16,846 research outputs found
QCD at high baryon density in a random matrix model
A high density diquark phase seems to be a generic feature of QCD. If so it
should also be reproduced by random matrix models. We discuss a specific one in
which the random matrix elements of the Dirac operator are supplemented by a
finite chemical potential and by non-random elements which model the formation
of instanton-anti-instanton molecules. Comparing our results to those found in
a previous investigation by Vanderheyden and Jackson we find additional support
for our starting assumption, namely that the existence of a high density
diquark phase is common to all QCD-like models.Comment: 16 pages, 4 figures, final version to appear in Eur.Phys.J.
The Tunneling Hybrid Monte-Carlo algorithm
The hermitian Wilson kernel used in the construction of the domain-wall and
overlap Dirac operators has exceptionally small eigenvalues that make it
expensive to reach high-quality chiral symmetry for domain-wall fermions, or
high precision in the case of the overlap operator. An efficient way of
suppressing such eigenmodes consists of including a positive power of the
determinant of the Wilson kernel in the Boltzmann weight, but doing this also
suppresses tunneling between topological sectors. Here we propose a
modification of the Hybrid Monte-Carlo algorithm which aims to restore
tunneling between topological sectors by excluding the lowest eigenmodes of the
Wilson kernel from the molecular-dynamics evolution, and correcting for this at
the accept/reject step. We discuss the implications of this modification for
the acceptance rate.Comment: improved discussion in appendix B, RevTeX, 19 page
Diffractive charged meson pair production
We investigate the possibility to measure the nonforward gluon distribution
function by means of diffractively produced \pi^+\pi^- and K^+K^- pairs in
polarized lepton nucleon scattering. The resulting cross sections are small and
are dominated by the gluonic contribution. We find relatively large spin
asymmetries, both for \pi^+\pi^- and for K^+K^- pairs.Comment: 15 pages, version with changed kinematical cuts, to be pubished in
Phys.Lett.
From X-ray dips to eclipse: Witnessing disk reformation in the recurrent nova USco
The 10th recorded outburst of the recurrent eclipsing nova USco was observed
simultaneously in X-ray, UV, and optical by XMM-Newton on days 22.9 and 34.9
after outburst. Two full passages of the companion in front of the nova ejecta
were observed, witnessing the reformation of the accretion disk. On day 22.9,
we observed smooth eclipses in UV and optical but deep dips in the X-ray light
curve which disappeared by day 34.9, then yielding clean eclipses in all bands.
X-ray dips can be caused by clumpy absorbing material that intersects the line
of sight while moving along highly elliptical trajectories. Cold material from
the companion could explain the absence of dips in UV and optical light. The
disappearance of X-ray dips before day 34.9 implies significant progress in the
formation of the disk. The X-ray spectra contain photospheric continuum
emission plus strong emission lines, but no clear absorption lines. Both
continuum and emission lines in the X-ray spectra indicate a temperature
increase from day 22.9 to day 34.9. We find clear evidence in the spectra and
light curves for Thompson scattering of the photospheric emission from the
white dwarf. Photospheric absorption lines can be smeared out during scattering
in a plasma of fast electrons. We also find spectral signatures of resonant
line scattering that lead to the observation of the strong emission lines.
Their dominance could be a general phenomenon in high-inclination systems such
as Cal87.Comment: Submitted to ApJ. 16 pages, 16 figure
QCD critical region and higher moments for three flavor models
One of the distinctive feature of the QCD phase diagram is the possible
emergence of a critical endpoint. The critical region around the critical point
and the path dependency of the critical exponents is investigated within
effective chiral (2+1)-flavor models with and without Polyakov-loops. Results
obtained in no-sea mean-field approximations where a divergent vacuum part in
the fermion-loop contribution is neglected, are confronted to the renormalized
ones. Furthermore, the modifications caused by the back-reaction of the matter
fluctuations on the pure Yang-Mills system are discussed. Higher order,
non-Gaussian moments of event-by-event distributions of various particle
multiplicities are enhanced near the critical point and could serve as a probe
to determine its location in the phase diagram. By means of a novel derivative
technique higher order generalized quark-number susceptibilities are calculated
and their sign structure in the phase diagram is analyzed.Comment: 12 pages, 11 figures. Final PRD version (references and one more
equation added
Ultracold collisions between two light indistinguishable diatomic molecules: elastic and rotational energy transfer in HD+HD
A close coupling quantum-mechanical calculation is performed for rotational
energy transfer in a HD+HD collision at very low energy, down to the ultracold
temperatures: K. A global six-dimensional H-H
potential energy surface is adopted from a previous work [Boothroyd {\it et
al.}, J. Chem. Phys., {\bf 116}, 666 (2002).] State-resolved integral cross
sections of different
quantum-mechanical rotational transitions in the HD
molecules and corresponding state-resolved thermal rate coefficients
have been computed. Additionally, for comparison,
H+H calculations for a few selected rotational transitions have also
been performed. The hydrogen and deuterated hydrogen molecules are treated as
rigid rotors in this work. A pronounced isotope effect is identified in the
cross sections of these collisions at low and ultracold temperatures.Comment: 9 pages, 9 figures. Accepted for publication in Physical Review
Near-infrared studies of the 2010 outburst of the recurrent nova U Scorpii
We present near-infrared (near-IR) observations of the 2010 outburst of U Sco. JHK photometry is presented on 10 consecutive days starting from 0.59 d after outburst. Such photometry can gainfully be integrated into a larger data base of other multiwavelength data which aim to comprehensively study the evolution of U Sco. Early near-IR spectra, starting from 0.56 d after outburst, are presented and their general characteristics discussed. Early in the eruption, we see very broad wings in several spectral lines, with tails extending up to ∼10 000 km s−1 along the line of sight; it is unexpected to have a nova with ejection velocities equal to those usually thought to be exclusive to supernovae. From recombination analysis, we estimate an upper limit of [inline image] for the ejected mass
Clinical Reasoning: A 71-year-old woman with subacute progressive distal weakness and paresthesia after vaccination.
info:eu-repo/semantics/publishedVersio
The -parameter in 3-flavour QCD and by the ALPHA collaboration
We present results by the ALPHA collaboration for the -parameter in
3-flavour QCD and the strong coupling constant at the electroweak scale,
, in terms of hadronic quantities computed on the CLS gauge
configurations. The first part of this proceedings contribution contains a
review of published material \cite{Brida:2016flw,DallaBrida:2016kgh} and yields
the -parameter in units of a low energy scale, . We
then discuss how to determine this scale in physical units from experimental
data for the pion and kaon decay constants. We obtain MeV which translates to
using perturbation theory to match between 3-, 4- and 5-flavour QCD.Comment: 21 pages. Collects contributions of A. Ramos, S. Sint and R. Sommer
to the 34th annual International Symposium on Lattice Field Theory; LaTeX
input encoding problem fixe
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