436 research outputs found
Electromagnetic corrections to light hadron masses
At the precision reached in current lattice QCD calculations, electromagnetic
effects are becoming numerically relevant. We will present preliminary results
for electromagnetic corrections to light hadron masses, based on simulations in
which a degree of freedom is superimposed on QCD
configurations from the BMW collaboration.Comment: 7 pages, 2 figures, The XXVIII International Symposium on Lattice
Field Theory, June 14-19,2010, Villasimius, Sardinia Ital
Experimental quantum tossing of a single coin
The cryptographic protocol of coin tossing consists of two parties, Alice and
Bob, that do not trust each other, but want to generate a random bit. If the
parties use a classical communication channel and have unlimited computational
resources, one of them can always cheat perfectly. Here we analyze in detail
how the performance of a quantum coin tossing experiment should be compared to
classical protocols, taking into account the inevitable experimental
imperfections. We then report an all-optical fiber experiment in which a single
coin is tossed whose randomness is higher than achievable by any classical
protocol and present some easily realisable cheating strategies by Alice and
Bob.Comment: 13 page
Rho decay width from the lattice
The XXVIII International Symposium on Lattice Field Theory, June 14-19, 2010, Villasimius, Sardinia ItalyInternational audienceWhile the masses of light hadrons have been extensively studied in lattice QCD simulations, there exist only a few exploratory calculations of the strong decay widths of hadronic resonances. We will present preliminary results of a computation of the rho meson width obtained using flavor simulations. The work is based on L\"uscher's formalism and its extension to moving frames
Ab-initio Determination of Light Hadron Masses
More than 99% of the mass of the visible universe is made up of protons and
neutrons. Both particles are much heavier than their quark and gluon
constituents, and the Standard Model of particle physics should explain this
difference. We present a full ab-initio calculation of the masses of protons,
neutrons and other light hadrons, using lattice quantum chromodynamics. Pion
masses down to 190 mega electronvolts are used to extrapolate to the physical
point with lattice sizes of approximately four times the inverse pion mass.
Three lattice spacings are used for a continuum extrapolation. Our results
completely agree with experimental observations and represent a quantitative
confirmation of this aspect of the Standard Model with fully controlled
uncertainties.Comment: 22 pages, 3 Tables, 8 Figures. Published in Science (21 November
2008) with Supporting Online Material. Submission to arXiv has been delayed
by 6 months to respect the journal's embargo polic
Sigma term and strangeness content of the nucleon
A status report is given for a joint project of the
Budapest-Marseille-Wuppertal collaboration and the Regensburg group to study
the quark mass-dependence of octet baryons in SU(3) Baryon XPT. This
formulation is expected to extend to larger masses than Heavy-Baryon XPT. Its
applicability is tested with 2+1 flavor data which cover three lattice spacings
and pion masses down to about 190 MeV, in large volumes. Also polynomial and
rational interpolations in M_\pi^2 and M_K^2 are used to assess the uncertainty
due to the ansatz. Both frameworks are combined to explore the precision to be
expected in a controlled determination of the nucleon sigma term and
strangeness content.Comment: Lattice 201
Urban agriculture: a global analysis of the space constraint to meet urban vegetable demand
Urban agriculture (UA) has been drawing a lot of attention recently for several reasons: the majority of the world population has shifted from living in rural to urban areas; the environmental impact of agriculture is a matter of rising concern; and food insecurity, especially the accessibility of food, remains a major challenge. UA has often been proposed as a solution to some of these issues, for example by producing food in places where population density is highest, reducing transportation costs, connecting people directly to food systems and using urban areas efficiently. However, to date no study has examined how much food could actually be produced in urban areas at the global scale. Here we use a simple approach, based on different global-scale datasets, to assess to what extent UA is constrained by the existing amount of urban space. Our results suggest that UA would require roughly one third of the total global urban area to meet the global vegetable consumption of urban dwellers. This estimate does not consider how much urban area may actually be suitable and available for UA, which likely varies substantially around the world and according to the type of UA performed. Further, this global average value masks variations of more than two orders of magnitude among individual countries. The variations in the space required across countries derive mostly from variations in urban population density, and much less from variations in yields or per capita consumption. Overall, the space required is regrettably the highest where UA is most needed, i.e., in more food insecure countries. We also show that smaller urban clusters (i.e., <100 km2 each) together represent about two thirds of the global urban extent; thus UA discourse and policies should not focus on large cities exclusively, but should also target smaller urban areas that offer the greatest potential in terms of physical space
Isospin splittings in the light-baryon octet from lattice QCD and QED
While electromagnetic and up-down quark mass difference effects on octet
baryon masses are very small, they have important consequences. The stability
of the hydrogen atom against beta decay is a prominent example. Here we include
these effects by adding them to valence quarks in a lattice QCD calculation
based on simulations with 5 lattice spacings down to 0.054 fm,
lattice sizes up to 6 fm and average up-down quark masses all the way down to
their physical value. This allows us to gain control over all systematic
errors, except for the one associated with neglecting electromagnetism in the
sea. We compute the octet baryon isomultiplet mass splittings, as well as the
individual contributions from electromagnetism and the up-down quark mass
difference. Our results for the total splittings are in good agreement with
experiment.Comment: 5 pages, 3 figures. Version accepted for publication by Phys. Rev.
Let
Sigma term and strangeness content of octet baryons
By using lattice QCD computations we determine the sigma terms and
strangeness content of all octet baryons by means of an application of the
Hellmann-Feynman theorem. In addition to polynomial and rational expressions
for the quark mass dependence of octet members, we use SU(3) covariant baryon
chiral perturbation theory to perform the extrapolation to the physical up and
down quark masses. Our N_f=2+1 lattice ensembles include pion masses down to
about 190 MeV in large volumes (M_\pi L > 4), and three values of the lattice
spacing. Our main results are the nucleon sigma term \sigma_{\pi N} =
39(4)(^{+18}_{-7}) and the strangeness content y_{N} = 0.20(7)(^{+13}_{-17}).
Under the assumption of validity of covariant baryon \chi PT in our range of
masses one finds y_{N} = 0.276(77)(^{+90}_{-62}).Comment: LaTeX. 15 pages, 5 figures. Text and results corrected according to
Erratum [Phys. Rev. D 93, 039905(E) (2016)
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