11 research outputs found
Finite size effects in Neutron Star and Nuclear matter simulations
In this work we study molecular dynamics simulations of symmetric nuclear
matter using a semi-classical nucleon interaction model. We show that, at
sub-saturation densities and low temperatures, the solutions are
non-homogeneous structures reminiscent of the ``nuclear pasta'' phases expected
in Neutron Star Matter simulations, but shaped by artificial aspects of the
simulations. We explore different geometries for the periodic boundary
conditions imposed on the simulation cell: cube, hexagonal prism and truncated
octahedron. We find that different cells may yield different solutions for the
same physical conditions (i.e. density and temperature). The particular shape
of the solution at a given density can be predicted analytically by energy
minimization. We also show that even if this behavior is due to finite size
effects, it does not mean that it vanishes for very large systems and it
actually is independent of the system size: The system size sets the only
characteristic length scale for the inhomogeneities.
We then include a screened Coulomb interaction, as a model of Neutron Star
Matter, and perform simulations in the three cell geometries. In this case, the
competition between competing interactions of different range produces the well
known nuclear pasta, with (in most cases) several structures per cell. However,
we find that the results are affected by finite size in different ways
depending on the geometry of the cell. In particular, at the same physical
conditions and system size, the hexagonal prism yields a single structure per
cell while the cubic and truncated octahedron show consistent results with more
than one structure per cell. In this case, the results in every cell are
expected to converge for systems much larger than the characteristic length
scale that arises from the competing interactions.Comment: 17 pages, 10 figure
Isoscaling and the nuclear EOS
Experiments with rare isotopes are shedding light on the role isospin plays
in the equation of state (EoS) of nuclear matter, and isoscaling -an
straight-forward comparison of reactions with different isospin- could deliver
valuable information about it. In this work we test this assertion
pragmatically by comparing molecular dynamics simulations of isoscaling
reactions using different equations of state and looking for changes in the
isoscaling parameters; to explore the possibility of isoscaling carrying
information from the hot-and-dense stage of the reaction, we perform our study
in confined and expanding systems. Our results indicate that indeed isoscaling
can help us learn about the nuclear EoS, but only in some range of excitation
energies
Topological characterization of neutron star crusts
Neutron star crusts are studied using a classical molecular dynamics model
developed for heavy ion reactions. After the model is shown to produce a
plethora of the so-called "pasta" shapes, a series of techniques borrowed from
nuclear physics, condensed matter physics and topology are used to craft a
method that can be used to characterize the shape of the pasta structures in an
unequivocal way
Nuclear Equation of state for Compact Stars and Supernovae
International audienceThe equation of state (EoS) of hot and dense matter is a fundamental input to describe static and dynamical properties of neutron stars, core-collapse supernovae and binary compact-star mergers. We review the current status of the EoS for compact objects, that have been studied with both ab-initio many-body approaches and phenomenological models. We limit ourselves to the description of EoSs with purely nucleonic degrees of freedom, disregarding the appearance of strange baryonic matter and/or quark matter. We compare the theoretical predictions with different data coming from both nuclear physics experiments and astrophysical observations. Combining the complementary information thus obtained greatly enriches our insights into the dense nuclear matter properties. Current challenges in the description of the EoS are also discussed, mainly focusing on the model dependence of the constraints extracted from either experimental or observational data (specifically, concerning the symmetry energy), the lack of a consistent and rigorous many-body treatment at zero and finite temperature of the matter encountered in compact stars (e.g. problem of cluster formation and extension of the EoS to very high temperatures), the role of nucleonic three-body forces, and the dependence of the direct URCA processes on the EoS