arXiv subjects

Gabriel Martínez-Pinedo

Publications and source records attributed to Gabriel Martínez-Pinedo.

43 records · Page 3Linked to original sources

arXiv2015

Toward global beyond-mean-field calculations of nuclear masses and low-energy spectra

Self-consistent mean field (MF) and beyond-mean-field (BMF) calculations of masses, separation energies and $2^{+}_{1}$ excitation energies of even-even nuclei where experimental data is available are presented. The functionals used are based on the Gogny D1S and D1M parametrizations and the method includes beyond-mean-field corrections coming from both axial quadrupole shape mixing and symmetry restorations without assuming gaussian overlap approximations. A comparison between mean field, beyond-mean-field approaches and the experimental data is provided. Additionally, the convergence of the results and the possible reduction of the magic shell gaps by including BMF effects are also discussed.

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arXiv2014

Correlations and neutrinoless $ββ$ decay nuclear matrix elements of $pf$-shell nuclei

We calculate the nuclear matrix elements (NMEs) for neutrinoless double-beta decays ($0νββ$) of $pf$-shell nuclei using the shell model (SM) and energy density functional (EDF) methods. The systematic study of non-physical decays (except for $^{48}$Ca) of Ca$\rightarrow$Ti, Ti$\rightarrow$Cr and Cr$\rightarrow$Fe allows for a detailed comparison between the two nuclear structure approaches. We observe that while the dominant Gamow-Teller part of the NME differs roughly by a factor of two between SM and EDF, when we restrict the calculations to spherical EDF states and seniority-zero SM configurations, the NMEs obtained by both methods are strikingly similar. This points out to the important role of nuclear structure correlations for $0νββ$ decay NMEs. We identify correlations associated with high-seniority components in the initial and final states of the decay as one of the reasons for the discrepancies between SM and EDF results. We also explore exact projection to good isospin, and conclude that it has only a moderate effect in the Gamow-Teller part of the NMEs but strongly affects the Fermi contribution. This work opens up the door for NME benchmarks between different theoretical approaches, and constitutes a step forward towards more reliable estimations of the NMEs.

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arXiv2013

Impact of active-sterile neutrino mixing on supernova explosion and nucleosynthesis

We show that for the active-sterile flavor mixing parameters suggested by the reactor neutrino anomaly, substantial \ν_e-\ν_s and \bar \ν_e-\bar \ν_s conversion occurs in regions with electron fraction of \approx 1/3 near the core of an 8.8 M_sun electron-capture supernova. Compared to the case without such conversion, the neutron-richness of the ejected material is enhanced to allow production of elements from Sr, Y, and Zr up to Cd in broad agreement with observations of the metal-poor star HD 122563. Active-sterile flavor conversion also strongly suppresses neutrino heating at times when it is important for the revival of the shock. Our results suggest that simulations of supernova explosion and nucleosynthesis may be used to constrain active-sterile mixing parameters in combination with neutrino experiments and cosmological considerations.

astro-ph.HE↗

arXiv2012

Neutrinoless $ββ$ decay nuclear matrix elements in an isotopic chain

We analyze nuclear matrix elements (NME) of neutrinoless double beta decay calculated for the Cadmium isotopes. Energy density functional methods including beyond mean field effects such as symmetry restoration and shape mixing are used. Strong shell effects are found associated to the underlying nuclear structure of the initial and final nuclei. Furthermore, we show that NME for two-neutrino double beta decay evaluated in the closure approximation, $M^{2ν}_{\mathrm{cl}}$, display a constant proportionality with respect to the Gamow-Teller part of the neutrinoless NME, $M^{0ν}_{\mathrm{GT}}$. This opens the possibility of determining the $M^{0ν}_{\mathrm{GT}}$ matrix elements from $β^{\mp}$ Gamow-Teller strength functions. Finally, the interconnected role of deformation, pairing, configuration mixing and shell effects in the NMEs is discussed.

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arXiv2012

Nucleosynthesis in core-collapse supernova explosions triggered by a quark-hadron phase transition

We explore heavy element nucleosynthesis in the explosion of massive stars which are triggered by a quark-hadron phase transition during the early post bounce phase of core-collapse supernovae. The present study is based on general relativistic radiation hydrodynamics simulations with three-flavor Boltzmann neutrino transport in spherical symmetry, which utilize a quark-hadron hybrid equation of state based on the MIT bag model for strange quark matter. The quark-hadron phase transition inside the stellar core forms a shock wave propagating towards the surface of the proto-neutron star. The shock wave results in an explosion and ejects neutron-rich matter which is piled up or accreting on the proto-neutron star. Later, during the cooling phase, the proto-neutron star develops a proton-rich neutrino-driven wind. We present a detailed analysis of the nucleosynthesis outcome in both neutron-rich and proton-rich ejecta and compare our integrated nucleosynthesis with observations of metal poor stars.

astro-ph.HE↗

arXiv2012

Sensitivity study of explosive nucleosynthesis in Type Ia supernovae: I. Modification of individual thermonuclear reaction rates

We explore the sensitivity of the nucleosynthesis due to type Ia supernovae with respect to uncertainties in nuclear reaction rates. We have adopted a standard one-dimensional delayed detonation model of the explosion of a Chandrasekhar-mass white dwarf, and have post-processed the thermodynamic trajectories of every mass-shell with a nucleosynthetic code, with increases (decreases) by a factor of ten on the rates of 1196 nuclear reactions. We have computed as well hydrodynamic models for different rates of the fusion reactions of 12C and of 16O. For selected reactions, we have recomputed the nucleosynthesis with alternative prescriptions for their rates taken from the JINA REACLIB database, and have analyzed the temperature ranges where modifications of their rates have the strongest effect on nucleosynthesis. The nucleosynthesis resulting from the Type Ia supernova models is quite robust with respect to variations of nuclear reaction rates, with the exception of the reaction of fusion of 12C nuclei. The energy of the explosion changes by less than \sim4%. The changes in the nucleosynthesis due to the modification of the rates of fusion reactions are as well quite modest, for instance no species with a mass fraction larger than 0.02 experiences a variation of its yield larger than a factor of two. We provide the sensitivity of the yields of the most abundant species with respect to the rates of the most intense reactions with protons, neutrons, and alphas. In general, the yields of Fe-group nuclei are more robust than the yields of intermediate-mass elements. Among the charged particle reactions, the most influential on supernova nucleosynthesis are 30Si + p \rightleftarrows 31P + γ, 20Ne + α \rightleftarrows 24Mg + γ, and 24Mg + α \rightleftarrows 27Al + p. The temperatures at which a modification of their rate has a larger impact are in the range 2 < T < 4 GK. (abridged)

astro-ph.SR↗

arXiv2008

Complete inclusion of parity-dependent level densities in the statistical description of astrophysical reaction rates

Microscopic calculations show a strong parity dependence of the nuclear level density at low excitation energy of a nucleus. Previously, this dependence has either been neglected or only implemented in the initial and final channels of Hauser-Feshbach calculations. We present an indirect way to account for a full parity dependence in all steps of a reaction, including the one of the compound nucleus formed in a reaction. To illustrate the impact on astrophysical reaction rates, we present rates for neutron captures in isotopic chains of Ni and Sn. Comparing with the standard assumption of equipartition of both parities, we find noticeable differences in the energy regime of astrophysical interest caused by the parity dependence of the nuclear level density found in the compound nucleus even at sizeable excitation energies.

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