# Dr Arnau Rios Huguet

Qualifications: PhD

Email:
Phone: Work: 01483 68 9412
Room no: 13 BB 03

## Biography

Further details can be found on my personal web page.

A full list of publications, conference presentations, and patents can be found here.

## Publications

### Highlights

• . (2012) 'Self-consistent Green's functions calculation of the nucleon mean free path'. American Physical Society Physical Review Letters, 108 Article number 012501

#### Abstract

The extension of Green’s functions techniques to the complex energy plane provides access to fully dressed quasiparticle properties from a microscopic perspective. Using self-consistent ladder selfenergies, we find both spectra and lifetimes of such quasiparticles in nuclear matter. With a consistent choice of the group velocity, the nucleon mean-free path can be computed. Our results indicate that, for energies above 50 MeV at densities close to saturation, a nucleon has a mean-free path of 4 to 5 fm.

• . (2009) 'Density dependence of the nuclear symmetry energy: A microscopic perspective'. American Physical Society Physical Review C, 80 (4) Article number 045806

#### Abstract

We perform a systematic analysis of the density dependence of nuclear symmetry energy within the microscopic Brueckner-Hartree-Fock (BHF) approach using the realistic Argonne V18 nucleon-nucleon potential plus a phenomenological three-body force of Urbana type. Our results are compared thoroughly with those arising from several Skyrme and relativistic effective models. The values of the parameters characterizing the BHF equation of state of isospin asymmetric nuclear matter fall within the trends predicted by those models and are compatible with recent constraints coming from heavy ion collisions, giant monopole resonances, or isobaric analog states. In particular we find a value of the slope parameter L=66.5 MeV, compatible with recent experimental constraints from isospin diffusion, L=88±25 MeV. The correlation between the neutron skin thickness of neutron-rich isotopes and the slope L and curvature Ksym parameters of the symmetry energy is studied. Our BHF results are in very good agreement with the correlations already predicted by other authors using nonrelativistic and relativistic effective models. The correlations of these two parameters and the neutron skin thickness with the transition density from nonuniform to β-stable matter in neutron stars are also analyzed. Our results confirm that there is an inverse correlation between the neutron skin thickness and the transition density.

• . (2009) 'Hot neutron matter from a self-consistent Green's-functions approach'. American Physical Society Physical Review C (Nuclear Physics), 79 Article number 025802

#### Abstract

A systematic study of the microscopic and thermodynamical properties of pure neutron matter at finite temperature within the self-consistent Green's-function approach is performed. The model dependence of these results is analyzed by both comparing the results obtained with two different microscopic interactions, the CD Bonn and the Argonne V18 potentials, and by analyzing the results obtained with other approaches, such as the Brueckner-Hartree-Fock approximation, the variational approach, and the virial expansion.

• . (2008) 'Liquid-gas phase transition in nuclear matter from realistic many-body approaches'. American Physical Society Physical Review C (Nuclear Physics), 78 Article number 044314

#### Abstract

The existence of a liquid-gas phase transition for hot nuclear systems at subsaturation densities is a well-established prediction of finite-temperature nuclear many-body theory. In this paper, we discuss for the first time the properties of such a phase transition for homogeneous nuclear matter within the self-consistent Green's function approach. We find a substantial decrease of the critical temperature with respect to the Brueckner-Hartree-Fock approximation. Even within the same approximation, the use of two different realistic nucleon-nucleon interactions gives rise to large differences in the properties of the critical point.

### Journal articles

• . (2014) 'Density and isospin asymmetry dependence of high-momentum components'. Physical Review C: Nuclear Physics, 89
[ Status: Submitted ]

#### Abstract

We study the one-body momentum distribution at different densities in nuclear matter, with special emphasis on its components at high momentum. Explicit calculations for finite neutron-proton asymmetry, based on the ladder self-consistent Green's function approach, allow us to access the isospin dependence of momentum distributions and elucidate their role in neutron-rich systems. Comparisons with the deuteron momentum distribution indicate that a substantial proportion of high-momentum components are dominated by tensor correlations. We identify the density dependence of these tensor correlations in the momentum distributions. Further, we find that high-momentum components are determined by the density of each sub-species and we provide a new isospin asymmetry scaling of these components. We use different realistic nucleon-nucleon interactions to quantify the model dependence of our results.

• . (2013) 'Dipole response of $^76$Se above 4 MeV'. American Physical Society Phys. Rev. C, 88 (6), pp. 064308-064308.

#### Abstract

The dipole response of 76 34 Se in the energy range from 4 to 9 MeV has been analyzed using a (γ ⃗ ,γ ′ ) polarized photon scattering technique, performed at the High Intensity γ -Ray Source facility at Triangle Universities Nuclear Laboratory, to complement previous work performed using unpolarized photons. The results of this work offer both an enhanced sensitivity scan of the dipole response and an unambiguous determination of the parities of the observed J=1 states. The dipole response is found to be dominated by E1 excitations, and can reasonably be attributed to a pygmy dipole resonance. Evidence is presented to suggest that a significant amount of directly unobserved excitation strength is present in the region, due to unobserved branching transitions in the decays of resonantly excited states. The dipole response of the region is underestimated when considering only ground state decay branches. We investigate the electric dipole response theoretically, performing calculations in a three-dimensional (3D) Cartesian-basis time-dependent Skyrme-Hartree-Fock framework.

• . (2013) 'Self-consistent Green's functions formalism with three-body interactions'. American Physical Society Physical Review C: Nuclear Physics, 88 (5)

#### Abstract

We extend the self-consistent Green's functions formalism to take into account three-body interactions. We analyze the perturbative expansion in terms of Feynman diagrams and define effective one- and two-body interactions, which allows for a substantial reduction of the number of diagrams. The procedure can be taken as a generalization of the normal ordering of the Hamiltonian to fully correlated density matrices. We give examples up to third order in perturbation theory. To define nonperturbative approximations, we extend the equation of motion method in the presence of three-body interactions. We propose schemes that can provide nonperturbative resummation of three-body interactions. We also discuss two different extensions of the Koltun sum rule to compute the ground state of a many-body system.

• . (2013) 'Symmetric nuclear matter with chiral three-nucleon forces in the self-consistent Green's functions approach'. American Physical Society Physical Review C: Nuclear Physics, 88 (4) Article number 044302 , pp. 044302-1-044302-11.
• . (2013) 'Tensor force effects and high-momentum components in the nuclear symmetry energy'.

#### Abstract

We analyze microscopic many-body calculations of the nuclear symmetry energy and its density dependence. The calculations are performed in the framework of the Brueckner-Hartree-Fock and the Self-Consistent Green's Functions methods. Within Brueckner-Hartree-Fock, the Hellmann-Feynman theorem gives access to the kinetic energy contribution as well as the contributions of the different components of the nucleon-nucleon interaction. The tensor component gives the largest contribution to the symmetry energy. The decomposition of the symmetry energy in a kinetic part and a potential energy part provides physical insight on the correlated nature of the system, indicating that neutron matter is less correlated than symmetric nuclear matter. Within the Self-Consistent Green's Function approach, we compute the momentum distributions and we identify the effects of the high momentum components in the symmetry energy. The results are obtained for the realistic interaction Argonne V18 potential, supplemented by the Urbana IX three-body force in the Brueckner-Hartree-Fock calculations.

• . (2013) 'Charge radius isotope shift across the N=126 shell gap'. Physical Review Letters, 110 (3)

#### Abstract

We revisit the problem of the kink in the charge radius shift of neutron-rich even isotopes near the N=126 shell closure. We show that the ability of a Skyrme force to reproduce the isotope shift is determined by the occupation of the neutron 1i orbital beyond N=126 and the corresponding change it causes to deeply-bound protons orbitals with a principal quantum number of 1. Given the observed position of the single-particle energies, one must either ensure occupation is allowed through correlations, or not demand that the single-particle energies agree with experimental values at the mean-field level. © 2013 American Physical Society.

• . (2012) 'Comparative study of neutron and nuclear matter with simplifi ed Argonne nucleon-nucleon potentials'. American Physical Society Physical Review C: Nuclear Physics, 86 (6) Article number 064001

#### Abstract

We present calculations of the energy per particle of pure neutron and symmetric nuclear matter with simplified Argonne nucleon-nucleon potentials for different many-body theories. We compare critically the Brueckner-Hartree-Fock results to other formalisms, such as the Brueckner-Bethe-Goldstone expansion up to third order, self-consistent Green's functions, auxiliary field diffusion Monte Carlo, and Fermi hypernetted chain. We evaluate the importance of spin-orbit and tensor correlations in the equation of state and find these to be important in a wide range of densities.

• . (2012) 'Symmetry energy within the BHF approach'. Institute of Physics Journal of Physics: Conference Series, 342 Article number 012012

#### Abstract

We analyze the correlations of the slope and curvature parameters of the symmetry energy with the neutron skin thickness of neutron-rich isotopes, and the crust-core transition density in neutron stars. Microscopic Brueckner–Hartree–Fock results are compared with those obtained with several Skyrme and relativistic mean field models. Our results confirm that there is an inverse correlation between the neutron skin thickness and the transition density.

• . (2012) 'Liquid-gas phase transition in nuclear matter: Mean-field and beyond'. EDP Sciences - Web of Conferences EPJ Web of Conferences, 32 Article number 00003
• . (2012) 'High-momentum components in the nuclear symmetry energy'. EDP Sciences Europhysics Letters: a letters journal exploring the frontiers of physics, 97 Article number 22001

#### Abstract

The short-range and tensor correlations associated to realistic nucleon-nucleon interactions induce a population of high-momentum components in the many-body nuclear wave function. We study the impact of such high-momentum components on bulk observables associated to isospin asymmetric matter. The kinetic part of the symmetry energy is strongly reduced by correlations when compared to the non-interacting case. The origin of this behavior is elucidated using realistic interactions with different short-range and tensor structures.

• . (2012) 'Self-consistent Green's functions calculation of the nucleon mean free path'. American Physical Society Physical Review Letters, 108 Article number 012501

#### Abstract

The extension of Green’s functions techniques to the complex energy plane provides access to fully dressed quasiparticle properties from a microscopic perspective. Using self-consistent ladder selfenergies, we find both spectra and lifetimes of such quasiparticles in nuclear matter. With a consistent choice of the group velocity, the nucleon mean-free path can be computed. Our results indicate that, for energies above 50 MeV at densities close to saturation, a nucleon has a mean-free path of 4 to 5 fm.

• . (2011) 'Towards a nonequilibrium Green's function description of nuclear reactions: One-dimensional mean-field dynamics'. Elsevier Annals of Physics, 326 (5), pp. 1274-1319.

#### Abstract

Nonequilibrium Green’s function methods allow for an intrinsically consistent description of the evolution of quantal many-body body systems, with inclusion of different types of correlations. In this paper, we focus on the practical developments needed to build a Green’s function methodology for nuclear reactions. We start out by considering symmetric collisions of slabs in one dimension within the mean-field approximation. We concentrate on two issues of importance for actual reaction simulations. First, the preparation of the initial state within the same methodology as for the reaction dynamics is demonstrated by an adiabatic switching on of the mean-field interaction, which leads to the mean-field ground state. Second, the importance of the Green’s function matrix-elements far away from the spatial diagonal is analyzed by a suitable suppression process that does not significantly affect the evolution of the elements close to the diagonal. The relative lack of importance of the far-away elements is tied to system expansion. We also examine the evolution of the Wigner function and verify quantitatively that erasing of the off-diagonal elements corresponds to averaging out of the momentum–space details in the Wigner function.

• . (2011) 'Latent heat of nuclear matter'. American Physical Society Physical Review C (Nuclear Physics), 83 (2) Article number 024308

#### Abstract

We study the latent heat of the liquid-gas phase transition in symmetric nuclear matter using self-consistent mean-field calculations with a few Skyrme forces. The temperature dependence of the latent heat is rather independent of the mean-field parametrization and it can be characterized by a few parameters. At low temperatures, the latent heat tends to the saturation energy. Near the critical point, the latent heat goes to zero with a well-determined mean-field critical exponent. A maximum value of the latent heat in the range l similar to 25-30 MeV is found at intermediate temperatures, which might have experimental relevance. All these features can be explained from very basic principles.

• . (2011) 'Liquid-gas phase transition in nuclear matter in the mean-field approximation'. Institute of Physics Journal of Physics, Conference Series, 321 (1) Article number 012058

#### Abstract

The liquid gas phase transition in nuclear systems is a unique phenomenon, at the frontier of nuclear, many-body and statistical physics. We use self-consistent mean-field calculations to quantify the properties of the transition in symmetric nuclear matter. We explore the available parameter space of critical properties by analyzing the mean-field dependence of the phase transition. The latent heat of the transition is computed and we find that it exhibits a model independent temperature dependence due to basic physical principles.

• . (2011) 'Symmetry Energy, Neutron Star Crust and Neutron Skin Thickness'. Springer Few Body Physics, 50 (1-4), pp. 327-329.
• . (2011) 'Role of short-range and tensor correlations in nuclei'. Institute of Physics Journal of Physics, Conference Series, 312 (2) Article number 022007

#### Abstract

The present theoretical understanding of the role of short-range correlations in nuclei near stability is reviewed. Two effects are identified in particular: first, the depletion of mean-field single-particle strength that is no longer available to participate in low-lying excitations. Second, the admixture of high-momentum nucleons in the ground state that is implied by the vanishing relative wave functions of pairs in the medium. The role of the tensor force will be further clarified by discussing isospin-polarized matter. It is demonstrated that the depletion of the proton and neutron Fermi seas depends strongly on the nuclear tensor force and appears to be determined by nucleon-nucleon scattering data. The increased role of short-range and tensor correlations for the minority species makes the case for further experimental scrutiny of nuclei with large neutron excess. Appropriate data of single- and two-nucleon knockout experiments are employed to illustrate the role of short-range and tensor correlations.

• . (2011) 'Role of short-range and tensor correlations in nuclei'. Institute of Physics Journal of Physics, Conference Series, 321 (1) Article number 012038

#### Abstract

The role of short-range and tensor correlations in nuclei can be investigated through a careful comparison with microscopic nuclear matter calculations. We focus on the momentum distribution, a one-body operator which is particularly sensitive to correlations. We identify a depletion of the population of hole states of around 15% in symmetric matter and a significant isospin dependence due to the tensor force. The increased role of short-range and tensor correlations for the minority species makes the case for further experimental scrutiny of nuclei with large neutron excess.

• . (2010) 'Nucleon correlations and the equation of state of nuclear matter'. American Institute of Physics AIP Conference Proceedings, 1322 Article number 99 , pp. 99-107.

#### Abstract

The self-consistent Green's function method within the ladder approximation provides a microscopic description of correlated nuclear systems which properly treats the nucleon-nucleon correlations induced by the short-range and tensor components present in any realistic interaction. These correlations produce a sizable depletion of low momenta below the Fermi surface as well as the occupation of high momenta in the nuclear ground state. A few representative results for nuclear matter are presented to illustrate the present progress in the application of this method to nuclear systems

• . (2010) 'Effective interaction dependence of the liquid-gas phase transition in symmetric nuclear matter'. ELSEVIER SCIENCE BV NUCLEAR PHYSICS A, 845, pp. 58-87.
• . (2009) 'Density dependence of the nuclear symmetry energy: A microscopic perspective'. American Physical Society Physical Review C, 80 (4) Article number 045806

#### Abstract

We perform a systematic analysis of the density dependence of nuclear symmetry energy within the microscopic Brueckner-Hartree-Fock (BHF) approach using the realistic Argonne V18 nucleon-nucleon potential plus a phenomenological three-body force of Urbana type. Our results are compared thoroughly with those arising from several Skyrme and relativistic effective models. The values of the parameters characterizing the BHF equation of state of isospin asymmetric nuclear matter fall within the trends predicted by those models and are compatible with recent constraints coming from heavy ion collisions, giant monopole resonances, or isobaric analog states. In particular we find a value of the slope parameter L=66.5 MeV, compatible with recent experimental constraints from isospin diffusion, L=88±25 MeV. The correlation between the neutron skin thickness of neutron-rich isotopes and the slope L and curvature Ksym parameters of the symmetry energy is studied. Our BHF results are in very good agreement with the correlations already predicted by other authors using nonrelativistic and relativistic effective models. The correlations of these two parameters and the neutron skin thickness with the transition density from nonuniform to β-stable matter in neutron stars are also analyzed. Our results confirm that there is an inverse correlation between the neutron skin thickness and the transition density.

• . (2009) 'Depletion of the nuclear Fermi sea'. Phys. Rev. C 79, 064308 (2009),

#### Abstract

The short-range and tensor components of the bare nucleon-nucleon interaction induce a sizeable depletion of low momenta in the ground state of a nuclear many-body system. The self-consistent Green's function method within the ladder approximation provides an \textit{ab-initio} description of correlated nuclear systems that accounts properly for these effects. The momentum distribution predicted by this approach is analyzed in detail, with emphasis on the depletion of the lowest momentum state. The temperature, density, and nucleon asymmetry (isospin) dependence of the depletion of the Fermi sea is clarified. A connection is established between the momentum distribution and the time-ordered components of the self-energy, which allows for an improved interpretation of the results. The dependence on the underlying nucleon-nucleon interaction provides quantitative estimates of the importance of short-range and tensor correlations in nuclear systems.

• . (2009) 'Hot neutron matter from a self-consistent Green's-functions approach'. American Physical Society Physical Review C (Nuclear Physics), 79 Article number 025802

#### Abstract

A systematic study of the microscopic and thermodynamical properties of pure neutron matter at finite temperature within the self-consistent Green's-function approach is performed. The model dependence of these results is analyzed by both comparing the results obtained with two different microscopic interactions, the CD Bonn and the Argonne V18 potentials, and by analyzing the results obtained with other approaches, such as the Brueckner-Hartree-Fock approximation, the variational approach, and the virial expansion.

• . (2008) 'Liquid-gas phase transition in nuclear matter from realistic many-body approaches'. American Physical Society Physical Review C (Nuclear Physics), 78 Article number 044314

#### Abstract

The existence of a liquid-gas phase transition for hot nuclear systems at subsaturation densities is a well-established prediction of finite-temperature nuclear many-body theory. In this paper, we discuss for the first time the properties of such a phase transition for homogeneous nuclear matter within the self-consistent Green's function approach. We find a substantial decrease of the critical temperature with respect to the Brueckner-Hartree-Fock approximation. Even within the same approximation, the use of two different realistic nucleon-nucleon interactions gives rise to large differences in the properties of the critical point.

• . (2008) 'Time-dependent Green's functions approach to nuclear reactions'. AIPConf.Proc.995:98-103,2008,

#### Abstract

Nonequilibrium Green's functions represent underutilized means of studying the time evolution of quantum many-body systems. In view of a rising computer power, an effort is underway to apply the Green's functions formalism to the dynamics of central nuclear reactions. As the first step, mean-field evolution for the density matrix for colliding slabs is studied in one dimension. The strategy to extend the dynamics to correlations is described.

• . (2006) 'Neutrino propagation in dense hadronic matter'. Acta Phys.Polon. B37 (2006) 2403-2410,

#### Abstract

Neutrino propagation in protoneutron stars requires the knowledge of the composition as well as the dynamical response function of dense hadronic matter. Matter at very high densities is probably composed of other particles than nucleons and little is known on the Fermi liquid properties of hadronic multicomponent systems. We will discuss the effects that the presence of $\Lambda$ hyperons might have on the response and, in particular, on its influence on the thermodynamical stability of the system and the mean free path of neutrinos in dense matter.

• . (2006) 'The entropy of a correlated system of nucleons'. Phys.Rev. C74 (2006) 054317,

#### Abstract

Realistic nucleon-nucleon interaction induce correlations to the nuclear many-body system which lead to a fragmentation of the single-particle strength over a wide range of energies and momenta. We address the question of how this fragmentation affects the thermodynamical properties of nuclear matter. In particular, we show that the entropy can be computed with the help of a spectral function which can be evaluated in terms of the self-energy obtained in the Self-Consistent Green's Function approach. Results for the density and temperature dependences of the entropy per particle for symmetric nuclear matter are presented and compared to the results of lowest order finite temperature Brueckner--Hartree--Fock calculations. The effects of correlations on the calculated entropy are small, if the appropriate quasi-particle approximation is used. The results demonstrate the thermodynamical consistency of the self-consistent T-matrix approximation for the evaluation of the Green's functions.

• . (2005) 'Sum rules of single-particle spectral functions in hot asymmetric nuclear matter'.

#### Abstract

The neutron and proton single-particle spectral functions in asymmetric nuclear matter fulfill energy weighted sum rules. The validity of these sum rules within the self-consistent Green's function approach is investigated. The various contributions to these sum rules and their convergence as a function of energy provide information about correlations induced by the realistic interaction between the nucleons. These features are studied as a function of the asymmetry of nuclear matter.

• . (2005) 'Bulk and single-particle properties of hyperonic matter at finite temperature'. Phys.Rev. C72 (2005) 024316,

#### Abstract

Bulk and single-particle properties of hot hyperonic matter are studied within the Brueckner-Hartree-Fock approximation extended to finite temperature. The bare interaction in the nucleon sector is the Argonne V18 potential supplemented with an effective three-body force to reproduce the saturating properties of nuclear matter. The modern Nijmegen NSC97e potential is employed for the hyperon-nucleon and hyperon-hyperon interactions. The effect of the temperature on the in-medium effective interaction is found to be, in general, very small and the single-particle potentials differ by at most 25% for temperatures in the range from 0 to 60 MeV. The bulk properties of infinite matter of baryons, either nuclear isospin symmetric or a beta-stable composition which includes a non-zero fraction of hyperons, are obtained. It is found that the presence of hyperons can modify the thermodynamical properties of the system in a non-negligible way.

• . (2005) 'Ferromagnetic instabilities in neutron matter at finite temperature with the Skyrme interaction'. Phys.Rev. C71 (2005) 055802,

#### Abstract

The properties of spin polarized neutron matter are studied both at zero and finite temperature using Skyrme-type interactions. It is shown that the critical density at which ferromagnetism takes place decreases with temperature. This unexpected behaviour is associated to an anomalous behaviour of the entropy which becomes larger for the polarized phase than for the unpolarized one above a certain critical density. This fact is a consequence of the dependence of the entropy on the effective mass of the neutrons with different third spin component and a new constraint on the parameters of the effective Skyrme force is derived in order to avoid such a behaviour.

### Conference papers

• . (2013) 'Towards a nonequilibrium Green's function description of nuclear reactions'. IOP PUBLISHING LTD PROGRESS IN NONEQUILIBRIUM GREEN'S FUNCTIONS V (PNGF V), Univ Jyvaskyla, Jyvaskyla, FINLAND: 5th Interdisciplinary Conference on Progress in Nonequilibrium Green's Functions (PNGF) 427
• . (2013) 'Self-consistent Green's functions calculation of the nucleon mean-free path'. IOP PUBLISHING LTD PROGRESS IN NONEQUILIBRIUM GREEN'S FUNCTIONS V (PNGF V), Univ Jyvaskyla, Jyvaskyla, FINLAND: 5th Interdisciplinary Conference on Progress in Nonequilibrium Green's Functions (PNGF) 427

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