715 research outputs found
QCD vacuum structure
Several issues related to the structure of the QCD vacuum are reviewed. We
concentrate mostly on results concerning instantons and center vortices.Comment: Lattice 2000 (Plenary), 8 pages, 2 figures; typos corrected,
hep-numbers of references updated, one figure replaced by black and whit
An Abelian effective action reproducing screening and confinement in quenched SU(2) QCD
In an Abelian projection SU(2) gluodynamics contains Abelian gauge fields
(diagonal degrees of freedom) and Abelian matter fields (off-diagonal degrees).
The matter fields are essential for the breaking of the adjoint string. We
obtain numerically the effective action of the Abelian fields in quenched SU(2)
QCD and show that the Abelian matter fields provide an essential contribution
to the total action even in the infrared region.Comment: 3 pages, 3 figures, 1 table, uses espcrc2.sty; Lattice2003(topology
The deconfinement transition in SU(N) gauge theories
We investigate the properties of the deconfinement transition in SU(4) and
SU(6) gauge theories. We find that it is a `normal' first order transition in
both cases, from which we conclude that the transition is first order in the
N->infinity limit. Comparing our preliminary estimates of the continuum values
of Tc/sqrt(K) with existing values for SU(2) and SU(3) demonstrates a weak
dependence on N for all values of N.Comment: 18 page
SU(2) vortex configuration in Laplacian Center Gauge
We study how Laplacian Center Gauge identifies the vortex content of a thick
SU(2) vortex configuration on the lattice. This configuration is a solution of
the Yang-Mills classical equations of motion having vortex properties. We find
that this gauge fixing procedure cleanly identifies the underlying vortex
properties. We also study the monopole content of this configuration detected
with this procedure. We obtain two monopole curves lying on the surface of the
vortex.Comment: 22 pages, 10 PostScript figures. v2, 21 pages, 10 Postscript figures.
Part of the results and part of the conclusions change in v2. v3, 13 pages, 4
Postscript figures, shortened version to appear in PL
Topological aspects of QCD
We review recent results from lattice on topological aspects of QCD: most of
the results refer to monopoles and to instantons. We discuss in detail the
evidence for condensation of monopoles in the vacuum and confinement of colour
by dual superconductivity, and the major role of monopoles in dynamics
(monopole dominance). As for instantons we review the problem, a
possible determination of the spin content of the proton, and new lattice data
relevant to instanton liquid models.Comment: 8 pages, to be published in the Proceedings of Lattice 95, uuencoded
postscript file. IFUP-TH 49/9
Center symmetry and the orientifold planar equivalence
We study the center symmetry of SU(N) gauge theories with fermions in the
two-index representations, by computing the effective potential of the Polyakov
loop in the large-mass expansion on the lattice. In the large-N limit and at
non-zero temperature, we find that the center symmetry is Z_N for fermions in
the adjoint representation and just Z_2 for fermions in the (anti)symmetric
representation. We discuss the fact that our results do not contradict the
orientifold planar equivalence, which relates a common sector defined by the
bosonic gauge-invariant C-even states of theories with fermions in different
two-index representations. Our results complement the work of Armoni et al.
(2007), who showed how at zero temperature a Z_N center symmetry is dynamically
recovered also for fermions in the (anti)symmetric representation, by
considering the theories at finite temperature.Comment: 27 pages, 7 eps figure
Center vortex model for the infrared sector of Yang-Mills theory - Quenched Dirac spectrum and chiral condensate
The Dirac operator describing the coupling of continuum quark fields to SU(2)
center vortex world-surfaces composed of elementary squares on a hypercubic
lattice is constructed. It is used to evaluate the quenched Dirac spectral
density in the random vortex world-surface model, which previously has been
shown to quantitatively reproduce both the confinement properties and the
topological susceptibility of SU(2) Yang-Mills theory. Under certain conditions
on the modeling of the vortex gauge field, a behavior of the quenched chiral
condensate as a function of temperature is obtained which is consistent with
measurements in SU(2) lattice Yang-Mills theory.Comment: 36 LaTeX pages, 13 ps figures included via epsf; minor reformulations
and added cross-referencing for the purpose of clarit
Non-perturbative results for large-N gauge theories
It has been known for a long time that large- methods can give invaluable insights into non-perturbative phenomena such as confinement. Lattice techniques can be used to compute quantities at large . In this contribution, I review some recent large-N lattice results and discuss their implications for our understanding of non-perturbative QCD
Matter degrees of freedom and string breaking in Abelian projected quenched SU(2) QCD
In the Abelian projection the Yang--Mills theory contains Abelian gauge
fields (diagonal degrees of freedom) and the Abelian matter fields
(off-diagonal degrees) described by a complicated action. The matter fields are
essential for the breaking of the adjoint string. We obtain numerically the
effective action of the Abelian gauge and the Abelian matter fields in quenched
SU(2) QCD and show that the Abelian matter fields provide an essential
contribution to the total action even in the infrared region. We also observe
the breaking of an Abelian analog of the adjoint string using Abelian
operators. We show that the adjoint string tension is dominated by the Abelian
and the monopole contributions similarly to the case of the fundamental
particles. We conclude that the adjoint string breaking can successfully be
described in the Abelian projection formalism.Comment: 16 pages, 10 figures, 2 table
Transauricular nerve stimulation in acute ischaemic stroke requiring mechanical thrombectomy: Protocol for a phase 2A, proof-of-concept, sham-controlled randomised trial.
BACKGROUND: Labile blood pressure after acute ischaemic stroke requiring mechanical thrombectomy is independently associated with poor patient outcomes. OBJECTIVES: This study protocol describes is designed to determine whether transauricular nerve stimulation, improves baroreflex sensitivity, reduces blood pressure variability in the first 24 hours after acute ischaemic stroke requiring mechanical thrombectomy. DESIGN: PHASE 2A, PROOF-OF-CONCEPT, SHAM-CONTROLLED RANDOMISED TRIAL: Methods and Analysis: 36 individuals undergoing mechanical thrombectomy for acute ischaemic stroke with established hypertension aged >18 years will be randomly allocated to receive bilateral active or sham transauricular nerve stimulation for the duration of the mechanical thrombectomy procedure (AffeX-CT/001 investigational device). The intervention will be repeated for 1h the morning following the mechanical thrombectomy. Non-invasive blood pressure will be measured â„2h for 24h after mechanical thrombectomy. Holter electrocardiographic monitoring will be recorded during transauricular nerve stimulation. Participants, clinicians and investigators will be masked to treatment allocations. The primary outcome will be the coefficient of variation of systolic blood pressure. Secondary outcomes include additional estimates of blood pressure variability and time/frequency-domain measures of autonomic cardiac modulation An adjusted sample size of 36 patients is required to have a 90% chance of detecting, as significant at the 5% level, a difference in the coefficient of variation in systolic blood pressure of 5±4mmHg between sham and active stimulation [assuming 5% non-compliance rate in each group]. Ethics: confirmed on 16 March 2023 by HRA and Health and Care Research Wales ethics committee (reference 23/WA/0013). DISCUSSION: This study will provide proof-of-concept data that examines whether non-invasive autonomic neuromodulation can be used to favourably modify blood pressure and autonomic control after acute ischaemic stroke requiring mechanical thrombectomy. TRIAL REGISTRATION: Trial registration number: NCT05417009
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