Direct Measurement of Initial-State Energy Loss in Cold Nuclear Matter at Fermilab E906/SeaQuest
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Atomic, Nuclear and Particle Physics↗
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Direct Measurement of Initial-State Energy Loss in Cold Nuclear Matter at Fermilab E906/SeaQuest
Explore the source record for details and available documents.
Atomic, Nuclear and Particle Physics↗
Constraining the properties of dark matter with observations of the cosmic microwave background
We examine how the properties of dark matter, parameterized by an equation-of-state parameter w and two perturbative generalized dark matter (GDM) parameters, c {sup 2} {sub s} (the sound speed) and c{sub vis}{sup 2} (the viscosity), are constrained by existing cosmological data, particularly the Planck 2015 data release. We find that the GDM parameters are consistent with zero, and are strongly constrained, showing no evidence for extending the model of dark matter beyond the cold dark matter (CDM) paradigm. The equation of state of dark matter is constrained to be within −0.000896<w<0.00238 at the 99.7% confidence level (CL), which is several times stronger than constraints found previously using WMAP data. The parameters c {sup 2} {sub s} and c{sub vis}{sup 2} are constrained to be less than 3.21×10{sup −6} and 6.06 × 10{sup −6} respectively at the 99.7% CL. The inclusion of the GDM parameters does significantly affect the error bars on several ΛCDM parameters, notably the dimensionless dark matter density ω {sub g} and the derived parameters σ {sub 8} and H {sub 0}. This can be partially alleviated with the inclusion of data constraining the expansion history of the universe.
79 ASTRONOMY AND ASTROPHYSICS↗
Quark matter droplets in neutron stars
We show that, for physically reasonable bulk and surface properties, the lowest energy state of dense matter consists of quark matter coexisting with nuclear matter in the presence of an essentially uniform background of electrons. We estimate the size and nature of spatial structure in this phase, and show that at the lowest densities the quark matter forms droplets embedded in nuclear matter, whereas at higher densities it can exhibit a variety of different topologies. A finite fraction of the interior of neutron stars could consist of matter in this new phase, which would provide new mechanisms for glitches and cooling.
Heiselberg, H.↗
Rapidly rotating neutron stars in general relativity: Realistic equations of state
We construct equilibrium sequences of rotating neutron stars in general relativity. We compare results for 14 nuclear matter equations of state. We determine a number of important physical parameters for such stars, including the maximum mass and maximum spin rate. The stability of the configurations to quasi-radial perturbations is assessed. We employ a numerical scheme particularly well suited to handle rapid rotation and large departures from spherical symmetry. We provide an extensive tabulation of models for future reference. Two classes of evolutionary sequences of fixed baryon rest mass and entropy are explored: normal sequences, which behave very much like Newtonian sequences, and supramassive sequences, which exist for neutron stars solely because of general relativistic effects. Adiabatic dissipation of energy and angular momentum causes a star to evolve in quasi-stationary fashion along an evolutionary sequence. Supramassive sequences have masses exceeding the maximum mass of a nonrotating neutron star. A supramassive star evolves toward eventual catastrophic collapse to a black hole. Prior to collapse, the star actually spins up as it loses angular momentum, an effect that may provide an observable precursor to gravitational collapse to a black hole.
Cook, Gregory B.↗
Unified nonparametric equation-of-state inference from the neutron-star crust to perturbative-QCD densities
Perturbative quantum chromodynamics (pQCD), while valid only at densities exceeding those found in the cores of neutron stars, could provide constraints on the dense-matter equation of state (EOS). Here, in this work, we examine the impact of pQCD information on the inference of the EOS using a nonparametric framework based on Gaussian processes (GPs). We examine the application of pQCD constraints through a ``pQCD likelihood,'' and verify the findings of previous works; namely, a softening of the EOS at the central densities of the most massive neutron stars and a reduction in the maximum neutron-star mass. Although the pQCD likelihood can be easily integrated into existing EOS inference frameworks, this approach requires an arbitrary selection of the density at which the constraints are applied. The EOS behavior is also treated differently on either side of the chosen density. To mitigate these issues, we extend the EOS model to higher densities, thereby constructing a ``unified'' description of the EOS from the neutron-star crust to densities relevant for pQCD. In this approach the pQCD constraints effectively become part of the prior. Since the EOS is unconstrained by any calculation or data between the densities applicable to neutron stars and pQCD, we argue for maximum modeling flexibility in that regime. We compare the unified EOS with the traditional pQCD likelihood, and although we confirm the EOS softening, we do not see a reduction in the maximum neutron-star mass or any impact on macroscopic observables. Though residual model dependence cannot be ruled out, we find that pQCD suggests the speed of sound in the densest neutron-star cores has already started decreasing toward the asymptotic limit; we find that the speed of sound squared at the center of the most massive neutron star has an upper bound of $\sim 0.5$ at the 90% level.
equations of state of nuclear matter↗
Non-Equilibrium relaxation, aging scaling, and critical depinning dynamics of skyrmions in disordered magnetic films. Final Report
Technical applications of type-II superconductors, especially high-Tc compounds, in external magnetic fields require an effective flux pinning mechanism to reduce Ohmic losses due to flux creep and flow. Naturally abundant point defects, dislocations, and twin boundaries as well as artificially introduced disorder may serve as effective pinning centers for magnetic vortices. The properties of interacting flux lines subject to strong thermal fluctuations and point-like or extended pinning centers have therefore been a major research focus in condensed matter physics, and considerable progress has been achieved in the characterization and mathematical description of the equilibrium phases and non-equilibrium steady states of vortex matter. Detailed studies of the rich phase diagrams that reveal novel glassy states as well as the associated complex dynamical phenomena have in turn enriched the theoretical understanding of condensed matter systems, elucidating specifically the kinetics of elastic objects driven through disordered media and the important role of topological defects such as vortices and dislocations in various materials.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Impact of the equation of state on f - and p - mode oscillations of neutron stars
We investigate the impact of the neutron-star matter equation of state on the f- and p1-mode oscillations of neutron stars obtained within the Cowling approximation and linearized general relativity. The f- and p 1 -mode oscillation frequencies, and their damping times are calculated using representative sets of Skyrme Hartree-Fock and relativistic mean-field models, all of which reproduce nuclear systematics and support 2M ⊙ neutron stars. Our study shows strong correlations between the frequencies of f- and p 1 -modes and their damping times with the pressure of β-equilibrated matter at densities equal to or slightly higher than the nuclear saturation density ρ 0 . Such correlations are found to be almost independent of the composition of the stars. The frequency of the p 1 -mode of 1.4M ⊙ star is strongly correlated with the slope of the symmetry energy L 0 and β-equilibrated pressure at density ρ 0 . Compared to GR calculations, the error in the Cowling approximation for the f-mode is about 30% for neutron stars of low mass, whereas it decreases with increasing mass. Here, the accuracy of the p 1 -mode is better than 15% for neutron stars of maximum mass, and improves for lower masses and higher number of radial nodes. I.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Non-abelian dark matter solutions for Galactic gamma-ray excess and Perseus 3.5 keV X-ray line
We attempt to explain simultaneously the Galactic center gamma-ray excess and the 3.5 keV X-ray line from the Perseus cluster based on a class of non-abelian SU(2) DM models, in which the dark matter and an excited state comprise a “dark” SU(2) doublet. The non-abelian group kinetically mixes with the standard model gauge group via dimensions-5 operators. The dark matter particles annihilate into standard model fermions, followed by fragmentation and bremsstrahlung, and thus producing a continuous spectrum of gamma-rays. On the other hand, the dark matter particles can annihilate into a pair of excited states, each of which decays back into the dark matter particle and an X-ray photon, which has an energy equal to the mass difference between the dark matter and the excited state, which is set to be 3.5 keV. The large hierarchy between the required X-ray and γ-ray annihilation cross-sections can be achieved by a very small kinetic mixing between the SM and dark sector, which effectively suppresses the annihilation into the standard model fermions but not into the excited state.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Crust-cooling Models Are Insensitive to the Crust–Core Transition Pressure for Realistic Equations of State
Neutron stars cooling after sustained accretion outbursts provide unique information about the neutron star crust and underlying dense matter. Comparisons between astronomical observations of these cooling transients and model calculations of neutron star crust cooling have frequently been used to constrain neutron star properties such as the mass, radius, crust composition, and presence of nuclear pasta. These calculations often use a fixed pressure at which the crust–core transition happens, though this quantity depends on the dense matter equation of state. We demonstrate that varying the crust–core transition pressure in a manner consistent with adopting various equations of state results in modest changes to the crust-cooling light curve. Finally, this validates the approach adopted in most crust-cooling studies to date, where the neutron star mass and radius are varied while leaving the crust–core transition pressure constant.
79 ASTRONOMY AND ASTROPHYSICS↗
Influence of site and soil properties on the DRIFT spectra of northern cold-region soils [Influence of site and soil properties on the mid-infrared spectra of northern cold-region soils]
Here, we investigated the influence of site characteristics and soil properties on the chemical composition of organic matter in soils collected from a latitudinal transect across Alaska through analysis of diffuse reflectance Fourier transform mid infrared (MidIR) spectra of bulk soils. The study included 119 soil samples collected from 28 sites including tundra, boreal forest, and grassland ecosystems. Organic, mineral, and cryoturbated soil horizons, both seasonally and perennially frozen, from a variety of depths and edaphic conditions were examined. The amount and chemical composition of organic matter as well as site and soil properties exerted a strong influence on the MidIR spectra. The spectra were highly sensitive to the extent of organic matter decomposition, enabling the ordination of Oi, Oe and Oa organic horizons. Differences in absorbance intensity for several spectral bands indicated that Oi horizons contained greater abundance of relatively fresh residues, phenolic-OH compounds, aliphatic compounds (waxes, lipids and fats), and carbohydrates. In contrast, Oa horizons had a greater presence of amide groups (possibly from microbial residues), aromatics, C=C bonds, carboxylates and carboxylic acids. Another significant factor differentiating these horizons was the incorporation of clays and silicates into the decomposing organic matter of Oa horizons. Calculated height peak ratios showed a clear trend to greater decomposition among Oi, Oe and Oa. The MidIR spectra were related to many site/soil attributes including land cover type, parent material, and associated factors, such as permafrost presence/absence, soil drainage, horizon depth, bulk density, cation exchange capacity, and pH. Single MidIR spectral bands were identified that might be used in future studies to quickly estimate the organic and inorganic carbon, total nitrogen, and carbon:nitrogen ratios of soils from northern latitudes. Lastly, our results demonstrate that the information contained in MidIR spectra of bulk soil integrates the quantity and chemical composition of soil organic matter with soil forming factors and highlights the potential for using this information to assess the degradation state of organic matter stored in northern cold-region soils.
58 GEOSCIENCES↗
Simultaneous fitting of neutron star structure and cooling data
Using a model for the equation of state and composition of dense matter and the magnitude of singlet proton superconductivity and triplet neutron superfluidity, we perform the first simultaneous fit of neutron star masses and radii determined from observations of quiescent low-mass X-ray binaries and luminosities and ages determined from observations of isolated neutron stars. We find that the Vela pulsar strongly determines the values inferred for the superfluid/superconducting gaps and the neutron star radius. Here, we find, regardless of whether or not the Vela pulsar is included in the analysis, that the threshold density for the direct Urca process lies between the central density of 1.7 and 2 solar mass neutron stars. We also find that 2 solar mass stars are unlikely to cool principally by the direct Urca process because of the suppression by neutron triplet superfluidity.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
QUARK MATTER IN MASSIVE COMPACT STARS
The recent observation of the pulsar PSR J1614-2230 with a mass of 1.97 {+-} 0.04 M{sub sun} gives a strong constraint on the quark and nuclear matter equations of state (EoS). We explore the parameter ranges for a parameterized EoS for quark stars. We find that strange stars, made of absolutely stable strange quark matter, comply with the new constraint only if effects from the strong coupling constant and color-superconductivity are taken into account. Hybrid stars, compact stars with a quark matter core and a hadronic outer layer, can be as massive as 2 M{sub sun}, but only for a significantly limited range of parameters. We demonstrate that the appearance of quark matter in massive stars crucially depends on the stiffness of the nuclear matter EoS. We show that the masses of hybrid stars stay below the ones of hadronic and pure quark stars, due to the softening of the EoS at the quark-hadron phase transition.
79 ASTRONOMY AND ASTROPHYSICS↗
Robustness of neutron star merger simulations to changes in neutrino transport and neutrino-matter interactions
Binary neutron star mergers play an important role in nuclear astrophysics: Their gravitational wave and electromagnetic signals carry information about the equation of state of cold matter above nuclear saturation density, and they may be one of the main sources of r-process elements in the Universe. Neutrino-matter interactions during and after merger impact the properties of these electromagnetic signals and the relative abundances of the produced r-process elements. Existing merger simulations are, however, limited in their ability to realistically model neutrino transport and neutrino-matter interactions. Here, we perform a comparison of the impact of the use of state-of-the art two-moment or Monte Carlo transport schemes on the outcome of merger simulations, for a single binary neutron star system with a short-lived neutron star remnant [(5–10) ms]. We also investigate the use of different reaction rates in the simulations. While the best transport schemes generally agree well on the qualitative impact of neutrinos on the system, differences in the behavior of the high-density regions can significantly impact the collapse time and the properties of the hot tidal arms in this metastable merger remnant. The chosen interaction rates and transport algorithm as well as recent improvements by Radice et al. to the two-moment algorithms can all contribute to changes at the (10–30)% level in the global properties of the merger remnant and outflows. Furthermore, the limitations of previous moment schemes fixed by Radice et al. also appear sufficient to explain the large difference that we observed in the production of heavy-lepton neutrinos in a previous comparison of Monte Carlo and moment schemes in the context of a low-mass binary neutron star system.
79 ASTRONOMY AND ASTROPHYSICS↗
The EOS of neutron matter, and the effect of Lambda hyperons to neutron star structure
The following topics are addressed: the model and the method; equation of state of neutron matter, role of three-neutron force; symmetry energy; Λ-hypernuclei; Λ-neutron matter; and neutron star structure. In summary, quantum Monte Carlo methods are useful to study nuclear systems in a coherent framework; the three-neutron force is the bridge between E sym and neutron star structure; and neutron star observations are becoming competitive with experiments. Λ-nucleon data are very limited, but ΛNN is very important. The role of Λ in neutron stars is far from understood; more ΛN data are needed. The author's conclusion: We cannot conclude anything with present models.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Cold quark matter in compact stars
We used an equation of state for the cold quark matter to the study of properties of quark stars. We also discuss the absolute stability of quark matter and compute the mass-radius relation for self-bound stars.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
From hadrons to quarks in neutron stars: a review
In recent years our understanding of neutron stars has advanced remarkably, thanks to research converging from many directions. The importance of understanding neutron star behavior and structure has been underlined by the recent direct detection of gravitational radiation from merging neutron stars. The clean identification of several heavy neutron stars, of order two solar masses, challenges our current understanding of how dense matter can be sufficiently stiff to support such a mass against gravitational collapse. Furthermore, programs underway to determine simultaneously the mass and radius of neutron stars will continue to constrain and inform theories of neutron star interiors. At the same time, an emerging understanding in quantum chromodynamics (QCD) of how nuclear matter can evolve into deconfined quark matter at high baryon densities is leading to advances in understanding the equation of state of the matter under the extreme conditions in neutron star interiors.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Inner bremsstrahlung as a source of X-rays in the steady-state universe.
Consideration of the compatibility of matter creation in steady-state cosmology with certain X-ray observations. It is shown that, because of inner bremsstrahlung from neutron decay, the steady-state universe with neutron creation in diffuse regions is inconsistent with X-ray observations around 100 keV, unless the particle density of the universe is less than 0.1 per cu m.
Petrosian, V.↗