927 research outputs found
Dense matter equation of state for neutron star mergers
In simulations of binary neutron star mergers, the dense matter equation of
state (EOS) is required over wide ranges of density and temperature as well as
under conditions in which neutrinos are trapped, and the effects of magnetic
fields and rotation prevail. Here we assess the status of dense matter theory
and point out the successes and limitations of approaches currently in use. A
comparative study of the excluded volume (EV) and virial approaches for the
system using the equation of state of Akmal, Pandharipande and
Ravenhall for interacting nucleons is presented in the sub-nuclear density
regime. Owing to the excluded volume of the -particles, their mass
fraction vanishes in the EV approach below the baryon density 0.1 fm,
whereas it continues to rise due to the predominantly attractive interactions
in the virial approach. The EV approach of Lattimer et al. is extended here to
include clusters of light nuclei such as d, H and He in addition to
-particles. Results of the relevant state variables from this
development are presented and enable comparisons with related but slightly
different approaches in the literature. We also comment on some of the sweet
and sour aspects of the supra-nuclear EOS. The extent to which the neutron star
gravitational and baryon masses vary due to thermal effects, neutrino trapping,
magnetic fields and rotation are summarized from earlier studies in which the
effects from each of these sources were considered separately. Increases of
about occur for rigid (differential) rotation with
comparable increases occurring in the presence of magnetic fields only for
fields in excess of Gauss. Comparatively smaller changes occur due to
thermal effects and neutrino trapping. Some future studies to gain further
insight into the outcome of dynamical simulations are suggested.Comment: Revised manuscript with one additional figure and previous Fig. 4
replaced, 19 additional references and new tex
Generalized seniority for the shell model with realistic interactions
The generalized seniority scheme has long been proposed as a means of
dramatically reducing the dimensionality of nuclear shell model calculations,
when strong pairing correlations are present. However, systematic benchmark
calculations, comparing results obtained in a model space truncated according
to generalized seniority with those obtained in the full shell model space, are
required to assess the viability of this scheme. Here, a detailed comparison is
carried out, for semimagic nuclei taken in a full major shell and with
realistic interactions. The even-mass and odd-mass Ca isotopes are treated in
the generalized seniority scheme, for generalized seniority v<=3. Results for
level energies, orbital occupations, and electromagnetic observables are
compared with those obtained in the full shell model space.Comment: 13 pages, 8 figures; published in Phys. Rev.
Singlet vs Nonsinglet Perturbative Renormalization factors of Staggered Fermion Bilinears
In this paper we present the perturbative computation of the difference
between the renormalization factors of flavor singlet
(, : flavor index) and nonsinglet
() bilinear quark operators
(where ) on the lattice. The computation is performed to
two loops and to lowest order in the lattice spacing, using Symanzik improved
gluons and staggered fermions with twice stout-smeared links. The stout
smearing procedure is also applied to the definition of bilinear operators. A
significant part of this work is the development of a method for treating some
new peculiar divergent integrals stemming from the staggered formalism. Our
results can be combined with precise simulation results for the renormalization
factors of the nonsinglet operators, in order to obtain an estimate of the
renormalization factors for the singlet operators. The results have been
published in Physical Review D.Comment: 8 pages, 3 figures, 2 tables, Proceedings of the 35th International
Symposium on Lattice Field Theory, 18-24 June 2017, Granada, Spai
Nucleon form factors and moments of parton distributions in twisted mass lattice QCD
We present results on the electroweak form factors and on the lower moments
of parton distributions of the nucleon, within lattice QCD using two dynamical
flavors of degenerate twisted mass fermions. Results are obtained on lattices
with three different values of the lattice spacings, namely a=0.089 fm, a=0.070
fm and a=0.056 fm, allowing the investigation of cut-off effects. The volume
dependence is examined by comparing results on two lattices of spatial length
L=2.1 fm and L=2.8 fm. The simulations span pion masses in the range of 260-470
MeV. Our results are renormalized non-perturbatively and the values are given
in the MS-scheme at a scale mu=2 GeV.Comment: Talk presented in the XXIst International Europhysics Conference on
High Energy Physics, 21-27 July 2011, Grenoble, Rhones Alpes Franc
The nucleon spin and momentum decomposition using lattice QCD simulations
We determine within lattice QCD, the nucleon spin carried by valence and sea
quarks, and gluons. The calculation is performed using an ensemble of gauge
configurations with two degenerate light quarks with mass fixed to
approximately reproduce the physical pion mass. We find that the total angular
momentum carried by the quarks in the nucleon is and the gluon contribution is giving a total of consistent with the spin sum. For the quark intrinsic spin contribution
we obtain . All quantities are given in the scheme at
2~GeV. The quark and gluon momentum fractions are also computed and add up to
satisfying the momentum sum.Comment: Version published in PR
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