593 research outputs found
“Please Unlock Your Phone”: Why Reasonable Suspicion Should Be Extended to Cursory Searches of Electronic Devices at the Border
Gossip on Main Street: Visualizing Oral Exchange in Mid-Twentieth-Century Small-Town Photography and Art
Dark Energy as a Born-Infeld Gauge Interaction Violating the Equivalence Principle
We investigate the possibility that dark energy does not couple to
gravitation in the same way than ordinary matter, yielding a violation of the
weak and strong equivalence principles on cosmological scales. We build a
transient mechanism in which gravitation is pushed away from general relativity
by a Born-Infeld gauge interaction acting as an "Abnormally Weighting" (dark)
Energy. This mechanism accounts for the Hubble diagram of far-away supernovae
by cosmic acceleration and time variation of the gravitational constant while
accounting naturally for the present tests on general relativity.Comment: 5 pages, 3 figures, sequel of Phys. Rev. D 73 023520 (2006), to
appear in Physical Review Letter
Nonlocal Cosmology
We explore nonlocally modified models of gravity, inspired by quantum loop
corrections, as a mechanism for explaining current cosmic acceleration. These
theories enjoy two major advantages: they allow a delayed response to cosmic
events, here the transition from radiation to matter dominance, and they avoid
the usual level of fine tuning; instead, emulating Dirac's dictum, the required
large numbers come from the large time scales involved. Their solar system
effects are safely negligible, and they may even prove useful to the black hole
information problem.Comment: Expanded(!) version, to appear in Phys. Rev. Letter
Bigger Rip with No Dark Energy
By studying a modified Friedmann equation which arises in an extension of
general relativity which accommodates a time-dependent fundamental length
, we consider cosmological models where the scale factor diverges with an
essential singularity at a finite future time. Such models have no dark energy
in the conventional sense of energy possessing a truly simple pressure-energy
relationship. Data on supernovae restrict the time from the present until the
Rip to be generically longer than the current age of the Universe.Comment: 10 pages latex including 2 figures. Grammar improved. References
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Post-Newtonian expansion for Gauss-Bonnet Gravity
The Parametrized Post-Newtonian expansion of gravitational theories with a
scalar field coupled to the Gauss-Bonnet invariant is performed and
confrontation of such theories with Solar system experiments is discussed.Comment: 4 pages; typos corrected, published versio
Translational Invariance and the Anisotropy of the Cosmic Microwave Background
Primordial quantum fluctuations produced by inflation are conventionally
assumed to be statistically homogeneous, a consequence of translational
invariance. In this paper we quantify the potentially observable effects of a
small violation of translational invariance during inflation, as characterized
by the presence of a preferred point, line, or plane. We explore the imprint
such a violation would leave on the cosmic microwave background anisotropy, and
provide explicit formulas for the expected amplitudes of
the spherical-harmonic coefficients.Comment: Notation improve
Spontaneous Lorentz Violation and the Long-Range Gravitational Preferred-Frame Effect
Lorentz-violating operators involving Standard Model fields are tightly
constrained by experimental data. However, bounds are more model-independent
for Lorentz violation appearing in purely gravitational couplings. The
spontaneous breaking of Lorentz invariance by the vacuum expectation value of a
vector field selects a universal rest frame. This affects the propagation of
the graviton, leading to a modification of Newton's law of gravity. We compute
the size of the long-range preferred-frame effect in terms of the coefficients
of the two-derivative operators in the low-energy effective theory that
involves only the graviton and the Goldstone bosons.Comment: 11 pages, no figures, revtex4. v4: Replaced to match version to
appear in Phys. Lett. B (minor corrections of form
Interventions for treating distal intestinal obstruction syndrome (DIOS) in cystic fibrosis
BACKGROUND: Cystic fibrosis is the most common life-limiting autosomal recessive genetic disorder in white populations. Distal intestinal obstruction syndrome (DIOS) is an important morbidity in cystic fibrosis. It is the result of the accumulation of viscid faecal material within the bowel which combines with thick, sticky mucus produced in the intestines of people with cystic fibrosis. The intestine may be completely blocked (complete DIOS) or only partially blocked (incomplete DIOS). Once a diagnosis of DIOS has been made, the goal of therapy is to relieve the acute complete or incomplete faecal obstruction and ultimately prevent the need for surgical intervention. OBJECTIVES: This review aimed to evaluate the effectiveness and safety of different treatment regimens for the treatment of DIOS (complete and incomplete) in children and adults with cystic fibrosis. SEARCH METHODS: We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group Trials Register comprising references identified from comprehensive electronic database searches and handsearches of relevant journals and abstract books of conference proceedings. Date of search: 09 September 2021. We also searched online trial registries. Date of last search: 12 October 2021. SELECTION CRITERIA: Randomised controlled trials, quasi-randomised controlled trials (including cross-over trials (to be judged on an individual basis)) comparing the use of laxative agents or surgery for treating DIOS in children, young people and adults with cystic fibrosis to each other, placebo or no intervention. DATA COLLECTION AND ANALYSIS: Two authors independently screened papers, extracted trial details and assessed for risk of bias. The authors assessed the quality of evidence using GRADE. MAIN RESULTS: There was one trial with 20 participants (16 females) included in the review. The mean age of participants was 13.1 years. The trial was a double-blinded, randomised cross-over trial which had a duration of 12 months in total and compared high-dose and low-dose pancreatic enzyme therapy. As only the abstract of the trial was available, the overall risk of bias was judged to be unclear. The trial did not address either of our primary outcomes (time until resolution of DIOS and treatment failure rate), but reported episodes of acute DIOS, presence of abdominal mass and abdominal pain. There were no numerical data available for these outcomes, but the authors stated that there was no difference between treatment with high-dose or low-dose pancreatic enzymes. The overall certainty of the evidence was found to be very low. AUTHORS' CONCLUSIONS: There is a clear lack of evidence for the treatment of DIOS in people with cystic fibrosis. The included abstract did not address our primary outcome measures and did not provide numerical data for the two secondary outcomes it did address. Therefore, we cannot justify the use of high-dose pancreatic enzymes for treating DIOS, nor can we comment on the efficacy and safety of other laxative agents. From our findings, it is clear that more randomised controlled trials need to be conducted in this area
Metric-affine f(R) theories of gravity
General Relativity assumes that spacetime is fully described by the metric
alone. An alternative is the so called Palatini formalism where the metric and
the connections are taken as independent quantities. The metric-affine theory
of gravity has attracted considerable attention recently, since it was shown
that within this framework some cosmological models, based on some generalized
gravitational actions, can account for the current accelerated expansion of the
universe. However we think that metric-affine gravity deserves much more
attention than that related to cosmological applications and so we consider
here metric-affine gravity theories in which the gravitational action is a
general function of the scalar curvature while the matter action is allowed to
depend also on the connection which is not {\em a priori} symmetric. This
general treatment will allow us to address several open issues such as: the
relation between metric-affine gravity and General Relativity (in vacuum
as well as in the presence of matter), the implications of the dependence (or
independence) of the matter action on the connections, the origin and role of
torsion and the viability of the minimal-coupling principle.Comment: typos corrected, replaced to match published versio
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