3,767 research outputs found
Black-Hole Bombs and Photon-Mass Bounds
Generic extensions of the standard model predict the existence of ultralight
bosonic degrees of freedom. Several ongoing experiments are aimed at detecting
these particles or constraining their mass range. Here we show that massive
vector fields around rotating black holes can give rise to a strong
superradiant instability which extracts angular momentum from the hole. The
observation of supermassive spinning black holes imposes limits on this
mechanism. We show that current supermassive black hole spin estimates provide
the tightest upper limits on the mass of the photon (mv<4x10^{-20} eV according
to our most conservative estimate), and that spin measurements for the largest
known supermassive black holes could further lower this bound to mv<10^{-22}
eV. Our analysis relies on a novel framework to study perturbations of rotating
Kerr black holes in the slow-rotation regime, that we developed up to second
order in rotation, and that can be extended to other spacetime metrics and
other theories.Comment: 5 pages, 2 figures. References added. Matches published versio
A study of collider signatures for two Higgs doublet models with a Pseudoscalar mediator to Dark Matter
Two Higgs doublet models with an additional pseudoscalar particle coupling to
the Standard Model and to a new stable, neutral particle, provide an attractive
and fairly minimal route to solving the problem of Dark Matter. They have been
the subject of several searches at the LHC. We study the impact of existing LHC
measurements on such models, first in the benchmark regions addressed by
searches and then after relaxing some of their assumptions and broadening the
parameter ranges considered. In each case we study how the new parameters
change the potentially visible signatures at the LHC, and identify which of
these signatures should already have had a significant impact on existing
measurements. This allows us to set some first constraints on a number of so
far unstudied scenarios.Comment: 20 pages, 9 figures; added EW constraints contours, extended
explanation of WW model-dependency, extended motivation for pseudoscalar
mediators, corrected typo
Longitudinal study of the effect of a 5-year exercise intervention on structural brain complexity in older adults. A Generation 100 substudy
Physical inactivity has been identified as an important risk factor for dementia. High levels of cardiorespiratory fitness (CRF) have been shown to reduce the risk of dementia. However, the mechanism by which exercise affects brain health is still debated. Fractal dimension (FD) is an index that quantifies the structural complexity of the brain. The purpose of this study was to investigate the effects of a 5-year exercise intervention on the structural complexity of the brain, measured through the FD, in a subset of 105 healthy older adults participating in the randomized controlled trial Generation 100 Study. The subjects were randomized into control, moderate intensity continuous training, and high intensity interval training groups. Both brain MRI and CRF were acquired at baseline and at 1-, 3- and 5-years follow-ups. Cortical thickness and volume data were extracted with FreeSurfer, and FD of the cortical lobes, cerebral and cerebellar gray and white matter were computed. CRF was measured as peak oxygen uptake (VO2peak) using ergospirometry during graded maximal exercise testing. Linear mixed models were used to investigate exercise group differences and possible CRF effects on the brain's structural complexity. Associations between change over time in CRF and FD were performed if there was a significant association between CRF and FD. There were no effects of group membership on the structural complexity. However, we found a positive association between CRF and the cerebral gray matter FD (p < 0.001) and the temporal lobe gray matter FD (p < 0.001). This effect was not present for cortical thickness, suggesting that FD is a more sensitive index of structural changes. The change over time in CRF was associated with the change in temporal lobe gray matter FD from baseline to 5-year follow-up (p < 0.05). No association of the change was found between CRF and cerebral gray matter FD. These results demonstrated that entering old age with high and preserved CRF levels protected against loss of structural complexity in areas sensitive to aging and age-related pathology
Perturbations of slowly rotating black holes: massive vector fields in the Kerr metric
We discuss a general method to study linear perturbations of slowly rotating
black holes which is valid for any perturbation field, and particularly
advantageous when the field equations are not separable. As an illustration of
the method we investigate massive vector (Proca) perturbations in the Kerr
metric, which do not appear to be separable in the standard Teukolsky
formalism. Working in a perturbative scheme, we discuss two important effects
induced by rotation: a Zeeman-like shift of nonaxisymmetric quasinormal modes
and bound states with different azimuthal number m, and the coupling between
axial and polar modes with different multipolar index l. We explicitly compute
the perturbation equations up to second order in rotation, but in principle the
method can be extended to any order. Working at first order in rotation we show
that polar and axial Proca modes can be computed by solving two decoupled sets
of equations, and we derive a single master equation describing axial
perturbations of spin s=0 and s=+-1. By extending the calculation to second
order we can study the superradiant regime of Proca perturbations in a
self-consistent way. For the first time we show that Proca fields around Kerr
black holes exhibit a superradiant instability, which is significantly stronger
than for massive scalar fields. Because of this instability, astrophysical
observations of spinning black holes provide the tightest upper limit on the
mass of the photon: mv<4x10^-20 eV under our most conservative assumptions.
Spin measurements for the largest black holes could reduce this bound to
mv<10^-22 eV or lower.Comment: v1: 29 pages, 9 figures, 3 appendices. v2: References added and
improved discussion. Matches the version to appear in Physical Review D.
Mathematica notebooks available here http://blackholes.ist.utl.pt/?page=Files
and http://www.phy.olemiss.edu/~berti/qnms.htm
Instability of hyper-compact Kerr-like objects
Viable alternatives to astrophysical black holes include hyper-compact
objects without horizon, such as gravastars, boson stars, wormholes and
superspinars. The authors have recently shown that typical rapidly-spinning
gravastars and boson stars develop a strong instability. That analysis is
extended in this paper to a wide class of horizonless objects with approximate
Kerr-like geometry. A detailed investigation of wormholes and superspinars is
presented, using plausible models and mirror boundary conditions at the
surface. Like gravastars and boson stars, these objects are unstable with very
short instability timescales. This result strengthens previous conclusions that
observed hyper-compact astrophysical objects with large rotation are likely to
be black holes.Comment: 15 pages, 3 figures. To be published in CQ
Multi-site observations of Delta Scuti stars 7 Aql and 8 Aql (a new Delta Scuti variable): The twelfth STEPHI campaign in 2003
We present an analysis of the pulsation behaviour of the Delta Scuti stars 7
Aql (HD 174532) and 8 Aql (HD 174589) -- a new variable star -- observed in the
framework of STEPHI XII campaign during 2003 June--July. 183 hours of high
precision photometry were acquired by using four-channel photometers at three
sites on three continents during 21 days. The light curves and amplitude
spectra were obtained following a classical scheme of multi-channel photometry.
Observations in different filters were also obtained and analyzed. Six and
three frequencies have been unambiguously detected above a 99% confidence level
in the range 0.090 mHz--0.300 mHz and 0.100 mHz-- 0.145 mHz in 7 Aql and 8 Aql
respectively. A comparison of observed and theoretical frequencies shows that 7
Aql and 8 Aql may oscillate with p modes of low radial orders, typical among
Delta Scuti stars. In terms of radial oscillations the range of 8 Aql goes from
n=1 to n=3 while for 7 Aql the range spans from n=4 to n=7. Non-radial
oscillations have to be present in both stars as well. The expected range of
excited modes according to a non adiabatic analysis goes from n=1 to n=6 in
both stars.Comment: 8 pages, 7 fugures, 5 tables, accepted for publication in
Astronomical Journa
Exact Black Holes and Universality in the Backreaction of non-linear Sigma Models with a potential in (A)dS4
The aim of this paper is to construct accelerated, stationary and
axisymmetric exact solutions of the Einstein theory with self interacting
scalar fields in (A)dS4. To warm up, the backreaction of the (non)-minimally
coupled scalar field is solved, the scalar field equations are integrated and
all the potentials compatible with the metric ansatz and Einstein gravity are
found. With these results at hand the non-linear sigma model is tackled. The
scalar field Lagrangian is generic; neither the coupling to the curvature,
neither the metric in the scalar manifold nor the potential, are fixed ab
initio. The unique assumption in the analysis is the metric ansatz: it has the
form of the most general Petrov type D vacuum solution of general relativity;
it is a a cohomogeneity two Weyl rescaling of the Carter metric and therefore
it has the typical Plebanski-Demianski form with two arbitrary functions of one
variable and one arbitrary functions of two variables. It is shown, by an
straightforward manipulation of the field equations, that the metric is
completely integrable without necessity of specifiying anything in the scalar
Lagrangian. This results in that the backreaction of the scalar fields, within
this class of metrics, is universal. The metric functions generically show an
explicit dependence on a dynamical exponent that allows to smoothly connect
this new family of solutions with the actual Plebanski-Demianski spacetime. The
remaining field equations imply that the scalar fields follow geodesics in the
scalar manifold with an affine parameter given by a non-linear function of the
spacetime coordinates and define the on-shell form of the potential plus a
functional equation that it has to satisfy. Finally, a general family of (A)dS4
static hairy black holes is explicitly constructed and its properties are
outlined.Comment: Several typos correcte
CDK4/6 Inhibitors in Breast Cancer Treatment: Potential Interactions with Drug, Gene, and Pathophysiological Conditions
Palbociclib, ribociclib, and abemaciclib belong to the third generation of cyclin-dependent kinases inhibitors (CDKis), an established therapeutic class for advanced and metastatic breast cancer. Interindividual variability in the therapeutic response of CDKis has been reported and some individuals may experience increased and unexpected toxicity. This narrative review aims at identifying the factors potentially concurring at this variability for driving the most appropriate and tailored use of CDKis in the clinic. Specifically, concomitant medications, pharmacogenetic profile, and pathophysiological conditions could influence absorption, distribution, metabolism, and elimination pharmacokinetics. A personalized therapeutic approach taking into consideration all factors potentially contributing to an altered pharmacokinetic/pharmacodynamic profile could better drive safe and effective clinical use
The experience of long-term opiate maintenance treatment and reported barriers to recovery: A qualitative systematic review
Background/Aim: To inform understanding of the experience of long-term opiate maintenance and identify barriers to recovery. Methods: A qualitative systematic review. Results: 14 studies in 17 papers, mainly from the USA (65%), met inclusion criteria, involving 1,088 participants. Studies focused on methadone prescribing. Participants reported stability; however, many disliked methadone. Barriers to full recovery were primarily ‘inward focused'. Conclusion: This is the first review of qualitative literature on long-term maintenance, finding that universal service improvements could be made to address reported barriers to recovery, including involving ex-users as positive role models, and increasing access to psychological support. Treatment policies combining harm minimisation and abstinence-orientated approaches may best support individualised recovery
Buprenorphine versus dihydrocodeine for opiate detoxification in primary care: a randomised controlled trial
Background
Many drug users present to primary care requesting detoxification from illicit opiates. There are a number of detoxification agents but no recommended drug of choice. The purpose of this study is to compare buprenorphine with dihydrocodeine for detoxification from illicit opiates in primary care.
Methods
Open label randomised controlled trial in NHS Primary Care (General Practices), Leeds, UK. Sixty consenting adults using illicit opiates received either daily sublingual buprenorphine or daily oral dihydrocodeine. Reducing regimens for both interventions were at the discretion of prescribing doctor within a standard regimen of not more than 15 days. Primary outcome was abstinence from illicit opiates at final prescription as indicated by a urine sample. Secondary outcomes during detoxification period and at three and six months post detoxification were recorded.
Results
Only 23% completed the prescribed course of detoxification medication and gave a urine sample on collection of their final prescription. Risk of non-completion of detoxification was reduced if allocated buprenorphine (68% vs 88%, RR 0.58 CI 0.35–0.96, p = 0.065). A higher proportion of people allocated to buprenorphine provided a clean urine sample compared with those who received dihydrocodeine (21% vs 3%, RR 2.06 CI 1.33–3.21, p = 0.028). People allocated to buprenorphine had fewer visits to professional carers during detoxification and more were abstinent at three months (10 vs 4, RR 1.55 CI 0.96–2.52) and six months post detoxification (7 vs 3, RR 1.45 CI 0.84–2.49).
Conclusion
Informative randomised trials evaluating routine care within the primary care setting are possible amongst drug using populations. This small study generates unique data on commonly used treatment regimens
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