507 research outputs found
Infrared Renormalons and Finite Volume
We analyze the perturbative expansion of a condensate in the O(N) non-linear
sigma model for large N on a two dimensional finite lattice. On an infinite
volume this expansion is affected by an infrared renormalon. We extrapolate
this analysis to the case of the gluon condensate of Yang-Mills theory and
argue that infrared renormalons can be detected by performing perturbative
studies even on relatively small lattices.Comment: LaTeX file, 6 figures in postscrip
Topology in 2D CP**(N-1) models on the lattice: a critical comparison of different cooling techniques
Two-dimensional CP**(N-1) models are used to compare the behavior of
different cooling techniques on the lattice. Cooling is one of the most
frequently used tools to study on the lattice the topological properties of the
vacuum of a field theory. We show that different cooling methods behave in an
equivalent way. To see this we apply the cooling methods on classical
instantonic configurations and on configurations of the thermal equilibrium
ensemble. We also calculate the topological susceptibility by using the cooling
technique.Comment: 24 pages, 10 figures (from 16 eps files
Sbacchiite, Ca2AlF7, a new fumarolic mineral from the Vesuvius volcano, Napoli, Italy
The new mineral sbacchiite (IMA 2017-097), Ca2AlF7, was found in a fossil fumarole (1944 eruption, T 80 C) at the rim of the crater of the Vesuvius volcano, Napoli, Italy, associated with gearsksutite, usovite, creedite and opal. It forms elongated crystals up to about 60 lm in length. On the basis of powder X-ray diffraction data and chemical analysis, the mineral was
recognized to be identical to the corresponding synthetic phase. Crystals are transparent or translucent and colourless, with vitreous lustre and white streak. The tenacity is brittle. The measured density is 3.08(2) g/cm3, the calculated density is 3.116 g/cm3. The empirical formula, (based on 10 atoms per formula unit, apfu) is Ca2.02Mg0.03Al0.99F6.97. Sbacchiite is orthorhombic, space group Pnma, with a = 7.665(2), b = 6.993(1), c = 9.566(2) \uc5, V = 512.2(2) \uc53 and Z = 4. The eight strongest X-ray powder diffraction lines are [dobs \uc5(I)(hkl)]: 3.840(45)(200), 3.563(85)(201), 3.499(100)(020), 2.899(55)(013), 2.750(30)(212), 2.281(20)(104), 2.255(52)(302) and 2.173(36)(131). The structure was refined to R = 0.0479 for 457 reflections with I > 2r(I). The asymmetric unit
contains one Al3+ and two independent Ca2+ cations and five fluorine anions. Aluminium is octahedrally coordinated by six fluorine atoms; the arrangement of F around the 7-coordinated Ca(1) conforms to a distorted pentagonal bipyramid and that around Ca(2) to a very distorted polyhedron (in 7 + 1 coordination). All the fluorine atoms are threefold coordinated. The structure framework shows \u2018\u2018isolated\u2019\u2019 [AlF6] octahedra, whereas the coordination polyhedra around Ca are linked by common edges [sequence: Ca(1)\u2013Ca(2)\u2013Ca(1). . .] along [010] and the same holds for the connection along [001]. Along [100], however, only the pentagonal bipyramids around Ca(1) are connected by bridging corners
Acmonidesite, a new ammonium sulfate chloride from La Fossa crater, Vulcano, Aeolian Islands, Italy
The new mineral acmonidesite, (NH4,K,Pb2+,Na)9Fe42+(SO4)5Cl8, was found in an active fumarole (fumarole FA, temperature 3c250\ub0C) at La Fossa crater, Vulcano, Aeolian Islands, Sicily, Italy. It occurs on a pyroclastic breccia as brown prismatic crystals up to 0.10 mm long, in association with salammoniac, alunite and adranosite. The mineral is orthorhombic, space group C2221 (no. 20) with a = 9.841(1), b = 19.448(3) c = 17.847(3) \uc5, V = 3415.7(9) \uc53 and Z = 4. The six strongest reflections in the powder X-ray diffraction pattern are: [dobs in \uc5(I)(hkl)] 8.766(100)(110), 1.805(88)(390), 5.178(45)(131), 4.250(42)(221), 2.926(42)(330) and 2.684(32)(261). The empirical formula (based on 28 anions per formula unit [pfu]) is (NH4)5.77K1.42Pb0.62Na1.24Fe3.96Mn0.08S5.04O20.16Cl7.97Br0.08. The idealised formula is (NH4,K,Pb2+,Na)9Fe42+(SO4)5Cl8. The calculated density is 2.551 g cm\u20133. Using single-crystal diffraction data, the structure was refined to a final R(F) = 0.0363 for 4614 independent observed reflections [I > 2\u3c3(I)]. The structure contains two independent, distorted octahedral iron sites, Fe1 and Fe2, with the iron atoms in the 2+ oxidation state, as confirmed by the interatomic distances and bond-valence calculations (2.06 and 1.94 vu, respectively). Fe1 is surrounded by two chlorine atoms and four oxygens of the sulfate ions, with the following average distances (\uc5): Fe1\u2013O 2.125 and Fe1\u2013Cl 2.472; and Fe2 is surrounded by three chlorine atoms and three oxygens of the sulfate ions, with the following average distances (\uc5): Fe2\u2013O 2.110 and Fe2\u2013Cl 2.531. Three independent sulfate anions are also present and are connected with the iron polyhedra to form a three-dimensional structure containing voids occupied by four independent ammonium ions (two of them partially replaced by K+), one Na+/Pb2+ site and one Cl\u2013 ion
Confinement from Instantons or Merons
In contrast to ensembles of singular gauge instantons, which are well known
to fail to produce confinement, it is shown that effective theories based on
ensembles of merons or regular gauge instantons do produce confinement.
Furthermore, when the scale is set by the string tension, the action density,
topological susceptibility, and glueball masses are similar to those arising in
lattice QCD.Comment: 3 pages, 5 figures. Talk given at Lattice2004 (topology and
confinement) Fermilab June 21-26, 200
The Intrinsic Coupling in Integrable Quantum Field Theories
The intrinsic 4-point coupling, defined in terms of a truncated 4-point
function at zero momentum, provides a well-established measure for the
interaction strength of a QFT. We show that this coupling can be computed
non-perturbatively and to high accuracy from the form factors of an
(integrable) QFT. The technique is illustrated and tested with the Ising model,
the XY-model and the O(3) nonlinear sigma-model. The results are compared to
those from high precision lattice simulations.Comment: 69 pages, Late
Renormalon disappearance in Borel sum of the 1/N expansion of the Gross-Neveu model mass gap
The exact mass gap of the O(N) Gross-Neveu model is known, for arbitrary ,
from non-perturbative methods. However, a "naive" perturbative expansion of the
pole mass exhibits an infinite set of infrared renormalons at order 1/N,
formally similar to the QCD heavy quark pole mass renormalons, potentially
leading to large perturbative ambiguities. We examine the
precise vanishing mechanism of such infrared renormalons, which avoids this
(only apparent)contradiction, and operates without need of (Borel) summation
contour prescription, usually preventing unambiguous separation of perturbative
contributions. As a consequence we stress the direct Borel summability of the
(1/N) perturbative expansion of the mass gap. We briefly speculate on a
possible similar behaviour of analogous non-perturbative QCD quantities.Comment: 16 pp., 1 figure. v2: a few paragraphs and one appendix added, title
and abstract slightly changed, essential results unchange
Large-N phase transition in lattice 2-d principal chiral models
We investigate the large-N critical behavior of 2-d lattice chiral models by
Monte Carlo simulations of U(N) and SU(N) groups at large N. Numerical results
confirm strong coupling analyses, i.e. the existence of a large-N second order
phase transition at a finite .Comment: 12 pages, Revtex, 8 uuencoded postscript figure
Ritrovamento di Atacamite in cristalli al Vesuvio
In the small vacuoles of an older lava from one
of the quarries of Villa Inglese (Torre del Greco,
Napoli) atacamite as crystalline have been
discovered. This is a rare event in this volcanic
complex
Nuovo ritrovamento di corindone al Monte Somma
After the occurrence described by of Balassone et al. (2001), a second finding of corundum, Al2O3, occurred
in a small fragment of carbonatic rock at San Vito quarry, Ercolano, Napoli, Campania. It is the section
of a 2 mm bluish crystal. The identification was done through SEM-EDX analysis at 30 kV excitation
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