Cold Dense Matter Research Articles

Hydrodynamic simulation of XUV laser-produced plasmas

With the construction of novel XUV sources, such as VUV FEL’s, XUV laser-matter interaction will become available at ultra-high intensities. But even tabletop facilities such as XUV lasers or High Harmonic Generation, are starting to reach intensities high enough to produce dense plasmas. XUV laser-matter interaction is studied by a 1D hydrodynamic Lagrangian code with radiative transfer for a range of interesting XUV sources. Heating is found to be very different for Z = 12-14 elements having L-edges around the XUV laser wavelength. Possible absorption mechanisms were investigated in order to explain this behaviour, and interaction with cold dense matter proved to be dominant. Plasma sensitivity to XUV laser parameters such as energy, pulse duration, and wavelength was also studied, covering ranges of existing XUV lasers. We found that XUV laser-produced plasmas could be studied using tabletop lasers, paving the way for future VUV-FEL high intensity experiments.

Nuclear Pasta Structure in Hot Neutron Stars

The structure of cold and hot dense matter at subnuclear densities is investigated by quantum molecular dynamics simulations. The phase diagrams obtained show that the density of the phase boundaries between the different nuclear structures decreases with increasing temperature due to the thermal expansion of the nuclear matter region.

Strange quarks in colour superconductors

Cold dense quark matter is a colour superconductor. At high densities the preferred phase is the colour-flavour-locked (CFL) phase with equal numbers of up, down and strange quarks. At intermediate densities (as in a neutron star), the nonzero strange quark mass upsets the SU(3) flavour symmetry of the CFL phase and unlocked colour superconducting phases can prevail. One unlocked phase is the crystalline phase, in which the Cooper pair condensate spontaneously breaks translational invariance by forming a face-centred-cubic pattern (this FCC pattern might also be detected in a crystalline superfluid of cold fermionic atoms). Another unlocked phase is the single-flavour phase, a J = 1 condensate that spontaneously breaks rotational invariance. I will describe these new phases and discuss implications for the physics of compact stars.

Microscopic study of nuclear “pasta”: Quantum molecular dynamics approach

Structure of cold dense matter at subnuclear densities is investigated by quantum molecular dynamics (QMD) simulations. We succeeded in showing that the phases with slab-like and rod-like nuclei etc. can be formed dynamically without any assumptions on the nuclear shape. We also observe intermediate phases, which has complicated nuclear shapes. Geometrical structures of matter are analyzed, and it is found out that intemediate phases can be characterized as those with negative Euler characteristic.

Angular momentum mixing in crystalline color superconductivity

In crystalline color superconductivity, quark pairs form at nonzero total momentum. This crystalline order potentially enlarges the domain of color superconductivity in cold dense quark matter. We present a perturbative calculation of the parameters governing the crystalline phase and show that this is indeed the case. Nevertheless, the enhancement is modest, and to lowest order is independent of the strength of the color interaction.

Microscopic study of slablike and rodlike nuclei: Quantum molecular dynamics approach

The structure of cold dense matter at subnuclear densities is investigated by quantum molecular dynamics simulations. We succeeded in showing that the phases with slablike and rodlike nuclei, etc., can be formed dynamically from hot uniform nuclear matter without any assumptions on nuclear shape. We also observe intermediate phases, which have complicated nuclear shapes. Geometrical structures of matter are analyzed with Minkowski functionals, and it is found that intermediate phases can be characterized as those with negative Euler characteristic. Our result suggests the existence of these kinds of phases in addition to the simple ``pasta'' phases in neutron star crusts.

Mass-induced crystalline color superconductivity

We demonstrate that crystalline color superconductivity may arise as a result of pairing between massless quarks and quarks with nonzero mass m_s. Previous analyses of this phase of cold dense quark matter have all utilized a chemical potential difference \delta\mu to favor crystalline color superconductivity over ordinary BCS pairing. In any context in which crystalline color superconductivity occurs in nature, however, it will be m_s-induced. The effect of m_s is qualitatively different from that of \delta\mu in one crucial respect: m_s depresses the value of the BCS gap \Delta_0 whereas \delta\mu leaves \Delta_0 unchanged. This effect in the BCS phase must be taken into account before m_s-induced and \delta\mu-induced crystalline color superconductivity can sensibly be compared.

Illuminating dense quark matter.

We imagine shining light on a lump of cold dense quark matter, in the color-flavor locked phase and therefore a transparent insulator. We calculate the angles of reflection and refraction, and the intensity of the reflected and refracted light. Although the only potentially observable context for this phenomenon (reflection of light from and refraction of light through an illuminated quark star) is unlikely to be realized, our calculation casts new light on the old idea that confinement makes the QCD vacuum behave as if filled with a condensate of color-magnetic monopoles.

Microscopic Study of Nuclear “Pasta” by Quantum Molecular Dynamics

Structure of cold dense stellar matter at subnuclear densities is investigated with quantum molecular dynamics (QMD). We succeeded in showing that the phases with slab-like and rod-like nuclei etc. can be formed dynamically without any assumptions on the nuclear shape. Our result suggests the existence of these kinds of phases in neutron star crusts.

Opening the crystalline color superconductivity window

Cold dense quark matter is in a crystalline color superconducting phase wherever pairing occurs between species of quarks with chemical potentials whose difference \delta\mu lies within an appropriate window. If the interaction between quarks is modeled as point-like, this window is rather narrow. We show that when the interaction between quarks is modeled as single-gluon exchange, the window widens by about a factor of ten at accessible densities and by much larger factors at higher density. This striking enhancement reflects the increasingly (1+1)-dimensional nature of the physics at weaker and weaker coupling. Our results indicate that crystalline color superconductivity is a generic feature of the phase diagram of cold dense quark matter, occurring wherever one finds quark matter which is not in the color-flavor locked phase. If it occurs within the cores of compact stars, a crystalline color superconducting region may provide a new locus for glitch phenomena.

Magnetic fields within color superconducting neutron star cores

We discuss the Meissner effect for a color superconductor formed by cold dense quark matter. Though color and ordinary electromagnetism are broken in a color superconductor, there is a linear combination of the photon and a gluon that remains massless. Consequently, a color superconducting region may be penetrated by an external magnetic field. We show that at most a small fraction of the magnetic field is expelled, and if the screening distance is the smallest length scale in the problem there is no expulsion at all. We calculate the behavior of the magnetic field for a spherical geometry relevant for compact stars. If a neutron star contains a quark matter core, this core is a color superconductor. Our results demonstrate that such cores admit magnetic fields without restricting them to quantized flux tubes. Such magnetic fields within color superconducting neutron star cores are stable on time scales longer than the age of the universe, even if the spin period of the neutron star is changing.

Mapping the QCD phase diagram

The QCD vacuum in which we live, which has the familiar hadrons as its excitations, is but one phase of QCD, and far from the simplest one at that. One way to better understand this phase and the nonperturbative dynamics of QCD more generally is to study other phases and the transitions between phases. We are engaged in a voyage of exploration, mapping the QCD phase diagram as a function of temperature T and baryon number chemical potential μ. Because of asymptotic freedom, the high temperature and high baryon density phases of QCD are more simply and more appropriately described in terms of quarks and gluons as degrees of freedom, rather than hadrons. The chiral symmetry breaking condensate which characterizes the vacuum phase melts away. At high densities, quarks form Cooper pairs and new condensates develop. The formation of such superconducting phases [1–4] requires only weak attractive interactions; these phases may nevertheless break chiral symmetry [5] and have excitations which are indistinguishable from those in a confined phase [5–8]. These cold dense quark matter phases may arise in the centers of neutron stars; mapping this region of the phase diagram will require an interplay between theory and neutron star phenomenology. The goal of the experimental heavy ion physics program is to explore and map the higher temperature regions of the diagram. Recent theoretical developments suggest that a key qualitative feature, namely a critical point which in a sense defines the landscape to be mapped, may be within reach of discovery and analysis by the CERN SPS, if data is taken at several different energies [9,10]. The discovery of the critical point would in a stroke transform the map of the QCD phase diagram which we sketch below from one based only on reasonable inference from universality, lattice gauge theory and models into one with a solid experimental basis.

Thomas‐Fermi Calculations of Atoms and Matter in Magnetic Neutron Stars. II. Finite Temperature Effects

We present numerical calculations of the equation of state for dense matter in high magnetic fields, using a temperature dependent Thomas-Fermi theory with a magnetic field that takes all Landau levels into account. Free energies for atoms and matter are also calculated as well as profiles of the electron density as a function of distance from the atomic nucleus for representative values of the magnetic field strength, total matter density, and temperature. The Landau shell structure, which is so prominent in cold dense matter in high magnetic fields, is still clearly present at finite temperature as long as it is less than approximately one tenth of the cyclotron energy. This structure is reflected in an oscillatory behaviour of the equation of state and other thermodynamic properties of dense matter and hence also in profiles of the density and pressure as functions of depth in the surface layers of magnetic neutron stars. These oscillations are completely smoothed out by thermal effects at temperatures of the order of the cyclotron energy or higher.

Thomas-Fermi Calculations of Atoms and Matter in Magnetic Neutron Stars: Effects of Higher Landau Bands

view Abstract Citations (28) References (27) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Thomas-Fermi Calculations of Atoms and Matter in Magnetic Neutron Stars: Effects of Higher Landau Bands Roegnvaldsson, Oe. E. ; Fushiki, I. ; Gudmundsson, E. H. ; Pethick, C. J. ; Yngvason, J. Abstract We calculate the equation of state for cold dense matter in high magnetic fields in the Thomas-Fermi approximation, taking all Landau levels into account. Total energies and chemical potentials for atoms and matter are also calculated, and we present detailed profiles of the electron density as a function of the distance from the atomic nucleus for various values of the magnetic field strength and the total matter density. The profiles show a Landau shell structure, which for iron atoms at low pressure is particularly pronounced for magnetic fields of order 1011 G. In compressed matter this structure is reflected in a high compressibility when the density is such that electrons at the boundary of a unit cell start to occupy a new Landau band. This leads to an oscillatory behavior of the density gradient as a function of depth in the surface layers of magnetic neutron stars. Publication: The Astrophysical Journal Pub Date: October 1993 DOI: 10.1086/173234 Bibcode: 1993ApJ...416..276R Keywords: ATOMIC PROCESSES; DENSE MATTER; EQUATION OF STATE; STARS: MAGNETIC FIELDS; STARS: NEUTRON full text sources ADS | data products CDS (1)

Dense matter at nuclear subsaturation densities

A model is proposed for cold dense matter at subsaturation densities which is composed of neutron-rich nuclei immersed in a neutron gas as well as an electron gas. The equation of state is calculated by means of a Wigner-Seitz approximation. The result shows a discontinuity at a critical matter density ~ 5 × 10 12 g/cm 3. This discontinuity, which corresponds to the point where one valley on the energy surface empties into another from above, is related to a sharp peak in the dependence of the nuclear surface tension on the nuclear asymmetry.

Gamma-ray bursts from extinct neutron stars.

The paper concentrates on disks around old extinct pulsars, that can produce gamma-ray bursts owing to viscous evolution of the disk bringing it into the near vicinity of the neutron star, with runaway ionization of the disk and simultaneous precipitation of this plasma onto the neutron star. An old extinct pulsar is modeled as a magnetized neutron star circled by a ring of cold dense matter with an orbital period approximately equal to the rotational period of the neutron star. The numerical estimates produced are found to be consistent with the observed properties of gamma-ray bursters.

Surface structure of neutron stars with high magnetic fields

The equation of state of cold dense matter in strong magnetic fields is calculated in the Thomas-Fermi and Thomas-Fermi-Dirac approximations. For use in the latter calculation, a new expression is derived for the exchange energy of the uniform electron gas in a strong magnetic field. Detailed calculations of the density profile in the surface region of a neutron star are described for a variety of equations of state, and these show that the surface density profile is strongly affected by the magnetic field, irrespective of whether or not matter in a magnetic field has a condensed state bound with respect to isolated atoms. It is also shown that, as a consequence of the field dependence of the screening potential, magnetic fields can significantly increase nuclear reaction rates. 38 refs.

COLD DENSE FERMIONIC MATTER IN THE ELECTROWEAK THEORY: ANISOTROPIC W-BOSON CONDENSATE AT B≠L

The one loop effective potential of cold dense fermionic matter is calculated in the standard electroweak theory. It is shown that the anisotropic W-boson condensate is formed at sufficiently high density and B≠L. The anisotropic part of the energy-momentum tensor is calculated for this state. It is shown that this state is metastable, the instability being due to the electroweak baryon number violating transitions.

Inhomogeneous W-boson condensates in the standard electroweak theory at high fermionic densities

Cold dense fermionic matter at non-zero densities of broken gauge charges is considered in the context of the standard electroweak theory. It is shown that at sufficiently high densities, the system undergoes the second-order phase transition into a state with an inhomogeneous and anisotropic W-boson condensate. This state is metastable because of the anomalous non-conservation of ( B + L ). A possible scenario is outlined for the decay of this state which could occur instead of the instanton transitions.

Phase transitions in cold and warm dense matter

We consider the phase transitions, in dense matter, from nuclei to bubbles and from bubbles to uniform matter. A simplified version of the compressible liquid-drop model allows us to discuss analytically the densities at which the free energies of the different phases are equal, and the density discontinuities of the phases in equilibrium. A reasonable agreement with detailed numerical calculations is obtained only if the compressibility of the matter inside nuclei, and particularly outside bubbles, is taken into account. The dependence of the bubbles-uniform matter transition on the various elements of the Coulomb energy is discussed in detail: the transition is actually a first-order one, but it becomes of second order if the lattice Coulomb energy is turned off. The insight into the effect on the transition of the ratio of surface-plus-Coulomb energy to compression modulus allows us to understand the dependence of the transition densities on temperature and on the microscopic model employed.