Search results for " chiral"
showing 10 items of 80 documents
Near-unity third-harmonic circular dichroism driven by a quasibound state in the continuum in asymmetric silicon metasurfaces
2021
We use numerical simulations to demonstrate third-harmonic generation with near-unity nonlinear circular dichroism (CD) and high conversion efficiency $({10}^{\ensuremath{-}2}\phantom{\rule{4pt}{0ex}}{\text{W}}^{\ensuremath{-}2})$ in asymmetric Si-on-$\mathrm{Si}{\mathrm{O}}_{2}$ metasurfaces. The working principle relies on the spin-selective excitation of a quasibound state in the continuum, characterized by a very high $(g{10}^{5})$ quality factor. By tuning multimode interference with the variation of the metasurface geometrical parameters, we show the possibility to control both linear CD and nonlinear CD. Our results pave the way for the development of all-dielectric metasurfaces for …
Dispersion relations and the spin polarizabilities of the nucleon
1997
A forward dispersion calculation is implemented for the spin polarizabilities $\gamma_1, ... ,\gamma_4$ of the proton and the neutron. These polarizabilities are related to the spin structure of the nucleon at low energies and are structure-constants of the Compton scattering amplitude at ${\cal O}(\omega^3)$. In the absence of a direct experimental measurement of these quantities, a dispersion calculation serves the purpose of constraining the model building, and of comparing with recent calculations in heavy baryon chiral perturbation theory.
Muon capture by a proton in heavy baryon chiral perturbation theory
1997
The matrix element for muon capture by a proton is calculated to O(p^3) within heavy baryon chiral perturbation theory using the new O(p^3) Lagrangian of Ecker and Mojzis. External nucleon fields are renormalized using the appropriate definition of the wave function renormalization factor Z_N. Our expression for Z_N differs somewhat from that found in existing literature, but is the one which is consistent with the Lagrangian we use and the one which ensures, within our approach, the nonrenormalization of the vector coupling as required by the conserved vector current. Expressions for the standard muon capture form factors are derived and compared to experimental data and we determine three…
Improved unitarized Heavy Baryon Chiral Perturbation Theory for π N scattering
2000
We show how the unitarized description of pion nucleon scattering within Heavy Baryon Chiral Perturbation Theory can be considerably improved, by a suitable reordering of the expansion over the nucleon mass. Within this framework, the $\Delta$ resonance and its associated pole can be recovered from the chiral parameters obtained from low-energy determinations. In addition, we can obtain a good description of the six $S$ and $P$ wave phase shifts in terms of chiral parameters with a natural size and compatible with the Resonance Saturation Hypothesis.
Radiative pion capture by a nucleon
2000
The differential cross sections for $\pi^- p \to \gamma n$ and $\pi^+ n \to \gamma p$ are computed up to $O(p^3)$ in heavy baryon chiral perturbation theory (HBChPT). The expressions at $O(p)$ and $O(p^2)$ have no free parameters. There are three unknown parameters at $O(p^3)$, low energy constants of the HBChPT Lagrangian, which are determined by fitting to experimental data. Two acceptable fits are obtained, which can be separated by comparing with earlier dispersion relation calculations of the inverse process. Expressions for the multipoles, with emphasis on the p-wave multipoles, are obtained and evaluated at threshold. Generally the results obtained from the best of the two fits are i…
Burkhardt-Cottingham sum rule and forward spin polarizabilities in Heavy Baryon Chiral Perturbation Theory
2002
We study spin-dependent sum rules for forward virtual Compton scattering(VVCS) off the nucleon in heavy baryon chiral perturbation theory at order $O(p^4)$. We show how these sum rules can be evaluated from low energy expansions (in the virtual photon energy) of the forward VVCS amplitudes. We study in particular the Burkhardt -Cottingham sum rule in HBChPT and higher terms in the low energy expansion, which can be related to the generalized forward spin polarizabilities of the nucleon. The dependence of these observables on the photon virtuality $Q^2$ can be accessed, at small and intermediate $Q^2$ values, from existing and forthcoming data at Jefferson Lab.
Search for the decay K-s -> pi(0)e(+)e(-)
2001
Abstract A search for the decay K S →π 0 e + e − has been made using the NA48 detector at the CERN SPS. Using data collected in 1999 during a 40-hour run with a high-intensity KS beam, an upper limit for the branching fraction B (K S →π 0 e + e − ) −7 at 90% confidence level has been obtained.
Generalized polarizabilities of the nucleon in chiral effective theories
1999
Using the techniques of chiral effective field theories we evaluate the so called generalized polarizabilities of the nucleon, which characterize the structure dependent components in virtual Compton scattering (VCS) as probed in the electron scattering reaction e N \to e' N gamma. Results are given for both spin-dependent and spin-independent structure effects to O(p^3) in SU(2) Heavy Baryon Chiral Perturbation Theory and to O(epsilon^3) in the SU(2) Small Scale Expansion. Finally we compare our calculations with results from the pioneering VCS experiment on the proton from Mainz.
Radiative and non radiative muon capture on the proton in heavy baryon chiral perturbation theory
1998
We have evaluated the amplitude for muon capture by a proton, mu + p --> n + nu, to O(p^3) within the context of heavy baryon chiral perturbation theory (HBChPT) using the new O(p^3) Lagrangian of Ecker and Mojzis (E&M). We obtain expressions for the standard muon capture form factors and determine three of the coefficients of the E&M Lagrangian, namely, b_7, b_{19}, and b_{23}. We describe progress on the next step, a calculation of the radiative muon capture process, mu + p --> n + nu + gamma.
Axial resonances in the open and hidden charm sectors
2007
13 pages, 2 figures.-- PACS nrs.: 11.10.St, 11.80.Gw, 12.39.Hg, 12.39.Fe.-- ISI Article Identifier: 000249271600001.-- ArXiv pre-print available at: http://arxiv.org/abs/0704.2314