Influence of the Tachocline on Solar Evolution

Recently helioseismic observations have revealed the presence of a shear layer at the base of the convective zone related to the transition from differential rotation in the convection zone to almost uniform rotation in the radiative interior, the tachocline. At present, this layer extends only over a few percent of the solar radius and no definitive explanations have been given for this thiness. Following Spiegel and Zahn (1992, Astron. Astrophys.), who invoke anisotropic turbulence to stop the spread of the tachocline deeper in the radiative zone as the Sun evolves, we give some justifications for their hypothesis by taking into account recent results on rotating shear instability (Richard and Zahn 1999, Astron. Astrophys.). We study the impact of the macroscopic motions present in this layer on the Sun's structure and evolution by introducing a macroscopic diffusivity $D_T$ in updated solar models. We find that a time dependent treatment of the tachocline significantly improves the agreement between computed and observed surface chemical species, such as the $^7$Li and modify the internal structure of the Sun (Brun, Turck-Chi\`eze and Zahn, 1999, in Astrophys. J.).Comment: to appear in Annals of the New York Academy of Sciences, vol 898. Postscript file, 9 pages and 5 figures New Email Address for A. S. Brun: [email protected]

Novel String Banana Template Method of Track Reconstruction for high Multiplicity Events with Significant Multiple Scattering

Novel String Banana Template Method (SBTM) for track reconstruction in high multiplicity events in non-uniform magnetic field spectrometer with emphasis on the lowest momenta tracks with significant Multiple Scattering (MS) is described. Two steps model of track with additional parameter/s which takes into account MS for this particular track is introduced. SBTM is time efficient and demonstrates better resolutions than another method equivalent to the Least Squares method (LSM).Comment: 3 pages, 3 figures, DPF2004 Proceeding, International Journal of Modern Physics

Nonextensive statistics in stellar plasma and solar neutrinos

Nonextensive and quantum uncertainty effects (related to the quasiparticles composing the stellar core) have strong influence on the nuclear rates and, of course, affect solar neutrino fluxes. Both effects do coexist and are due to the frequent collisions among the ions. The weakly nonextensive nature of the solar core is confirmed. The range of predictions for the neutrino fluxes is enlarged and the solar neutrino problem becomes less dramatic.Comment: 4 pages. Proc. of TAUP99, Sept. 6-10 1999, Paris. To appear in Nucl. Phys. B, Proc. Supp

Antiproton and Positron Signal Enhancement in Dark Matter Mini-Spikes Scenarios

The annihilation of dark matter (DM) in the Galaxy could produce specific imprints on the spectra of antimatter species in Galactic cosmic rays, which could be detected by upcoming experiments such as PAMELA and AMS02. Recent studies show that the presence of substructures can enhance the annihilation signal by a "boost factor" that not only depends on energy, but that is intrinsically a statistical property of the distribution of DM substructures inside the Milky Way. We investigate a scenario in which substructures consist of $\sim 100$ "mini-spikes" around intermediate-mass black holes. Focusing on primary positrons and antiprotons, we find large boost factors, up to a few thousand, that exhibit a large variance at high energy in the case of positrons and at low energy in the case of antiprotons. As a consequence, an estimate of the DM particle mass based on the observed cut-off in the positron spectrum could lead to a substantial underestimate of its actual value.Comment: 13 pages, 9 figures, minor changes, version accepted for publication in PR

Exploring the PcycP_{cyc} vs ProtP_{rot} relation with flux transport dynamo models of solar-like stars

Aims: To understand stellar magnetism and to test the validity of the Babcock-Leighton flux transport mean field dynamo models with stellar activity observations Methods: 2-D mean field dynamo models at various rotation rates are computed with the STELEM code to study the sensitivity of the activity cycle period and butterfly diagram to parameter changes and are compared to observational data. The novelty is that these 2-D mean field dynamo models incorporate scaling laws deduced from 3-D hydrodynamical simulations for the influence of rotation rate on the amplitude and profile of the meridional circulation. These models make also use of observational scaling laws for the variation of differential rotation with rotation rate. Results: We find that Babcock-Leighton flux transport dynamo models are able to reproduce the change in topology of the magnetic field (i.e. toward being more toroidal with increasing rotation rate) but seem to have difficulty reproducing the cycle period vs activity period correlation observed in solar-like stars if a monolithic single cell meridional flow is assumed. It may however be possible to recover the $P_{cyc}$ vs $P_{rot}$ relation with more complex meridional flows, if the profile changes in a particular assumed manner with rotation rate. Conclusions: The Babcock-Leighton flux transport dynamo model based on single cell meridional circulation does not reproduce the $P_{cyc}$ vs $P_{rot}$ relation unless the amplitude of the meridional circulation is assumed to increase with rotation rate which seems to be in contradiction with recent results obtained with 3-D global simulations.Comment: 12 pages, 8 figures, accepted for publication by A&A 1: AIM, CEA/DSM-CNRS-Univ. Paris 7, IRFU/SAp, France, 2: D.A.M.T.P., Centre for Mathematical Sciences, Univ. of Cambridge, UK, 3: JILA and Department of Astrophysical and Planetary Sciences, Univ. of Colorado, US

Flux-tube geometry and solar wind speed during an activity cycle

The solar wind speed at 1 AU shows variations in latitude and in time which reflect the evolution of the global background magnetic field during the activity cycle. It is commonly accepted that the terminal wind speed in a magnetic flux-tube is anti-correlated with its expansion ratio, which motivated the definition of widely-used semi-empirical scaling laws relating one to the other. In practice, such scaling laws require ad-hoc corrections. A predictive law based solely on physical principles is still missing. We test whether the flux-tube expansion is the controlling factor of the wind speed at all phases of the cycle and at all latitudes using a very large sample of wind-carrying open magnetic flux-tubes. We furthermore search for additional physical parameters based on the geometry of the coronal magnetic field which have an influence on the terminal wind flow speed. We use MHD simulations of the corona and wind coupled to a dynamo model to provide a large statistical ensemble of open flux-tubes which we analyse conjointly in order to identify relations of dependence between the wind speed and geometrical parameters of the flux-tubes which are valid globally (for all latitudes and moments of the cycle). Our study confirms that the terminal speed of the solar wind depends very strongly on the geometry of the open magnetic flux-tubes through which it flows. The total flux-tube expansion is more clearly anti-correlated with the wind speed for fast rather than for slow wind flows, and effectively controls the locations of these flows during solar minima. Overall, the actual asymptotic wind speeds attained are also strongly dependent on field-line inclination and magnetic field amplitude at the foot-points. We suggest ways of including these parameters on future predictive scaling-laws for the solar wind speed.Comment: Accepted for publicaton on Astronomy & Astrophysic