336 research outputs found
Noncommutative Dipole Field Theories And Unitarity
We extend the argument of Gomis and Mehen for violation of unitarity in field
theories with space-time noncommutativity to dipole field theories. In dipole
field theories with a timelike dipole vector, we present 1-loop amplitudes that
violate the optical theorem. A quantum mechanical system with nonlocal
potential of finite extent in time also shows violation of unitarity.Comment: typos corrected, more details added in Sec 5, version to appear in
JHE
Phases and geometry of the N=1 A_2 quiver gauge theory and matrix models
We study the phases and geometry of the N=1 A_2 quiver gauge theory using
matrix models and a generalized Konishi anomaly. We consider the theory both in
the Coulomb and Higgs phases. Solving the anomaly equations, we find that a
meromorphic one-form sigma(z)dz is naturally defined on the curve Sigma
associated to the theory. Using the Dijkgraaf-Vafa conjecture, we evaluate the
effective low-energy superpotential and demonstrate that its equations of
motion can be translated into a geometric property of Sigma: sigma(z)dz has
integer periods around all compact cycles. This ensures that there exists on
Sigma a meromorphic function whose logarithm sigma(z)dz is the differential. We
argue that the surface determined by this function is the N=2 Seiberg-Witten
curve of the theory.Comment: 41 pages, 2 figures, JHEP style. v2: references adde
D-brane Spectrum and K-theory Constraints of D=4, N=1 Orientifolds
We study the spectrum of stable BPS and non-BPS D-branes in Z_2 x Z_2
orientifolds for all choices of discrete torsion between the orbifold and
orientifold generators. We compute the torsion K-theory charges in these D=4,
N=1 orientifold models directly from worldsheet conformal field theory, and
compare with the K-theory constraints obtained indirectly using D-brane probes.
The K-theory torsion charges derived here provide non-trivial constraints on
string model building. We also discuss regions of stability for non-BPS
D-branes in these examples.Comment: 40 pages, 5 table
Noncommutative Inspired Black Holes in Extra Dimensions
In a recent string theory motivated paper, Nicolini, Smailagic and Spallucci
(NSS) presented an interesting model for a noncommutative inspired,
Schwarzschild-like black hole solution in 4-dimensions. The essential effect of
having noncommutative co-ordinates in this approach is to smear out matter
distributions on a scale associated with the turn-on of noncommutativity which
was taken to be near the 4-d Planck mass. In particular, NSS took this smearing
to be essentially Gaussian. This energy scale is sufficiently large that in 4-d
such effects may remain invisible indefinitely. Extra dimensional models which
attempt to address the gauge hierarchy problem, however, allow for the
possibility that the effective fundamental scale may not be far from 1
TeV, an energy regime that will soon be probed by experiments at both the LHC
and ILC. In this paper we generalize the NSS model to the case where flat,
toroidally compactified extra dimensions are accessible at the Terascale and
examine the resulting modifications in black hole properties due to the
existence of noncommutativity. We show that while many of the
noncommutativity-induced black hole features found in 4-d by NSS persist, in
some cases there can be significant modifications due the presence of extra
dimensions. We also demonstrate that the essential features of this approach
are not particularly sensitive to the Gaussian nature of the smearing employed
by NSS.Comment: 30 pages, 12 figures; slight text modifications and references adde
R Symmetries in the Landscape
In the landscape, states with symmetries at the classical level form a
distinct branch, with a potentially interesting phenomenology. Some preliminary
analyses suggested that the population of these states would be significantly
suppressed. We survey orientifolds of IIB theories compactified on Calabi-Yau
spaces based on vanishing polynomials in weighted projective spaces, and find
that the suppression is quite substantial. On the other hand, we find that a
R-parity is a common feature in the landscape. We discuss whether the
cosmological constant and proton decay or cosmology might select the low energy
branch. We include also some remarks on split supersymmetry.Comment: 13 page
Is There A String Theory Landscape
We examine recent claims of a large set of flux compactification solutions of
string theory. We conclude that the arguments for AdS solutions are plausible.
The analysis of meta-stable dS solutions inevitably leads to situations where
long distance effective field theory breaks down. We then examine whether these
solutions are likely to lead to a description of the real world. We conclude
that one must invoke a strong version of the anthropic principle. We explain
why it is likely that this leads to a prediction of low energy supersymmetry
breaking, but that many features of anthropically selected flux
compactifications are likely to disagree with experiment.Comment: 39 pages, Latex, ``Terminology surrounding the anthropic principle
revised to conform with accepted usage. More history of the anthropic
principle included. Various references added.
Tocilizumab in Hospitalized Patients with Severe Covid-19 Pneumonia
BACKGROUND
Coronavirus disease 2019 (Covid-19) is associated with immune dysregulation and hyperinflammation, including elevated interleukin-6 levels. The use of tocilizu- mab, a monoclonal antibody against the interleukin-6 receptor, has resulted in better outcomes in patients with severe Covid-19 pneumonia in case reports and retrospective observational cohort studies. Data are needed from randomized, placebo-controlled trials.
METHODS
In this phase 3 trial, we randomly assigned patients who were hospitalized with severe Covid-19 pneumonia in a 2:1 ratio receive a single intravenous infusion of tocilizumab (at a dose of 8 mg per kilogram of body weight) or placebo. Approxi- mately one quarter of the participants received a second dose of tocilizumab or placebo 8 to 24 hours after the first dose. The primary outcome was clinical status at day 28 on an ordinal scale ranging from 1 (discharged or ready for discharge) to 7 (death) in the modified intention-to-treat population, which included all the patients who had received at least one dose of tocilizumab or placebo.
RESULTS
Of the 452 patients who underwent randomization, 438 (294 in the tocilizumab group and 144 in the placebo group) were included in the primary and secondary analyses. The median value for clinical status on the ordinal scale at day 28 was 1.0 (95% confidence interval [CI], 1.0 to 1.0) in the tocilizumab group and 2.0 (non-ICU hospitalization without supplemental oxygen) (95% CI, 1.0 to 4.0) in the placebo group (between-group difference, â1.0; 95% CI, â2.5 to 0; P=0.31 by the van Elteren test). In the safety population, serious adverse events occurred in 103 of 295 patients (34.9%) in the tocilizumab group and in 55 of 143 patients (38.5%) in the placebo group. Mortality at day 28 was 19.7% in the tocilizumab group and 19.4% in the placebo group (weighted difference, 0.3 percentage points (95% CI, â7.6 to 8.2; nominal P=0.94).
CONCLUSIONS
In this randomized trial involving hospitalized patients with severe Covid-19 pneu- monia, the use of tocilizumab did not result in significantly better clinical status or lower mortality than placebo at 28 days. (Funded by F. HoffmannâLa Roche and the Department of Health and Human Services; COVACTA ClinicalTrials.gov num- ber, NCT04320615.
Perspective from a Younger Generation -- The Astro-Spectroscopy of Gisbert Winnewisser
Gisbert Winnewisser's astronomical career was practically coextensive with
the whole development of molecular radio astronomy. Here I would like to pick
out a few of his many contributions, which I, personally, find particularly
interesting and put them in the context of newer results.Comment: 14 pages. (Co)authored by members of the MPIfR (Sub)millimeter
Astronomy Group. To appear in the Proceedings of the 4th
Cologne-Bonn-Zermatt-Symposium "The Dense Interstellar Medium in Galaxies"
eds. S. Pfalzner, C. Kramer, C. Straubmeier, & A. Heithausen (Springer:
Berlin
Understanding physical activity promotion in physiotherapy practice: A qualitative study
Objective: Physical inactivity is a major public health issue and healthcare professionals are encouraged to promote physical activity during routine patient contacts in order to reduce non-communicable diseases and enhance individualsâ quality of life. Little is known about physical activity promotion in physiotherapy practice in the UK. The aim of this study was to better understand physiotherapistsâ experience of physical activity promotion in clinical practice.
Design: A qualitative study was undertaken comprising 12 telephone interviews with participants using a quota sampling approach. The qualitative data was analysed using a thematic analysis approach and written up according to COREQ guidelines.
Findings: Four themes were identified (1) Current physiotherapy practice (2) Barriers to, and facilitators of physical activity promotion, (3) Exercise or physical activity? and (4) Functional restoration versus general wellbeing.
Conclusions: Physiotherapists use routine clinical contacts to discuss physical activity. However, brief interventions are not consistently used and no common framework to guide physical activity promotion was identified. Approaches appear to be inconsistent and informal and focus largely on short-term restoration of function rather than health promotion. There is scope to improve practice in line with current guidance to maximise potential impact on inactivity
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