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Theoretical estimates of stellar e-captures from first-principles simulations

ECT* LISC Seminar

Simone Taioli

04 Jun 2015 - 11:00
Villa Tambosi 2nd Floor, Seminar Room

The evolution of Li content in the Universe is still unexplained, presenting various puzzles to astrophysics. One of the open issues is the determination of reliable electron capture rates, notably in Be, for density and temperature conditions different from solar; this input is of crucial importance to model the Galactic nucleosynthesis of Li. As a contribution to the solution of this problem, I will discuss state-of-the-art and novel theoretical approaches for calculating electron capture rates in conditions typical of evolved stars. These methods include: "traditional" estimates of the electronic density at the nucleus, to which the electroncapture decay rates for Be is proportional, based on the widely used Debye-Hückel model for the electron screening; decay rate calculations from Thomas-Fermi and Maxwell-Boltzmann approximations; a new computation based on a formalism going beyond the previous approaches and adopting a mean-field adiabatic approximation to the scattering process; a benchmark of the previous results by including very accurately the e-e correlation via a recently developed Path-Integral Monte Carlo technique for fermions. It is found that, already for solar conditions, where the Debye-Hückel approximation holds, we obtain sizeably different results with respect to our approach. Furthermore, we apply both our method and state-of-the-art models to a rather broad range of T and ρ values, embracing those typical of red giant stars, where both bound and continuum states contribute to the capture. In this more general case, the Debye-Hückel approximation does not stand, so that the more general ab-initio methods that we suggest should be preferred. Furthermore an extension of the method to the treatment of beta-decay in lanthanides will be outlined.