Light-by-light scattering and muon’s anomalous magnetic moment

A study of hadron production by photons opens unique ways to address a number of fundamental problems in strong interaction physics as well as fundamental questions in Quantum Field Theory. In particular, an understanding of two-photon processes is of crucial importance for constraining the hadronic uncertainties in precision measurements and in searches for new physics. The process of

Interaction between axial force, shear and bending moment in reinforced concrete elements

Il collasso di diverse colonne, caratterizzate da danneggiamenti simili, quali ampie fessure fortemente inclinate ad entrambe le estremità dell’elemento, lo schiacciamento del calcestruzzo e l’instabilità dei ferri longitudinali, ha portato ad interrogarsi riguardo gli effetti dell’interazione tra lo sforzo normale, il taglio ed il momento flettente. Lo studio è iniziato con una ricerca bibliografica che ha evidenziato una sostanziale carenza nella trattazione dell’argomento. Il problema è stato approcciato attraverso una ricerca di formule della scienza delle costruzioni, allo scopo di mettere in relazione lo sforzo assiale, il taglio ed il momento; la ricerca si è principalmente concentrata sulla teoria di Mohr. In un primo momento è stata considerata l’interazione tra solo due componenti di sollecitazione: sforzo assiale e taglio. L’analisi ha condotto alla costruzione di un dominio elastico di taglio e sforzo assiale che, confrontato con il dominio della Modified Compression Field Theory, trovata tramite ricerca bibliografica, ha permesso di concludere che i risultati sono assolutamente paragonabili. L’analisi si è poi orientata verso l’interazione tra sforzo assiale, taglio e momento flettente. Imponendo due criteri di rottura, il raggiungimento della resistenza a trazione ed a compressione del calcestruzzo, inserendo le componenti di sollecitazione tramite le formule di Navier e Jourawsky, sono state definite due formule che mettono in relazione le tre azioni e che, implementate nel software Matlab, hanno permesso la costruzione di un dominio tridimensionale. In questo caso non è stato possibile confrontare i risultati, non avendo la ricerca bibliografica mostrato niente di paragonabile. Lo studio si è poi concentrato sullo sviluppo di una procedura che tenta di analizzare il comportamento di una sezione sottoposta a sforzo normale, taglio e momento: è stato sviluppato un modello a fibre della sezione nel tentativo di condurre un calcolo non lineare, corrispondente ad una sequenza di analisi lineari. La procedura è stata applicata a casi reali di crollo, confermando l’avvenimento dei collassi.

Axion-like particles and the 3.5 keV line in 4D string models

This work is focused on axions and axion like particles (ALPs) and their possible relation with the 3.55 keV photon line detected, in recent years, from galaxy clusters and other astrophysical objects. We focus on axions that come from string compactification and we study the vacuum structure of the resulting low energy 4D N=1 supergravity effective field theory. We then provide a model which might explain the 3.55 keV line through the following processes. A 7.1 keV dark matter axion decays in two light axions, which, in turn, are transformed into photons thanks to the Primakoff effect and the existence of a kinetic mixing between two U(1)s gauge symmetries belonging respectively to the hidden and the visible sector. We present two models, the first one gives an outcome inconsistent with experimental data, while the second can yield the desired result.

Alternative derivative expansion in Functional RG and application

We give a brief review of the Functional Renormalization method in quantum field theory, which is intrinsically non perturbative, in terms of both the Polchinski equation for the Wilsonian action and the Wetterich equation for the generator of the proper verteces. For the latter case we show a simple application for a theory with one real scalar field within the LPA and LPA' approximations. For the first case, instead, we give a covariant "Hamiltonian" version of the Polchinski equation which consists in doing a Legendre transform of the flow for the corresponding effective Lagrangian replacing arbitrary high order derivative of fields with momenta fields. This approach is suitable for studying new truncations in the derivative expansion. We apply this formulation for a theory with one real scalar field and, as a novel result, derive the flow equations for a theory with N real scalar fields with the O(N) internal symmetry. Within this new approach we analyze numerically the scaling solutions for N=1 in d=3 (critical Ising model), at the leading order in the derivative expansion with an infinite number of couplings, encoded in two functions V(phi) and Z(phi), obtaining an estimate for the quantum anomalous dimension with a 10% accuracy (confronting with Monte Carlo results).

Chiral symmetry of QCD with twelve light flavors

We study QCD with twelve light flavors at intermediate values of the bare lattice coupling. We contrast the results for the order parameter with different theoretical models motivated by the physics of the Goldstone phase and of the symmetric phase, and we perform a model independent analysis of the meson spectrum inspired by universal properties of chiral symmetry. Our analysis favors chiral symmetry restoration.

NS5-branes, holography and CFT deformations

A few supergravity solutions representing configurations of NS5-branes admit exact conformal field theory (CFT) description. Deformations of these solutions should be described by exactly marginal operators of the corresponding theories. We briefly review the essentials of these constructions and present, as a new case, the operators responsible for turning on angular momentum.

Kaon and D meson masses with N_f = 2+1+1 twisted mass lattice QCD

We discuss the computation of the kaon and D meson masses in the N_f = 2+1+1 twisted mass lattice QCD setup, where explicit heavy flavor and parity breaking occurs at finite lattice spacing. We present three methods suitable in this context and verify their consistency.

Interplay Between Finite Resources and a Local Defect in an Asymmetric Simple Exclusion Process

When particle flux is regulated by multiple factors such as particle supply and varying transport rate, it is important to identify the respective dominant regimes. We extend the well-studied totally asymmetric simple exclusion model to investigate the interplay between a controlled entrance and a local defect site. The model mimics cellular transport phenomena where there is typically a finite particle pool and nonuniform moving rates due to biochemical kinetics. Our simulations reveal regions where, despite an increasing particle supply, the current remains constant while particles redistribute in the system. Exploiting a domain wall approach with mean-field approximation, we provide a theoretical ground for our findings. The results in steady-state current and density profiles provide quantitative insights into the regulation of the transcription and translation process in bacterial protein synthesis.

Bulk Metallic Glasses Deform via Slip Avalanches

For the first time in metallic glasses, we extract both the exponents and scaling functions that describe the nature, statistics, and dynamics of slip events during slow deformation, according to a simple mean field model. We model the slips as avalanches of rearrangements of atoms in coupled shear transformation zones (STZs). Using high temporal resolution measurements, we find the predicted, different statistics and dynamics for small and large slips thereby excluding self-organized criticality. The agreement between model and data across numerous independent measures provides evidence for slip avalanches of STZs as the elementary mechanism of inhomogeneous deformation in metallic glasses.

Thermal right-handed neutrino self-energy in the non-relativistic regime

Recently the issue of radiative corrections to leptogenesis has been raised. Considering the "strong washout" regime, in which OPE-techniques permit to streamline the setup, we report the thermal self-energy matrix of heavy right-handed neutrinos at NLO (resummed 2-loop level) in Standard Model couplings. The renormalized expression describes flavour transitions and "inclusive" decays of chemically decoupled right-handed neutrinos. Although CP-violation is not addressed, the result may find use in existing leptogenesis frameworks.