Conveners
WG1 parallel session
- Susan Schadmand (GSI Darmstadt)
WG1 parallel session
- Susan Schadmand (GSI Darmstadt)
WG1 parallel session
- Rory Miskimen (University of Massachusetts, Amherst)
WG1 parallel session
- Sinya Aoki (Yukawa Institute for Theoretical Physics, Kyoto Unversity)
WG1 parallel session
- Bing-Song Zou (Tsinghua University)
In this talk, we will review the theory underlying the chiral anomaly $\gamma \pi \to \pi \pi$. This includes its extractions based on dispersion relations, lattice QCD and the constraints from the crossed channel $\gamma^* \to 3\pi$.
Electromagnetic polarizabilities are fundamental properties of composite systems, and measure the 'stiffness' of a system to electromagnetic deformation. Measurements of hadron polarizabilities provide a test of effective field theories, dispersion theories, and lattice calculations. While significant progress has been made in measuring proton polarizabilities, with uncertainties at the level...
One of the most preplexing predictions of Chiral Perturbation Theory is the negative electric polarizability of the neutral pion. We revisit this problem and argue that in an ultraviolet-complete calculation the polarizabilty is positive. A novel light-front QCD calculation will be presented, corroborating this point.
Precision calculations of flavour physics processes such as leptonic decays of pions and kaons allow for indirect searches of new physics. For instance, the Cabibbo-Kobayashi-Maskawa matrix elements $|V_{ud}|$ and $|V_{us}|$ accessible in these decays satisfy a unitarity relation within the Standard Model that can be probed with lattice QCD simulations. With a goal of (sub-)percent precision,...
The rare radiative $K^+\to\pi^+\ell^+\ell^-$ decays ($\ell=e,\mu$) provide experimental access to the $K^+\to\pi^+\gamma^*$ transition. The relevant form factor is conventionally written in terms of two hadronic parameters, $a_+$ and $b_+$, which are being measured by NA62 in both electron and muon channels. Comparing the two channels allows for a stringent test of lepton-flavor universality....
The decays of the light meson π0, η and η′ offer a flavor-conserving laboratory to assess the low-energy QCD and to search for new physics Beyond the Standard Model. The QCD symmetries and symmetry breakings at low-energy, such as the chiral symmetry or the axial anomalies, are manifested in their most unambiguous form in the sector of light pseudoscalar mesons. An experimental study of...
The pseudoscalar $\eta$ and $\eta'$ mesons play a special role in the context of chiral dynamics as their physics properties are intimately linked to the chiral anomaly. While the $\eta$ meson would be a massless state in a $SU(3)$ flavor symmetric world like the other pseudoscalar octet mesons, the $\eta'$ remains massive even in the chiral limit due to the anomalous breaking of the axial...
We performed a theoretical analysis of the semileptonic decays $\eta^{(\prime)} \to \pi^0 \ell^+ \ell^-$ and $\eta' \to \eta \ell^+ \ell^-$, where $\ell = e, \mu$, via a charge-conjugation-conserving two-photon mechanism. The underlying form factors are modeled using vector-meson dominance, phenomenological input, and $U(3)$ flavor symmetry. We considered both a monopole and a dipole model,...
The uncertainty of the Standard Model prediction of the anomalous magnetic moment of the muon $g-2$ is dominated by hadronic contributions. As part of these hadronic inputs, the pseudoscalar-pole contribution in hadronic-light-by-light scattering plays a vital role. The currently sought precision of the Standard Model prediction of $(g-2)_μ$ requires a careful evaluation not only of the...
The sector of decay constants of the octet of light pseudoscalar mesons in the framework of 'resummed' $SU(3)$ chiral perturbation theory is investigated. A theoretical prediction for the decay constant of $\eta$-meson is compared to a range of available determinations. Compatibility of these determinations with the latest fits of the $SU(3)$ low energy coupling constants is discussed. Using a...
Our current understanding of hadrons is through QCD, and confinement in QCD leads to a rich spectrum of hadrons. Experimentally, hadronic resonances can appear as peaks in the invariant mass distributions. However, universal parameters of hadronic resonances are encoded theoretically in the poles of the $S$-matrix. Still, not all observed peaks necessarily correspond to hadronic...
In this talk I review established as well as recently uncovered connections between string-derived scalar amplitudes (Z-theory) and amplitudes of pions in the chiral non-linear sigma model (NLSM). Non-abelian Z-theory [1] amplitudes generalize the open string Veneziano amplitude and represent a stringy completion (including corrections in the string scale $\alpha$') of a cubic bi-adjoint field...
We propose the Gauge Theory Bootstrap --- a method to compute the pion S-matrix that describes the low energy physics of the strong interaction and other similar gauge theories. Using this method, we compute pion scattering phase shifts for all partial waves with angular momentum $\ell \le 3$ up to $2$ GeV and calculate the low energy $\chi$PT coefficients $L_{1,2,4,6}$. The method looks for...
Using the most recent experimental data and lattice calculations of scattering lengths of $\pi\pi$ scattering and employing dispersive representation of the amplitude based on Roy equations, we compute the subthreshold parameters of this process. We use Monte Carlo sampling to numerically model the probability distribution of the results based on all uncertainties in the inputs. In the second...
Three-hadron systems are an active topic in lattice QCD, primarily due to their relevance to the study of hadronic resonances with three-body decays. The systematics of such challenging systems -- finite-volume effects and the pion-mass dependence -- can be connected to the elastic three-to-three scattering amplitude, which can in turn be computed in chiral perturbation theory. I describe a...
We discuss various aspects of (multi-) Higgs boson production from longitudinal electroweak gauge bosons $W_L W_L \to n \times h$ in the TeV region as the necessary information to characterise the Flare function, $\mathcal{F}(h)$, which determines whether the Standard Model EFT (SMEFT) or the Higgs EFT (HEFT -also sometimes referred as the EW Chiral Lagrangian-) is the appropriate description....
Hypergeometric function theory and Feynman Integral calculus go hand in hand. A series of recent investigations that culminated in the construction of several Mathematica packages that are based on Mellin-Barnes techniques, Method of Regions, hypergeometric function theory, etc., is reviewed in this talk to encourage the community to explore the use of these packages. Two-loop integrals...
The presence of the long-range forces brings novel aspects in the formulation of the finite-volume two-body quantization condition, which relates the lattice spectrum with the infinite-volume scattering phase shifts. In particular, the higher partial waves start to contribute substantially to the quantization condition that makes the analysis more complicated. Furthermore, the so-called...
In this talk, I will present a novel effective-field-theory-based approach for extracting two-body scattering information from finite volume energies. By explicitly incorporating one-pion exchange, we overcome the challenging left-hand cut problem in Lüscher’s method and can handle finite volume energy levels both below and above the left-hand cut. Additionally, we utilize the plane wave basis...
We introduce a novel method that utilizes the overlaps between test states and Hamiltonian eigenstates to determine resonance positions, applicable both in lattice and in finite-volume continuum calculations. We demonstrate the efficiency of this method through explicit examples. Using simple spatially compact test states, we obtained Breit-Wigner peaks in the energy distribution for the...
During the talk, I will discuss progress in applying the relativistic three-particle scattering formalism of Hansen and Sharpe to systems of non-degenerate mesons of arbitrary angular momenta. For concreteness, I will focus on the $DD\pi$ system in the charm $C=2$ and isospin $I=0$ sectors, where the doubly charmed tetraquark $T_{cc}^+(3875)$ should appear as a pole in the elastic $3 \to 3$...
We study systems of two and three mesons composed of pions and kaons at maximal isospin using the E250 CLS ensemble with physical quark masses. Using the stochastic LapH method, we determine the energy spectrum of these systems including many levels in different momentum frames. Using the two- and three-body finite-volume formalism, we constrain the two and three-meson K matrix, including not...
The NA62 experiment at CERN collected the world's largest dataset of charged kaon decays in 2016--2018. In this talk, we report a new preliminary result of the $\pi^0 \rightarrow e^+ e^-$ branching fraction measurement at NA62. The result is based on a sample of signal decay candidates collected using a dedicated scaled-down di-electron trigger. Other recent NA62 results with analyses of rare...
$K\to\pi\pi$ decay amplitudes and the measure of its direct CP violation, $\varepsilon'$, are expected to play a key role in searching for new physics beyond the Standard Model because of the highly suppressed value of $\varepsilon'$. While, NA48 and KTeV experiments gave a well-resolved result, Re$(\varepsilon'/\varepsilon) = 16.6(2.3)\times10^{-4}$, there have been tremendous obstacles to...
In this talk, we provide compact analytic expressions for the one- and two-loop pion-pion partial-wave ChPT amplitudes for $J=0,\,1,\, 2$. We use these results to analyze lattice-QCD data of the ππ → ππ P wave obtained at unphysical-high pion masses using the inverse-amplitude method at next-to-leading order and next-to-next-to-leading order. We then extrapolate to the physical pion mass and...
The R value, defined as the ratio of inclusive hadronic cross section over dimu cross-section from electron-positron annihilation, is an important quantity that contributes to the SM prediction of the muon anomalous magnetic moment, and in the determination of the QED running coupling constant evaluated at the Z pole. At BESIII, the R value is measured with a total of 14 data points with the...
I will present the work on short-distance contributions to the hadronic light-by-light part of the muon g-2 as in the Standard Model. Work done since the previous chiral dynamics is working out how to calculate in principle the higher order corrections to the Melnikov-Vainshtein result, published in JHEP 02 (2023) 167 [2211.17183 [hep-ph]]. In addition I will preesent the sofar unpublished...
A dispersive implementation of the $\pi\eta/K\bar{K}$ scattering to $(g-2)_\mu$ requires the knowledge of the double-virtual $S$-wave $\gamma^*\gamma^*\to\pi\eta/ K\bar{K}_{I=1}$ amplitudes. To obtain these amplitudes we used a modified coupled-channel Muskhelishvili–Omnes formalism, with the input from the left-hand cuts and the hadronic Omnes function. The latter were obtained using a...
I describe recent advances in the development and application of the three-particle formalism that connects the finite-volume spectrum of three (and two) particles to infinite volume three- (and two-) particle scattering amplitudes. Specifically, I will present results from applying this formalism to systems of three pions and/or kaons at maximal isospin at near physical quark masses (work...
