“Pasta phases” in neutron stars studied with extended relativistic mean field models

Gupta, Neha; Arumugam, P.

doi:10.1103/physrevc.87.028801

Cited by 16 publications

(13 citation statements)

References 19 publications

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“…There are other approaches that do not explicitly assume any shape for the nuclear pasta phase. These include calculations based on the Thomas-Fermi approximation [20,[25][26][27], non-relativistic Skyrme Hartree-Fock methods [28][29][30][31], relativistic density-functional theory [23], relativistic mean field-approximation [32][33][34], quantum molecular dynamics (QMD) [1,2,[35][36][37][38][39] and semi-classical molecular dynamics (MD) [3-5, 10, 40-46] simulations. Recently using MD simulations more exotic structures have also been identified, such as flat plates with a lattice of holes, termed as "nuclear waffles" [44], and flat plates that are connected by spiral ramps [45].…”

Section: Introductionmentioning

confidence: 99%

Quantum nuclear pasta and nuclear symmetry energy

2017

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Complex and exotic nuclear geometries are expected to appear naturally in dense nuclear matter found in the crust of neutron stars and supernovae environment collectively referred to as "nuclear pasta". The pasta geometries depend on the average baryon density, proton fraction and temperature and are critically important in the determination of many transport properties of matter in supernovae and the crust of neutron stars. Using a set of self-consistent microscopic nuclear energy density functionals we present the first results of large scale quantum simulations of pasta phases at baryon densities 0.03 ≤ ρ ≤ 0.10 fm −3 , proton fractions 0.05 ≤ Yp ≤ 0.40, and zero temperature. The full quantum simulations, in particular, allow us to thoroughly investigate the role and impact of the nuclear symmetry energy on pasta configurations. We use the Sky3D code that solves the Skyrme Hartree-Fock equations on a three-dimensional Cartesian grid. For the nuclear interaction we use the state of the art UNEDF1 parametrization, which was introduced to study largely deformed nuclei, hence is suitable for studies of the nuclear pasta. Density dependence of the nuclear symmetry energy is simulated by tuning two purely isovector observables that are insensitive to the current available experimental data. We find that a minimum total number of nucleons A = 2000 is necessary to prevent the results from containing spurious shell effects and to minimize finite size effects. We find that a variety of nuclear pasta geometries are present in the neutron star crust and the result strongly depends on the nuclear symmetry energy. The impact of the nuclear symmetry energy is less pronounced as the proton fractions increase. Quantum nuclear pasta calculations at T = 0 MeV are shown to get easily trapped in meta-stable states, and possible remedies to avoid meta-stable solutions are discussed.

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Section: Introductionmentioning

confidence: 99%

Quantum nuclear pasta and nuclear symmetry energy

2017

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“…For example, some mean-field calculations solve the equations of motion of dense matter in a Wigner-Seitz approximation in one, two and three dimensions and choose the favored geometry as the one that minimizes the energy density of the system for a given density and proton fraction [6][7][8][9][10]. Other works based on liquid-drop models and Thomas-Fermi approximation also have explicit assumptions about the geometrical shapes of nuclear pasta [11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

Nuclear “waffles”

et al. 2014

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Background:The dense neutron-rich matter found in supernovae and inside neutron stars is expected to form complex nonuniform phases, often referred to as nuclear pasta. The pasta shapes depend on density, temperature and proton fraction and determine many transport properties in supernovae and neutron star crusts. Purpose: To characterize the topology and compute two observables, the radial distribution function (RDF) g (r) and the structure factor S(q), for systems with proton fractions Yp = 0.10, 0.20, 0.30, and 0.40 at about one-third of nuclear saturation density, n = 0.050 fm 3, and temperatures near kT = 1 MeV. Methods:We use two recently developed hybrid CPU/GPU codes to perform large scale molecular dynamics (MD) simulations with 51 200 and 409 600 nucleons. From the output of the MD simulations we obtain the two desired observables. Results: We compute and discuss the differences in topology and observables for each simulation. We observe that the two lowest proton fraction systems simulated, Yp = 0.10 and 0.20, equilibrate quickly and form liquidlike structures. Meanwhile, the two higher proton fraction systems, Yp = 0.30 and 0.40, take a longer time to equilibrate and organize themselves in solidlike periodic structures. Furthermore, the Yp = 0.40 system is made up of slabs, lasagna phase, interconnected by defects while the Yp = 0.30 systems consist of a stack of perforated plates, the nuclear waffle phase. Conclusions:The periodic configurations observed in our MD simulations for proton fractions Yp ^ 0.30 have important consequences for the structure factors S(q) of protons and neutrons, which relate to many transport properties of supernovae and neutron star crust. A detailed study of the waffle phase and how its structure depends on temperature, size of the simulation, and the screening length showed that finite-size effects appear to be under control and, also, that the plates in the waffle phase merge at temperatures slightly above 1.0 MeV and the holes in the plates form a hexagonal lattice at temperatures slightly lower than 1.0 MeV.

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“…Many works based on a compressible liquid-drop model [4,[8][9][10] have explicit assumptions about the geometrical shapes of nuclear pasta. Some even include more exotic phases such as gyroid and double-diamond morphologies [11].…”

Section: Introductionmentioning

confidence: 99%

“…Some of these works, mainly the ones using a liquid-drop model and Thomas-Fermi approximation, use a WignerSeitz cell approximation to determine the periodicity of arXiv:1307.1678v1 [nucl-th] 5 Jul 2013 the pasta shapes [4,8,10,11,14,18] while other works use a unit cell to account for the periodicity of the system [2,9,13,[15][16][17]. Meanwhile, works based on QMD and MD methods use larger volumes and do not assume any periodicity in the pasta shapes besides the one imposed by periodic boundary conditions [6,7,[20][21][22][23][24][25][26][27][28][29][30].…”

Section: Introductionmentioning

confidence: 99%

“…Approaches to the problem that do not explicitly assume any shape for the nuclear pasta have also been considered. They include calculations based on the ThomasFermi approximation [2,[12][13][14], Hartree-Fock methods [15][16][17], density-functional theory [18], relativistic mean field approximation [10,19], quantum molecular dynamics (QMD) [20][21][22][23][24][25][26] and semi-classical molecular dynamics (MD) [6,7,[27][28][29][30].…”

Section: Introductionmentioning

confidence: 99%

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Nuclear “pasta” formation

et al. 2013

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The formation of complex nonuniform phases of nuclear matter, known as nuclear pasta, is studied with molecular dynamics simulations containing 51 200 nucleons. A phenomenological nuclear interaction is used that reproduces the saturation binding energy and density of nuclear matter. Systems are prepared at an initial density of 0.10 fm −3 and then the density is decreased by expanding the simulation volume at different rates to densities of 0.01 fm −3 or less. An originally uniform system of nuclear matter is observed to form spherical bubbles ("swiss cheese"), hollow tubes, flat plates ("lasagna"), thin rods ("spaghetti") and, finally, nearly spherical nuclei with decreasing density. We explicitly observe nucleation mechanisms, with decreasing density, for these different pasta phase transitions. Topological quantities known as Minkowski functionals are obtained to characterize the pasta shapes. Different pasta shapes are observed depending on the expansion rate. This indicates non equilibrium effects. We use this to determine the best ways to obtain lower energy states of the pasta system from MD simulations and to place constrains on the equilibration time of the system.

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“Pasta phases” in neutron stars studied with extended relativistic mean field models

Cited by 16 publications

References 19 publications

Quantum nuclear pasta and nuclear symmetry energy

Quantum nuclear pasta and nuclear symmetry energy

Nuclear “waffles”

Nuclear “pasta” formation

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