4,759 research outputs found
The phase diagram of QCD with four degenerate quarks
We revisit the determination of the pseudo-critical line of QCD with four
degenerate quarks at non-zero temperature and baryon density by the method of
analytic continuation. We determine the pseudo-critical couplings at imaginary
chemical potentials by high-statistics Monte Carlo simulations and reveal
deviations from the simple quadratic dependence on the chemical potential
visible in earlier works on the same subject. Finally, we discuss the
implications of our findings for the shape of the pseudo-critical line at real
chemical potential, comparing different possible extrapolations.Comment: 8 pages, 8 figures, 2 table
Masses of the Bottom-Charm Hybrid States
QCD sum rules are used to study the mass spectrum of bottom-charm hybrid
systems. The correlation functions and the spectral densities are
calculated up to dimension six condensates at leading order of for
several quantum numbers. After performing the QCD sum rule analysis, we
predict the masses of the
bottom-charm hybrids. These mass predictions show a similar supermultiplet
structure as the bottomonium and charmonium hybrids. Using the QCD sum-rule
mass predictions we analyze the possible hadronic decay patterns of the , and hybrids including the open-flavour and
hidden-flavour mechanisms.Comment: 14 pages, 8 figures, 6 tables. Version to appear in Journal of
Physics
The critical line of two-flavor QCD at finite isospin or baryon densities from imaginary chemical potentials
We determine the (pseudo)critical lines of QCD with two degenerate staggered
fermions at nonzero temperature and quark or isospin density, in the region of
imaginary chemical potentials; analytic continuation is then used to prolongate
to the region of real chemical potentials. We obtain an accurate determination
of the curvatures at zero chemical potential, quantifying the deviation between
the case of finite quark and of finite isospin chemical potential. Deviations
from a quadratic dependence of the pseudocritical lines on the chemical
potential are clearly seen in both cases: we try different extrapolations and,
for the case of nonzero isospin chemical potential, confront them with the
results of direct Monte Carlo simulations. Finally we find that, as for the
finite quark density case, an imaginary isospin chemical potential can
strengthen the transition till turning it into strong first order.Comment: 11 pages, 11 figures, 4 table
Monte Carlo simulation of SU(2) Yang-Mills theory with light gluinos
In a numerical Monte Carlo simulation of SU(2) Yang-Mills theory with light
dynamical gluinos the low energy features of the dynamics as confinement and
bound state mass spectrum are investigated. The motivation is supersymmetry at
vanishing gluino mass. The performance of the applied two-step multi-bosonic
dynamical fermion algorithm is discussed.Comment: latex, 48 pages, 16 figures with epsfi
Impact of Numerical Relativity information on effective-one-body waveform models
We present a comprehensive comparison of the spin-aligned effective-one-body
(EOB) waveform model of Nagar et al. [Phys. Rev. D93, 044046 (2016)], informed
using 40 numerical-relativity (NR) datasets, against a set of 149, ,
NR waveforms freely available through the Simulation Extreme Spacetime (SXS)
catalog. We find that, without further calibration, these EOBNR waveforms have
unfaithfulness (at design Advanced-LIGO sensitivity and evaluated with total
mass varying as ) always below
against all NR waveforms except for three outliers, that still never exceed the
level; with a minimal retuning of the (effective)
next-to-next-to-next-to-leading-order spin-orbit coupling parameter for the
non-equal-mass and non-equal-spin sector, that only needs three more NR
waveforms, one is left with another two (though different) outliers, with
maximal unfaithfulness of up to only for a total mass of . We
show this is the effect of slight inaccuracies in the phenomenological
description of the postmerger waveform of Del Pozzo and Nagar
[arXiv:1606.03952] that was constructed by interpolating over only 40NR
simulations. We argue that this is easily fixed by using either an alternative
ringdown description (e.g., the superposition of quasi-normal-modes) or an
improved version of the phenomenological representation. By analyzing a NR
waveform with mass ratio and dimensionless spins obtained with the
BAM code, we conclude that the model would benefit from NR simulations
specifically targeted at improving the postmerger-ringdown phenomenological
fits for mass ratios and spins .Comment: 24 pages, 20 figures, submitted to Phys. Rev.
Advances in QCD sum rule calculations
We review the recent progress in the applications of QCD sum rules to hadron
properties with the emphasis on the following selected problems: (i)
development of new algorithms for the extraction of ground-state parameters
from two-point correlators; (ii) form factors at large momentum transfers from
three-point vacuum correlation functions; (iii) properties of exotic tetraquark
hadrons from correlation functions of four-quark currents.Comment: 12 pages, plenary talk given at the XIth International Conference on
Quark Confinement and the Hadron Spectrum, Saint Petersburg, Russia,
September 8-12, 201
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