57 research outputs found
Vanishing chiral couplings in the large-N_C resonance theory
The construction of a resonance theory involving hadrons requires
implementing the information from higher scales into the couplings of the
effective Lagrangian. We consider the large-Nc chiral resonance theory
incorporating scalars and pseudoscalars, and we find that, by imposing LO
short-distance constraints on form factors of QCD currents constructed within
this theory, the chiral low-energy constants satisfy resonance saturation at
NLO in the 1/Nc expansion.Comment: 5 pages, 2 figures. Version published in Physical Review D. Some
equations to facilitate the discussion have been adde
Lepton-flavour violation in hadronic tau decays and μ-τ conversion in nuclei
Within the Standard Model Effective Field Theory framework, with operators up to dimension 6, we perform a model-independent analysis of the lepton-flavour-violating processes involving tau leptons. Namely, we study hadronic tau decays and ℓ-τ conversion in nuclei, with ℓ = e, μ. Based on available experimental limits, we establish constraints on the Wilson coefficients of the operators contributing to these processes. Our work paves the way to extract the related information from Belle II and foreseen future experiments
Diseño, modelado y análisis por elementos finitos de un chasis de motocicleta
Diseño y Modelado de un chasis de motocicleta en acero, basado en la geometría de uno real fabricado en aluminio. Con objeto de solucionar un problema que presenta el chasis original en aluminio cuando se quiere acondicionarlo para la disciplina deportiva llamada Supermoto. Análisis posterior por elementos finitos del comportamiento del chasis en acero,frente a una serie de hipótesis de carga: Frenada, Aceleración e Impacto
Photophysical properties of blue-emitting silicon nanoparticles
Silicon nanoparticles with strong blue photoluminescence were synthesized by electrochemical etching of silicon wafers and ultrasonically removed under N2 atmosphere in organic solvents to produce colloids. Thermal treatment leads to the formation of colloidal Si particles of 3 ± 1 nm diameter, which upon excitation with 340−380 nm light exhibited room temperature luminescence in the range from 400 to 500 nm. The emission and the one- and two-photon excitation spectra of the particles are not sensitive to surface functionalization with methyl 2-methylprop-2-enoate. However, the derivatized particles show higher emission quantum yields in air-saturated suspensions (44%) than the underivatized particles (27%), as well as higher stability of its dispersions. FTIR and XPS spectra indicate a significant surface oxidation of the particles. The Si:O:C ratio at the surface of the derivatized particles estimated from XPS is Si3O6(C5O2Hy)1, with y = 7−8. Vibronic spacing is observed in both the emission and excitation spectra. The information obtained from one-photon excitation experiments (emission and excitation spectra, photoluminescence quantum yields, luminescence decay lifetimes, and anisotropy correlation lifetimes), as well as from two-photon excitation fluorescence correlation spectroscopy (brightness and diffusion coefficients) and TEM, indicate that the blue-emitting particles are monodisperse and ball-shaped. Particle size clearly determines the emission and excitation spectral region, as expected from quantum confinement, but the presence and extent of Si−O species on the silicon networks seem crucial for determining the spectrum features and intensity of emission. The nanoparticles could hold great potential as quantum dots for applications as luminescence sensors in biology and environmental science.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada
The <SPP> Green function and SU(3) breaking in Kl3 decays
Using the 1=/N-C expansion scheme and truncating the hadronic spectrum to the lowest-lying resonances, we match a meromorphic approximation to the Green function onto QCD by imposing the correct large-momentum falloff, both off- shell and on the relevant hadron mass shells. In this way we determine a number of chiral low-energy constants of O(p(6)), in particular the ones governing SU(3) breaking in the K-l3 vector form factor at zero momentum transfer. The main result of our matching procedure is that the known loop contributions largely dominate the corrections of O(p(6)) to f(+)(0). We discuss the implications of our final value f(+)(K0 pi-) (0) = 0.984 +/- 0.012 for the extraction of V-us from K-l3 decays
What can be learned from the Belle spectrum for the decay tau- -> nu_tau K_S pi-
A theoretical description of the differential decay spectrum for the decay
tau- -> nu_tau K_S pi-, which is based on the contributing K pi vector and
scalar form factors F_+^{K pi}(s) and F_0^{K pi}(s) being calculated in the
framework of resonance chiral theory (RT), additionally imposing
constraints from dispersion relations as well as short distance QCD, provides a
good representation of a recent measurement of the spectrum by the Belle
collaboration. Our fit allows to deduce the total branching fraction B[tau- ->
nu_tau K_S pi-] = 0.427 +- 0.024 % by integrating the spectrum, as well as the
K^* resonance parameters M_{K^*} = 895.3 +- 0.2 MeV and Gamma_{K^*} = 47.5 +-
0.4 MeV, where the last two errors are statistical only. From our fits, we
confirm that the scalar form factor F_0^{K pi}(s) is required to provide a good
description, but we were unable to further constrain this contribution.
Finally, from our results for the vector form factor F_+^{K pi}(s), we update
the corresponding slope and curvature parameters lambda'_+ = (25.2 +-
0.3)*10^{-3} and lambda''_+ = (12.9 +- 0.3)*10^{-4}, respectively.Comment: 15 pages, 2 figure
Spin-1 resonance contributions to the weak Chiral Lagrangian: the vector field formulation
We use the Vector formulation to evaluate vector and axial-vector exchange
contributions to the O(p^4) weak Chiral Lagrangian. We recover in this
framework the bulk of the contributions found previously by Ecker et al. in the
antisymmetric formulation of vectors and axial-vectors, but new interesting
features arise: i) most of our results are independent of Factorization and ii)
novel contributions to non-leptonic kaon decays, proper of this formulation and
phenomenologically interesting, are found. The phenomenological implications
for K -> pi pi (pi) and radiative (anomalous and non-anomalous) non-leptonic
kaon decays are thus investigated and found particularly relevant.Comment: 34 pages, plain LaTeX file, uses rotating.sty also include
Snowmass 2021 White Paper: Charged lepton flavor violation in the tau sector
Charged lepton flavor violation has long been recognized as unambiguous
signature of New Physics. Here we describe the physics capabilities and
discovery potential of New Physics models with charged lepton flavor violation
in the tau sector as its experimental signature. Current experimental status
from the B-Factory experiments BaBar, Belle and Belle II, and future prospects
at Super Tau Charm Factory, LHC, EIC and FCC-ee experiments to discover New
Physics via charged lepton flavor violation in the tau sector are discussed in
detail.
Submitted to the Proceedings of the US Community Study on the Future of
Particle Physics (Snowmass 2021)Comment: Contribution to Snowmass 202
Photophysical properties of blue-emitting silicon nanoparticles
Silicon nanoparticles with strong blue photoluminescence were synthesized by electrochemical etching of silicon wafers and ultrasonically removed under N2 atmosphere in organic solvents to produce colloids. Thermal treatment leads to the formation of colloidal Si particles of 3 ± 1 nm diameter, which upon excitation with 340−380 nm light exhibited room temperature luminescence in the range from 400 to 500 nm. The emission and the one- and two-photon excitation spectra of the particles are not sensitive to surface functionalization with methyl 2-methylprop-2-enoate. However, the derivatized particles show higher emission quantum yields in air-saturated suspensions (44%) than the underivatized particles (27%), as well as higher stability of its dispersions. FTIR and XPS spectra indicate a significant surface oxidation of the particles. The Si:O:C ratio at the surface of the derivatized particles estimated from XPS is Si3O6(C5O2Hy)1, with y = 7−8. Vibronic spacing is observed in both the emission and excitation spectra. The information obtained from one-photon excitation experiments (emission and excitation spectra, photoluminescence quantum yields, luminescence decay lifetimes, and anisotropy correlation lifetimes), as well as from two-photon excitation fluorescence correlation spectroscopy (brightness and diffusion coefficients) and TEM, indicate that the blue-emitting particles are monodisperse and ball-shaped. Particle size clearly determines the emission and excitation spectral region, as expected from quantum confinement, but the presence and extent of Si−O species on the silicon networks seem crucial for determining the spectrum features and intensity of emission. The nanoparticles could hold great potential as quantum dots for applications as luminescence sensors in biology and environmental science.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada
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