653 research outputs found
Unified equation of state for neutron stars on a microscopic basis
We derive a new equation of state (EoS) for neutron stars (NS) from the outer
crust to the core based on modern microscopic Brueckner-Hartree-Fock (BHF)
calculations using the Argonne potential plus three-body forces
computed with the Urbana model. To deal with the inhomogeneous structures of
matter in the NS crust, we use the recent Barcelona-Catania-Paris-Madrid (BCPM)
nuclear energy density functional that is directly based on the same
microscopic BHF calculations, and which is able to reproduce the ground-state
properties of nuclei along the periodic table. The EoS of the outer crust
requires the masses of neutron-rich nuclei, which are obtained through
Hartree-Fock-Bogoliubov calculations with the BCPM functional when they are
unknown experimentally. To compute the inner crust, Thomas-Fermi calculations
in Wigner-Seitz cells are performed with the same functional. Existence of
nuclear pasta is predicted in a range of average baryon densities between
0.067 fm and 0.0825 fm, where the transition to
the core takes place. The NS core is computed from the nuclear EoS of the BHF
calculation assuming non-exotic constituents (core of matter). In each
region of the star, we discuss the comparison of the new EoS with previous
EoSes for the complete NS structure, in particular, with the Lattimer-Swesty
EoS and with the Shen et al. EoS widely used in astrophysical calculations. The
new microscopically derived EoS fulfills at the same time a NS maximum mass of
2~ with a radius of 10 km, and a 1.5~ NS with a radius of
11.7 km.Comment: 23 pages, 17 figures, revised version accepted for publication in
Astronomy & Astrophysic
Gauge potential singularities and the gluon condensate at finite temperatures
The continuum limit of SU(2) lattice gauge theory is carefully investigated
at zero and at finite temperatures. It is found that the continuum gauge field
has singularities originating from center degrees of freedom being discovered
in Landau gauge. Our numerical results show that the density of these
singularities properly extrapolates to a non-vanishing continuum limit. The
action density of the non-trivial Z_2 links is tentatively identified with the
gluon condensate. We find for temperatures larger than the deconfinement
temperature that the thermal fluctuations of the embedded Z_2 gauge theory
result in an increase of the gluon condensate with increasing temperature.Comment: 3 pages, 2 figures, talk presented by K. Langfeld at the 19th
International Symposium on Lattice Field Theory (LATTICE2001), Berlin,
19.-24.8.2001, to appear in the proceeding
A holistic multimodal approach to the non-invasive analysis of watercolour paintings
A holistic approach using non-invasive multimodal imaging and spectroscopic techniques to study the materials (pigments, drawing materials and paper) and painting techniques of watercolour paintings is presented. The non-invasive imaging and spectroscopic techniques include VIS-NIR reflectance spectroscopy and multispectral imaging, micro-Raman spectroscopy, X-ray fluorescence spectroscopy (XRF) and optical coherence tomography (OCT). The three spectroscopic techniques complement each other in pigment identification. Multispectral imaging (near infrared bands), OCT and micro-Raman complement each other in the visualisation and identification of the drawing material. OCT probes the microstructure and light scattering properties of the substrate while XRF detects the elemental composition that indicates the sizing methods and the filler content . The multiple techniques were applied in a study of forty six 19th century Chinese export watercolours from the Victoria & Albert Museum (V&A) and the Royal Horticultural Society (RHS) to examine to what extent the non-invasive analysis techniques employed complement each other and how much useful information about the paintings can be extracted to address art conservation and history questions
Two-loop critical mass for Wilson fermions
We have redone a recent two-loop computation of the critical mass for Wilson
fermions in lattice QCD by evaluating Feynman integrals with the
coordinate-space method. We present the results for different types of infrared
regularization. We confirm both the previous numerical estimates and the power
of the coordinate-space method whenever high accuracy is needed.Comment: 13 LaTeX2e pages, 2 ps figures include
Structure of hybrid protoneutron stars within the Nambu--Jona-Lasinio model
We investigate the structure of protoneutron stars (PNS) formed by hadronic
and quark matter in -equilibrium described by appropriate equations of
state (EOS). For the hadronic matter, we use a finite temperature EOS based on
the Brueckner-Bethe-Goldstone many-body theory, with realistic two- and
three-body forces. For the quark sector, we employ the Nambu--Jona-Lasinio
model. We find that the maximum allowed masses are comprised in a narrow range
around 1.8 solar masses, with a slight dependence on the temperature.
Metastable hybrid protoneutron stars are not found.Comment: 7 pages, 6 figures, revised version accepted for publication in Phys.
Rev.
Hybrid protoneutron stars with the MIT bag model
We study the hadron-quark phase transition in the interior of protoneutron
stars. For the hadronic sector, we use a microscopic equation of state
involving nucleons and hyperons derived within the finite-temperature
Brueckner-Bethe-Goldstone many-body theory, with realistic two-body and
three-body forces. For the description of quark matter, we employ the MIT bag
model both with a constant and a density-dependent bag parameter. We calculate
the structure of protostars with the equation of state comprising both phases
and find maximum masses below 1.6 solar masses. Metastable heavy hybrid
protostars are not found.Comment: 12 pages, 9 figures submitted to Phys. Rev.
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