiral symmetry breaking of the Wilson-type
fermions, in the case of the degenerate quarks. Distinct features of
the results are (1) the additive renormalization for the mass parameter
in the Lagrangian, (2) corrections to the chiral log ()
term, (3) the existence of more singular term, , generated by
contributions, and (4) the existence of both and terms
in the quark mass from the axial Ward-Takahashi identity, . By
fitting the mass dependence of and , obtained by the
CP-PACS collaboration for full QCD simulations, we have found that the
data are consistently described by the derived formulae. Resumming the most
singular terms , we have also derived the modified formulae, which
show a better control over the next-to-leading order correction.Comment: 21 pages, 4 figures (10 eps files), Revtex4, some discussions and
references added, the final version to appear in PR
Chiral Extrapolations and the Covariant Small Scale Expansion
We calculate the nucleon and the delta mass to fourth order in a covariant
formulation of the small scale expansion. We analyze lattice data from the MILC
collaboration and demonstrate that the available lattice data combined with our
knowledge of the physical values for the nucleon and delta masses lead to
consistent chiral extrapolation functions for both observables up to fairly
large pion masses. This holds in particular for very recent data on the delta
mass from the QCDSF collaboration. The resulting pion-nucleon sigma term is
sigma_{piN} = 48.9 MeV. This first quantitative analysis of the quark-mass
dependence of the structure of the Delta(1232) in full QCD within chiral
effective field theory suggests that (the real part of) the nucleon-delta
mass-splitting in the chiral limit, Delta_0 = 0.33 GeV, is slightly larger than
at the physical point. Further analysis of simultaneous fits to nucleon and
delta lattice data are needed for a precision determination of the properties
of the first excited state of the nucleon.Comment: 11 pp, 2 figs, version accepted for publication in Phys. Lett.
Reducing the Vulnerability of Electric Power Infrastructure Against Natural Disasters by Promoting Distributed Generation
Natural disasters cause significant damage to the electrical power infrastructure every year. Therefore, there is a crucial need to reduce the vulnerability of the electric power grid against natural disasters. Distributed generation (DG) represents small-scale decentralized power generation that can help reduce the vulnerability of the grid, among many other benefits. Examples of DG include small-scale photo-voltaic (PV) systems. Accordingly, the goal of this paper is to investigate the benefits of DG in reducing the vulnerability of the electric power infrastructure by mitigating against the impact of natural disasters on transmission lines. This was achieved by developing a complex system-of-systems (SoS) framework using agent-based modeling (ABM) and optimal power flow (OPF). N-1 contingency analysis and optimization were performed under two approaches: The first approach determined the minimum DG needed at any single location on the electric grid to avoid blackouts. The second approach used a genetic algorithm (GA) to identify the minimum total allocation of DG distributed over the electric grid to mitigate against the failure of any transmission line. Accordingly, the model integrates ABM, OPF, and GA to optimize the allocation of DG and reduce the vulnerability of electric networks. The model was tested on a modified IEEE 6-bus system as a proof of concept. The outcomes of this research are intended to support the understanding of the benefits of DG in reducing the vulnerability of the electric power grid. The presented framework can guide future research concerning policies and incentives that can strategically influence consumer decision to install DG and reduce the vulnerability of the electric power infrastructure
Nucleon mass, sigma term and lattice QCD
We investigate the quark mass dependence of the nucleon mass M_N. An
interpolation of this observable, between a selected set of fully dynamical
two-flavor lattice QCD data and its physical value, is studied using
relativistic baryon chiral perturbation theory up to order p^4. In order to
minimize uncertainties due to lattice discretization and finite volume effects
our numerical analysis takes into account only simulations performed with
lattice spacings a5. We have also restricted ourselves to
data with m_pi<600 MeV and m_sea=m_val. A good interpolation function is found
already at one-loop level and chiral order p^3. We show that the
next-to-leading one-loop corrections are small. From the p^4 numerical analysis
we deduce the nucleon mass in the chiral limit, M_0 approx 0.88 GeV, and the
pion-nucleon sigma term sigma_N= (49 +/- 3) MeV at the physical value of the
pion mass.Comment: 12 pages, 4 figures, revised journal versio
Lattice QCD at the physical point: Simulation and analysis details
We give details of our precise determination of the light quark masses
m_{ud}=(m_u+m_d)/2 and m_s in 2+1 flavor QCD, with simulated pion masses down
to 120 MeV, at five lattice spacings, and in large volumes. The details concern
the action and algorithm employed, the HMC force with HEX smeared clover
fermions, the choice of the scale setting procedure and of the input masses.
After an overview of the simulation parameters, extensive checks of algorithmic
stability, autocorrelation and (practical) ergodicity are reported. To
corroborate the good scaling properties of our action, explicit tests of the
scaling of hadron masses in N_f=3 QCD are carried out. Details of how we
control finite volume effects through dedicated finite volume scaling runs are
reported. To check consistency with SU(2) Chiral Perturbation Theory the
behavior of M_\pi^2/m_{ud} and F_\pi as a function of m_{ud} is investigated.
Details of how we use the RI/MOM procedure with a separate continuum limit of
the running of the scalar density R_S(\mu,\mu') are given. This procedure is
shown to reproduce the known value of r_0m_s in quenched QCD. Input from
dispersion theory is used to split our value of m_{ud} into separate values of
m_u and m_d. Finally, our procedure to quantify both systematic and statistical
uncertainties is discussed.Comment: 45 page
Experimental Tests of Factorization in Charmless Non-Leptonic Two-Body B Decays
Using a theoretical framework based on the next-to-leading order QCD-improved
effective Hamiltonian and a factorization Ansatz for the hadronic matrix
elements of the four-quark operators, we reassess branching fractions in
two-body non-leptonic decays , involving the lowest lying
light pseudoscalar and vector mesons in the standard model. Using
the sensitivity of the decay rates on the effective number of colors, , as
a criterion of theoretical predictivity, we classify all the current-current
(tree) and penguin transitions in five different classes. The recently measured
charmless two-body decays and charge conjugates) are
dominated by the -stable QCD penguins (class-IV transitions) and their
estimates are consistent with data. The measured charmless and transition ,
on the other hand, belong to the penguin (class-V) and tree (class-III)
transitions. The class-V penguin transitions are in general more difficult to
predict. We propose a number of tests of the factorization framework in terms
of the ratios of branching ratios for some selected decays
involving light hadrons and , which depend only moderately on the
form factors. We also propose a set of measurements to determine the effective
coefficients of the current-current and QCD penguin operators. The potential
impact of decays on the CKM phenomenology is emphasized by
analyzing a number of decay rates in the factorization framework.Comment: 64 pages (LaTex) including 13 figures, requires epsfig.sty; submitted
to Phys. Rev.
An analysis of two-body non-leptonic B decays involving light mesons in the standard model
We report a theoretical analysis of the exclusive non-leptonic decays of B
mesons into two light mesons,some of which have been measured recently by the
CLEO collaboration. Our analysis is carried out in the context of an effective
Hamiltonian based on the Standard Model using next-to-leading order
perturbative QCD calculations. Using a factorization ansatz for the hadronic
matrix elements, we show that existing data are accounted for in this approach.
Thus, theoretical scenarios with a substantially enhanced Wilson coefficient of
the chromomagnetic dipole operator (as compared to the SM) and/or those with a
substantial color-singlet component in the wave function of
are not required by these data. Implications of some of these
measurements for the parameters of the CKM matrix are presented.Comment: 42 pages including 21 postscript figures; uses epsfig, some ref.
added; improved mixing scheme for (eta,eta') system implemented; error
corrected in (3.61) as explained below eq. (3.64) in the present version.
Figs. 17-20 update
The Delta-resonance in a finite volume
We study the extraction of Delta-resonance parameters from lattice data for
small quark masses, corresponding to the case of an unstable Delta. To this
end, we calculate the spectrum of the correlator of two Delta-fields in a
finite Euclidian box up-to-and-including O(epsilon^3) in the small scale
expansion using infrared regularization. On the basis of our numerical study,
we argue that the extraction of the parameters of the Delta-resonance (in
particular, of the mass and the pion-nucleon-delta coupling constant) from the
measured volume dependence of the lowest energy levels should be feasible.Comment: 20 pages, 8 postscript figure
Nucleon mass and sigma term from lattice QCD with two light fermion flavors
We analyze Nf=2 nucleon mass data with respect to their dependence on the
pion mass down to mpi = 157 MeV and compare it with predictions from covariant
baryon chiral perturbation theory (BChPT). A novel feature of our approach is
that we fit the nucleon mass data simultaneously with the directly obtained
pion-nucleon sigma-term. Our lattice data below mpi = 435 MeV is well described
by O(p^4) BChPT and we find sigma=37(8)(6) MeV for the sigma-term at the
physical point. Using the nucleon mass to set the scale we obtain a Sommer
parameter of r_0=0.501(10)(11) fm.Comment: 26 pages, 11 figures, 5 tables. Version to appear in NPB with a few
more details on the fit parameter
Light Hadron Spectrum and Quark Masses from Quenched Lattice QCD
We present details of simulations for the light hadron spectrum in quenched
QCD carried out on the CP-PACS parallel computer. Simulations are made with the
Wilson quark action and the plaquette gauge action on 32^3x56 - 64^3x112
lattices at four lattice spacings (a \approx 0.1-0.05 fm) and the spatial
extent of 3 fm. Hadronic observables are calculated at five quark masses
(m_{PS}/m_V \approx 0.75 - 0.4), assuming the u and d quarks being degenerate
but treating the s quark separately. We find that the presence of quenched
chiral singularities is supported from an analysis of the pseudoscalar meson
data. We take m_\pi, m_\rho and m_K (or m_\phi) as input. After chiral and
continuum extrapolations, the agreement of the calculated mass spectrum with
experiment is at a 10% level. In comparison with the statistical accuracy of
1-3% and systematic errors of at most 1.7% we have achieved, this demonstrates
a failure of the quenched approximation for the hadron spectrum: the meson
hyperfine splitting is too small, and the octet masses and the decuplet mass
splittings are both smaller than experiment. Light quark masses are calculated
using two definitions: the conventional one and the one based on the
axial-vector Ward identity. The two results converge toward the continuum
limit, yielding m_{ud}=4.29(14)^{+0.51}_{-0.79} MeV. The s quark mass depends
on the strange hadron mass chosen for input: m_s = 113.8(2.3)^{+5.8}_{-2.9} MeV
from m_K and m_s = 142.3(5.8)^{+22.0}_{-0} MeV from m_\phi, indicating again a
failure of the quenched approximation. We obtain \Lambda_{\bar{MS}}^{(0)}=
219.5(5.4) MeV. An O(10%) deviation from experiment is observed in the
pseudoscalar meson decay constants.Comment: 60 pages, 49 figure
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