Hadronic Light-by-Light Contribution to Muon g-2 in Chiral Perturbation Theory

We compute the hadronic light-by-light scattering contributions to the muon anomalous magnetic moment, \amulbl, in chiral perturbation theory that are enhanced by large logarithms and a factor of $N_C$. They depend on a low-energy constant entering pseudoscalar meson decay into a charged lepton pair. The uncertainty introduced by this constant is $\pm 60\times 10^{-11}$, which is comparable in magnitude to the present uncertainty entering the leading-order vacuum polarization contributions to the anomalous moment. It may be reduced to some extent through an improved measurement of the $\pi^0\to e^+ e^-$ branching ratio. However, the dependence of \amulbl on non-logarithmically enhanced effects cannot be constrained except through the measurement of the anomalous moment itself. The extraction of information on new physics would require a future experimental value for the anomalous moment differing significantly from the 2001 result reported by the E821 collaboration.Comment: 7 pages, 2 figure

Spiders (Araneae) from Agricultural fields near foothill of Satpura Mountain ranges of Amravati District, Maharashtra, India.

This paper deals with the study of spider distribution in agricultural fields adjoining the Satpura Mountain Ranges of the Amravati district. The total collection of spiders comprises 12 families, 37 genera and 76 species. The Araneidae and Thomisidae families were dominant, followed by Saltisidae from the selected agricultural area. Lycosidae and Tetragnathidae were also found in a decreasing number of species due to their specific habitation. The analysis of guild structure revealed six feeding guilds. Orb web weavers and Ambushers constituted the dominant feeding guild representing 33% and 22% of the total collection respectively. Stalkers and ground runners represent 20% and 17% and foliage hunters and sheet web weavers represent 5% and 3% respectively. A new species of genus Sassacus (Beetle like spider), family Saltisidae was found for the first time in the Vidarbha region. The richness of spider diversity is a sign of the overall biodiversity which is a useful indicator of the species richness of the agro-ecosystem.
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Hadronic light-by-light scattering contribution to the muon g-2: an effective field theory approach

The hadronic light-by-light contribution to a_{mu}, the anomalous magnetic moment of the muon, is discussed from the point of view of an effective low-energy theory. As an application, the coefficient of the leading logarithm arising from the two-loop graphs involving two anomalous vertices is computed, and found to be positive. This corresponds to a positive sign for the pion-pole contribution to the hadronic light-by-light correction to a_{mu}, and to a sizeable reduction of the discrepancy between the present experimental value of a_{mu} and its theoretical counterpart in the standard model.Comment: 4 pages, 1 figure. v2: published versio

The Muon g-2 Revisited

I present a short review of the present status of the Standard Model prediction of the anomalous magnetic moment of the muon, with special emphasis on the hadronic contributions.Comment: Invited talk at the XVI Rencontres de Physique at La Thuil

Comment on the Pion Pole Part of the Light-by-Light Contribution to the Muon g−2g-2

We comment on the recent calculations of the pion pole part of the light-by-light contribution to the muon anomalous magnetic moment and we point out where the analysis in our previous work was mistaken.Comment: 2 page

The Standard Model and low-energy experiments: from lepton-flavour violation to dark photons

This note is a concise theoretical summary of the first session on new physics searches at the high-intensity frontier of the IFAE2017 Conference. Recent theoretical developments related to muonic lepton-flavour violation and $g-2$ are reviewed.Comment: 5 pages, IFAE2017 Conferenc

Towards a data-driven analysis of hadronic light-by-light scattering

The hadronic light-by-light contribution to the anomalous magnetic moment of the muon was recently analyzed in the framework of dispersion theory, providing a systematic formalism where all input quantities are expressed in terms of on-shell form factors and scattering amplitudes that are in principle accessible in experiment. We briefly review the main ideas behind this framework and discuss the various experimental ingredients needed for the evaluation of one- and two-pion intermediate states. In particular, we identify processes that in the absence of data for doubly-virtual pion-photon interactions can help constrain parameters in the dispersive reconstruction of the relevant input quantities, the pion transition form factor and the helicity partial waves for $\gamma^*\gamma^*\to\pi\pi$.Comment: 7 pages, 4 figures, 2 tables, journal versio

Rescattering effects in the hadronic-light-by-light contribution to the anomalous magnetic moment of the muon

We present a first model-independent calculation of $\pi\pi$ intermediate states in the hadronic-light-by-light (HLbL) contribution to the anomalous magnetic moment of the muon $(g-2)_\mu$ that goes beyond the scalar QED pion loop. To this end we combine a recently developed 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. Using dispersive fits to high-statistics data for the pion vector form factor, we provide an evaluation of the full pion box, $a_\mu^{\pi\text{-box}}=-15.9(2)\times 10^{-11}$. We then construct suitable input for the $\gamma^*\gamma^*\to\pi\pi$ helicity partial waves based on a pion-pole left-hand cut and show 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 our final estimate for the sum of these two contributions: $a_\mu^{\pi\text{-box}} + a_{\mu,J=0}^{\pi\pi,\pi\text{-pole LHC}}=-24(1)\times 10^{-11}$.Comment: 7 pages, 1 figure; version to appear in PR