538 research outputs found
Walking, Weak first-order transitions, and Complex CFTs II. Two-dimensional Potts model at
We study complex CFTs describing fixed points of the two-dimensional
-state Potts model with . Their existence is closely related to the
weak first-order phase transition and walking RG behavior present in the real
Potts model at . The Potts model, apart from its own significance, serves
as an ideal playground for testing this very general relation. Cluster
formulation provides nonperturbative definition for a continuous range of
parameter , while Coulomb gas description and connection to minimal models
provide some conformal data of the complex CFTs. We use one and two-loop
conformal perturbation theory around complex CFTs to compute various properties
of the real walking RG flow. These properties, such as drifting scaling
dimensions, appear to be common features of the QFTs with walking RG flows, and
can serve as a smoking gun for detecting walking in Monte Carlo simulations.
The complex CFTs discussed in this work are perfectly well defined, and can
in principle be seen in Monte Carlo simulations with complexified coupling
constants. In particular, we predict a pair of -symmetric complex CFTs
with central charges describing the fixed points
of a 5-state dilute Potts model with complexified temperature and vacancy
fugacity.Comment: 34 pages, 13 figures. v2: refs added; v3 refs added, typos corrected,
presentation of several arguments clarifie
Walking, Weak first-order transitions, and Complex CFTs
We discuss walking behavior in gauge theories and weak first-order phase
transitions in statistical physics. Despite appearing in very different systems
(QCD below the conformal window, the Potts model, deconfined criticality) these
two phenomena both imply approximate scale invariance in a range of energies
and have the same RG interpretation: a flow passing between pairs of fixed
point at complex coupling. We discuss what distinguishes a real theory from a
complex theory and call these fixed points complex CFTs. By using conformal
perturbation theory we show how observables of the walking theory are
computable by perturbing the complex CFTs. This paper discusses the general
mechanism while a companion paper [1] will treat a specific and computable
example: the two-dimensional Q-state Potts model with Q > 4. Concerning walking
in 4d gauge theories, we also comment on the (un)likelihood of the light
pseudo-dilaton, and on non-minimal scenarios of the conformal window
termination.Comment: 38 pages, added reference
Non-gaussianity of the critical 3d Ising model
We discuss the 4pt function of the critical 3d Ising model, extracted from
recent conformal bootstrap results. We focus on the non-gaussianity Q - the
ratio of the 4pt function to its gaussian part given by three Wick
contractions. This ratio reveals significant non-gaussianity of the critical
fluctuations. The bootstrap results are consistent with a rigorous inequality
due to Lebowitz and Aizenman, which limits Q to lie between 1/3 and 1.Comment: 10 pages, 6 figures; v2: refs added; v3: refs updated, published
version; v4: acknowledgement adde
A scaling theory for the long-range to short-range crossover and an infrared duality
We study the second-order phase transition in the -dimensional Ising model
with long-range interactions decreasing as a power of the distance .
For below some known value , the transition is described by a
conformal field theory without a local stress tensor operator, with critical
exponents varying continuously as functions of . At , the phase
transition crosses over to the short-range universality class. While the
location of this crossover has been known for 40 years, its physics has
not been fully understood, the main difficulty being that the standard
description of the long-range critical point is strongly coupled at the
crossover. In this paper we propose another field-theoretic description which,
on the contrary, is weakly coupled near the crossover. We use this description
to clarify the nature of the crossover and make predictions about the critical
exponents. That the same long-range critical point can be reached from two
different UV descriptions provides a new example of infrared duality.Comment: 57pp, detailed version of arXiv:1703.03430, v2: misprints corrected,
v3: refs and discussion of log corrections at the crossover added, v4:
published version plus extra comments in appendix A,B and an acknowledgement,
v5: published version plus extra comments in appendix A,B and an
acknowledgement (replacing the wrong tex file of v4
Conformal Invariance in the Long-Range Ising Model
We consider the question of conformal invariance of the long-range Ising
model at the critical point. The continuum description is given in terms of a
nonlocal field theory, and the absence of a stress tensor invalidates all of
the standard arguments for the enhancement of scale invariance to conformal
invariance. We however show that several correlation functions, computed to
second order in the epsilon expansion, are nontrivially consistent with
conformal invariance. We proceed to give a proof of conformal invariance to all
orders in the epsilon expansion, based on the description of the long-range
Ising model as a defect theory in an auxiliary higher-dimensional space. A
detailed review of conformal invariance in the d-dimensional short-range Ising
model is also included and may be of independent interest.Comment: 52pp; V2: refs added; V3: ref added, published versio
Discrete Chiral Symmetry and Mass Shift in Lattice Hamiltonian Approach to Schwinger Model
We revisit the lattice formulation of the Schwinger model using the
Kogut-Susskind Hamiltonian approach with staggered fermions. This model,
introduced by Banks et al., contains the mass term , and setting it to zero is often assumed to
provide the lattice regularization of the massless Schwinger model. We instead
argue that the relation between the lattice and continuum mass parameters
should be taken as . The model with is
shown to possess a discrete chiral symmetry that is generated by the unit
lattice translation accompanied by the shift of the -angle by .
While the mass shift vanishes as the lattice spacing approaches zero, we
find that including this shift greatly improves the rate of convergence to the
continuum limit. We demonstrate the faster convergence using both numerical
diagonalizations of finite lattice systems, as well as extrapolations of the
lattice strong coupling expansions.Comment: 14 pages, 7 figures; v2 refs added, minor improvement
Phase Diagram of the Two-Flavor Schwinger Model at Zero Temperature
We examine the phase structure of the two-flavor Schwinger model as a
function of the -angle and the two masses, and . In
particular, we find interesting effects at : along the
-invariant line , in the regime where is much smaller
than the charge , the theory undergoes logarithmic RG flow of the
Berezinskii-Kosterlitz-Thouless type. As a result, in this regime there is a
non-perturbatively small mass gap . The -invariant
line lies within a region of the phase diagram where the charge conjugation
symmetry is spontaneously broken and whose boundaries we determine numerically.
Our numerical results are obtained using the Hamiltonian lattice gauge
formulation that includes the mass shift dictated
by the discrete chiral symmetry.Comment: 7 pages, 3 figures; v2 minor improvements, refs adde
Prevalence, associated factors and outcomes of pressure injuries in adult intensive care unit patients: the DecubICUs study
Funder: European Society of Intensive Care Medicine; doi: http://dx.doi.org/10.13039/501100013347Funder: Flemish Society for Critical Care NursesAbstract: Purpose: Intensive care unit (ICU) patients are particularly susceptible to developing pressure injuries. Epidemiologic data is however unavailable. We aimed to provide an international picture of the extent of pressure injuries and factors associated with ICU-acquired pressure injuries in adult ICU patients. Methods: International 1-day point-prevalence study; follow-up for outcome assessment until hospital discharge (maximum 12 weeks). Factors associated with ICU-acquired pressure injury and hospital mortality were assessed by generalised linear mixed-effects regression analysis. Results: Data from 13,254 patients in 1117 ICUs (90 countries) revealed 6747 pressure injuries; 3997 (59.2%) were ICU-acquired. Overall prevalence was 26.6% (95% confidence interval [CI] 25.9â27.3). ICU-acquired prevalence was 16.2% (95% CI 15.6â16.8). Sacrum (37%) and heels (19.5%) were most affected. Factors independently associated with ICU-acquired pressure injuries were older age, male sex, being underweight, emergency surgery, higher Simplified Acute Physiology Score II, Braden score 3 days, comorbidities (chronic obstructive pulmonary disease, immunodeficiency), organ support (renal replacement, mechanical ventilation on ICU admission), and being in a low or lower-middle income-economy. Gradually increasing associations with mortality were identified for increasing severity of pressure injury: stage I (odds ratio [OR] 1.5; 95% CI 1.2â1.8), stage II (OR 1.6; 95% CI 1.4â1.9), and stage III or worse (OR 2.8; 95% CI 2.3â3.3). Conclusion: Pressure injuries are common in adult ICU patients. ICU-acquired pressure injuries are associated with mainly intrinsic factors and mortality. Optimal care standards, increased awareness, appropriate resource allocation, and further research into optimal prevention are pivotal to tackle this important patient safety threat
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Prevalence, associated factors and outcomes of pressure injuries in adult intensive care unit patients: the DecubICUs study
Funder: European Society of Intensive Care Medicine; doi: http://dx.doi.org/10.13039/501100013347Funder: Flemish Society for Critical Care NursesAbstract: Purpose: Intensive care unit (ICU) patients are particularly susceptible to developing pressure injuries. Epidemiologic data is however unavailable. We aimed to provide an international picture of the extent of pressure injuries and factors associated with ICU-acquired pressure injuries in adult ICU patients. Methods: International 1-day point-prevalence study; follow-up for outcome assessment until hospital discharge (maximum 12 weeks). Factors associated with ICU-acquired pressure injury and hospital mortality were assessed by generalised linear mixed-effects regression analysis. Results: Data from 13,254 patients in 1117 ICUs (90 countries) revealed 6747 pressure injuries; 3997 (59.2%) were ICU-acquired. Overall prevalence was 26.6% (95% confidence interval [CI] 25.9â27.3). ICU-acquired prevalence was 16.2% (95% CI 15.6â16.8). Sacrum (37%) and heels (19.5%) were most affected. Factors independently associated with ICU-acquired pressure injuries were older age, male sex, being underweight, emergency surgery, higher Simplified Acute Physiology Score II, Braden score 3 days, comorbidities (chronic obstructive pulmonary disease, immunodeficiency), organ support (renal replacement, mechanical ventilation on ICU admission), and being in a low or lower-middle income-economy. Gradually increasing associations with mortality were identified for increasing severity of pressure injury: stage I (odds ratio [OR] 1.5; 95% CI 1.2â1.8), stage II (OR 1.6; 95% CI 1.4â1.9), and stage III or worse (OR 2.8; 95% CI 2.3â3.3). Conclusion: Pressure injuries are common in adult ICU patients. ICU-acquired pressure injuries are associated with mainly intrinsic factors and mortality. Optimal care standards, increased awareness, appropriate resource allocation, and further research into optimal prevention are pivotal to tackle this important patient safety threat
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