31 research outputs found
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
Cosmology in three dimensions: steps towards the general solution
We use covariant and first-order formalism techniques to study the properties
of general relativistic cosmology in three dimensions. The covariant approach
provides an irreducible decomposition of the relativistic equations, which
allows for a mathematically compact and physically transparent description of
the 3-dimensional spacetimes. Using this information we review the features of
homogeneous and isotropic 3-d cosmologies, provide a number of new solutions
and study gauge invariant perturbations around them. The first-order formalism
is then used to provide a detailed study of the most general 3-d spacetimes
containing perfect-fluid matter. Assuming the material content to be dust with
comoving spatial 2-velocities, we find the general solution of the Einstein
equations with non-zero (and zero) cosmological constant and generalise known
solutions of Kriele and the 3-d counterparts of the Szekeres solutions. In the
case of a non-comoving dust fluid we find the general solution in the case of
one non-zero fluid velocity component. We consider the asymptotic behaviour of
the families of 3-d cosmologies with rotation and shear and analyse their
singular structure. We also provide the general solution for cosmologies with
one spacelike Killing vector, find solutions for cosmologies containing scalar
fields and identify all the PP-wave 2+1 spacetimes.Comment: 35 pages, 2 figure
Dynamical formation and evolution of (2+1)-dimensional charged black holes
In this paper, we investigate the dynamical formation and evolution of 2 +
1-dimensional charged black holes. We numerically study dynamical collapses of
charged matter fields in an anti de Sitter background and note the formation of
black holes using the double-null formalism. Moreover, we include re-normalized
energy-momentum tensors assuming the S-wave approximation to determine
thermodynamical back-reactions to the internal structures. If there is no
semi-classical effects, the amount of charge determines the causal structures.
If the charge is sufficiently small, the causal structure has a space-like
singularity. However, as the charge increases, an inner Cauchy horizon appears.
If we have sufficient charge, we see a space-like outer horizon and a time-like
inner horizon, and if we give excessive charge, black hole horizons disappear.
We have some circumstantial evidences that weak cosmic censorship is still
satisfied, even for such excessive charge cases. Also, we confirm that there is
mass inflation along the inner horizon, although the properties are quite
different from those of four-dimensional cases. Semi-classical back-reactions
will not affect the outer horizon, but they will affect the inner horizon. Near
the center, there is a place where negative energy is concentrated. Thus,
charged black holes in three dimensions have two types of curvature
singularities in general: via mass inflation and via a concentration of
negative energy. Finally, we classify possible causal structures.Comment: 40 pages, 15 figure
Naked Singularity Formation In f(R) Gravity
We study the gravitational collapse of a star with barotropic equation of
state in the context of theories of gravity.
Utilizing the metric formalism, we rewrite the field equations as those of
Brans-Dicke theory with vanishing coupling parameter. By choosing the
functionality of Ricci scalar as , we
show that for an appropriate initial value of the energy density, if
and satisfy certain conditions, the resulting singularity would be naked,
violating the cosmic censorship conjecture. These conditions are the ratio of
the mass function to the area radius of the collapsing ball, negativity of the
effective pressure, and the time behavior of the Kretschmann scalar. Also, as
long as parameter obeys certain conditions, the satisfaction of the
weak energy condition is guaranteed by the collapsing configuration.Comment: 15 pages, 4 figures, to appear in GR
Performance of the CMS High Granularity Calorimeter prototype to charged pion beams of 20300 GeV/c
The upgrade of the CMS experiment for the high luminosity operation of the
LHC comprises the replacement of the current endcap calorimeter by a high
granularity sampling calorimeter (HGCAL). The electromagnetic section of the
HGCAL is based on silicon sensors interspersed between lead and copper (or
copper tungsten) absorbers. The hadronic section uses layers of stainless steel
as an absorbing medium and silicon sensors as an active medium in the regions
of high radiation exposure, and scintillator tiles directly readout by silicon
photomultipliers in the remaining regions. As part of the development of the
detector and its readout electronic components, a section of a silicon-based
HGCAL prototype detector along with a section of the CALICE AHCAL prototype was
exposed to muons, electrons and charged pions in beam test experiments at the
H2 beamline at the CERN SPS in October 2018. The AHCAL uses the same technology
as foreseen for the HGCAL but with much finer longitudinal segmentation. The
performance of the calorimeters in terms of energy response and resolution,
longitudinal and transverse shower profiles is studied using negatively charged
pions, and is compared to GEANT4 predictions. This is the first report
summarizing results of hadronic showers measured by the HGCAL prototype using
beam test data.Comment: To be submitted to JINS
A High Performance Implementation of the Data Space Transfer Protocol (DSTP)
With the emergence of high performance networks, clusters of workstations can now be connected by commodity networks (meta-clusters) or high speed networks (super-clusters) such as the very high speed Backbone Network Service (vBNS) or Internet2's Abilene. Distributed clusters are enabling a new class of data mining applications in which large amounts of data can be transferred using high performance networks and statistically and numerically intensive computations can be done using clusters of workstations