97 research outputs found
Isospin-0 s-wave scattering length from twisted mass lattice QCD
We present results for the isospin-0 s-wave scattering length
calculated with Osterwalder-Seiler valence quarks on Wilson twisted mass gauge
configurations. We use three ensembles with unitary (valence) pion
mass at its physical value (250MeV), at 240MeV (320MeV) and
at 330MeV (400MeV), respectively. By using the stochastic Laplacian
Heaviside quark smearing method, all quark propagation diagrams contributing to
the isospin-0 correlation function are computed with sufficient
precision. The chiral extrapolation is performed to obtain the scattering
length at the physical pion mass. Our result agrees reasonably well with various experimental measurements and
theoretical predictions. Since we only use one lattice spacing, certain
systematics uncertainties, especially those arising from unitary breaking, are
not controlled in our result.Comment: 21 pages, 5 figures, 6 table
Ratio of kaon and pion leptonic decay constants with Wilson-clover twisted-mass fermions
We present a determination of the ratio of kaon and pion leptonic decay
constants in isosymmetric QCD (isoQCD), , making use of the gauge
ensembles produced by the Extended Twisted Mass Collaboration (ETMC) with flavors of Wilson-clover twisted-mass quarks, including
configurations close to the physical point for all dynamical flavors. The
simulations are carried out at three values of the lattice spacing ranging from
to fm with linear lattice size up to ~fm.
The scale is set by the PDG value of the pion decay constant, MeV, at the isoQCD pion point, MeV,
obtaining for the gradient-flow (GF) scales the values fm,
fm and fm. The data are
analyzed within the framework of SU(2) Chiral Perturbation Theory (ChPT)
without resorting to the use of renormalized quark masses. At the isoQCD kaon
point MeV we get , where the error includes both statistical and systematic
uncertainties. Implications for the Cabibbo-Kobayashi-Maskawa (CKM) matrix
element and for the first-row CKM unitarity are discussed.Comment: 68 pages, 14 figures, 12 tables. Version to appear in PR
Time windows of the muon HVP from twisted-mass lattice QCD
We present a lattice determination of the leading-order hadronic vacuum polarization (HVP) contribution to the muon anomalous magnetic moment, aHVPμ , in the so-called short and intermediate time-distance windows, aSDμ and aWμ . We employ gauge ensembles produced by the Extended Twisted Mass Collaboration (ETMC) with Nf=2+1+1
flavours of Wilson-clover twisted-mass quarks with masses of all the dynamical quark flavours tuned close to their physical values. The simulations are carried out at three values of the lattice spacing equal to ≃0.057,0.068 and 0.080 fm with spatial lattice sizes up to L≃7.6 ~fm. For the short distance window we obtain aSDμ=69.27(34)⋅10−10
, in agreement with the dispersive determination based on experimental e+e−
data. For the intermediate window we get instead aWμ=236.3(1.3)⋅10−10
, which is consistent with recent determinations by other lattice collaborations, but disagrees with the dispersive determination at the level of 3.6σ
Optical Absorption of an Interacting Many-Polaron Gas
The optical absorption of a many (continuum) polaron gas is derived in the
framework of a variational approach at zero temperature and weak or
intermediate electron-phonon coupling strength. We derive a compact formula for
the optical conductivity of the many-polaron system taking into account
many-body effects in the electron or hole system. Within the method presented
here, these effects are contained completely in the dynamical structure factor
of the electron or hole system. This allows to build on well-established
studies of the interacting electron gas. Based on this approach a novel feature
in the absorption spectrum of the many-polaron gas, related to the emission of
a plasmon together with a phonon, is identified. As an application and
illustration of the technique, we compare the theoretical many-polaron optical
absorption spectrum as derived in the present work with the `d-band' absorption
feature in NdCuO. Similarities are shown between the theoretically
and the experimentally derived first frequency moment of the optical absorption
of a family of differently doped NdCeCuO materials.Comment: 24 pages, 5 figures; revised and expanded versio
Pion vector form factor from lattice QCD at the physical point
We present an investigation of the electromagnetic pion form factor, FπðQ2Þ, at small values of the four- momentum transfer Q2 (≲0.25 GeV2), based on the gauge configurations generated by the European Twisted Mass Collaboration with Nf = 2 twisted-mass quarks at maximal twist including a clover term. Momentum is injected using nonperiodic boundary conditions and the calculations are carried out at a fixed lattice spacing (a ≃ 0.09 fm) and with pion masses equal to its physical value, 240 MeV and 340 MeV. Our data are successfully analyzed using chiral perturbation theory at next-to-leading order in the light-quark mass. For each pion mass two different lattice volumes are used to take care of finite size effects. Our final result for the squared charge radius is hr2iπ = 0.443ð29Þ fm2, where the error includes several sources of systematic errors except the uncertainty related to discretization effects. The corresponding value of the SU(2) chiral low-energy constant l ̄6 is equal to l ̄6 = 16.2ð1.0Þ
Isospin-0 ππ scattering from twisted mass lattice QCD
We present results for the isospin-0 s-wave scattering length
calculated in twisted mass lattice QCD. We use three ensembles with
unitary pion mass at its physical value, 240~MeV and 330~MeV respectively. We
also use a large set of ensembles with unitary pion masses
varying in the range of 230~MeV - 510~MeV at three different values of the
lattice spacing. A mixed action approach with the Osterwalder-Seiler action in
the valence sector is adopted to circumvent the complications arising from
isospin symmetry breaking of the twisted mass quark action. Due to the
relatively large lattice artefacts in the ensembles, we do not
present the scattering lengths for these ensembles. Instead, taking the
advantage of the many different pion masses of these ensembles, we
qualitatively discuss the pion mass dependence of the scattering properties of
this channel based on the results from the ensembles. The
scattering length is computed for the ensembles and the chiral
extrapolation is performed. At the physical pion mass, our result agrees reasonably well with various
experimental measurements and theoretical predictions
The Role of CO2-EOR for the Development of a CCTS Infrastructure in the North Sea Region: A Techno-Economic Model and Application
Scenarios of future energy systems attribute an important role to Carbon Capture, Transport, and Storage (CCTS) in achieving emission reductions. Using captured CO2 for enhanced oil recovery (CO2-EOR) can improve the economics of the technology. This paper examines the potential for CO2-EOR in the North Sea region. UK oil fields are found to account for 47% of the estimated additional recovery potential of 3739 Mbbl (1234 MtCO2 of storage potential). Danish and Norwegian fields add 28% and 25%, respectively. Based on a comprehensive dataset, the paper develops a unique techno-economic market equilibrium model of CO2 supply from emission sources and CO2 demand from CO2-EOR to assess implications for a future CCTS infrastructure. A detailed representation of decreasing demand for fresh CO2 for CO2-EOR operation is accomplished via an exponential storage cost function. In all scenarios of varying CO2 and crude oil price paths the assumed CO2-EOR potential is fully exploited. CO2-EOR does add value to CCTS operations but the potential is very limited and does not automatically induce long term CCTS activity. If CO2 prices stay low, little further use of CCTS can be expected after 2035
The Nexus Bioenergy-Economy-Land-use-GHG Emissions: Experience from Colombia
In the 20th century, industrialization and population growth led to a rapid increase in world energy consumption. This trend has been followed in recent years by various emerging economies (e.g. BRICS) and it is likely that other developing countries move along that path in the future. However, the need to meet a growing energy demand to sustain economic growth has resulted in serious negative impacts including climate change, deforestation, soil and water contamination, loss of biodiversity and concerns on water supply.
The depth and intensity of linkages between climate, energy, water, land and development make a multidisciplinary approach necessary, in order to thoroughly investigate their nexus and achieve a more efficient use of resources as well as cross-sectorial consistence.
In this context, this lecture presents some guidelines gained by applying a modeling framework which addresses the energy, economy, emissions and land use nexus when exploiting bioenergy in developing countries. The modeling framework combines a qualitative and a quantitative element. The qualitative element integrates two components: 1) technology roadmapping to identify long-term technology targets through expert judgment and 2) scenario analysis to investigate different future storylines. The quantitative element comprises four integrated tools, namely the energy system model (ESM), the land use and trade model (LUTM), an economic model, and an external climate model. An overview of the modeling framework, scenario analysis, structure of the models, modelling techniques, mathematical formulations and assumptions is presented and discussed.
The modeling framework is applied to the particular context of Colombia, as a case study of a developing country with large bioenergy potential. The impacts that an accelerated deployment of bioenergy technologies might cause on the energy demand and supply, emissions and land use until 2030 are evaluated
Methodology for improving the reliability of biomass energy potential estimation
This paper presents a novel approach to address uncertainty and improve reliability of the estimation of the biomass energy potential at a country level, particularly suitable for situations when quality and availability of data are limited. The proposed methodology improves the prediction reliability by following four steps: 1) using a simple accounting framework, 2) using a robust selection of probability density functions, 3) using a probabilistic propagation of uncertainty and 4) using sensitivity analysis to identify key variables contributing to uncertainty as well as a root cause analysis and a set of sub-models to improve estimation of key variables.
The application of the methodology to the energy scenario in Colombia shows that the improved estimation of the theoretical energy potential has an almost identical mean value compared to the preliminary estimate, but the uncertainty is significantly lower (less than 50%). Moreover, the mean value of the technical energy potential obtained through the methodology is 25% lower than the preliminary potential and the uncertainty reduces by one third
- …