731 research outputs found
Accessibility of color superconducting quark matter phases in heavy-ion collisions
We discuss a hybrid equation of state (EoS) that fulfills constraints for
mass-radius relationships and cooling of compact stars. The quark matter EoS is
obtained from a Polyakov-loop Nambu--Jona-Lasinio (PNJL) model with color
superconductivity, and the hadronic one from a relativistic mean-field (RMF)
model with density-dependent couplings (DD-RMF). For the construction of the
phase transition regions we employ here for simplicity a Maxwell construction.
We present the phase diagram for symmetric matter which exhibits two remarkable
features: (1) a "nose"-like structure of the hadronic-to-quark matter phase
border with an increase of the critical density at temperatures below T ~ 150
MeV and (2) a high critical temperature for the border of the two-flavor color
superconducting (2SC) phase, T_c > 160 MeV. We show the trajectories of
heavy-ion collisions in the plane of excitation energy vs. baryon density
calculated using the UrQMD code and conjecture that for incident energies of 4
... 8 A GeV as provided, e.g., by the Nuclotron-M at JINR Dubna or by lowest
energies at the future heavy-ion collision experiments CBM@FAIR and NICA@JINR,
the color superconducting quark matter phase becomes accessible.Comment: 5 pages, 1 figure, Poster presented at the XXVI. Max Born Symposium
"Three Days of Strong Interactions", Wroclaw (Poland), July 9-11, 200
Color superconducting quark matter in compact stars
Recent indications for high neutron star masses (M \sim 2 M_sun) and large
radii (R > 12 km) could rule out soft equations of state and have provoked a
debate whether the occurence of quark matter in compact stars can be excluded
as well. We show that modern quantum field theoretical approaches to quark
matter including color superconductivity and a vector meanfield allow a
microscopic description of hybrid stars which fulfill the new, strong
constraints. For these objects color superconductivity turns out to be an
essential ingredient for a successful description of the cooling phenomenology
in accordance with recently developed tests. We discuss the energy release in
the neutrino untrapping transition as a new aspect of the problem that hybrid
stars masquerade themselves as neutron stars. Quark matter searches in future
generations of low-temperature/high-density nucleus-nucleus collision
experiments such as low-energy RHIC and CBM @ FAIR might face the same problem
of an almost crossover behavior of the deconfinement transition. Therefore,
diagnostic tools shall be derived from effects of color superconductivity.Comment: 8 pages, 3 figures, To appear in the proceedings of EXOCT 2007:
International Symposium on Exotic States of Nuclear Matter, Catania, Italy,
11-15 Jun 200
Unexpected Structures for Intercalation of Sodium in Epitaxial Graphene-SiC Interfaces
We show using scanning tunneling microscopy, spectroscopy, and ab initio
calculations that several intercalation structures exist for Na in epitaxial
graphene on SiC(0001). Intercalation takes place at room temperature and Na
electron-dopes the graphene. It intercalates in-between single-layer graphene
and the carbon-rich interfacial layer. It also penetrates beneath the
interfacial layer and decouples it to form a second graphene layer. This
decoupling is accelerated by annealing and is verified by direct Na deposition
onto the interface layer. Our observations show that intercalation in graphene
is fundamentally different than in graphite and is a versatile means of
electronic control.Comment: 10 pages text, 2 pages, references, and 4 figure page
Neutron Stars and the High Density Equation of State
One of the key ingredients to understand the properties of neutrons stars is
the equation of state at finite densities far beyond nuclear saturation.
Investigating the phase structure of quark matter that might be realized in the
core of NS inspires theory and observation. We discuss recent results of our
work to point out our view on challenges and possibilities in this evolving
field by means of a few examples.Comment: 10 pages, 6 figures, Proc. 5th ANL/MSU/JINA/INT FRIB Workshop on Bulk
Nuclear Properties, E. Lansing, Nov. 19-22, 200
Differences in reef fish assemblages between populated and remote reefs spanning multiple archipelagos across the central and western Pacific
Comparable information on the status of natural resources across large geographic and human impact scales provides invaluable context to ecosystem-based management and insights into processes driving differences among areas. Data on fish assemblages at 39 US flag coral reef-areas distributed across the Pacific are presented. Total reef fish biomass varied by more than an order of magnitude: lowest at densely-populated islands and highest on reefs distant from human populations. Remote reefs (<50 people within 100 km) averaged ~4 times the biomass of “all fishes” and 15 times the biomass of piscivores compared to reefs near populated areas. Greatest within-archipelagic differences were found in Hawaiian and Mariana Archipelagos, where differences were consistent with, but likely not exclusively driven by, higher fishing pressure around populated areas. Results highlight the importance of the extremely remote reefs now contained within the system of Pacific Marine National Monuments as ecological reference areas
The observational legacy of preon stars - probing new physics beyond the LHC
We discuss possible ways to observationally detect the superdense cosmic
objects composed of hypothetical sub-constituent fermions beneath the
quark/lepton level, recently proposed by us. The characteristic mass and size
of such objects depend on the compositeness scale, and their huge density
cannot arise within a context of quarks and leptons alone. Their eventual
observation would therefore be a direct vindication of physics beyond the
standard model of particle physics, possibly far beyond the reach of the Large
Hadron Collider (LHC), in a relatively simple and inexpensive manner. If relic
objects of this type exist, they can possibly be detected by present and future
x-ray observatories, high-frequency gravitational wave detectors, and
seismological detectors. To have a realistic detection rate, i.e., to be
observable, they must necessarily constitute a significant fraction of cold
dark matter.Comment: 8 pages, 4 figures. Added one reference [24]. Reformulated the
discussion at the end of Section II. Accepted for publication in Phys. Rev.
The Chandra X-ray Survey of Planetary Nebulae (ChanPlaNS): Probing Binarity, Magnetic Fields, and Wind Collisions
We present an overview of the initial results from the Chandra Planetary
Nebula Survey (ChanPlaNS), the first systematic (volume-limited) Chandra X-ray
Observatory survey of planetary nebulae (PNe) in the solar neighborhood. The
first phase of ChanPlaNS targeted 21 mostly high-excitation PNe within ~1.5 kpc
of Earth, yielding 4 detections of diffuse X-ray emission and 9 detections of
X-ray-luminous point sources at the central stars (CSPNe) of these objects.
Combining these results with those obtained from Chandra archival data for all
(14) other PNe within ~1.5 kpc that have been observed to date, we find an
overall X-ray detection rate of ~70%. Roughly 50% of the PNe observed by
Chandra harbor X-ray-luminous CSPNe, while soft, diffuse X-ray emission tracing
shocks formed by energetic wind collisions is detected in ~30%; five objects
display both diffuse and point-like emission components. The presence of X-ray
sources appears correlated with PN density structure, in that molecule-poor,
elliptical nebulae are more likely to display X-ray emission (either point-like
or diffuse) than molecule-rich, bipolar or Ring-like nebulae. All but one of
the X-ray point sources detected at CSPNe display X-ray spectra that are harder
than expected from hot (~100 kK) central star photospheres, possibly indicating
a high frequency of binary companions to CSPNe. Other potential explanations
include self-shocking winds or PN mass fallback. Most PNe detected as diffuse
X-ray sources are elliptical nebulae that display a nested shell/halo structure
and bright ansae; the diffuse X-ray emission regions are confined within inner,
sharp-rimmed shells. All sample PNe that display diffuse X-ray emission have
inner shell dynamical ages <~5x10^3 yr, placing firm constraints on the
timescale for strong shocks due to wind interactions in PNe.Comment: 41 pages, 6 figures; submitted to the Astronomical Journa
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.Comment: 51 pages, to appear in J. Phys. G as Topical Revie
How strange are compact star interiors ?
We discuss a Nambu--Jona-Lasinio (NJL) type quantum field theoretical
approach to the quark matter equation of state with color superconductivity and
construct hybrid star models on this basis. It has recently been demonstrated
that with increasing baryon density, the different quark flavors may occur
sequentially, starting with down-quarks only, before the second light quark
flavor and at highest densities also the strange quark flavor appears. We find
that color superconducting phases are favorable over non-superconducting ones
which entails consequences for thermodynamic and transport properties of hybrid
star matter. In particular, for NJL-type models no strange quark matter phases
can occur in compact star interiors due to mechanical instability against
gravitational collapse, unless a sufficiently strong flavor mixing as provided
by the Kobayashi-Maskawa-'t Hooft determinant interaction is present in the
model. We discuss observational data on mass-radius relationships of compact
stars which can put constraints on the properties of dense matter equation of
state.Comment: 7 pages, 2 figures, to appear in the Proceedings of the International
Conference SQM2009, Buzios, Rio de Janeiro, Brazil, Sep.27-Oct.2, 200
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