471 research outputs found
Quantum evaporation of a naked singularity
We investigate here quantum effects in gravitational collapse of a scalar
field model which classically leads to a naked singularity. We show that
non-perturbative semi-classical modifications near the singularity, based on
loop quantum gravity, give rise to a strong outward flux of energy. This leads
to the dissolution of the collapsing cloud before the singularity can form.
Quantum gravitational effects thus censor naked singularities by avoiding their
formation. Further, quantum gravity induced mass flux has a distinct feature
which may lead to a novel observable signature in astrophysical bursts.Comment: 4 pages, 2 figures. Minor changes to match published version in
Physical Review Letter
Gravitational Collapse of Inhomogeneous Dust in (2+1) Dimensions
We examine the gravitational collapse of spherically symmetric inhomogeneous
dust in (2+1) dimensions, with cosmological constant. We obtain the analytical
expressions for the interior metric. We match the solution to a vacuum
exterior. We discuss the nature of the singularity formed by analyzing the
outgoing radial null geodesics. We examine the formation of trapped surfaces
during the collapse.Comment: Accepted for publication in CQ
Effective State Metamorphosis in Semi-Classical Loop Quantum Cosmology
Modification to the behavior of geometrical density at short scales is a key
result of loop quantum cosmology, responsible for an interesting phenomenology
in the very early universe. We demonstrate the way matter with arbitrary scale
factor dependence in Hamiltonian incorporates this change in its effective
dynamics in the loop modified phase. For generic matter, the equation of state
starts varying near a critical scale factor, becomes negative below it and
violates strong energy condition. This opens a new avenue to generalize various
phenomenological applications in loop quantum cosmology. We show that different
ways to define energy density may yield radically different results, especially
for the case corresponding to classical dust. We also discuss implications for
frequency dispersion induced by modification to geometric density at small
scales.Comment: Revised version; includes expanded discussion of natural
trans-Planckian modifications to frequency dispersion and robustness to
quantization ambiguities. To appear in Class. Quant. Gra
Gravitational collapse with tachyon field and barotropic fluid
A particular class of space-time, with a tachyon field, \phi, and a
barotropic fluid constituting the matter content, is considered herein as a
model for gravitational collapse. For simplicity, the tachyon potential is
assumed to be of inverse square form i.e., V(\phi) \sim \phi^{-2}. Our purpose,
by making use of the specific kinematical features of the tachyon, which are
rather different from a standard scalar field, is to establish the several
types of asymptotic behavior that our matter content induces. Employing a
dynamical system analysis, complemented by a thorough numerical study, we find
classical solutions corresponding to a naked singularity or a black hole
formation. In particular, there is a subset where the fluid and tachyon
participate in an interesting tracking behaviour, depending sensitively on the
initial conditions for the energy densities of the tachyon field and barotropic
fluid. Two other classes of solutions are present, corresponding respectively,
to either a tachyon or a barotropic fluid regime. Which of these emerges as
dominant, will depend on the choice of the barotropic parameter, \gamma.
Furthermore, these collapsing scenarios both have as final state the formation
of a black hole.Comment: 18 pages, 7 figures. v3: minor changes. Final version to appear in
GR
Spherically symmetric dissipative anisotropic fluids: A general study
The full set of equations governing the evolution of self--gravitating
spherically symmetric dissipative fluids with anisotropic stresses is deployed
and used to carry out a general study on the behaviour of such systems, in the
context of general relativity. Emphasis is given to the link between the Weyl
tensor, the shear tensor, the anisotropy of the pressure and the density
inhomogeneity. In particular we provide the general, necessary and sufficient,
condition for the vanishing of the spatial gradients of energy density, which
in turn suggests a possible definition of a gravitational arrow of time. Some
solutions are also exhibited to illustrate the discussion.Comment: 28 pages Latex. To appear in Phys.Rev.
Long-Baseline Neutrino Facility (LBNF) and Deep Underground Neutrino Experiment (DUNE) Conceptual Design Report Volume 2: The Physics Program for DUNE at LBNF
The Physics Program for the Deep Underground Neutrino Experiment (DUNE) at
the Fermilab Long-Baseline Neutrino Facility (LBNF) is described
High fatigue scores in patients with idiopathic inflammatory myopathies: a multigroup comparative study from the COVAD e-survey
Idiopathic inflammatory myopathies (IIMs) confer a significant risk of disability and poor quality of life, though fatigue, an important contributing factor, remains under-reported in these individuals. We aimed to compare and analyze differences in visual analog scale (VAS) scores (0–10 cm) for fatigue (VAS-F) in patients with IIMs, non-IIM systemic autoimmune diseases (SAIDs), and healthy controls (HCs). We performed a cross-sectional analysis of the data from the COVID-19 Vaccination in Autoimmune Diseases (COVAD) international patient self-reported e-survey. The COVAD survey was circulated from December 2020 to August 2021, and details including demographics, COVID-19 history, vaccination details, SAID details, global health, and functional status were collected from adult patients having received at least one COVID-19 vaccine dose. Fatigue experienced 1 week prior to survey completion was assessed using a single-item 10 cm VAS. Determinants of fatigue were analyzed in regression models. Six thousand nine hundred and eighty-eight respondents (mean age 43.8 years, 72% female; 55% White) were included in the analysis. The overall VAS-F score was 3 (IQR 1–6). Patients with IIMs had similar fatigue scores (5, IQR 3–7) to non-IIM SAIDs [5 (IQR 2–7)], but higher compared to HCs (2, IQR 1–5; P < 0.001), regardless of disease activity. In adjusted analysis, higher VAS-F scores were seen in females (reference female; coefficient −0.17; 95%CI −0.21 to −13; P < 0.001) and Caucasians (reference Caucasians; coefficient −0.22; 95%CI −0.30 to −0.14; P < 0.001 for Asians and coefficient −0.08; 95%CI −0.13 to 0.30; P = 0.003 for Hispanics) in our cohort. Our study found that patients with IIMs exhibit considerable fatigue, similar to other SAIDs and higher than healthy individuals. Women and Caucasians experience greater fatigue scores, allowing identification of stratified groups for optimized multidisciplinary care and improve outcomes such as quality of life
Deep phenotyping and genomic data from a nationally representative study on dementia in India
The Harmonized Diagnostic Assessment of Dementia for the Longitudinal Aging Study in India (LASI-DAD) is a nationally representative in-depth study of cognitive aging and dementia. We present a publicly available dataset of harmonized cognitive measures of 4,096 adults 60 years of age and older in India, collected across 18 states and union territories. Blood samples were obtained to carry out whole blood and serum-based assays. Results are included in a venous blood specimen datafile that can be linked to the Harmonized LASI-DAD dataset. A global screening array of 960 LASI-DAD respondents is also publicly available for download, in addition to neuroimaging data on 137 LASI-DAD participants. Altogether, these datasets provide comprehensive information on older adults in India that allow researchers to further understand risk factors associated with cognitive impairment and dementia.Peer reviewe
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