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M. Baldo

Publications and source records attributed to M. Baldo.

At least 55 records · Page 3Linked to original sources
arXiv2009

Spatial correlation properties of the anomalous density matrix in a slab of nuclear matter with realistic NN-forces

Spatial correlation characteristics of the anomalous density matrix $κ$ in a slab of nuclear matter with the Paris and Argonne v18 forces are calculated. A detailed comparison with predictions of the effective Gogny force is made. It is found that the two realistic forces lead to very close results which are qualitatively similar to those for the Gogny force. At the same time, the magnitude of $κ$ for realistic forces is essentially smaller than the one for the Gogny force. The correlation characteristics are practically independent of the magnitude of $κ$ and turn out to be quite close for the three kinds of the force. In particular, all of them predict a small value of the local correlation length at the surface of the slab and a big one, inside. These results are in agreement with those obtained recently by Pillet at al. for finite nuclei with the Gogny force.

nucl-th↗
arXiv2009

Testing the Field Correlator Method with astrophysical constraints

We study the structure of hybrid stars with the Field Correlator Method, extended to the zero temperature limit, for the quark phase. For the hadronic phase, we use the microscopic Brueckner-Hartree- Fock many-body theory. The comparison with the neutron star mass phenomenology puts serious constraints on the currently adopted values of the gluon condensate $G_2 \simeq 0.006-0.007 \rm {GeV^4}$, and the large distance static $Q \bar Q$ potential.

hep-ph↗
arXiv2008

Astrophysical constraints on the confining models : the Field Correlator Method

We explore the relevance of confinement in quark matter models for the possible quark core of neutron stars. For the quark phase, we adopt the equation of state (EoS) derived with the Field Correlator Method, extended to the zero temperature limit. For the hadronic phase, we use the microscopic Brueckner-Hartree-Fock many-body theory. We find that the currently adopted value of the gluon condensate $G_2 \simeq 0.006-0.007 \rm {GeV^4}$, which gives a critical temperature $T_c \simeq 170 \rm MeV$, produces maximum masses which are only marginally consistent with the observational limit, while larger masses are possible if the gluon condensate is increased.

hep-ph↗
arXiv2008

Probing protoneutron star density profile from neutrino signals

Supernovae of Type II is a phenomenon that occurs at the end of evolution of massive stars when the iron core of the star exceeds a mass limit. After collapse of the core under gravity the shock wave alone does not succeed in expelling the mass of the star and in this sense the role of neutrinos is the most important mechanism to do so. During the emission of neutrinos flavor conversion is possible, related the phenomenon of oscillations, which however depends directly on the particular density profile of the medium. In this paper we present results of numerical simulations of neutrino flavor conversion in protoneutron stars and after collapse. The probabilities of survival for a given flavor in a complete three-flavors framework is estimated through an algorithm which conserves unitarity to a high degree of accuracy. The sensitivity of the results to the different adopted models for the protoneutron star structure is examined in detail demonstrating how the neutrino signal could be used to check the validity of models.

astro-ph↗
arXiv2008

Deformation properties of the BCP energy density functional

We explore the deformation properties of the newly postulated BCP energy density functional (EDF). The results obtained for three isotope chains of Mg, Dy and Ra are compared to the available experimental data as well as to the results of the Gogny-D1S force. Results for the fission barrier of $^{240}$Pu are also discussed.

nucl-th↗
arXiv2008

Khon-Sham Density Functional Inspired Approach to Nuclear Binding

A non-relativisitic nuclear density functional theory is constructed, not as usual, from an effective density dependent nucleon-nucleon force but directly introducing in the functional results from microscopic nuclear and neutron matter Bruckner G-matrix calculations at various densities. A purely phenomenological finite range part to account for surface properties is added. The striking result is that only four to five adjustable parameters, spin-orbit included, suffice to reproduce nuclear binding energies and radii with the same quality as obtained with the most performant effective forces, containing on the order of ten parameters. In this pilot work, for the pairing correlations, simply a density dependent zero range force is adopted from the literature. Possible future extensions of this approach are pointed out.

nucl-th↗
arXiv2007

Neutron matter at low density and the unitary limit

Neutron matter at low density is studied within the hole-line expansion. Calculations are performed in the range of Fermi momentum $k_F$ between 0.4 and 0.8 fm$^{-1}$. It is found that the Equation of State is determined by the $^1S_0$ channel only, the three-body forces contribution is quite small, the effect of the single particle potential is negligible and the three hole-line contribution is below 5% of the total energy and indeed vanishing small at the lowest densities. Despite the unitary limit is actually never reached, the total energy stays very close to one half of the free gas value throughout the considered density range. A rank one separable representation of the bare NN interaction, which reproduces the physical scattering length and effective range, gives results almost indistinguishable from the full Brueckner G-matrix calculations with a realistic force. The extension of the calculations below $k_F = 0.4$ fm$^{-1}$ does not indicate any pathological behavior of the neutron Equation of State.

nucl-th↗
arXiv2007

Hybrid neutron stars within the Nambu-Jona-Lasinio model and confinement

Recently, it has been shown that the standard Nambu-Jona-Lasinio (NJL) model is not able to reproduce the correct QCD behavior of the gap equation at large density, and therefore a different cutoff procedure at large momenta has ben proposed. We found that, even with this density dependent cutoff procedure, the pure quark phase in neutron stars (NS) interiors is unstable, and we argue that this could be related to the lack of confinement in the original NJL model.

hep-ph↗
arXiv2007

Upper edge of the neutron star crust : the drip point and around

A semi-microscopic self-consistent quantum approach developed recently to describe the inner crust structure of neutron stars within the Wigner-Seitz method with the explicit inclusion of neutron and proton pairing correlations is used for finding the neutron drip point which separates the outer and inner crusts. The equilibrium configurations of the crust are examined in vicinity of the drip point and in the upper part of the inner crust, for the density region corresponding to average Fermi momenta $k_{\rm F}{=}0.2 ÷0.5 $fm$^{-1}$.

nucl-th↗
arXiv2007

Properties of the Two-Dimensional Electron Gas Close to the Fermi-Liquid Quantum Critical Point

The rearrangement of single-particle degrees of freedom of a dilute two-dimensional electron gas in the vicinity of the quantum critical point is examined within a microscopic approach. It is shown that just beyond the critical point, the Landau state undergoes self-consistent rearrangement of the quasiparticle spectrum and momentum distribution. At very low temperatures, there emerges a multi-connected quasiparticle momentum distribution. With increasing temperature, two crossovers occur: a fermion condensate appears in the first and disappears in the second, giving way to universal non-Fermi-liquid behavior. Manifestations of these crossovers in thermodynamic properties of the electron gas are studied and characterized. The four quasiparticle phases predicted to exist in the vicinity of the critical point are collected in a schematic phase diagram.

cond-mat.str-el↗
arXiv2007

Equation of State of Nuclear Matter at high baryon density

A central issue in the theory of astrophysical compact objects and heavy ion reactions at intermediate and relativistic energies is the Nuclear Equation of State (EoS). On one hand, the large and expanding set of experimental and observational data is expected to constrain the behaviour of the nuclear EoS, especially at density above saturation, where it is directly linked to fundamental processes which can occur in dense matter. On the other hand, theoretical predictions for the EoS at high density can be challenged by the phenomenological findings. In this topical review paper we present the many-body theory of nuclear matter as developed along different years and with different methods. Only nucleonic degrees of freedom are considered. We compare the different methods at formal level, as well as the final EoS calculated within each one of the considered many-body schemes. The outcome of this analysis should help in restricting the uncertainty of the theoretical predictions for the nuclear EoS.

nucl-th↗
arXiv2007

Quark matter in neutron stars within the Nambu - Jona-Lasinio model and confinement

The quark matter equation of state (EOS) derived from the standard Nambu - Jona-Lasinio (NJL) model is soft enough to render neutron stars (NS) unstable at the onset of the deconfined phase, and no pure quark matter can be actually present in its interior. Since this is a peculiarity of the NJL model, we have studied a modified NJL model with a momentum cut-off which depends on the density. This procedure, which improves the agreement between QCD and NJL model at large density, modifies the standard NJL equation of state, and then it is potentially relevant for the stability analysis of neutron stars. We show that also within this approach, the NS instability still persists, and that the vacuum pressure, as a signal of quark confinement, has a fundamental role for the NS stability. In this respect, our conclusions point to a relationship between confinement and NS stability.

hep-ph↗
arXiv2006

A microscopic equation of state for protoneutron stars

We study the structure of protoneutron stars within the finite temperature Brueckner-Bethe-Goldstone many-body theory. If nucleons, hyperons, and leptons are present in the stellar core, we find that neutrino trapping stiffens considerably the equation of state, because hyperon onsets are shifted to larger baryon density. However, the value of the critical mass turns out to be smaller than the ``canonical'' value 1.44 $M_\odot$. We find that the inclusion of a hadron-quark phase transition increases the critical mass and stabilizes it at about 1.5--1.6 $M_\odot$.

astro-ph↗
arXiv2006

A realistic model of superfluidity in the neutron star inner crust

A semi-microscopic self-consistent quantum approach developed recently to describe the inner crust structure of neutron stars within the Wigner-Seitz (WS) method with the explicit inclusion of neutron and proton pairing correlations is further developed. In this approach, the generalized energy functional is used which contains the anomalous term describing the pairing. It is constructed by matching the realistic phenomenological functional by Fayans et al. for describing the nuclear-type cluster in the center of the WS cell with the one calculated microscopically for neutron matter. Previously the anomalous part of the latter was calculated within the BCS approximation. In this work corrections to the BCS theory which are known from the many-body theory of pairing in neutron matter are included into the energy functional in an approximate way. These modifications have a sizable influence on the equilibrium configuration of the inner crust, i.e. on the proton charge Z and the radius R_c of the WS cell. The effects are quite significant in the region where the neutron pairing gap is larger.

nucl-th↗
arXiv2006

Hybrid protoneutron stars with the MIT bag model

We study the hadron-quark phase transition in the interior of protoneutron stars. For the hadronic sector, we use a microscopic equation of state involving nucleons and hyperons derived within the finite-temperature Brueckner-Bethe-Goldstone many-body theory, with realistic two-body and three-body forces. For the description of quark matter, we employ the MIT bag model both with a constant and a density-dependent bag parameter. We calculate the structure of protostars with the equation of state comprising both phases and find maximum masses below 1.6 solar masses. Metastable heavy hybrid protostars are not found.

astro-ph↗
arXiv2006

Role of the boundary conditions in the Wigner-Seitz approximation applied to the neutron star inner crust

The influence of the boundary conditions used in the Wigner-Seitz (WS) approximation applied to the neutron star inner crust is examined. The generalized energy functional method which includes the neutron and proton pairing correlations is used. Predictions of two versions of the boundary conditions are compared with each other. The uncertainties in the equilibrium configuration (Z,R_c) of the crust, where Z is the proton charge and R_c, the radius of the WS cell, correspond to variation of Z by 2 - 6 units and of R_c, by 1 - 2 fm. The effect of the boundary conditions is enhanced at increasing density. These uncertainties are smaller than the variation of Z and R_c coming from the pairing effects. In the case of high densities, k_F greater than 1 1/fm, the most important uncertainty occurs in the value of the neutron gap. In the WS approximation, it originates from the shell effect in the neutron single-particle spectrum which is rather pronounced in the case of larger k_F and, correspondingly, small R_c values, but it becomes negligible at lower density near the drip point. An approximate recipe to avoid this uncertainty is suggested.

nucl-th↗
arXiv2006

The role of the boundary conditions in the Wigner-Seitz approximation applied to the neutron star inner crust

The influence of the boundary conditions used in the Wigner-Seitz approximation applied to the neutron star inner crust is examined. The generalized energy functional method which includes neutron and proton pairing correlations is used. Predictions of two versions of the boundary conditions are compared with each other. The uncertainties in the equilibrium configuration (Z,R_c) of the crust, where Z is the proton charge and R_c the radius of the Wigner-Seitz cell, correspond to variation of Z by 2 -- 6 units and of R_c, by 1 -- 2 fm. The effect of the boundary conditions is enhanced at increasing density. These uncertainties are smaller than the variation of Z and R_c coming from the inclusion of pairing. The value of the pairing gap itself, especially at high density, can depend on the boundary condition used.

nucl-th↗