Heavy quarkonia in strong magnetic fields

We investigate the influence of a homogeneus and constant strong external magnetic field on the heavy-meson spectrum. Quarkonium states $c\bar{c}$ and $b\bar{b}$ are described within a non-relativistic framework and by means of a suitable potential model based on the Cornell parametrization. In particular, in this work we propose a model which takes into account the possible anisotropies emerging at the level of the static quark-antiquark potential, as observed in recent lattice studies. The investigation is perfomed both with and without taking into account the anisotropy of the static potential, in order to better clarify its effectsComment: 10 pages, 9 figures, 3 tables, minor changes, references adde

Quark-antiquark interactions in background magnetic fields

Introduction - The properties of strong interacting matter in the presence of large external fields have attracted much interest in the recent past. The investigation of such properties is relevant in different physical conditions. For example, it is believed that strong magnetic fields, of the order of 1016 Tesla ∼ 1 GeV^2 , may have been produced in the early Universe. In addition, slightly lower magnetic fields, up to about 10^15 Tesla, are expected to be created in non-central ultra-relativistic heavy-ion collisions. In this context, the theory representing our current understanding of strong interaction, the Quantum Chromodynamics (QCD), allows to predict many important results. As regards the investigation in the non-perturbative regime, the lattice formulation (LQCD) reveals to be one of the most suitable approach. Within this framework, the properties of the strong interacting matter in the presence of external magnetic field have been studied extensively, leading to relevant results such as the effects on the QCD phase diagram at finite temperatures and those on of deconfinement and chiral system restauration. The work presented in this thesis lies exactly in this context. It is based on the study presented in a very recent paper 1 about the properties of the confining potential between two heavy quarks in the presence of a constant and uniform external magnetic field, performed within the LQCD formulation at zero temperature. It has been found that the potential is anisotropic for non-vanishing magnetic fields, showing different behaviours in the directions transverse and parallel to the external field. In particular, adopting the standard Cornell parametrization, i.e. a linear rising confining term (σr ) supplied with a Coulomb-like one (α/r ), it has been found that anisotropies emerge in both the string tension σ and in the strength of the Coulomb coupling α of the static potential, which acquire a non-trivial dependence on magnetic field, i.e. σ = σ(θ; B ) and α = α(θ; B ) with θ azimutal angle with respect to the direction of B . Controlling idea and methods - The original study proposed in this thesis is focused on the phenomelogical effects that such anisotropies may produce. The main idea is that the observed behaviour of the static quark-antiquark potential in the presence of strong magnetic fields should affect the observables directly related on it. To this aim, it has been chosen to follow two distinct lines of investigations. The first involves the direct effects of the anisotropic static quark-antiquark potential on the energy levels, i.e. the masses of the heavy-meson spectrum; the second, instead, generalizes the investigation at finite temperature and it focalized on the behaviour of the correlator between the so-called Polyakov loops L(x), defined as the temporal loop made up by the parallel transports (gauge links living) living on the lattice, which is strictly connected with the static potential. In the first case, the work has been based on an non-relativistic approach for describing the heavy-mesons, i.e. the bound states c c and b b. The reason lies exactly in the nature of the quenched potential, which is formally valid in the infinite mass limit and hence represents a suitable parametrization of the heavy quark-antiquark interaction. The model describing the dynamics of a bound state in an external magnetic field has been solved making use of a numerical algorithm (based on a finite-difference scheme) allowing the extraction of both eigenstates and eigenvalues through an Euclidean finite-time step evolution. This procedure, supplied with a state-mixing algorithm, has provided the computation of the masses of the lower part of the heavy-meson spectrum, i.e. that corresponding to the 1S and 1P states. Simulations have been performed in the range B = 0.1 − 0.3 GeV2 , both considering or not the presence of the anisotropy, in order to check and separate the possible mass differences. As regards the second part of this study, it is focused on the effects of external magnetic fields at finite temperature and, hence, representing a natural continuation of the investigation of the anisotropy. The expectation values of the Polyakov loop correlators have been extracted from lattice configuration samples corresponding to a 2+1 lattice QCD theory, i.e. with dynamical quarks u, d , s such that m_u = m_d =m_s . In order to check the possible effect of the magnetic anisotropy, correlators been computed separating the contributions along the spatial directions transverse and parallel with respect to the applied external magnetic field. Such a procedure also requires the application of a specific strategy to decrease the noise due to the UV fluctuation on the lattice (gauge link smearing). Simulations have been performed for different magnetic fields of the order of B ∼ 1015 Tesla and for a single lattice volume 32×8 at the temperature of about T ∼ 140 MeV, i.e. slightly before the expected chiral and deconfinement transitions. Obtained results - In both cases, the study suggests that the presence of an external strong magnetic field has relevant effects. Concerning the heavy-meson mass spectrum, the model predicts that the anisotropy, within the range investigated, may increase the mass value by an amount of the same order (or, in some cases, slightly higher) of those related to the effect of the magnetic field only. These are expected to be of the order of about 50-100 MeV in the case of the charmonium spectru, and of about 10 − 30 MeV for bottomonium states. In addition, the model predicts also non-trivial mixing between the particle states, depending on the module of the external field, which may creates concrete effects on, for example, the decay rates or the possible decay channels. Non-negligible effects have been also found, at finite temperature, on the correlator between Polyakov loops. Their behaviour for large distances seems to agree with the expected picture of a decreasing of the temperature of the confinement-deconfinement crossover in the presence of an external magnetic field. As regards the static quark-antiquark potential, a curve fitting procedure of the data suggest that for B = 0 there is a clear splitting between the shapes in the directions parallel and orthogonal with respect to the magnetc field axes. At the level of the string tension σ or the parameter α, the anisotropy effect is more noticeable and, as regards in particular the string tension, up to about 20 − 25% for |e|B ∼ 1 GeV2 . Such a study is clearly not exhaustive. Indeed, there are several lines of investigation which may be followed. As concerns the heavy-meson mass spectum, for example, one may try both to improve the non-relativistic model or to proceed with a more quantitative investigation about the reliability of a measurement of the observed effects. At finite temperatures, possible prospectives are more. Indeed, the study may be generalized to a wide range of both temperatures or densities, leading to a more detailed description of the possible effect on the QCD phase diagram

Analisi e applicazione di criteri di verifica a fatica di giunture saldate per roller coasters

Questa tesi, svolta in collaborazione con l'azienda Antonio Zamperla S.p.A, costruttrice di giostre meccaniche e roller coasters, si propone di analizzare alcuni criteri di verifica di giunti saldati sottoposti a carichi affaticanti, proposti dalle normative di riferimento e ritenuti di maggior interesse industriale, al fine di comprenderne i principi e valutarne le potenzialità. Nella fattispecie, si è posto particolare riguardo alla normativa europea EUROCODICE 3 che sostituisce la ben nota norma italiana UNI CNR 10011. La nuova normativa europea include una classificazione dei dettagli strutturali che ricorrono più frequentemente nelle strutture saldate sottoposte a carichi variabili che richiedono maggiore cautela in fase progettuale, in quanto direttamente imputabili di una riduzione della resistenza meccanica. I criteri di verifica studiati, previsti dall'EUROCODICE 3, sono stati applicati, in primo luogo, ad una categoria di dettaglio inclusa nella normativa, per la quale è stata condotta una analisi FEM, come suggerito dalla stessa normativa, al fine di stimare i gradienti di tensione in prossimità dei cordoni di saldatura. Successivamente si è proceduto col verificare la resistenza a fatica del binario di un roller coaster, di fabbricazione Zamperla, sempre mediante l'applicazione di suddetti criteri, per cui si è resa indispensabile la creazione di un modello FEM idoneo a rappresentare la geometria delle giunture saldate di collegamento tra le rotaie e i traversini. L'analisi condotta su entrambi i dettagli strutturali ha consentito, inoltre, di stabilire l'efficacia e l'efficienza dei modelli creati, in termini di risoluzione, di tempi di realizzazione e di tecniche di sviluppo

Influence of magnetic fields on the color screening masses

We present some recent results obtained in the study of the color magnetic and electric screening masses in the QCD plasma. In particular, we discuss how the masses get modified by strong external fields which are expected to be created in physical situations such as heavy-ion collisions.Comment: Talk presented at the 35th annual International Symposium on Lattice Field Theory (LATTICE 2017), 18-24 June 2017, Granada, Spain. 8 Pages, 7 Figure

Flux tubes in Nf=2+1N_f=2+1 QCD with external magnetic fields

We study the behavior of the confining flux tube in $N_f=2+1$ QCD at the physical point, discretized with the stout smearing improved staggered quark action and the tree level Symanzik gauge action. We discuss how it depends on a uniform external magnetic field, showing how it displays anisotropies with respect to the magnetic field direction. Moreover, we compare the observed anisotropy pattern with that of the static quark-antiquark potential we obtained in our previous works.Comment: 8 pages, 35th International Symposium on Lattice Field Theory, Granada, Spai

Magnetic field effects on the static quark potential at zero and finite temperature

We investigate the static $Q\bar{Q}$ potential at zero and finite temperature in the presence of a constant and uniform external magnetic field $\vec{B}$, for several values of the lattice spacing and for different orientations with respect to $\vec{B}$. As a byproduct, we provide continuum limit extrapolated results for the string tension, the Coulomb coupling and the Sommer parameter at $T = 0$ and $B = 0$. We confirm the presence in the continuum of a $B$-induced anisotropy, regarding essentially the string tension, for which it is of the order of 15\% at $|e| B \sim 1~{\rm GeV}^2$ and would suggest, if extrapolated to larger fields, a vanishing string tension along the magnetic field for $|e| B \gtrsim 4$ GeV$^2$. The angular dependence for $|e| B \lesssim 1$ GeV$^2$ can be nicely parametrized by the first allowed term in an angular Fourier expansion, corresponding to a quadrupole deformation. Finally, for $T \neq 0$, the main effect of the magnetic field is a general suppression of the string tension, leading to a precocious loss of the confining properties: this happens even before the appearance of inverse magnetic catalysis in the chiral condensate, supporting the idea that the influence of the magnetic field on the confining properties is the leading effect originating the decrease of $T_c$ as a function of $B$.Comment: 13 pages, 4 tables, 14 figure

Screening masses in strong external magnetic fields

We present results for the (color)magnetic and (color)electric screening masses of the Quark-Gluon Plasma in the presence of an external magnetic field. The screening masses are extracted from the correlators of Polyakov loops, determined by lattice QCD simulations at the physical point. We explore temperatures in the range $200\,\mathrm{MeV}\lesssim T\lesssim 330\,\mathrm{MeV}$ and magnetic field intensities up to $|e|B \sim 1.3\,\mathrm{GeV}^2$. We find that both screening masses are increasing functions of the magnetic field and that the dependence on $B$ becomes weaker for larger temperatures. In the case of the magnetic screening mass a slight anisotropy is also observable.Comment: 8 pages, 2 tables, 10 eps figures; This version matches the published on

Quantum Effects in the Aubry Transition

The Aubry transition between sliding and pinned phases, driven by the competition between two incommensurate length scales, represents a paradigm that is applicable to a large variety of microscopically distinct systems. Despite previous theoretical studies, it remains an open question to what extent quantum effects modify the transition, or are experimentally observable. An experimental platform that can potentially reach the quantum regime has recently become available in the form of trapped laser-cooled ions subject to a periodic optical potential [A. Bylinskii, D. Gangloff, I. Counts, and V. Vuletic, Nature Materials 15, 717 (2016)]. Using Path-Integral Monte Carlo (PIMC) simulation methods, we analyze the impact of quantum tunneling on the sliding-to-pinned transition in this system, and determine the phase diagram in terms of incommensuration and potential strength. We propose new signatures of the quantum Aubry transition that are robust against thermal and finite-size effects, and that can be observed in future experiments.Comment: 10 pages, 7 figure

Impact of high resolution radar imagery on reservoir monitoring

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c-Src and IL-6 inhibit osteoblast differentiation and integrate IGFBP5 signalling

Interleukin-6 (IL-6) and c-Src impair osteoblast maturation in vitro and in vivo. Given the similar effects of these factors, they are likely to establish a functional loop to maintain osteoblasts in a less mature status. Here we describe a pathway whereby c-Src stimulates IL-6 expression through the STAT3 factor, which, in response to IL-6 induces insulin-like growth factor 5 (IGFBP5), a c-Src activating factor that amplifies this loop only in immature osteoblasts. In contrast, in mature osteoblasts, IGFBP5 is enhanced by Runx2, but is no longer able to stimulate c-Src activation, as this tyrosine kinase at this stage is downregulated. We find that the IGFBP5 produced by osteoblasts stimulates osteoclastogenesis and bone resorption, acting as an osteoblast-osteoclast coupling factor. Finally, we demonstrate that the integrated actions of c-Src, IL-6 and IGFBP5 also have a role in vivo. We conclude that this pathway is relevant for bone metabolism, both in physiological and in pathological conditions