Introduction to QCD+QED in finite volume

• Agostino Patella

Lattice QCD simulations have entered the precision era. Thanks to the combined efforts of several lattice collaborations, the masses, leptonic and semileptonic decay rates of light pseudoscalar mesons are presently known, in QCD, with sub-percent relative errors. At this level of precision strong isospin breaking and QED radiative corrections cannot be neglected and have to be taken into account with the required non-perturbative accuracy. This can in principle be done by performing lattice simulations of QCD+QED. The inclusion of the electromagnetic interactions in finite volume lattice simulations, however, poses both theoretical and numerical problems. In particular, as a consequence of Gauss law, electrically-charged states are absent in a finite volume with periodic boundary conditions. While this statement is fairly trivial al the classical level, I will discuss in some detail what it means at the quantum-mechanical level. We will see how C-parity boundary conditions can be used to circumvent this problem in a fully consistent way (and in fact it is the only way if one insists on gauge and translational invariance). A possible lattice discretization of QCD+QED will also be discussed.

Machine learning for sampling in lattice field theory

• Phiala Shanahan

In the context of lattice quantum field theory calculations in particle and nuclear physics, I will describe avenues to accelerate sampling from known probability distributions using machine learning. I will focus in particular on flow-based generative models, and describe how guarantees of exactness and the incorporation of complex symmetries (e.g., gauge symmetry) into model architectures can be achieved. I will show the results of proof-of-principle studies that demonstrate that sampling from generative models can be orders of magnitude more efficient than traditional Hamiltonian/hybrid Monte Carlo approaches in this context.

Strong coupling constant from the lattice

• Luigi Del Debbio

The strong coupling constant is one of the crucial ingredients for precision predictions for the LHC. We discuss lattice inputs for the determination of the strong coupling with a specific focus on the systematic errors.

A new strategy for the determination of alpha_s

• Alberto Ramos Martinez

Introduction to Scale Setting in QCD

• Tomasz Korzec

In this lecture I will explain, how a dimensionful scale is introduced in lattice QCD simulations. All sources of systematic uncertainties are discussed before the whole procedure is demonstrated for the case of the 2+1 flavor simulations of the CLS consortium.

High precision scale setting in lattice QCD

• Lukas Varnhorst

Sp(2N) gauge theories for beyond the standard model physics

• Davide Vadacchino

"Lies-to-Children" and Science Communication

• Ernesto Lozano Tellechea

Lies-to-children is a common concept in science education. It refers to the simplified versions of a subject that are usually taught to students in order to provide them with the mental structure needed to move beyond those same lies. One typical example is classical mechanics: a "wrong" picture of reality that is however extremely useful if one wants to understand quantum mechanics and relativity. In this talk I will explain why lies-to-children is also a pivotal concept to understand science communication. Here it works differently because it is encoded in metaphors, not in the subjects of a curriculum, but the idea is the same. We'll also see how lies-to-children are unavoidable when communicating theoretical physics to a lay audience, and we'll learn how to be aware of their pros and cons in order to use them properly. Finally, through some motivating examples, I will encourage all EuroPLEx members to lie as much and as finely as possible about QCD in QuarkBits, the EuroPLEx collaborative blog.

The QCD Phase diagram: introduction

• Claudia Ratti

I will review our current knowledge of the phase diagram of strongly interacting matter. In particular, I will focus on the chiral and deconfinement phase transitions, the corresponding order parameters and their behavior at finite temperature and density.

Nucleon axial structure from lattice QCD: Controlling pion pole enhanced excited states

• Phlipp Wein

We present a new analysis method that allows you to understand and model excited state contributions in observables that are dominated by a pion pole. We apply this method to extract axial and (induced) pseudoscalar nucleon isovector form factors, which satisfy the constraints due to the partial conservation of the axial current up to expected discretization effects. Effective field theory predicts that the leading contribution to the (induced) pseudoscalar form factor originates from an exchange of a virtual pion, and thus exhibits pion pole dominance. Using our new method, we can recover this behavior directly from lattice data. (Work in collaboration with Gunnar Bali, Lorenzo Barca, Sara Collins, Michael Gruber, Marius Löffler, Andreas Schäfer, Wolfgang Söldner, Simon Weishäupl and Thomas Wurm.)

Estimating finite volume effects in QCD+QED simulations by using relativistic EFTs

• Nazario Tantalo

Lattice QCD simulations have entered the precision era. Thanks to the combined efforts of several lattice collaborations, the masses, leptonic and semileptonic decay rates of light pseudoscalar mesons are presently known, in QCD, with sub-percent relative errors. At this level of precision strong isospin breaking and QED radiative corrections cannot be neglected and have to be taken into account with the required non-perturbative accuracy. This can in principle be done by performing lattice simulations of QCD+QED. The inclusion of the electromagnetic interactions in finite volume lattice simulations, however, poses both theoretical and numerical problems. A particularly important issue are the finite volume effects. In the case of the masses of stable hadrons these are power-law suppressed in QCD+QED while they vanish exponentially fast in QCD. The issue becomes much more delicate in the case of decay rates where one has to cope with the well known problem of the infrared divergences, i.e. with diverging finite volume effects, that might appear at intermediate stages of the calculations. In this lecture I will discuss how finite volume effects in QCD+QED can be understood and estimated by using relativistic effective field theories techniques. I will discuss in particular the cases of the finite volume effects on the masses of stable hadrons and of the infrared divergences appearing in the leptonic decay rates of pseudoscalar mesons.

The QCD phase diagram: state of the art

• Claudia Ratti

I will present the state of the art results on the QCD transition line and constraints on the location of the critical point from lattice QCD simulations.