190 research outputs found
Analyticity constraints for hadron amplitudes : going high to heal low energy issues
Analyticity constitutes a rigid constraint on hadron scattering amplitudes. This property is used to relate models in different energy regimes. Using meson photoproduction as a benchmark, we show how to test contemporary low-energy models directly against high-energy data. This method pinpoints deficiencies of the models and treads a path to further improvement. The implementation of this technique enables one to produce more stable and reliable partial waves for future use in hadron spectroscopy and new physics searches
Determination of the pole position of the lightest hybrid meson candidate
Mapping states with explicit gluonic degrees of freedom in the light sector
is a challenge, and has led to controversies in the past. In particular, the
experiments have reported two different hybrid candidates with spin-exotic
signature, pi1(1400) and pi1(1600), which couple separately to eta pi and eta'
pi. This picture is not compatible with recent Lattice QCD estimates for hybrid
states, nor with most phenomenological models. We consider the recent partial
wave analysis of the eta(') pi system by the COMPASS collaboration. We fit the
extracted intensities and phases with a coupled-channel amplitude that enforces
the unitarity and analyticity of the S-matrix. We provide a robust extraction
of a single exotic pi1 resonant pole, with mass and width 1564 +- 24 +- 86 MeV
and 492 +- 54 +- 102 MeV, which couples to both eta(') pi channels. We find no
evidence for a second exotic state. We also provide the resonance parameters of
the a2(1320) and a2'(1700).Comment: 6 pages + 3 pages of supplemental material. Version to appear on
Phys.Rev.Let
Towards breeding less allergenic spelt-wheat with low fodmap content â A review
Consumption of âgluten-containingâ diet causes disease for a significant minority of people who consume foods derived from wheat, rye, barley, and possibly oat. The fact is, however, that in several types of diseases related to the consumption of âgluten-containingâ cereals, the trigger compounds are not components of gluten. The current view of medical experts is that, excluding people suffering from celiac disease, the majority of individuals who are feeling better on the âwheat-freeâ or âgluten-freeâ diet could select a food containing much healthier, low level of fermentable oligosaccharides (often called as FODMAP). To satisfy the specific health related demands of certain consumer groups, the challenge is in front of cereal breeding to develop new, âhealthierâ germplasms, suitable to produce such products by the food industry. This report aims to give an overview of some aspects of recent developments in this booming area, (i) summarizing the up-to-date knowledge on cereals-related health disorders; (ii) reporting on the status of developing celiac-safe cereals, and finally (iii) highlighting the potential of developing âhealthierâ spelt-based cereal products through the progress in an ongoing spelt breeding program
Dispersion relations for hadronic light-by-light scattering and the muon g
The largest uncertainties in the Standard Model calculation of the anomalous magnetic moment of the muon (g â 2)ÎŒ come from hadronic effects, and in a few years the subleading hadronic light-by-light (HLbL) contribution might dominate the theory error. We present a dispersive description of the HLbL tensor, which is based on unitarity, analyticity, crossing symmetry, and gauge invariance. This opens up the possibility of a data-driven determination of the HLbL contribution to (g â 2)ÎŒ with the aim of reducing model dependence and achieving a reliable error estimate.
Our dispersive approach defines unambiguously the pion-pole and the pion-box contribution to the HLbL tensor. Using Mandelstam double-spectral representation, we have proven that the pion-box contribution coincides exactly with the one-loop scalar-QED amplitude, multiplied by the appropriate pion vector form factors. Using dispersive fits to high-statistics data for the pion vector form factor, we obtain αΌÏ-box=â15.92Ă10â11. A first model-independent calculation of effects of ÏÏ intermediate states that go beyond the scalar-QED pion loop is also presented. We combine our dispersive description of the HLbL tensor with a partial-wave expansion and demonstrate that the known scalar-QED result is recovered after partial-wave resummation. After constructing suitable input for the Îł*Îł* â ÏÏ helicity partial waves based on a pion-pole left-hand cut (LHC), we find that for the dominant charged-pion contribution this representation is consistent with the two-loop chiral prediction and the COMPASS measurement for the pion polarizability. This allows us to reliably estimate S-wave rescattering effects to the full pion box and leads to αΌÏ-box+αΌ,J=0ÏÏ,Ï-pole LHC=â241Ă10â11
The hadronic vacuum polarization contribution to the muon g â 2 from lattice QCD
We present a calculation of the hadronic vacuum polarization contribution to
the muon anomalous magnetic moment, , in lattice QCD
employing dynamical up and down quarks. We focus on controlling the infrared
regime of the vacuum polarization function. To this end we employ several
complementary approaches, including Pad\'e fits, time moments and the
time-momentum representation. We correct our results for finite-volume effects
by combining the Gounaris-Sakurai parameterization of the timelike pion form
factor with the L\"uscher formalism. On a subset of our ensembles we have
derived an upper bound on the magnitude of quark-disconnected diagrams and
found that they decrease the estimate for by at most 2%.
Our final result is , where the first error is statistical, and the second denotes the
combined systematic uncertainty. Based on our findings we discuss the prospects
for determining with sub-percent precision.Comment: 42 pages, 7 figures, version published in JHE
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