80 research outputs found
Bandgap and effective mass of epitaxial cadmium oxide
The bandgap and band-edge effective mass of single crystal cadmium oxide, epitaxially grown by metal-organic vapor-phase epitaxy, are determined from infrared reflectivity, ultraviolet/visible absorption, and Hall effect measurements. Analysis and simulation of the optical data, including effects of band nonparabolicity, Moss-Burstein band filling and bandgap renormalization, reveal room temperature bandgap and band-edge effective mass values of 2.16±0.02 eV and 0.21±0.01m0 respectively
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
Complete flavor decomposition of the spin and momentum fraction of the proton using lattice QCD simulations at physical pion mass
We evaluate the gluon and quark contributions to the spin of the proton using
an ensemble of gauge configuration generated at physical pion mass. We compute
all valence and sea quark contributions to high accuracy. We perform a
non-perturbative renormalization for both quark and gluon matrix elements. We
find that the contribution of the up, down, strange and charm quarks to the
proton intrinsic spin is
and to the total spin
. The gluon contribution to the spin is
yielding confirming the spin sum. The
momentum fraction carried by quarks in the proton is found to be
and by gluons , the sum of which gives confirming the
momentum sum rule. All scale and scheme dependent quantities are given in the
scheme at 2 GeV
Nucleon axial, tensor and scalar charges and -terms in lattice QCD
We determine the nucleon axial, scalar and tensor charges within lattice
Quantum Chromodynamics including all contributions from valence and sea quarks.
We analyze three gauge ensembles simulated within the twisted mass
formulation at approximately physical value of the pion mass. Two of these
ensembles are simulated with two dynamical light quarks and lattice spacing
~fm and the third with ~fm includes in addition the strange
and charm quarks in the sea. After comparing the results among these three
ensembles, we quote as final values our most accurate analysis using the latter
ensemble.
For the nucleon isovector axial charge we find in agreement with
the experimental value. We provide the flavor decomposition of the intrinsic
spin carried by quarks in the nucleon obtaining for
the up, down, strange and charm quarks ,
,
and
, respectively. The corresponding values
of the tensor and scalar charges for each quark flavor are also evaluated
providing valuable input for experimental searches for beyond the standard
model physics.
In addition, we extract the nucleon -terms and find for the light
quark content ~MeV and for the strange
~MeV. The y-parameter that is used in phenomenological
studies we find .Comment: Expanded version as accepted in Phys. Rev. D.20 pages and 20 figure
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
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
Pion transition form factor from twisted-mass lattice QCD and the hadronic light-by-light π 0 -pole contribution to the muon g − 2
The neutral pion generates the leading pole contribution to the hadronic
light-by-light tensor, which is given in terms of the nonperturbative
transition form factor . Here we
present an ab-initio lattice calculation of this quantity in the continuum and
at the physical point using twisted-mass lattice QCD. We report our results for
the transition form factor parameterized using a model-independent conformal
expansion valid for arbitrary space-like kinematics and compare it with
experimental measurements of the single-virtual form factor, the two-photon
decay width, and the slope parameter. We then use the transition form factors
to compute the pion-pole contribution to the hadronic light-by-light scattering
in the muon , finding .Comment: 21 pages, 17 figures, 4 tables, updated to published versio
Pseudoscalar-pole contributions to the muon at the physical point
Pseudoscalar-pole diagrams are an important component of estimates of the
hadronic light-by-light (HLbL) contribution to the muon g−2. We report on our computation of the transition form factors P→γ∗γ∗ for the neutral pseudoscalar mesons P=π0
and η . The calculation is performed using twisted-mass lattice QCD with physical quark masses. On the lattice, we have access to a broad range of (space-like) photon four-momenta and therefore produce form factor data complementary to the experimentally accessible single-virtual direction, which directly leads to an estimate of the pion- and η
-pole components of the muon g−2 . For the pion, our result for the g−2 contribution in the continuum is comparable with previous lattice and data-driven determinations, with combined relative uncertainties below 10% . For the η meson, we report on a preliminary determination from a single lattice spacing
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