10 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
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
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
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
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
Influence of hydrofluoric acid treatment on electroless deposition of Au clusters
The morphology of gold nanoparticles (AuNPs) deposited on a (100) silicon wafer by simple immersion in a solution containing a metal salt and hydrofluoric acid (HF) is altered by HF treatment both before and after deposition. The gold clusters are characterized by the presence of flat regions and quasispherical particles consistent with the layer-by-layer or island growth modes, respectively. The cleaning procedure, including HF immersion prior to deposition, affects the predominantly occurring gold structures. Flat regions, which are of a few tens of nanometers long, are present after immersion for 10 s. The three-dimensional (3D) clusters are formed after a cleaning procedure of 4 min, which results in a large amount of spherical particles with a diameter of ≈15 nm and in a small percentage of residual square layers of a few nanometers in length. The samples were also treated with HF after the deposition and we found out a general thickening of flat regions, as revealed by TEM and AFM analysis. This result is in contrast to the coalescence observed in similar experiments performed with Ag. It is suggested that the HF dissolves the silicon oxide layer formed on top of the thin flat clusters and promotes the partial atomic rearrangement of the layered gold atoms, driven by a reduction of the surface energy. The X-ray diffraction investigation indicated changes in the crystalline orientation of the flat regions, which partially lose their initially heteroepitaxial relationship with the substrate. A postdeposition HF treatment for almost 70 s has nearly the same effect of long duration, high temperature annealing. The process presented herein could be beneficial to change the spectral response of nanoparticle arrays and to improve the conversion efficiency of hybrid photovoltaic devices