Coordinate-space calculation of the window observable for the hadronic vacuum polarization contribution to (g−2)μ(g-2)_\mu

The `intermediate window quantity' of the hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon allows for a high-precision comparison between the data-driven approach and lattice QCD. The existing lattice results, which presently show good consistency among each other, are in strong tension with the data-driven determination. In order to check for a potentially common source of systematic error of the lattice calculations, which are all based on the time-momentum representation (TMR), we perform a calculation using a Lorentz-covariant coordinate-space (CCS) representation. We present results for the isovector and the connected strange-quark contributions to the intermediate window quantity at a reference point in the $(m_\pi,m_K)$ plane, in the continuum and infinite-volume limit, based on four different lattice spacings. Our results are in good agreement with those of the recent TMR-based Mainz-CLS publication.Comment: 35 pages, 6 figures, 6 table

Coordinate-space calculation of QED corrections to the hadronic vacuum polarization contribution to (g−2)μ(g-2)_\mu

As several lattice collaborations agree on the result for the window quantity of the hadronic vacuum polarization (HVP) contribution to $(g-2)_\mu$, whilst being in tension with the calculation using the dispersive approach, further effort is needed in order to pin down the cause for this difference. Here we want to focus on the isospin breaking corrections to the leading order HVP. In many lattice applications, the photon propagator is treated stochastically; however, by analogy with the hadronic light-by-light contribution (HLbL) to $(g-2)_\mu$, we suggest a coordinate-space approach to the HVP at next-to-leading order. We present a calculation of the two diagrams of the (2+2) topology at unphysical pion mass, where we apply a Pauli-Villars regularization for the extra photon propagator in the diagram that is UV-divergent. We compare the UV-finite diagram to the pseudoscalar exchange contributions calculated from a vector-meson dominance model.Comment: 8 pages, 3 figures, 2 tables, Proceedings of the The 40th International Symposium on Lattice Field Theory (Lattice 2023), July 31st - August 4th, 2023, Fermi National Accelerator Laborator

Hadronic light-by-light contribution to (g−2)μ(g-2)_\mu from lattice QCD with SU(3) flavor symmetry

We perform a lattice QCD calculation of the hadronic light-by-light contribution to $(g-2)_\mu$ at the SU(3) flavor-symmetric point $m_\pi=m_K\simeq 420\,$MeV. The representation used is based on coordinate-space perturbation theory, with all QED elements of the relevant Feynman diagrams implemented in continuum, infinite Euclidean space. As a consequence, the effect of using finite lattices to evaluate the QCD four-point function of the electromagnetic current is exponentially suppressed. Thanks to the SU(3)-flavor symmetry, only two topologies of diagrams contribute, the fully connected and the leading disconnected. We show the equivalence in the continuum limit of two methods of computing the connected contribution, and introduce a sparse-grid technique for computing the disconnected contribution. Thanks to our previous calculation of the pion transition form factor, we are able to correct for the residual finite-size effects and extend the tail of the integrand. We test our understanding of finite-size effects by using gauge ensembles differing only by their volume. After a continuum extrapolation based on four lattice spacings, we obtain $a_\mu^{\rm hlbl} = (65.4\pm 4.9 \pm 6.6)\times 10^{-11}$, where the first error results from the uncertainties on the individual gauge ensembles and the second is the systematic error of the continuum extrapolation. Finally, we estimate how this value will change as the light-quark masses are lowered to their physical values.Comment: 19 figures, 39 pages; improved references, in particular concerning the eta exchange; no figures or results change

The charm-quark contribution to light-by-light scattering in the muon (g−2)(g-2) from lattice QCD

We compute the hadronic light-by-light scattering contribution to the muon $g-2$ from the charm quark using lattice QCD. The calculation is performed on ensembles generated with dynamical $(u,d,s)$ quarks at the SU(3)$_{\rm f}$ symmetric point with degenerate pion and kaon masses of around 415 MeV. It includes the connected charm contribution, as well as the leading disconnected Wick contraction, involving the correlation between a charm and a light-quark loop. Cutoff effects turn out to be sizeable, which leads us to use lighter-than-physical charm masses, to employ a broad range of lattice spacings reaching down to 0.039 fm and to perform a combined charm-mass and continuum extrapolation. We use the $\eta_c$ meson to define the physical charm-mass point and obtain a final value of $a_\mu^{\rm HLbL,c} = (2.8\pm 0.5) \times 10^{-11}$, whose uncertainty is dominated by the systematics of the extrapolation. Our result is consistent with the estimate based on a simple charm-quark loop, whilst being free of any perturbative scheme dependence on the charm mass. The mixed charm-light disconnected contraction contributes a small negative amount to the final value.Comment: 21 pages, 8 figures, 9 table

Prospectives

Tiré de: Prospectives, vol. 11, no 4, oct. 1975Titre de l'écran-titre (visionné le 24 janv. 2013

Combinations of scleroderma hallmark autoantibodies associate with distinct clinical phenotypes

Systemic sclerosis (SSc) is characterized by the presence of SSc-specific or SSc-associated antibodies (SSc-Abs): anti-topoisomerase I (ATA), anti-centromere (ACA), anti-RNA polymerase III (ARA), anti-U3RNP (U3RNP), anti-U1RNP (U1RNP), anti-PmScl (PmScl), anti-Ku (Ku) and anti-Th/To (Th/To), each being associated with specific clinical features and prognosis. The detection of more than one SSc-Abs in SSc patients is rare and only few data about these patients' clinical phenotype is available. The aim of our study was to evaluate the frequency and the disease's features associated with the presence of > 1 SSc-Abs positivity in a large cohort of SSc patients. The autoantibody profiles of 2799 SSc patients from February 2001 to June 2017 were retrospectively reviewed. Patients with > 1 SSc-Abs were identified. Clinical features were collected and compared to a large historical cohort of SSc patients with single SSc-Ab positivity. SSc patients were excluded if previously treated with rituximab, intravenous immunoglobulins or stem cell transplantation. Non-parametric tests were used for statistical analysis. Nearly 5% of SSc patients from our cohort had ≥ 2 autoantibody positivity, and 2.3% (n = 72) had ≥ 2 SSc-Abs positivity. Th e most common combination was U1RNP and ATA (35%). These patients were younger than patients with single autoantibody positivity and showed more commonly a diffuse cutaneous SSc form. They also had higher rates of overlap features compared to ATA patients. Other combinations included U1RNP and ACA (13%), ATA and ACA (7%) and U1RNP and PmScl (5%). In our study we observed that, while infrequently, SSc patients can present with a combination of two SSc-Abs and that the double positivity can influence their clinical phenotype compared to patients with single SSc-Ab positivity. The importance of re-testing SSc-Abs in patients with changing clinical phenotypes was also highlighted, as this may confer a differing risk stratification

Forward light-by-light scattering and electromagnetic correction to hadronic vacuum polarization

Lattice QCD calculations of the hadronic vacuum polarization (HVP) have reached a precision where the electromagnetic (e.m.) correction can no longer be neglected. This correction is both computationally challenging and hard to validate, as it leads to ultraviolet (UV) divergences and to sizeable infrared (IR) effects associated with the massless photon. While we precisely determine the UV divergence using the operator-product expansion, we propose to introduce a separation scale $\Lambda\sim400\;$MeV into the internal photon propagator, whereby the calculation splits into a short-distance part, regulated in the UV by the lattice and in the IR by the scale $\Lambda$, and a UV-finite long-distance part to be treated with coordinate-space methods, thereby avoiding power-law finite-size effects altogether. In order to predict the long-distance part, we express the UV-regulated e.m. correction to the HVP via the forward hadronic light-by-light (HLbL) scattering amplitude and relate the latter via a dispersive sum rule to $\gamma^*\gamma^*$ fusion cross-sections. Having tested the relation by reproducing the two-loop QED vacuum polarization (VP) from the tree-level $\gamma^*\gamma^*\to e^+e^-$ cross-section, we predict the expected lattice-QCD integrand resulting from the $\gamma^*\gamma^*\to\pi^0$ process.Comment: 27 pages, 6 figures; additional references, typos corrected; a statement on the charged-current correlator has been correcte

Valorization of Napier grass via intermediate pyrolysis: Optimization using response surface methodology and pyrolysis products characterization

This study presents first optimization report on pyrolysis oil derived from Napier grass. Effects of temperature, heating rate and nitrogen flow rate on the intermediate pyrolysis of Napier grass biomass in a vertical fixed-bed tubular reactor were investigated collectively. Response surface methodology with central composite design was used for modelling the process and optimization of the process variables. Individual second order polynomial model was found to be adequate in predicting bio-oil, bio-char and non-condensable gas yield. The optimum bio-oil yield of 50.57 wt% was recorded at 600 �C, 50 �C/min and 5 L/min nitrogen flow. The bio-oil obtained throughout this study was two-phase liquid, organic and aqueous phase. The bio-oil, bio-char and non-condensable gas were characterized using standard analytical techniques. The results revealed that the organic phase consists of hydrocarbons and various benzene derivatives, which can be further processed into fuels and valuable chemicals. The aqueous phase was predominantly water, acids, ketones, aldehydes and some phenolics and other water-soluble organics. The non-condensable gas was made up high hydrogen/carbon monoxide ratio suitable for liquid fuel synthesis via Fischer-Tropsch Synthesis. The bio-char was a porous carbonaceous material with high energy content, which can be applied as a solid fuel, adsorbent or source of biofertilizer. This study demonstrated that Napier grass biomass is a viable feedstock for production of high-value bioenergy precursors

Near-Limb Zeeman and Hanle Diagnostics

"Weak" magnetic-field diagnostics in faint objects near the bright solar disk are discussed in terms of the level of non-object signatures, in particular, of the stray light in telescopes. Calculated dependencies of the stray light caused by diffraction at the 0.5-, 1.6-, and 4-meter entrance aperture are presented. The requirements for micro-roughness of refractive and reflective primary optics are compared. Several methods for reducing the stray light (the Lyot coronagraphic technique, multiple stages of apodizing in the focal and exit pupil planes, apodizing in the entrance aperture plane with a special mask), and reducing the random and systematic errors are noted. An acceptable level of stray light in telescopes is estimated for the V-profile recording with a signal-to-noise ratio greater than three. Prospects for the limb chromosphere magnetic measurements are indicated.Comment: 11 pages, 3 figure