Probing the phase of the elastic $pp$ scattering amplitude with vortex proton beams

in AIP Conference Proceedings (2013)

We show that colliding vortex proton beams instead of (approximate) plane waves can lead to a direct measurement of how the overall phase of the scattering amplitude changes with the scattering angle. In ... [more ▼]

We show that colliding vortex proton beams instead of (approximate) plane waves can lead to a direct measurement of how the overall phase of the scattering amplitude changes with the scattering angle. In elastic $pp$ scattering, this will open a novel way to measure the parameter $\rho(t)$ and probe the real part of the Pomeron. [less ▲]

Non-thermal radiation from a runaway early-type star

in AIP Conference Proceedings (2012, December), 1505

HD 195592 is an O-type supergiant star, known as a well-established runaway. Recently, a Fermi γ-ray source (2FGL J2030.7+4417) with a position compatible with that of HD 195592 has been reported. Our ... [more ▼]

HD 195592 is an O-type supergiant star, known as a well-established runaway. Recently, a Fermi γ-ray source (2FGL J2030.7+4417) with a position compatible with that of HD 195592 has been reported. Our goal is to explore a scenario where HD 195592 is the counterpart of the Fermi γ-ray source. The high-energy emission would be inverse Compton radiation produced in the bowshock of the runaway star. We calculate relativistic particle energy losses and the resulting radiation from the bowshock of HD 195592 and show that the latter is compatible with the detected γ-ray emission. We conclude that the Fermi source 2FGL J2030.7+4417 might be produced, under some energetic assumptions, by inverse Compton up-scattering of infrared photons from locally heated dust. HD 195592 might therefore be the very first object detected belonging to the category of γ-ray emitting runaway massive stars, whose existence has been recently predicted. [less ▲]

First- and second-order Fermi acceleration in thick relativistic shocks

in AIP Conference Proceedings (2012)

Shocks in relativistic jets are regions where cosmic ray acceleration takes place mainly via two kinds of Fermi acceleration mechanism: The first-order and the second-order Fermi acceleration. Moreover ... [more ▼]

Shocks in relativistic jets are regions where cosmic ray acceleration takes place mainly via two kinds of Fermi acceleration mechanism: The first-order and the second-order Fermi acceleration. Moreover, the back-reaction of accelerated particles in astrophysical shock fronts leads to the formation of a precursor (thick) shock with a length scale which can correspond to the diffusive scale of the energetic particles. Our scope here is to investigate the properties of particle shock acceleration, using test-particle simulation studies, assuming stochastic and diffusive acceleration mechanisms, in thick parallel and perpendicular relativistic shocks. The role of the above parameters in the acceleration efficiency and generated cosmic ray spectra, is important to understanding further the favourable subject of the cosmic ray shock acceleration in relativistic astrophysical environments. [less ▲]

New look at the $[{\bf 70},1^-]$ nonstrange and strange baryons in the $1/N_c$ expansion

in AIP Conference Proceedings (2011)

The masses of excited nonstrange and strange baryons belonging to the multiplet $[{\bf 70},1^-]$ are calculated in the $1/N_c$ expansion to order $1/N_c$ with a new method which allows to considerably ... [more ▼]

The masses of excited nonstrange and strange baryons belonging to the multiplet $[{\bf 70},1^-]$ are calculated in the $1/N_c$ expansion to order $1/N_c$ with a new method which allows to considerably reduce the number of linearly independent operators entering the mass formula. This study represents an extension to SU(6) of our work on nonstrange baryons, the framework of which was SU(4). [less ▲]

Maxwell rigidity and topological constraints in amorphous phase-change networks

in AIP Conference Proceedings (2011), 1393

By analyzing first-principles molecular-dynamics simulations of different telluride amorphous networks, we develop a method for the enumeration of radial and angular topological constraints, and show that ... [more ▼]

By analyzing first-principles molecular-dynamics simulations of different telluride amorphous networks, we develop a method for the enumeration of radial and angular topological constraints, and show that the phase diagram of the most popular system Ge-Sb-Te can be split into two compositional elastic phases: a tellurium rich flexible phase and a stressed rigid phase that contains most of the materials used in phase-change applications. This sound atomic scale insight should open new avenues for the understanding of phase-change materials and other complex amorphous materials from the viewpoint of rigidity. [less ▲]

Towards the Prediction of Damage Of Peritectic Steels During Continuous Casting Process

in AIP Conference Proceedings (2011), 1353

In the Continuous Casting process, products are sometimes rejected or called defective due to the presence of transversal cracks. This type of macroscopic damage is expected to be due to a ductility loss ... [more ▼]

In the Continuous Casting process, products are sometimes rejected or called defective due to the presence of transversal cracks. This type of macroscopic damage is expected to be due to a ductility loss during cooling in the bending and unbending areas of the CC line. In order to study this damage, a 2D model has been developed to predict at the mesoscopic level the intergranular crack event taking into account the creep and diffusion of voids. Already validated for a microalloyed steel, the model is identified and used in this study to predict the crack formation for three different grades of peritectic steels. Results show encouraging predictions of the damage. [less ▲]

Large-scale coherent orientations of quasar polarisation vectors: interpretation in terms of axion-like particles

in AIP Conference Proceedings (2010), 1274,

The observation of redshift-dependent coherent orientations of quasar polarisation vectors over cosmological distances in some regions of the sky is reviewed. Based on a good-quality sample of 355 ... [more ▼]

The observation of redshift-dependent coherent orientations of quasar polarisation vectors over cosmological distances in some regions of the sky is reviewed. Based on a good-quality sample of 355 measured quasars, this observation seems to infer the existence of a new effect acting on light propagation on such huge distances. A solution in terms of nearly massless axion-like particles has been proposed in the literature and its current status is discussed. [less ▲]

Asteroseismology of red-clump stars with CoRoT and Kepler

in AIP Conference Proceedings (2009), 1170

The availability of asteroseismic constraints for a large number of red giants with CoRoT and, in the near future with Kepler, paves the way for detailed studies of populations of galactic-disk red giants ... [more ▼]

The availability of asteroseismic constraints for a large number of red giants with CoRoT and, in the near future with Kepler, paves the way for detailed studies of populations of galactic-disk red giants. We investigate which information on the observed population can be recovered by the distribution of the observed seismic constraints: the frequency of maximum power of solar-like oscillations (νmax) and the large frequency separation (Δν). We use the distribution of νmax and of Δν observed by CoRoT in nearly 800 red giants in the first long observational run, as a tool to investigate the properties of galactic red-giant stars through the comparison with simulated distributions based on synthetic stellar populations. We can clearly identify the bulk of the red giants observed by CoRoT as red-clump stars, i.e. post-flash core-He-burning stars. The distribution of νmax and of Δν give us access to the distribution of the stellar radius and mass, and thus represent a most promising probe of the age and star formation rate of the disk, and of the mass-loss rate during the red-giant branch. This approach will be of great utility also in the interpretation of forthcoming surveys of variability of red giants with CoRoT and Kepler. In particular, an asteroseismic mass estimate of clump stars in the old-open clusters observed by Kepler, would represent a most valuable observational test of the poorly known mass-loss rate on the giant branch, and of its dependence on metallicity. [less ▲]

Progress in Sounding the Interior of Pulsating Hot Subdwarf Stars

in AIP Conference Proceedings (2009, September), 1170

Hot subdwarf stars, including helium core burning subdwarf B (sdB) stars and more evolved subdwarf O (sdO) stars, host three classes of nonradial pulsators. Two of them show rapid acoustic mode ... [more ▼]

Hot subdwarf stars, including helium core burning subdwarf B (sdB) stars and more evolved subdwarf O (sdO) stars, host three classes of nonradial pulsators. Two of them show rapid acoustic mode oscillations (with periods in the 60-600 s range), while the third class features slow gravity mode vibrations of period typically 1h. All three classes provide a strong potential for sounding the internal properties of stars in these evolved phases of stellar evolution through asteroseismology. This has so far been exploited mainly for the rapid p-mode sdB pulsators, but the long period g-mode sdB pulsators, with the advent of space observations, carry good promises for sounding even deeper regions inside these stars. In this review paper, we summarize the properties of pulsating hot subdwarf stars and we outline progress that have recently occured in the asteroseismic exploitation of the pulsations observed in sdB stars. [less ▲]

Exclusive central production of dijets at hadronic colliders

in AIP Conference Proceedings (2009), 1105