Soft gluon fields and anomalous magnetic moment of muon

An impact of nonperturbatively treated soft gluon modes on the value of anomalous magnetic moment of muon a_µ is studied within the mean-field approach to QCD vacuum and hadronization. It is shown that radial excitations of vector mesons strongly enhance contribution of hadronic vacuum polarization to a_µ, doubling the contribution of one-meson processes compared to the result for ground state mesons. The mean field also strongly influences the hadronic light-by-light scattering contribution due to the Wilson line in quark propagators.

Is sulfur the responsible for color of yellow Chiapas Amber?

Amber is a fossilized natural resin found in specific areas of the world; its geographical origin is associated to a characteristic color. Amber all over the world share basic characteristics due to a common polymeric matrix; however, its color is associated to the environment where it was formed. In this work, based on a compositional analysis, it is proposed that yellow color of Mexican amber is originated from the sulfur physical and chemical interaction within its polymeric matrix. The effect of sulfur present in yellow Mexican amber is studied by employing X-ray photoelectron and UV-Vis spectroscopies. Results show that sulfur is incorporated inside the polymer matrix with two different chemical environments; one related with sulfur-carbon bonds and the other with sulfur-sulfur bonds. The optical transmission spectrum simulated considering amber as a composite material reproduce the scattering contribution observed experimentally.

Holographic QCD and the muon anomalous magnetic moment

We review the recent progress made in using holographic QCD to study hadronic contributions to the anomalous magnetic moment of the muon, in particular the hadronic light-by-light scattering contribution, where the short-distance constraints associated with the axial anomaly are notoriously difficult to satisfy in hadronic models. This requires the summation of an infinite tower of axial vector mesons, which is naturally present in holographic QCD models, and indeed takes care of the longitudinal short-distance constraint due to Melnikov and Vainshtein. Numerically the results of simple hard-wall holographic QCD models point to larger contributions from axial vector mesons than assumed previously, while the predicted contributions from pseudo-Goldstone bosons agree nicely with data-driven approaches.

Towards an improved understanding of $$\varvec{\eta \rightarrow \gamma ^*\gamma ^*}$$

We argue that high-quality data on the reaction $$e^+e^-\rightarrow \pi ^+\pi ^-\eta $$ e + e - → π + π - η will allow one to determine the doubly-virtual form factor $$\eta \rightarrow \gamma ^*\gamma ^*$$ η → γ ∗ γ ∗ in a model-independent way with controlled accuracy. This is an important step towards a reliable evaluation of the hadronic light-by-light scattering contribution to the anomalous magnetic moment of the muon. When analyzing the existing data for $$e^+e^-\rightarrow \pi ^+\pi ^-\eta $$ e + e - → π + π - η for total energies squared $$k^2>1\,\text {GeV}^2$$ k 2 > 1 GeV 2 , we demonstrate that the effect of the $$a_2$$ a 2 meson provides a natural breaking mechanism for the commonly employed factorization ansatz in the doubly-virtual form factor $$F_{\eta \gamma ^*\gamma ^*}(q^2,k^2)$$ F η γ ∗ γ ∗ ( q 2 , k 2 ) . However, better data are needed to draw firm conclusions.

Medium-induced radiative kernel with the Improved Opacity Expansion

We calculate the fully differential medium-induced radiative spectrum at next-to-leading order (NLO) accuracy within the Improved Opacity Expansion (IOE) framework. This scheme allows us to gain analytical control of the radiative spectrum at low and high gluon frequencies simultaneously. The high frequency regime can be obtained in the standard opacity expansion framework in which the resulting power series diverges at the characteristic frequency ωc ∼ $$ \hat{q} $$ q ̂ L2. In the IOE, all orders in opacity are resumed systematically below ωc yielding an asymptotic series controlled by logarithmically suppressed remainders down to the thermal scale T « ωc, while matching the opacity expansion at high frequency. Furthermore, we demonstrate that the IOE at NLO accuracy reproduces the characteristic Coulomb tail of the single hard scattering contribution as well as the Gaussian distribution resulting from multiple soft momentum exchanges. Finally, we compare our analytic scheme with a recent numerical solution, that includes a full resummation of multiple scatterings, for LHC-inspired medium parameters. We find a very good agreement both at low and high frequencies showcasing the performance of the IOE which provides for the first time accurate analytic formulas for radiative energy loss in the relevant perturbative kinematic regimes for dense media.

Hadronic light-by-light contribution to $$(g-2)_\mu $$ from lattice QCD: a complete calculation

We compute the hadronic light-by-light scattering contribution to the muon $$g-2$$ g - 2 from the up, down, and strange-quark sector directly using lattice QCD. Our calculation features evaluations of all possible Wick-contractions of the relevant hadronic four-point function and incorporates several different pion masses, volumes, and lattice-spacings. We obtain a value of $$a_\mu ^{\text {Hlbl}}= 106.8(15.9) \times 10^{-11}$$ a μ Hlbl = 106.8 ( 15.9 ) × 10 - 11 (adding statistical and systematic errors in quadrature), which is consistent with current phenomenological estimates and a previous lattice determination. It now appears conclusive that the hadronic light-by-light contribution cannot explain the current tension between theory and experiment for the muon $$g-2$$ g - 2 .

Characterization of NIS neutron irradiation facility for calibration and metrological application

In this study, the Neutron Irradiation Facility (NIF) of the National Institute of Standards (NIS) was characterized for metrological applications to improve the accuracy of the calibration process. The NIS neutron irradiation facility consists of a 5 Ci Am-Be and 0.1 μg Cf-252 sources. The flux and dose rate of the Am-Be source was calculated by using MCNP5 code simulation at different distances from the source. The dose rate delivered by the source was determined using NM2-neutron monitor at different source-to-detector distances. A comparison between the measured and the calculated dose rate was performed and the deviation between them was explained in the skeletal arrangement of room scattering contribution. A shadow cone was designed and constructed to determine the scattering contribution at different source-to-detector distances. The optimum source-distance used for calibration was specified. It was found that the Am-Be calculated flux vary with distances from about 107–104 (n/cm2.S−1). The measured and the calculated dose rates were in agreement up to 150 cm distance from the source center after which the measured dose was greater than that calculated. The determined neutron scattering calculated from the measured-to-calculate dose ratio increased from 7% to 25% with increased distances from 150 to 300 cm. Moreover, the standard dose used in the calibration should be measured by a standard neutron monitor at each distance due to the higher value of the room scattering contribution where the optimum distance for calibration was 150 cm. The combined uncertainty of the measured neutron dose was 4.04%.

A Modified Geometrical Optical Model of Row Crops Considering Multiple Scattering Frame

The canopy reflectance model is the physical basis of remote sensing inversion. In canopy reflectance modeling, the geometric optical (GO) approach is the most commonly used. However, it ignores the description of a multiple-scattering contribution, which causes an underestimation of the reflectance. Although researchers have tried to add a multiple-scattering contribution to the GO approach for forest modeling, different from forests, row crops have unique geometric characteristics. Therefore, the modeling approach originally applied to forests cannot be directly applied to row crops. In this study, we introduced the adding method and mathematical solution of integral radiative transfer equation into row modeling, and on the basis of improving the overlapping relationship of the gap probabilities involved in the single-scattering contribution, we derived multiple-scattering equations suitable for the GO approach. Based on these modifications, we established a row model that can accurately describe the single-scattering and multiple-scattering contributions in row crops. We validated the row model using computer simulations and in situ measurements and found that it can be used to simulate crop canopy reflectance at different growth stages. Moreover, the row model can be successfully used to simulate the distribution of reflectances (RMSEs < 0.0404). During computer validation, the row model also maintained high accuracy (RMSEs < 0.0062). Our results demonstrate that considering multiple scattering in GO-approach-based modeling can successfully address the underestimation of reflectance in the row crops.