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We study the interaction between dark matter (DM) and highly magnetized neutron stars (NSs), focusing on how DM particle mass, mass fraction, and magnetic field (MF) strength affect NS structure and stability. We consider self-interacting, non-annihilating, asymmetric fermionic DM that couples to NSs only through gravitational interaction. Using the QMC-RMF4 relativistic mean-field model with density-dependent magnetic fields, we investigate the magnetized equation of state and examine the accumulation of DM under various conditions. Our results show that as the DM fraction increases, the maximum gravitational mass of the NS decreases, especially for heavier DM particles, while lighter DM particles can induce a transition from a dark core to a halo structure, increasing the maximum mass. Strong MFs soften the equation of state and reduce the dark mass a NS core can retain before transitioning to a halo., Comment: Comments are welcome

We investigate nonradial $f$-mode oscillations of hybrid neutron stars in full general relativity, employing hybrid equations of state describing a nuclear outer core and a pasta-phase transition to a quark-matter core. The validity of various universal relations is confirmed for those stars. Prospects of observations are also discussed., Comment: 13 pages, 10 figures

We investigate radial oscillations of proto-neutron stars, employing equations of state described by the Brueckner-Hartree-Fock theory or the relativistic mean field model, and assuming isentropy and fixed lepton fractions for the internal structure. We calculate the eigenfrequencies and corresponding oscillation functions, which show different characteristics in different mass regions. In the low-mass region around 1.4 solar mass, the radial oscillation frequencies are lowered by large entropy and neutrino trapping, along with a reduction of the average adiabatic index. In the region close to the maximum mass, the fundamental oscillation frequency drops rapidly and vanishes at the maximum mass, in accordance with the critical stability criterion $\partial M /\partial \rho_c = 0$, as for cold neutron stars., Comment: 8 pages, 6 figures

The proton drip line of (hyper)nuclei is examined within the framework of the deformed Skyrme-Hartree Fock approach by adjusting the nuclear force parameters to exactly reproduce the core binding energies. The impact of adding a {\Lambda} hyperon in a s or p state is studied, and it is found that in some cases the deformation effect facilitates the extension of the drip line by an added p-state hyperon. However, no extension of the drip line is found for s-state hypernuclei., Comment: 7 pages, 2 Figures

We systematically study the observable properties of dark-matter admixed neutron stars, employing a realistic nuclear EOS in combination with self-interacting fermionic dark matter respecting constraints on the self-interaction cross section. Deviations from universal relations valid for nucleonic neutron stars are analyzed over the whole parameter space of the model and unequivocal signals for the presence of dark matter in neutron stars are identified., Comment: 9 pages, 7 figures. arXiv admin note: substantial text overlap with arXiv:2307.11313

We study the cooling of isolated neutron stars, employing different nuclear equations of state with or without active direct Urca process, and investigate the interplay with the nuclear pairing gaps. We find that a consistent description of all current cooling data requires fast direct Urca cooling and reasonable proton 1S0 gaps, but no neutron 3P2 pairing. We then deduce the neutron star mass distributions compatible with the cooling analysis and compare with current theoretical models. Reduced 1S0 gaps and unimodal mass distributions are preferred by the analysis. The importance of statistical and systematic errors is also investigated., Comment: 14 pages, 10 figures, 2 tables, Published in Phys. Rev. D

We study the effects of dark matter on the properties of neutron stars by employing a DM-admixed model. The Brueckner-Hartree-Fock theory with realistic three-body forces and a generic bosonic self-interacting dark matter model describe the equations of state for nuclear matter and DM, respectively. We study the complete set of stable dark neutron stars and in particular the observable radii of these objects. A rich variety of stellar configurations is found and discussed in detail.

We investigate non-radial oscillations of pure and hybrid neutron stars, employing equations of state of nuclear matter from Brueckner-Hartree-Fock theory, and of quark matter from the Dyson-Schwinger quark model, performing a Gibbs construction for the mixed phase in hybrid stars. Characteristic differences between neutron-star and hybrid-star $g_1$-mode oscillation frequencies, damping times, and gravitational wave strains are pointed out. Prospects of observations are also discussed., Comment: 11 pages, 8 figures

A microscopic nuclear equation of state compatible with all current astrophysical constraints constructed within the Brueckner-Hartree-Fock formalism is presented and extended in a consistent way to finite temperature. The effects of finite temperature on the properties of neutron stars are studied in detail and a universal relation regarding stellar stability is proposed., Comment: 9 pages, 7 figures

A set of microscopic, covariant density-functional, and non-relativistic Skyrme-type equations of state is employed to study the structure of purely nucleonic neutron stars at finite temperature. After examining the agreement with presently available astrophysical observational constraints, we find that the magnitude of thermal effects depends on the nucleon effective mass as well as on the stiffness of the cold equation of state. We evidence a fairly small but model-dependent effect of finite temperature on stellar stability that is correlated with the relative thermal pressure inside the star., Comment: 10 pages, 8 figures

The deformations of multi-$\la$ hypernuclei corresponding to even-even core nuclei ranging from $^8$Be to $^{40}$Ca with 2, 4, 6, and 8 hyperons are studied in the framework of the deformed Skyrme-Hartree-Fock approach. It is found that the deformations are reduced when adding 2 or 8 $\la$ hyperons, but enhanced when adding 4 or 6 $\la$ hyperons. These differences are attributed to the fact that $\la$ hyperons are filled gradually into the three deformed $p$ orbits, of which the [110]1/2$^-$ orbit is prolately deformed and the degenerate [101]1/2$^-$ and [101]3/2$^-$ orbits are oblately deformed.

The effects of an additional $K^-$ meson on the neutron and proton drip lines are investigated within Skyrme-Hartree-Fock approach combined with a Skyrme-type kaon-nucleon interaction. While an extension of the proton drip line is observed due to the strongly attractive $K^-p$ interaction, contrasting effects (extension and reduction) on the neutron drip line of Be, O, and Ne isotopes are found. The origin of these differences is attributed to the behavior of the highest-occupied neutron single-particle levels near the neutron drip line., Comment: 6 pages, 6 figures

We review the current status and recent progress of microscopic many-body approaches and phenomenological models, which are employed to construct the equation of state of neutron stars. The equation of state is relevant for the description of their structure and dynamical properties, and it rules also the dynamics of core-collapse supernovae and binary neutron star mergers. We describe neutron star matter assuming that the main degrees of freedom are nucleons and hyperons, disregarding the appearance of quark matter. We compare the theoretical predictions of the different equation-of-state models with the currently available data coming from both terrestrial laboratory experiments and recent astrophysical observations. We also analyse the importance of the nuclear strong interaction and equation of state for the cooling properties of neutron stars. We discuss the main open challenges in the description of the equation of state, mainly focusing on the limits of the different many-body techniques, the so-called "hyperon puzzle," and the dependence of the direct URCA processes on the equation of state., Comment: 83 pages, 17 figures, 617 references. Accepted for publication in Progress in Particle and Nuclear Physics

We perform binary neutron star merger simulations using a newly derived set of finite-temperature equations of state in the Brueckner-Hartree-Fock approach. We point out the important and opposite roles of finite temperature and rotation for stellar stability and systematically investigate the gravitational-wave properties, matter distribution, and ejecta properties in the postmerger phase for the different cases. The validity of several universal relations is also examined and the most suitable EOSs are identified., Comment: Version submitted to PRD

We compute the free energy of asymmetric nuclear matter in a Brueckner-Hartree-Fock approach at finite temperature, paying particular attention to the dependence on isospin asymmetry. The first- and second-order symmetry energies are determined as functions of density and temperature and useful parametrizations are provided. We find small deviations from the quadratic isospin dependence and very small corresponding effects on (proto)neutron star structure., Comment: 6 pages, 4 figures

We investigate the use of hybrid equations of state in binary neutron-star simulations in full general relativity, where thermal effects are included in an approximate way through the adiabatic index $\Gamma_{\rm{th}}$. We employ a newly developed finite-temperature equation of state derived in the Brueckner-Hartree-Fock approach and carry out comparisons with the corresponding hybrid versions of the same equation of state, investigating how different choices of $\Gamma_{\rm{th}}$ affect the gravitational-wave signal and the hydrodynamical properties of the remnant. We also perform comparisons with the widely used SFHo equation of state, detailing the differences between the two cases. Overall, we determine that when using a hybrid equation of state in binary neutron-star simulations, the value of thermal adiabatic index $\Gamma_{\rm{th}} \approx 1.7$ best approximates the dynamical and thermodynamical behaviour of matter computed using complete, finite-temperature equations of state., Comment: 15 pages, 10 figures, accepted for publication in PRD

We model the cooling of hybrid neutron stars combining a microscopic nuclear equation of state in the Brueckner-Hartree-Fock approach with different quark models. We then analyze the neutron star cooling curves predicted by the different models and single out the preferred ones. We find that the possibility of neutron p-wave pairing can be excluded in our scenario., Comment: 10 pages, 6 figures

Nucleon effective masses are studied in the framework of the Brueckner-Hartree-Fock many-body approach at finite temperature. Self-consistent calculations using the Argonne $V_{18}$ interaction including microscopic three-body forces are reported for varying temperature and proton fraction up to several times the nuclear saturation density. Our calculations are based on the exact treatment of the center-of-mass momentum instead of the average-momentum approximation employed in previous works. We discuss in detail the effects of the temperature together with those of the three-body forces, the density, and the isospin asymmetry. We also provide an analytical fit of the effective mass taking these dependencies into account. The temperature effects on the cooling of neutron stars are briefly discussed based on the results for betastable matter., Comment: version accepted for publication in Physical Review C

The properties of $\Xi^-$ hypernuclei are studied systematically using a two-dimensional Skyrme-Hartree-Fock approach combined with three different $\Xi N$ Skyrme forces fitted to reproduce the existing data. We explore the impurity effect of a single $\Xi^-$ hyperon on the radii, deformations, and density distributions of the nuclear core and point out qualitative differences between the different forces. We find that the $\Xi^-$ removal energy of $^{\hskip0.10em13}_{\Xi p}$B [$^{12}$C(g.s.)+ $\Xi^-$(1p)] calculated by the SLX3 force is 0.7 MeV, which is in good agreement with a possible value of $0.82\pm0.17\;$MeV from the KEK E176 experiment. The theoretical prediction for this weakly bound state depends strongly on the deformation of the nuclear core, which is analyzed in detail.

The properties of kaonic nuclei are studied using a two-dimensional Skyrme-Hartree-Fock model with a $KN$ Skyrme force. We focus in particular on the instability of the solutions for a too strong $KN$ interaction, which determines a maximum value of the kaon binding in this approach. We then analyze the change of the deformation properties of several core-deformed nuclei caused by the added kaon, and find a shrinking of the core and in some cases a complete loss of deformation.

We investigate properties of nuclear matter and examine possible correlations with neutron star observables for a set of microscopic nuclear equations of state derived within the Brueckner-Hartree-Fock formalism employing compatible three-body forces. We find good candidates for a realistic nuclear EOS up to high density and confirm strong correlations between neutron star radius, tidal deformability, and the pressure of betastable matter. No correlations are found with the saturation properties of nuclear matter., Comment: 9 pages, 5 figures, accepted in European Physical Journal A (EPJA), Topical issue "First joint gravitational wave and electromagnetic observations: Implications for nuclear and particle physics"

The detection of the GW170817 neutron star merger event has incited an intense research activity towards the understanding of the nuclear matter equation of state. In this paper we compare in particular the pressure-density relation obtained from heavy-ion collisions with the analysis of the NS merger event. Moreover, we present recent calculations of neutron star's moment of inertia and tidal deformability using various microscopic equations of state for nuclear and hybrid star configurations, and confirm several universal relations. We also discuss the recent constraints for the NS radii determined by GW170817, and find compatible radii between 12 and 13 kilometers, thus identifying the suitable equations of state., Comment: Talk given by G. F. Burgio at XIII Quark Confinement and the Hadron Spectrum - Confinement2018 - 31 July - 6 August 2018, Maynooth University, Ireland

We study the properties of hot beta-stable nuclear matter using equations of state derived within the Brueckner-Hartree-Fock approach at finite temperature including consistent three-body forces. Simple and accurate parametrizations of the finite-temperature equations of state are provided. The properties of hot neutron stars are then investigated within this framework, in particular the temperature dependence of the maximum mass. We find very small temperature effects and analyze the interplay of the different contributions., Comment: 8 pages, 7 figures

We model neutron star cooling with several microscopic nuclear equations of state based on different nucleon-nucleon interactions and three-body forces, and compatible with the recent GW170817 neutron star merger event. They all feature strong direct Urca processes. We find that all models are able to describe well the current set of cooling data for isolated neutron stars, provided that large and extended proton 1S0 gaps and no neutron 3PF2 gaps are active in the stellar matter. We then analyze the neutron star mass distributions predicted by the different models and single out the preferred ones., Comment: 8 pages, 5 figures

We calculate neutron star's moment of inertia and deformabilities using various microscopic equations of state for nuclear and hybrid star configurations. Correlations between the various observables are examined and we confirm several universal relations. We focus in particular on the constraints for the neutron star radii imposed by a determination of the average tidal deformability of the binary neutron star system GW170817. We find compatible radii between 12 and 13 kilometers and identify the suitable equations of state., Comment: 18 pages, 5 figures, version accepted on Journal of Physics G : Nuclear and Particle Physics, Special issue on "Hadrons and Gravitational Waves after GW170817"

The decomposition of nuclear symmetry energy into spin and isospin components is discussed to elucidate the underlying properties of the NN bare interaction. This investigation was carried out in the framework of the Brueckner-Hartree-Fock theory of asymmetric nuclear matter with consistent two and three body forces. It is shown the interplay among the various two body channels in terms of isospin singlet and triplet components as well as spin singlet and triplet ones. The broad range of baryon densities enables to study the effects of three body force moving from low to high densities., Comment: 8 pages, 4 figures

The detection of GW170817 and its electromagnetic counterparts allows to constrain the equation of state of dense matter in new and complementary ways. Very stiff equations of state are ruled out by the upper limit on the average tidal deformability, $\tilde\Lambda \lesssim 800$, imposed by the detected gravitational wave signal. A lower limit, $\tilde\Lambda \gtrsim 400$, can also be extracted by considering the large amount of ejected matter which powers the kilonova AT2017gfo. By using several microscopic nucleonic equations of state, we first confirm the existence of a monotonic relation between $R_{1.5}$ (the radius of the $1.5M_{\odot}$ configuration) and $\tilde\Lambda$. This translates the limits on $\tilde\Lambda$ into limits on the radius: $11.8\,\text{km} \lesssim R_{1.5} \lesssim 13.1\,$km. We then show that the monotonic relation is violated, if a second branch of compact stars composed of quark matter exists, as in the two-families or the twin-stars scenarios. In particular, it is possible to fulfill the limits on $\tilde\Lambda$ while having $R_{1.5}$ significantly smaller than $12\,$km. In both those scenarios the event GW170817/AT2017gfo originates from the merger of a hadronic star and a star containing quark matter., Comment: 5 pages, 3 figures, final published version

Thermal conductivity and shear viscosity of npe$\mu$ matter in non-superfluid neutron star cores are considered in the framework of Brueckner-Hartree-Fock many-body theory. We extend our previous work (Shternin, Baldo and Haensel, 2013) by analysing different nucleon-nucleon potentials and different three-body forces. We find that the use of different potentials leads up to one order of magnitude variations in the values of the nucleon contribution to transport coefficients. The nucleon contribution dominates the thermal conductivity, but for all considered models the shear viscosity is dominated by leptons., Comment: 4 pages, 2 figures; in v.2 misprints in eqs. (5)-(9) corrected

We model the thermal states of both isolated neutron stars and accreting neutron stars in X-ray transients in quiescence and confront them with observations. We use an equation of state and superfluid baryon gaps, which are consistently calculated. We conclude that the direct Urca process is required to be consistent with low-luminous accreting neutron stars. In addition, proton superfluidity and sufficiently weak neutron superfluidity are necessary to explain the cooling of middle-aged neutron stars and to obtain a realistic distribution of neutron star masses.

We study the properties of two-flavor quark matter in the Dyson-Schwinger model and investigate the possible consequences for hybrid neutron stars, with particular regard to the two-solar-mass limit. We find that with some extreme values of the model parameters, the mass fraction of two-flavor quark matter in heavy neutron stars can be as high as 30 percent and the possible energy release during the conversion from nucleonic neutron stars to hybrid stars can reach $10^{52}\;$erg., Comment: 8 pages,5 figures. To be published in Chinese Physics C

We study rapidly rotating hybrid stars with the Dyson-Schwinger model for quark matter and the Brueckner-Hartree-Fock many-body theory with realistic two-body and three-body forces for nuclear matter. We determine the maximum gravitational mass, equatorial radius, and rotation frequency of stable stellar configurations by considering the constraints of the Keplerian limit and the secular axisymmetric instability, and compare with observational data. We also discuss the rotational evolution for constant baryonic mass, and find a spinup phenomenon for supramassive stars before they collapse to black holes., Comment: 9 pages,9 figures

Motivated by the recently observed hypernucleus (Kiso event) $^{15}_{\Xi}$C ($^{14}$N$+\Xi^-$), we identify the state of this system theoretically within the framework of the relativistic-mean-field and Skyrme-Hartree-Fock models. The $\Xi N$ interactions are constructed to reproduce the two possibly observed $\Xi^-$ removal energies, $4.38\pm 0.25$ MeV or $1.11\pm 0.25$ MeV. The present result is preferable to be $^{14}{\rm N}({\rm g.s.})+\Xi^-(1p)$, corresponding to the latter value., Comment: 8 pages, 3 figures, 1 table

We calculate the equation of state of strange quark matter and the interior structure of strange quark stars in a Dyson-Schwinger quark model within rainbow or Ball-Chiu vertex approximation. We emphasize constraints on the parameter space of the model due to stability conditions of ordinary nuclear matter. Respecting these constraints, we find that the maximum mass of strange quark stars is about 1.9 solar masses, and typical radii are 9 --11 km. We obtain an energy release as large as $3.6 \times 10^{53}\,\text{erg}$ from conversion of neutron stars into strange quark stars., Comment: 9 pages, 9 figures

We model neutron star cooling, in particular the current rapid cooldown of the neutron star Cas A, with a microscopic nuclear equation of state featuring strong direct Urca processes and using compatible nuclear pairing gaps as well as effective masses. Several scenarios are possible to explain the features of Cas A, but only large and extended proton $^1S_0$ gaps and small neutron $^3PF_2$ gaps are able to accommodate also the major part of the complete current cooling data. We conclude that the possibility of strong direct Urca processes cannot be excluded from the cooling analysis., Comment: 7 pages, 6 figures, submitted to Monthly Notices of the Royal Astronomical Society

Starting from a realistic constituent quark model for the nucleon-nucleon interaction, we derive the equation of state (EOS) of nuclear matter within the Bethe-Brueckner-Goldstone approach up to three-hole-line level, without need to introduce three-nucleon forces. To estimate the uncertainty of the calculations both the gap and the continuous choices for the single-particle potential are considered and compared. The resultant EOS is compatible with the phenomenological analysis on the saturation point, the incompressibility, the symmetry energy at low density and its slope at saturation, together with the high-density pressure extracted from flow data on heavy ion collisions. Although the symmetry energy is appreciably larger in the gap choice in the high-density region, the maximum neutron star masses derived from the continuous-choice EOS and the gap-choice EOS are similar and close to two solar masses, which is again compatible with recent observational data. Comparison with other microscopic EOS is presented and discussed., Comment: 15 pages, 11 figures, 8 tables

We study cold dense quark matter and hybrid neutron stars with a Dyson-Schwinger quark model and various choices of the quark-gluon vertex. We obtain the equation of state of quark matter in beta equilibrium and investigate the hadron-quark phase transition in combination with a hadronic equation of state derived within the Brueckner-Hartree-Fock many-body theory. Comparing with the results for quark matter with the rainbow approximation, the Ball-Chiu ansatz and the 1BC ansatz for the quark-gluon vertex lead to a reduction of the effective interaction at finite chemical potential, qualitatively similar to the effect of our gluon propagator. We find that the phase transition and the equation of state of the quark or mixed phase and consequently the resulting hybrid star mass and radius depend mainly on a global reduction of the effective interaction due to effects of both the quark-gluon vertex and gluon propagator, but are not sensitive to the vertex ansatz., Comment: 6 pages, 5 figures

We calculate the effective masses of neutrons and protons in dense nuclear matter within the microscopic Brueckner-Hartree-Fock many-body theory and study the impact on the neutrino emissivity processes of neutron stars. We compare results based on different nucleon-nucleon potentials and nuclear three-body forces. Useful parametrizations of the numerical results are given. We find substantial in-medium suppression of the emissivities, strongly dependent on the interactions., Comment: 5 pages, 3 figures, accepted for publication as Brief Report in Phys. Rev. C

We study the hadron-quark phase transition in the interior of hot protoneutron stars, combining the Brueckner-Hartree-Fock approach for hadronic matter with the MIT bag model or the Dyson-Schwinger model for quark matter. We examine the structure of the mixed phase constructed according to different prescriptions for the phase transition, and the resulting consequences for stellar properties. We find important effects for the internal composition, but only very small influence on the global stellar properties., Comment: 6 pages, 4 figures

We calculate the structure of neutron star interiors comprising both the hadronic and the quark phases. For the hadronic sector we employ a microscopic equation of state involving nucleons and hyperons derived within the Brueckner-Hartree-Fock many-body theory with realistic two-body and three-body forces. For the description of quark matter, we use several different models, e.g. the MIT bag, the Nambu--Jona-Lasinio (NJL), the Color Dielectric (CDM), the Field Correlator method (FCM), and one based on the Dyson-Schwinger model (DSM). We find that a two solar mass hybrid star is possible only if the nucleonic EOS is stiff enough., Comment: 8 pages, 3 figures. Talk given at "Xth Quark Confinement and the Hadron Spectrum", Munich, 8-12 October, 2012

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 Hyper Netted 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., Comment: 13 pages, 5 figures, 3 tables

We study the hadron-quark phase transition at finite temperature in the interior of protoneutron stars, combining the Dyson-Schwinger model for quark matter with the Brueckner-Hartree-Fock approach for hadronic matter. We discuss the dependence of the results on different nuclear three-body forces and on details of the quark model. %Compared to the bag model, the transition from the hadron phase %(without hyperons) to the quark phase appears at large density. A maximum mass exceeding two solar masses can be obtained with a strong three-body force and suitable parameter values in the Dyson-Schwinger model. With a hybrid configuration, the maximum mass of protoneutron stars is larger then that of cold neutron stars, such that a delayed collapse might be possible in principle., Comment: 10 pages, 5 figures

We study the hadron-quark phase transition in the interior of neutron stars. For the hadronic sector, we use a microscopic equation of state involving nucleons and hyperons derived within the Brueckner-Hartree-Fock many-body theory with realistic two-body and three-body forces. For the description of quark matter, we employ the Dyson-Schwinger approach and compare with the MIT bag model. We calculate the structure of neutron star interiors comprising both phases and find that with the Dyson-Schwinger model, the hadron-quark phase transition takes place only when hyperons are excluded, and that a two-solar-mass hybrid star is possible only if the nucleonic equation of state is stiff enough., Comment: 10 pages, 8 figures

We study how the frequencies and damping times of oscillations of a newly born, hot proto-neutron star depend on the physical quantities which characterize the star quasi-stationary evolution which follows the bounce. Stellar configurations are modeled using a microscopic equation of state obtained within the Brueckner-Hartree-Fock, nuclear many-body approach, extended to the finite-temperature regime. We discuss the mode frequency behaviour as function of the lepton composition, and of the entropy gradients which prevail in the interior of the star. We find that, in the very early stages, gravitational wave emission efficiently competes with neutrino processes in dissipating the star mechanical energy residual of the gravitational collapse., Comment: 11 pages, 4 tables, 3 figures

We perform Brueckner-Hartree-Fock calculations of hypernuclear matter at finite temperature and provide convenient analytical parametrizations of the results. We study then the properties of (proto)neutron stars containing hyperons. We find important effects of trapping and finite temperature on the structure of hyperonic stars., Comment: 6 pages, 5 figures, accepted for publication in Phys. Rev. C

We compare the Gibbs and Maxwell constructions for the hadron-quark phase transition in neutron and protoneutron stars, including interacting hyperons in the confined phase. We find that the hyperon populations are suppressed, and that neutrino trapping shifts the onset of the phase transition. The effects on the (proto)neutron star maximum mass are explored., Comment: 11 pages, 3 figures

Two-component liquid-vapor systems are modeled as two bulk phases divided by a two-dimensional surface phase and the mass and momentum balances are theoretically studied. Comparing the derived equations with some typical models of surface rheology, useful information about the interface location is obtained. It is demonstrated that the surface phase, set on the surface of tension, coincides with the equimolecular interface for insoluble surfactants, whereas it is placed on the surface of zero total mass density excess for soluble ones. The applicability of the model to surface electrostatics is also discussed by introduction of a two-dimensional Maxwell equation for the surface phase.