80 research outputs found
Topological excitations in statistical field theory at the upper critical dimension
We present a high-precision Monte Carlo study of the classical Heisenberg
model in four dimensions, showing that in the broken-symmetry phase it supports
topological, monopole-like excitations, whose properties confirm previous
analytical predictions derived in quantum field theory. We discuss the
relevance of these findings and their possible experimental applications in
condensed-matter physics.Comment: 1+13 pages, 9 pdf figures; v2: typos corrected, version published in
the journa
Confinement-deconfinement and universal string effects from random percolation
The 't Hooft criterion leading to confinement out of a percolating cluster of
central vortices suggests defining a novel three-dimensional gauge theory
directly on a random percolation process. Wilson loop is viewed as a counter of
topological linking with the random clusters. Beyond the percolation threshold
large Wilson loops decay with an area law and show the universal shape effects
due to flux tube fluctuations. Wilson loop correlators define a non-trivial
glueball spectrum. The crumbling of the percolating cluster when one periodic
direction narrows accounts for the finite temperature deconfinement, which
belongs to 2D percolation universality class.Comment: 3 pages, Lattice2003(topology
The quenched glueball spectrum from smeared spectral densities
The standard approach to compute the glueball spectrum on the lattice relies
on the evaluation of effective masses from two-point correlation functions of
operators with the quantum numbers of the desired state. In this work, we
propose an alternative procedure, based on the numerical computation of smeared
spectral densities. Even though the extraction of the latter from lattice
correlators is a notoriously ill-posed inverse problem, we show that a recently
developed numerical method, based on the Backus-Gilbert regularization,
provides a robust way to evaluate a smeared version of the spectral densities.
Fitting the latter to a combination of Gaussians, we extract the masses of the
lightest glueball and of its first excitation in the spectrum of the theory.
While the preliminary results presented in this contribution are restricted to
simulations at finite lattice spacing and finite volume, and for the purely
gluonic sector of QCD, they represent the first step in a systematic
investigation of glueballs using spectral-reconstruction methods.Comment: 10 pages, 3 figures, contribution to the 40th International Symposium
on Lattice Field Theory, 31st of July - 4th of August, 2023, Fermilab,
Batavia, U.S.
Fine corrections in the effective string describing SU(2) Yang-Mills theory in three dimensions
Nanostructured tin-carbon/ LiNi0.5Mn1.5O4 lithium-ion battery operating at low temperature
An advanced lithium ion battery using nanostructured tinecarbon lithium alloying anode and a high voltage LiNi0.5Mn1.5O4 spinel-type cathode is studied, with particular focus to the low temperature range. The stable behavior of the battery is assured by the use of an electrolyte media based on a LiPF6 salt dissolved in EC-DEC-DMC, i.e. a mixture particularly suitable for the low temperature application. Cycling tests, both in half cells and in full lithium ion battery using the SneC anode and the LiNi0.5Mn1.5O4 cathode, performed in a temperature range extending from room temperature to "30 C, indicate that the electrode/electrolyte configuration here adopted may be suitable for effective application in the lithium ion battery field. The full cell, cycled at -5 °C, shows stable capacity of about 105 mAh g-1 over more than 200 chargee-discharge cycles that is considered a relevant performance considering the low temperature region
Lattice QCD study of inclusive semileptonic decays of heavy mesons
We present an ab initio study of inclusive semileptonic decays of heavy
mesons from lattice QCD. Our approach is based on a recently proposed method,
that allows one to address the study of these decays from the analysis of
smeared spectral functions extracted from four-point correlators on the
lattice, where the smearing is defined in terms of the phase-space integration
relevant to the inclusive decays. We present results obtained from gauge-field
ensembles from the JLQCD and ETM collaborations, and discuss their relation
with theoretical predictions from the operator-product expansion.Comment: 49 pages, 25 figures and 4 table
Inclusive semileptonic -decays from lattice QCD
We present the lattice QCD calculation of inclusive semileptonic -meson
decays. We follow a recently proposed method, which is based on the extraction
of smeared spectral densities from Euclidean correlation functions and on the
numerical reconstruction of the integration kernel relevant for the inclusive
decay rate calculation. We compute four-point Euclidean correlation functions
using JLQCD and ETM gauge ensembles with unphysically light -quark masses,
and apply two different methods for the integration kernel reconstruction.
Finally, we show that the lattice results obtained in this work are in good
agreement with the analytic predictions of the operator-product-expansion. This
opens the path for a future full lattice QCD calculation to be used as
theoretical input for the determination of the magnitude of the CKM element
.Comment: 10 pages, 4 figures, contribution to the 39th International Symposium
on Lattice Field Theory, 8th-13th August, 2022, Bonn, Germany. arXiv admin
note: substantial text overlap with arXiv:2209.1549
Towards the computation of inclusive decay rates using lattice QCD
We present a non-perturbative computation of inclusive rates of semileptonic
decays of heavy mesons from lattice QCD simulations. The calculation is based
on the extraction of smeared spectral functions obtained from four-point
Euclidean correlation functions computed on configuration ensembles of the
JLQCD and ETM collaborations. We compare our results for the inclusive decay
rates with analytical predictions from the operator-product expansion, finding
a good agreement for the calculation of the inclusive decay rate. This opens
the path to the theoretical determination of the magnitude of the
Cabibbo-Kobayashi-Maskawa matrix element to a level of precision
competitive with the present experimental uncertainty.Comment: 7 pages, 1 figure, to appear in the proceedings of the 51st
International Symposium on Multiparticle Dynamics (ISMD
Electrochemical synthesis of nanowires electrodes and their application in energy storage devices
In this work, an electrochemical approach to synthesize Metal-MetalOxide/Hydroxide core-shell nanowires electrodes (NWE) is illustrated. NWE electrodes were obtained by electrodeposition of a targeted metal into the nanopores of nanoporous alumina templates generated by one-step anodization of aluminum. Following metal electrodeposition, the alumina template was selectively etched to obtain an array of free-standing metal nanowires. The imposed electrodeposition conditions allowed directly attaining a core-shell nanostructure, with a metal core covered by a thin metal oxide/hydroxide film. NWE electrodes produced by the proposed synthesis route were tested for the application as electrodes in lithium batteries and supercapacitors. To this purpose, an array of cobalt nanowires (CoNWs) supported by a nanostructured copper current collector was produced by sequential electrodeposition of cobalt and copper, and it was employed as anode in a lithium battery, while a NWE based on Ni-NiO/OH2 (NiNWs) was obtained by nickel electrodeposition and tested as electrode in a supercapacitor. A thorough analysis and characterization of the produced electrodes were performed. The experiments with the lithium cell evidenced the positive effect of metallic core on stability, while the electrochemical characterization of the supercapacitor showed the presence of both NiO and NiOH2 leading, when cycled, to a capacity close to the best literature value
SU(N_c) gauge theories at deconfinement
The deconfinement transition in SU() Yang--Mills is investigated by
Monte Carlo simulations of the gauge theory discretized on a spacetime lattice.
We present new results for (in particular, for and
), which are analysed together with previously published results. The
increased amount of data, the improved statistics and simulations closer to the
continuum limit provide us with better control over systematic errors. After
performing the thermodynamic limit, numerical results for the ratio of the
critical temperature over the square root of the string tension
obtained on lattices with temporal extensions
are extrapolated to the continuum limit. The continuum results at fixed
are then extrapolated to . We find that our data are accurately
described by the formula .
Possible systematic errors affecting our calculations are also discussed.Comment: 8 pages, 3 figures. Minor corrections. Version published on Physics
Letters
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