280 research outputs found
Cautionary remarks on the moduli space metric for multi-dyon simulations
We perform a detailed numerical investigation of the approximate moduli space
metric proposed by Diakonov and Petrov [arXiv:0704.3181] for a confining model
of dyons. Our findings strongly indicate that only for a small number of dyons
at sufficiently low density this metric is positive definite - and, therefore,
a valid moduli space metric - throughout a considerable part of configuration
space. This poses strong limitations on results obtained by an unrestricted
integration over collective coordinates in this model. It also indicates that
strong correlations between collective coordinates will be essential for the
physical content of a dyon model, which could be exhibited by a suitable
simulation algorithm.Comment: 20 pages, 6 figure
Local CP-violation and electric charge separation by magnetic fields from lattice QCD
We study local CP-violation on the lattice by measuring the local correlation
between the topological charge density and the electric dipole moment of
quarks, induced by a constant external magnetic field. This correlator is found
to increase linearly with the external field, with the coefficient of
proportionality depending only weakly on temperature. Results are obtained on
lattices with various spacings, and are extrapolated to the continuum limit
after the renormalization of the observables is carried out. This
renormalization utilizes the gradient flow for the quark and gluon fields. Our
findings suggest that the strength of local CP-violation in QCD with physical
quark masses is about an order of magnitude smaller than a model prediction
based on nearly massless quarks in domains of constant gluon backgrounds with
topological charge. We also show numerical evidence that the observed local
CP-violation correlates with spatially extended electric dipole structures in
the QCD vacuum.Comment: 19 pages, 7 figures. Additional lattice results about the induced
electric dipole structure, extended model description, specified terminology.
Version published in JHE
Chiral condensate and dressed Polyakov loop in the Nambu--Jona-Lasinio model
We investigate the chiral condensate and the dressed Polyakov loop or dual
chiral condensate at finite temperature and density in two-flavor
Nambu--Jona-Lasinio model. The dressed Polyakov loop is regarded as an
equivalent order parameter of deconfinement phase transition in a confining
theory. We find the behavior of dressed Polyakov loop in absence of any
confinement mechanism is quite interesting, with only quark degrees of freedom
present, it still shows an order parameter like behavior. It is found that in
the chiral limit, the critical temperature for chiral phase transition
coincides with that of the dressed Polyakov loop in the whole plane.
In the case of explicit chiral symmetry breaking, it is found that the
transition temperature for chiral restoration is smaller than that
of the dressed Polyakov loop in the low baryon density region
where the transition is a crossover. With the increase of current quark mass
the difference between the two transition temperatures is found to be
increasing. However, the two critical temperatures coincide in the high baryon
density region where the phase transition is of first order. We give an
explanation on the feature of in the case of 1st and
2nd order phase transitions, and in the case of
crossover, and expect this feature is general and can be extended to full QCD
theory. Our result might indicate that in the case of crossover, there exists a
small region where chiral symmetry is restored but the color degrees of freedom
are still confined.Comment: 7 pages, 10 figure
Thermodynamic properties of QCD in external magnetic fields
We consider the effect of strong external electromagnetic fields on
thermodynamic observables in QCD, through lattice simulations with 1+1+1
flavors of staggered quarks at physical quark masses. Continuum extrapolated
results are presented for the light quark condensates and for their tensor
polarizations, as functions of the temperature and the magnetic field. We find
the light condensates to undergo inverse magnetic catalysis in the transition
region, in a manner that the transition temperature decreases with growing
magnetic field. We also compare the results to other approaches and lattice
simulations. Furthermore, we relate the tensor polarization to the spin part of
the magnetic susceptibility of the QCD vacuum, and show that this contribution
is diamagnetic.Comment: 13 pages, 9 figures, talks presented by FB and GE at Xth Quark
Confinement and the Hadron Spectrum, 8-12 October 2012, TUM Campus Garching,
Munich, German
Dressed Polyakov loop and flavor dependent phase transitions
The chiral condensate and dressed Polyakov loop at finite temperature and
density have been investigated in the framework of Nf = 2+1 Nambu-Jona-Lasinio
(NJL) model with two degenerate u, d quarks and one strange quark. In the case
of explicit chiral symmetry breaking with physical quark masses, it is found
that the phase transitions for light u, d quarks and s quark are sequentially
happened, and the separation between the transition lines for different flavors
becomes wider and wider with the increase of baryon density. For each flavor,
the pseudo-critical temperatures for chiral condensate and dressed Polyakov
loop differ in a narrow transition range in the lower baryon density region,
and the two transitions coincide in the higher baryon density region.Comment: 9 pages, 9 figures; Version accepted in Phys. Rev.
Groping in the Dark: The First Decade of Global Modelling
This book is the real life history of global modelling. It is concerned with the major models and those who make them, the whole craft of modelling, and their principal results. A feature is the honesty, candour, and clarity with which the authors discuss what global modelling taught them about modelling and what it taught them about the world. It could be described as a book on the sociology of a new science struggling with problems too large for the participants but too important to ignore.
This book is written for those who make complex models of complex social systems, those who have to make these systems work, and those who live in and care about the social systems that modellers make and about which decision makers make decisions
QCD quark condensate in external magnetic fields
We present a comprehensive analysis of the light condensates in QCD with
1+1+1 sea quark flavors (with mass-degenerate light quarks of different
electric charges) at zero and nonzero temperatures of up to 190 MeV and
external magnetic fields B<1 GeV^2/e. We employ stout smeared staggered
fermions with physical quark masses and extrapolate the results to the
continuum limit. At low temperatures we confirm the magnetic catalysis scenario
predicted by many model calculations, while around the crossover the condensate
develops a complex dependence on the external magnetic field, resulting in a
decrease of the transition temperature.Comment: slight changes in the text, version accepted for publication in PRD.
5 pages, 5 figure
Critical Role of Transcript Cleavage in Arabidopsis RNA Polymerase II Transcriptional Elongation
Transcript elongation factors associate with elongating RNA polymerase II (RNAPII) to control the efficiency of mRNA synthesis and consequently modulate plant growth and development. Encountering obstacles during transcription such as nucleosomes or particular DNA sequences may cause backtracking and transcriptional arrest of RNAPII. The elongation factor TFIIS stimulates the intrinsic transcript cleavage activity of the polymerase, which is required for efficient rescue of backtracked/arrested RNAPII. A TFIIS mutant variant (TFIISmut) lacks the stimulatory activity to promote RNA cleavage, but instead efficiently inhibits unstimulated transcript cleavage by RNAPII. We could not recover viable Arabidopsis (Arabidopsis thaliana) tfIIs plants constitutively expressing TFIISmut. Induced, transient expression of TFIISmut in tfIIs plants provoked severe growth defects, transcriptomic changes and massive, transcription-related redistribution of elongating RNAPII within transcribed regions toward the transcriptional start site. The predominant site of RNAPII accumulation overlapped with the 11 nucleosome, suggesting that upon inhibition of RNA cleavage activity, RNAPII arrest prevalently occurs at this position. In the presence of TFIISmut, the amount of RNAPII was reduced, which could be reverted by inhibiting the proteasome, indicating proteasomal degradation of arrested RNAPII. Our findings suggest that polymerase backtracking/arrest frequently occurs in plant cells, and RNAPII-reactivation is essential for correct transcriptional output and proper growth/development
A study of the zero modes of the Faddeev-Popov operator in Euclidean Yang-Mills theories in the Landau gauge in d=2,3,4 dimensions
Examples of normalizable zero modes of the Faddeev-Popov operator in SU(2)
Euclidean Yang-Mills theories in the Landau gauge are constructed in d=2,3,4
dimensions.Comment: 18 pages. Text modifications. References added. Version accepted for
publication in the EPJ
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