49 research outputs found
Dense spectrum of resonances and spin-1/2 particle capture in a near-black-hole metric
We show that a spin-1/2 particle in the gravitational field of a massive body
of radius R which slightly exceeds the Schwarzschild radius r_s, possesses a
dense spectrum of narrow resonances. Their lifetimes and density tend to
infinity in the limit R -> r_s. We determine the cross section of the particle
capture into these resonances and show that it is equal to the spin-1/2
absorption cross section for a Schwarzschild black hole. Thus black-hole
properties may emerge in a non-singular static metric prior to the formation of
a black hole.Comment: 6 pages, submitted to PR
Resonant scattering of light in a near-black-hole metric
We show that low-energy photon scattering from a body with radius R slightly
larger than its Schwarzschild radius r_s resembles black-hole absorption. This
absorption occurs via capture to one of the many long-lived, densely packed
resonances that populate the continuum. The lifetimes and density of these
meta-stable states tend to infinity in the limit r_s -> R. We determine the
energy averaged cross-section for particle capture into these resonances and
show that it is equal to the absorption cross-section for a Schwarzschild black
hole. Thus, a non-singular static metric may trap photons for arbitrarily long
times, making it appear completely `black' before the actual formation of a
black hole.Comment: 6 pages, 4 figure
Bound states of spin-half particles in a static gravitational field close to the black hole field
We consider the bound-state energy levels of a spin-1/2 fermion in the
gravitational field of a near-black hole object. In the limit that the metric
of the body becomes singular, all binding energies tend to the rest-mass energy
(i.e. total energy approaches zero). We present calculations of the ground
state energy for three specific interior metrics (Florides, Soffel and
Schwarzschild) for which the spectrum collapses and becomes quasi-continuous in
the singular metric limit. The lack of zero or negative energy states prior to
this limit being reached prevents particle pair production occurring.
Therefore, in contrast to the Coulomb case, no pairs are produced in the
non-singular static metric. For the Florides and Soffel metrics the singularity
occurs in the black hole limit, while for the Schwarzschild interior metric it
corresponds to infinite pressure at the centre. The behaviour of the energy
level spectrum is discussed in the context of the semi-classical approximation
and using general properties of the metric.Comment: 16 pages, 6 Figures. Submitted to General Relativity and Gravitatio
Narrow resonances and black-hole-like absorption in a non-black-hole metric
A massive body with the Schwarzschild interior metric (perfect fluid of
constant density) develops a pressure singularity at the origin when the radius
of the body approaches , where is the Schwarzschild radius.
We show that a quantum scalar particle scattered in this gravitational field
possesses a dense spectrum of narrow resonances. Their density and lifetimes
tend to infinity in the limit , and we determine the cross
section of the particle capture into these quasibound states. Therefore, a body
that is not a black hole demonstrates black-hole-like absorption.Comment: 6 pages, 4 figure
New insights into the genetic etiology of Alzheimer's disease and related dementias
Characterization of the genetic landscape of Alzheimer's disease (AD) and related dementias (ADD) provides a unique opportunity for a better understanding of the associated pathophysiological processes. We performed a two-stage genome-wide association study totaling 111,326 clinically diagnosed/'proxy' AD cases and 677,663 controls. We found 75 risk loci, of which 42 were new at the time of analysis. Pathway enrichment analyses confirmed the involvement of amyloid/tau pathways and highlighted microglia implication. Gene prioritization in the new loci identified 31 genes that were suggestive of new genetically associated processes, including the tumor necrosis factor alpha pathway through the linear ubiquitin chain assembly complex. We also built a new genetic risk score associated with the risk of future AD/dementia or progression from mild cognitive impairment to AD/dementia. The improvement in prediction led to a 1.6- to 1.9-fold increase in AD risk from the lowest to the highest decile, in addition to effects of age and the APOE ε4 allele