1,510 research outputs found

    The dynamics of neutron star crusts: Lagrangian perturbation theory for a relativistic superfluid-elastic system

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    The inner crust of a mature neutron star is composed of an elastic lattice of neutron-rich nuclei penetrated by free neutrons. These neutrons can flow relative to the crust once the star cools below the superfluid transition temperature. In order to model the dynamics of this system, which is relevant for a range of problems from pulsar glitches to magnetar seismology and continuous gravitational-wave emission from rotating deformed neutron stars, we need to understand general relativistic Lagrangian perturbation theory for elastic matter coupled to a superfluid component. This paper develops the relevant formalism to the level required for astrophysical applications.Comment: 31 pages, double spacing, minor typos fixe

    A Relativistic Mean Field Model for Entrainment in General Relativistic Superfluid Neutron Stars

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    General relativistic superfluid neutron stars have a significantly more intricate dynamics than their ordinary fluid counterparts. Superfluidity allows different superfluid (and superconducting) species of particles to have independent fluid flows, a consequence of which is that the fluid equations of motion contain as many fluid element velocities as superfluid species. Whenever the particles of one superfluid interact with those of another, the momentum of each superfluid will be a linear combination of both superfluid velocities. This leads to the so-called entrainment effect whereby the motion of one superfluid will induce a momentum in the other superfluid. We have constructed a fully relativistic model for entrainment between superfluid neutrons and superconducting protons using a relativistic σ−ω\sigma - \omega mean field model for the nucleons and their interactions. In this context there are two notions of ``relativistic'': relativistic motion of the individual nucleons with respect to a local region of the star (i.e. a fluid element containing, say, an Avogadro's number of particles), and the motion of fluid elements with respect to the rest of the star. While it is the case that the fluid elements will typically maintain average speeds at a fraction of that of light, the supranuclear densities in the core of a neutron star can make the nucleons themselves have quite high average speeds within each fluid element. The formalism is applied to the problem of slowly-rotating superfluid neutron star configurations, a distinguishing characteristic being that the neutrons can rotate at a rate different from that of the protons.Comment: 16 pages, 5 figures, submitted to PR

    Slowly Rotating General Relativistic Superfluid Neutron Stars with Relativistic Entrainment

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    Neutron stars that are cold enough should have two or more superfluids/supercondutors in their inner crusts and cores. The implication of superfluidity/superconductivity for equilibrium and dynamical neutron star states is that each individual particle species that forms a condensate must have its own, independent number density current and equation of motion that determines that current. An important consequence of the quasiparticle nature of each condensate is the so-called entrainment effect, i.e. the momentum of a condensate is a linear combination of its own current and those of the other condensates. We present here the first fully relativistic modelling of slowly rotating superfluid neutron stars with entrainment that is accurate to the second-order in the rotation rates. The stars consist of superfluid neutrons, superconducting protons, and a highly degenerate, relativistic gas of electrons. We use a relativistic σ\sigma - ω\omega mean field model for the equation of state of the matter and the entrainment. We determine the effect of a relative rotation between the neutrons and protons on a star's total mass, shape, and Kepler, mass-shedding limit.Comment: 30 pages, 10 figures, uses ReVTeX

    The Equation of State for Cool Relativistic Two-Constituent Superfluid Dynamics

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    The natural relativistic generalisation of Landau's two constituent superfluid theory can be formulated in terms of a Lagrangian LL that is given as a function of the entropy current 4-vector sρs^\rho and the gradient ∇φ\nabla\varphi of the superfluid phase scalar. It is shown that in the ``cool" regime, for which the entropy is attributable just to phonons (not rotons), the Lagrangian function L(s⃗,∇φ)L(\vec s, \nabla\varphi) is given by an expression of the form L=P−3ψL=P-3\psi where PP represents the pressure as a function just of ∇φ\nabla\varphi in the (isotropic) cold limit. The entropy current dependent contribution ψ\psi represents the generalised pressure of the (non-isotropic) phonon gas, which is obtained as the negative of the corresponding grand potential energy per unit volume, whose explicit form has a simple algebraic dependence on the sound or ``phonon" speed cPc_P that is determined by the cold pressure function PP.Comment: 26 pages, RevTeX, no figures, published in Phys. Rev. D. 15 May 199

    The dynamics of dissipative multi-fluid neutron star cores

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    We present a Newtonian multi-fluid formalism for superfluid neutron star cores, focussing on the additional dissipative terms that arise when one takes into account the individual dynamical degrees of freedom associated with the coupled "fluids". The problem is of direct astrophysical interest as the nature of the dissipative terms can have significant impact on the damping of the various oscillation modes of the star and the associated gravitational-wave signatures. A particularly interesting application concerns the gravitational-wave driven instability of f- and r-modes. We apply the developed formalism to two specific three-fluid systems: (i) a hyperon core in which both Lambda and Sigma^- hyperons are present, and (ii) a core of deconfined quarks in the colour-flavour-locked phase in which a population of neutral K^0 kaons is present. The formalism is, however, general and can be applied to other problems in neutron-star dynamics (such as the effect of thermal excitations close to the superfluid transition temperature) as well as laboratory multi-fluid systems.Comment: RevTex, no figure

    Relativistic Kinetics of Phonon Gas in Superfluids

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    The relativistic kinetic theory of the phonon gas in superfluids is developed. The technique of the derivation of macroscopic balance equations from microscopic equations of motion for individual particles is applied to an ensemble of quasi-particles. The necessary expressions are constructed in terms of a Hamilton function of a (quasi-)particle. A phonon contribution into superfluid dynamic parameters is obtained from energy-momentum balance equations for the phonon gas together with the conservation law for superfluids as a whole. Relations between dynamic flows being in agreement with results of relativistic hydrodynamic consideration are found. Based on the kinetic approach a problem of relativistic variation of the speed of sound under phonon influence at low temperature is solved.Comment: 23 pages, Revtex fil

    Relativistic Two-stream Instability

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    We study the (local) propagation of plane waves in a relativistic, non-dissipative, two-fluid system, allowing for a relative velocity in the "background" configuration. The main aim is to analyze relativistic two-stream instability. This instability requires a relative flow -- either across an interface or when two or more fluids interpenetrate -- and can be triggered, for example, when one-dimensional plane-waves appear to be left-moving with respect to one fluid, but right-moving with respect to another. The dispersion relation of the two-fluid system is studied for different two-fluid equations of state: (i) the "free" (where there is no direct coupling between the fluid densities), (ii) coupled, and (iii) entrained (where the fluid momenta are linear combinations of the velocities) cases are considered in a frame-independent fashion (eg. no restriction to the rest-frame of either fluid). As a by-product of our analysis we determine the necessary conditions for a two-fluid system to be causal and absolutely stable and establish a new constraint on the entrainment.Comment: 15 pages, 2 eps-figure

    Temporal changes in fruit production between recurrent prescribed burns in pine woodlands of the Ouachita Mountains

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    The use of prescribed fire is integral to the restoration of open woodlands and savannas, including shortleaf pine (Pinus echinata) woodlands in the Ouachita Mountains of Oklahoma and Arkansas. Fire offers many potential benefits to numerous wildlife; however, short-term implications for understory fruit production are not fully understood, especially in stands subjected to frequent, recurrent burns. We examined the effects of dormant season prescribed burns on woody fruit production (kg ha−1) and fruit producing vegetative cover in the understory of restored pine woodlands. We inventoried 32 stands during four temporal periods after dormant season prescribed fires: 1, 2, 3, and 5 growing seasons post-burn. We counted fruit (\u3c2 m above the ground) throughout the summer and visually estimated vegetative cover of fruit producing plants. Fruit production was greatest in the 3rd year (18.2 kg ha−1), followed by 5th (10.9 kg ha−1) and 2nd (9.8 kg ha−1) years after burns. Overall, 87% of total production consisted of three genera: American beautyberry (Callicarpa americana [38%]), Vitis spp. (summer grapes [Vitis aestivalis; 11%] and muscadine grape [V. rotundifolia; 10%]), and Rubus spp. (blackberry [20%] and dewberry [R. flagellaris; 8%]). Production was recorded in 13 of the 14 fruit producing species present during the 5th year post-burn, indicating that production diversity increased over time. Percent cover and species richness (26 taxa) of fruit producing taxa were greatest in the 3rd year post-burn. Taxa such as poison ivy (Toxicodendron radicans) and sumac (Rhus spp.) comprised a sizable percent of coverage (\u3e7% each), but this did not translate into substantial fruit production. American beautyberry and summer grape had both substantial coverage and production. Results suggest that burning on a 3-year rotation maximizes and prolongs fruit production; however, occasional burning on a 5-year rotation will promote a higher diversity of woody mast-producing understory species

    Weed control and overstory reduction improve survival and growth of under‐planted oak and hickory seedlings

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    Weed control and overstory reduction are important silvicultural treatments for improving survival and growth of under‐planted oak and hickory seedlings. Mast‐producing trees in the bottomland forests of the blackland prairie and Post Oak Savannah ecoregions of Texas have declined in abundance. Oaks and hickories have been replaced by more shade‐tolerant species, including green ash (Fraxinus pennsylvanica Marshall) and sugarberry (Celtis laevigata Willd.), which do not produce significant hard mast for priority wildlife species. A split‐plot experiment design was installed on three sites at Richland Creek Wildlife Management Area in Freestone County, Texas, studying the effects of canopy coverage and competition control on survival and growth of bur oak (Quercus macrocarpa Michx.), Shumard oak (Quercus shumardii Buckl.), and pecan (Carya illinoinensis (Wagenh.) K. Koch) seedlings. Uprooting by hogs shortly after planting resulted in greater than 90% mortality of pecan on the two lower elevation sites. Year one survival of Shumard oak was significantly higher than bur oak. However, bur oak was more preferred by hogs than Shumard oak. Year one growth of bur oak was significantly greater than Shumard oak. Severe flooding during the second growing season caused complete mortality on the lower two sites. None of the species were well suited to such prolonged (3–4 months) inundation as seedlings. On the remaining site, density reduction and weed‐barrier mats improved growth and survival while herbaceous weed control with herbicides actually reduced both growth and survival

    Tensor mass and particle number peak at the same location in the scalar-tensor gravity boson star models - an analytical proof

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    Recently in boson star models in framework of Brans-Dicke theory, three possible definitions of mass have been identified, all identical in general relativity, but different in scalar-tensor theories of gravity.It has been conjectured that it's the tensor mass which peaks, as a function of the central density, at the same location where the particle number takes its maximum.This is a very important property which is crucial for stability analysis via catastrophe theory. This conjecture has received some numerical support. Here we give an analytical proof of the conjecture in framework of the generalized scalar-tensor theory of gravity, confirming in this way the numerical calculations.Comment: 9 pages, latex, no figers, some typos corrected, reference adde
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