Stability of the electroweak ground state in the Standard Model and its extensions

We review the formalism by which the tunnelling probability of an unstable ground state can be computed in quantum field theory, with special reference to the Standard Model of electroweak interactions. We describe in some detail the approximations implicitly adopted in such calculation. Particular attention is devoted to the role of scale invariance, and to the different implications of scale-invariance violations due to quantum effects and possible new degrees of freedom. We show that new interactions characterized by a new energy scale, close to the Planck mass, do not invalidate the main conclusions about the stability of the Standard Model ground state derived in absence of such terms.Comment: 12 pages, 5 figures. To appear in Physics Letters

Massive vectors and loop observables: the g−2g-2 case

We discuss the use of massive vectors for the interpretation of some recent experimental anomalies, with special attention to the muon $g-2$. We restrict our discussion to the case where the massive vector is embedded into a spontaneously broken gauge symmetry, so that the predictions are not affected by the choice of an arbitrary energy cut-off. Extended gauge symmetries, however, typically impose strong constraints on the mass of the new vector boson and for the muon $g-2$ they basically rule out, barring the case of abelian gauge extensions, the explanation of the discrepancy in terms of a single vector extension of the standard model. We finally comment on the use of massive vectors for $B$-meson decay and di-photon anomalies.Comment: 25 pages, 1 figure. References added, to appear in JHE

Modeling Time-Dependent Behavior of Concrete Affected by Alkali Silica Reaction in Variable Environmental Conditions

Alkali Silica Reaction (ASR) is known to be a serious problem for concrete worldwide, especially in high humidity and high temperature regions. ASR is a slow process that develops over years to decades and it is influenced by changes in environmental and loading conditions of the structure. The problem becomes even more complicated if one recognizes that other phenomena like creep and shrinkage are coupled with ASR. This results in synergistic mechanisms that can not be easily understood without a comprehensive computational model. In this paper, coupling between creep, shrinkage and ASR is modeled within the Lattice Discrete Particle Model (LDPM) framework. In order to achieve this, a multi-physics formulation is used to compute the evolution of temperature, humidity, cement hydration, and ASR in both space and time, which is then used within physics-based formulations of cracking, creep and shrinkage. The overall model is calibrated and validated on the basis of experimental data available in the literature. Results show that even during free expansions (zero macroscopic stress), a significant degree of coupling exists because ASR induced expansions are relaxed by meso-scale creep driven by self-equilibriated stresses at the meso-scale. This explains and highlights the importance of considering ASR and other time dependent aging and deterioration phenomena at an appropriate length scale in coupled modeling approaches

Experimental Assessment and Numerical Modeling of Self Healing Capacity of Cement Based Materials via Fracture Mechanics Concepts

The authors’ research group has undertaken for about a lustrum a comprehensive research project, focusing on both experimental characterization and numerical predictive modelling of the self-healing capacity of a broad category of cementitious composites, ranging from normal strength concrete to high performance cementitious composites reinforced with different kinds of industrial (steel) and natural fibers. In this paper reference will be made to normal strength concrete: both autogenous healing capacity has been considered and self-healing engineered through the use of crystalline admixtures. A tailored methodology has been employed to characterize the healing capacity of the investigated concrete, based on comparative evaluation of the mechanical performance measured through 3-point bending tests. Tests have been performed to pre-crack the specimens to target values of crack opening, and after scheduled conditioning times to selected exposure conditions, including water immersion and exposure to open air. The healing capacity has been quantified by means of the definition and calculation of suitable “healing indices”, based on the recovery of the mechanical properties, including load bearing capacity, stiffness, ductility, toughness etc. and correlated to the amount of crack closure also “estimated” through suitable indirect methodologies. Chemical characterization of the healing products by means of SEM has been performed to understand the different mechanisms governing the observed phenomena and also discriminate among the different amounts of recovery of the different mechanical properties. As a further step a predictive modelling approach, based on modified microplane model, has been formulated. This incorporates the self-healing effects, in particular, the delayed cement hydration, as well as the effects of cracking on the diffusivity and the opposite repairing effect of the self-healing on the micro-plane model constitutive laws. The whole experimental and numerical investigation represents a comprehensive and solid step towards the reliable and consistent incorporation of self-healing concepts and effects into a durability-based design framework for engineering applications made of or retrofitted with self-healing concrete and cementitious composites

Experimentally informed modeling of the early‐age stress evolution in cementitious materials using exponential conversion from creep to relaxation

This study presents comprehensive numerical modeling methods for simulating early-age stress (EAS) relaxation in cementitious materials, based on the autogenous deformation (AD), elastic modulus, creep, and stress continuously tested by a mini temperature stress testing machine (Mini-TSTM) and a mini AD testing machine from a very early age (i.e., from a few hours to a week). Four methods for converting creep compliance to relaxation modulus were discussed in detail and used for the one-dimensional (1D) and three-dimensional (3D) simulation of stress evolution in the Mini-TSTM test. Furthermore, virtual creep and relaxation tests were conducted using an exponential algorithm with either the Kelvin or Maxwell chains to show their applicability in simulating the viscoelastic behavior of early-age cementitious materials. The results showed that the exponential algorithm with the Maxwell chain using an exponential conversion function from creep to relaxation obtains good prediction accuracy of EAS in 3D analysis. The numerical solutions of the Volterra integral of creep compliance can lead to a negative relaxation modulus, thus introducing stress calculation errors in both 1D and 3D analysis

Orthotropic hygroscopic behavior of mass timber: theory, computation, and experimental validation

Recent rapid improvements in laminated timber technology have led to the increased use of wood in both mid- and high-rise construction, generally posed as a more carbon-friendly alternative to concrete. However, wood is significantly more sensitive to changes in relative humidity than concrete, which may impact the sustainability and durability of mass timber buildings. Moisture cycling in particular affects not only shrinkage and swelling but also strongly influences wood creep. This sensitivity is of high concern for engineered wood used in mass timber buildings. At the same time, wood, considered as an orthotropic material, exhibits varying diffusivity in all three directions, complicating efforts to characterize its behavior. In this work, an orthotropic hygroscopic model was developed for use in laminated timber. A species database for wood sorption isotherm was created and an existing model was used to fit species-based parameters. Diffusion behavior which considers the sorption isotherm was modeled through numerical simulations, and species-dependent orthotropic diffusion parameters were identified. A database of permeability in all directions for various species was created. The resulting model is able to predict diffusion behavior in glulam and cross-laminated timber (CLT) for multiple species of the lab tests. The model also predicts the moisture ranges for a CLT panel under environmental change with parameters from these sorption isotherm and diffusion databases

Measurement of the (30)Si Mole Fraction in the New Avogadro Silicon Material by Neutron Activation and High-Resolution γ-Spectrometry

The use of new silicon single crystals highly enriched in (28)Si recently produced for the upcoming redetermination of the Avogadro constant requires knowledge of their molar masses. The isotopic composition data are collected independently in different laboratories but all using the virtual element technique with multicollector inductively coupled plasma mass spectrometers. In this framework, the comparison of the results with an independent measurement of the amount of at least one of the depleted isotopes is useful to limit hidden systematic errors. To this aim, the (30)Si mole fraction of a sample of the new material was measured using a relative measurement protocol based on instrumental neutron activation analysis. The protocol is similar to that previously applied with the AVO28 silicon material used for the last determination of the Avogadro constant value with the exception that unknown and standard samples are not coirradiated. The x((30)Si) = 5.701 × 10(-7) mol mol(-1) estimate is close to the expected one and is given with a standard uncertainty of 8.8 × 10(-9) mol mol(-1). This value, if adopted, gives a contribution to the relative standard uncertainty of the Avogadro constant of 6.3 × 10(-10)

Numerical Simulation of Quasi-Static and Dynamic Experiments of Standard and Dam Concrete

Aggregate size effect is among several important factors that affect concrete mechanical behavior. In this study, this effect is investigated numerically, and the obtained results are compared with the gathered experimental data that are recently performed at Politecnico di Milano and the Joint Research Center of Ispra, Italy. Since concrete is a rate-dependent material, different types of static and dynamic experiments are carried out to study the aggregate size effect on concrete response. The Lattice Discrete Particle Model (LDPM), a three-dimensional mesoscale discrete model, is employed to simulate concrete mechanical response. LDPM simulates concrete at the level of coarse aggregate pieces and is capable of characterizing strain localization, distributed cracking in tension and compression and to reproduce post peak softening behavior. The parameters governing different aspects of LDPM from concrete mixture design to the meso-scale mechanical constitutive law are calibrated and used in the validation process

Discrete element framework for modeling tertiary creep of concrete in tension and compression

In this contribution, a computational framework for the analysis of tertiary concrete creep is presented, combining a discrete element framework with linear visco-elasticity and rate-dependency of damage. The Lattice Discrete Particle Model (LDPM) serves as constitutive model. Aging visco-elasticity is implemented based on the Micro-Prestress-Solidification (MPS) theory, linking the mechanical response to the underlying physical and chemical processes of hydration, heat transfer and moisture transport through a multi-physics approach. The numerical framework is calibrated on literature data, which include tensile and compressive creep tests, and tests at various loading rates. Afterwards, the framework is validated on time-to-failure tests, both for flexure and compression. It is shown that the numerical framework is capable of predicting the time-dependent evolution of concrete creep deformations in the primary, secondary but also tertiary domains, including very accurate estimates of times to failure. Finally, a predictive numerical study on the time-to-failure response is presented for load levels that are difficult to test experimentally, showing a deviation from the simple linear trend that is commonly assumed. Ultimately, two alternative functions for time-to-failure curves are proposed that are mechanically justified and in good agreement with both, experimental data and numerical simulations

Herpes Zoster Associated Hospital Admissions in Italy: Review of the Hospital Discharge Forms

In Italy a specific surveillance system for zoster does not exist, and thus updated and complete epidemiological data are lacking. The objective of this study was to retrospectively review the national hospital discharge forms database for the period 1999–2005 using the code ICD9-CM053. In the period 1999–2005, 35,328 hospital admissions have been registered with annual means of 4,503 hospitalizations and 543 day-hospital admissions. The great part of hospitalizations (61.9%) involved subjects older than 65 years; the mean duration of stay was 8 days. These data, even if restricted to hospitalizations registered at national level, confirm the epidemiological impact of shingles and of its complications