Equilibrium and stability of relativistic stars in extended theories of gravity

We study static, spherically symmetric equilibrium configurations in extended theories of gravity (ETG) following the notation introduced by Capozziello et al. We calculate the differential equations for the stellar structure in such theories in a very generic form i.e., the Tolman–Oppenheimer–Volkoff generalization for any ETG is introduced. Stability analysis is also investigated with special focus on the particular example of scalar–tensor gravity.     

Using GPU parallelization to perform realistic simulations of the LPCTrap experiments

We performed classical molecular dynamics (MD) simulations in order to search the conditions for efficient sympathetic cooling of highly charged ions (HCIs) in a linear Paul trap. Small two-component ion Coulomb crystals consisting of laser-cooled ions and HCIs were characterized by the results of the MD simulations. We found that the spatial distribution is determined by not only the charge-to-mass ratio but also the space charge effect. Moreover, the simulation results suggest that the temperature of HCIs do not necessarily decrease with increasing the number of laser-cooled ions in the cases of linear ion crystals. We also determined the cooling limit of sympathetically cooled ¹⁶⁵Ho¹⁴⁺ ions in small linear ion Coulomb crystals. The present results show that sub-milli-Kelvin temperatures of at least 10 Ho¹⁴⁺ ions will be achieved by sympathetic cooling with a single laser-cooled Be⁺.     

Precision measurements with LPCTrap at GANIL

The experimental achievements and the results obtained so far with the LPCTrap device installed at GANIL are presented. The apparatus is dedicated to the study of the weak interaction at low energy by means of precise measurements of the β ? ν angular correlation parameter in nuclear β decays. So far, the data collected with three isotopes have enabled to determine, for the first time, the charge state distributions of the recoiling ions, induced by shakeoff process. The analysis is presently refined to deduce the correlation parameters, with the potential of improving both the constraint deduced at low energy on exotic tensor currents (⁶He¹⁺) and the precision on the V _{u d} element of the quark-mixing matrix (³⁵Ar¹⁺ and ¹⁹Ne¹⁺) deduced from the mirror transitions dataset.     

Geant4 Monte Carlo simulations for the LPCTrap setup

The LPCTrap setup at GANIL is fully operational since 2006. The first breakthrough was the detection of 100000 coincidences between the $ \beta$ particles and the recoil ions from the decay of ⁶He⁺ produced by the SPIRAL source. After preparation, the decaying nuclei are confined in a transparent Paul trap which is surrounded by a $ \beta$ -telescope made of a double-sided silicon strip detector followed by a scintillator, and by a micro-channel plate position-sensitive detector to record in coincidence the $ \beta$ particles and the recoil ions. Simulations of this system are needed in order to study possible systematic effects and extract with high accuracy the $ \beta$ - $ \nu$ angular-correlation coefficient. A code based on Geant4 is well suited for this purpose. In this contribution the results from the simulations compared with those from the experiment will be presented and discussed.     

Temperature measurement of 6He?+? ions confined in a transparent Paul trap

The LPCTrap setup is a transparent Paul trap dedicated to the measurement of the ???C?? correlation coefficient a _?|? in the ?? decay of trapped radioactive nuclides. In a first experiment, the system has been used to record ??10⁵ coincidences between the ?? particles and recoiling ions emitted from the decay of ⁶He^?+? ions. The analysis of the collected data has already shown that the size of the ⁶He^?+? ion cloud confined in the Paul trap is a critical parameter, potentially limiting the accuracy on the a _?|? measurement. We report here the precise determination of the trapped ion cloud temperature and size. This was performed by extracting the trapped ions toward a position sensitive micro channel plate detector at different phases of the RF driving field. We find a temperature T _exp ?= 0.107(7) eV, consistent with the temperature values inferred using two other observables but 20% higher than the temperature T _sim ?= 0.09 eV predicted by realistic simulations of the ions interacting with the H₂ buffer gas.     

Does Chaplygin gas have salvation?

A mechanism capable to provide a natural solution to two major cosmological problems, i.e. the cosmic acceleration and the coincidence problem, is proposed. A specific brane–bulk energy exchange mechanism produces a total dark pressure, arising when adding all normal to the brane negative pressures in the interior of galactic core black holes. This astrophysically produced negative dark pressure explains cosmic acceleration and why the dark energy today is of the same order to the matter density for a wide range of the involved parameters. An exciting result of the analysis is that the recent rise of the galactic core black hole mass density causes the recent passage from cosmic deceleration to acceleration. Finally, it is worth mentioning that this work corrects a wide spread fallacy among brane cosmologists, i.e. that escaping gravitons result in positive dark pressure.     

Instabilities in intracavity pumped optical parametric oscillators and methods of stabilization

A high conversion efficiency and stability are the anticipated advantages of intracavity pumped parametric oscillators, as opposed to the traditional externally pumped ones. The dynamics of the coupled pump and signal cavities, however, is very complex and poses a considerable design challenge. In this paper we present a simulation of an optical parametric oscillator, pumped intracavity by a mode-locked solid-state laser. Different unstable modes of operation are identified in an experimental setup and the simulation is used to reproduce and analyze them. Based on this analysis we present techniques to amplitude stabilize the system.     

Semi-syntheses of new stemofoline derivatives

Semi-syntheses of several new stemofoline derivatives are described. Acidic hydrolysis of the tetronate moiety of stemofoline, followed by re-esterification gave homologues of stemofoline and isostemofoline. Hydrazinolysis resulted in new pyridazinones. Oxidative cleavage of stemofoline afforded the pentacyclic cage lactone, recently prepared by total synthesis.     

Constraints on unified models for dark matter and dark energy using <Emphasis Type="Italic">H</Emphasis>(<Emphasis Type="Italic">z</Emphasis>)

The differential age data of astrophysical objects that have evolved passively during the history of the universe (e.g. red galaxies) allows us to test theoretical cosmological models through the predicted Hubble function expressed in terms of the redshift z, H(z). We use the observational data for H(z) to test unified scenarios for dark matter and dark energy. Specifically, we focus our analysis on the Generalized Chaplygin Gas (GCG) and the viscous fluid (VF) models. For the GCG model, it is shown that the unified scenario for dark energy and dark matter requires some priors. For the VF model we obtain estimations for the free parameters, which may be compared with further analysis mainly at perturbative level.