seminario di fisica teorica

Peter Millington (University of Nottingham)

The effective action is a powerful tool for studying the non-perturbative behaviour of quantum field theories. In this talk, we will revisit the derivation of the so-called two-particle-irreducible effective action, paying particular attention to the role of the sources that appear in its definition. Working in the context of zero-dimensional quantum field theory, we will be able to accompany this derivation with a graphical and pedagogical exposition of the behaviour of the effective action, and its various ingredients. With this intuitive understanding, we will then be able to show that we have much greater control over the effective action than has perhaps previously been realised, and we will be able to use the sources to map between different realisations of the effective action and to preserve symmetry properties in its truncations. Finally, by associating the two-point source of the effective action with the regulator of the renormalisation group evolution, we will arrive at an exact flow equation that differs fundamentally from the well-known Wetterich-Morris-Ellwanger equation. We will conclude by commenting on the potential implications of our results and highlighting possible future directions.

Seminario di Fisica Teorica

Phases of 3d gauge theories (Riccardo Argurio Univ. Bruxelles)

We will consider gauge theories in 3d with fermionic matter and explore their low-energy phases as some parameters are varied, such as masses for the matter fields and the Chern-Simons level of the gauge group. We will discuss when the transitions between the various phases are first or second order, or go beyond the Landau-Ginzburg paradigm. We will

employ a variety of approaches: consistency conditions based on symmetries, a dual picture involving bosonization, large N limits and holography.

Seminario di Fisica Teorica

Dr. Francesco Bigazzi (INFN Firenze)

A holographic model of QCD axion is presented. It describes a

composite axion in the KSVZ class. Having a gravity dual, based on the

Witten-Sakai-Sugimoto model, it is calculable in the strongly coupled

regime and its UV completion is under control. Its basic properties are

derived, including the low energy Lagrangian, from which the axion

couplings to nucleons can be derived. Basic features in the deconfined

phase are studied as well. In particular, the temperature dependence of

the axion mass is extracted from the topological susceptibility.

Seminario di Fenomenologia

Dr. Oleh Fedkevych (Università di Genova & INFN Genova)

In spite of the recent progress in both theoretical and experimental studies of QCD, many aspects of multiple parton interactions (MPI) still require a detail investigation. In particular, double parton scattering (DPS) processes can play a dominant role for some specific kinematic regions of multi-jet production, especially in proton-nucleus (pA) collisions where the total DPS cross section is approximately âˆŒ3A times bigger than the corresponding total DPS cross section in proton-proton (pp) collisions.

In this talk, I will provide a general overview of the state-of-the-art of the “first principles” and Monte Carlo description of DPS (MPI) processes

with a special emphasize on the four-jet DPS production in pp and pA collisions and

different approaches to model double parton distribution functions.

Seminario di Fenomenologia Dr. Matthew Lim (Milano Bicocca)

The GENEVA framework allows fully differential, fixed order calculations at NNLO to be matched to parton shower programs while also achieving NNLL’ accuracy in the distribution of a jet resolution variable. To date, it has been successfully applied to jet production in e+e- collisions and also the Drell-Yan process at the LHC. In this talk I will discuss the methodology and present its application to VH production at the LHC, which has recently been measured for the first time. I will present comparisons with dedicated fixed order programs as well as showered distributions and discuss future avenues to be explored.

Seminario di Fisica Teorica Daniel Arean Fraga (Universidad Autonoma de Madrid)

In this talk I will review the topic of non-Hermitian PT-Symmetric quantum theories and present a proposal for a gravity dual of a non-Hermitian QFT.

Seminario di Fenomenologia Dr. Johannes Michel (DESY, Hamburg)

Differential measurements at the LHC involve many physical scales set by the hard production process and soft or collinear QCD dynamics. When these scales are widely separated, the perturbative series becomes dominated by logarithms of their ratios. Precise (or sometimes even just physical) theory predictions require the resummation of these large logarithms to all orders. In this talk I will provide an overview of the challenges encountered when extending the resummation program to multi-differential observables, and of the new insights one gains into the infrared structure of QCD. I will first briefly review single-differential resummation methods, focusing on TMD factorization and the inclusive transverse momentum spectrum of electroweak gauge bosons at the LHC as a key application. I will then discuss how additional measurements on the decay products of the Z or W affect the resummation (e.g. fiducial acceptance cuts, the lepton pT, or the phi* observable), and present ongoing work to incorporate these effects at the level of precision required for determinations of key electroweak parameters such as the W mass at the LHC.

In the second half of the talk I will show how treating a very basic QCD quantity (the Drell-Yan rapidity spectrum) in a multi-differential spirit leads to surprising new insight into its all-order perturbative structure, and generalizes the classic QCD result of threshold (or soft-gluon) resummation.

Seminario di Fisica Teorica Johanna Erdmenger (Wurzburg)

I will report on recent work of a team of researchers from both

AdS/CFT and condensed matter physics on proposing a new material with

an effective electron coupling three times larger than in graphene,

which is therefore expected to be even more suited for realizing

hydrodynamic electron flows than graphene. Also, the ratio of shear

viscosity over entropy density is expected to be smaller. The proposed

material is based on a Kagome lattice structure. Moreover, I will also

present new results on the Hall viscosity of electron flows in

channels. We find that at a critical magnetic field, the Hall viscosity

contribution cancels the ordinary Hall effect contribution to the total

Hall voltage. Finally, I will also mention recent results on how

quantum anomalies affect the Josephson current in inversion-asymmetric

Weyl semimetals.

Seminario di Fenomenologia

Prof. Lorenzo Calibbi (Nankai University)

Pseudo Nambu-Goldstone bosons (also known as axion-like particles) with

flavour-violating couplings to the Standard Model (SM) fermions are a

rather generic consequence of spontaneously-broken global U(1)

symmetries, e.g. if the SM fermions carry flavour non-universal charges.

A possible consequence is the occurrence of flavour-violating decays of

hadrons and leptons into light axion-like particles. These exotic

signatures are a powerful probe of such kind of scenarios. I will

discuss the phenomenological consequences at future experiments,

focusing in particular on searches for lepton flavour violation.

Seminario generale Prof. ssa Nadia Pastrone (INFN Torino)

After the discovery of the Higgs boson a new era of precise measurements has been started at LHC. The upcoming update of the European Strategy for Particle Physics will chart the future in the field at the high-energy frontier for the coming decades. The physics potentials and the key differences between the proposed linear or circular collider were evaluated at the various reachable collision energy. Hadron or lepton machines are confronted on their sensitivity to precisely measure the Higgs boson couplings and the possibility to make direct or indirect discoveries. Demanding technologies, bright solutions and vigorous R&D will be needed to launch such challenging projects and pave the future for novel accelerator concepts. The international scenario will be sketched with a personal view to stimulate discussions and suggestions.