1,191 research outputs found
Gravitational collisions and the quark-gluon plasma
This thesis addresses the thermalisation of heavy-ion collisions within the
context of the AdS/CFT duality. The first part clarifies the numerical set-up
and studies the relaxation of far-from-equilibrium modes in homogeneous
systems. Less trivially we then study colliding shock waves and uncover a
transparent regime where the strongly coupled shocks initially pass right
through each other. Furthermore, in this regime the later plasma relaxation is
insensitive to the longitudinal profile of the shock, implying in particular a
universal rapidity shape at strong coupling and high collision energies.
Lastly, we study radial expansion in a boost-invariant set-up, allowing us to
find good agreement with head-on collisions performed at the LHC accelerator.
As a secondary goal of this thesis, a special effort is made to clearly
expose numerical computations by providing commented Mathematica notebooks for
most calculations presented. Furthermore, we provide interpolating functions of
the geometries computed, which can be of use in other projects.Comment: PhD thesis, 100 pages, 80 figures.
http://dspace.library.uu.nl/handle/1874/294809 , Mathematica notebooks can be
found at sites.google.com/site/wilkevanderschee/phd-thesi
Optical effects related to Keplerian discs orbiting Kehagias-Sfetsos naked singularities
We demonstrate possible optical signatures of the Kehagias-Sfetsos naked
singularity spacetimes representing spherically symmetric vacuum solution of
the modified Ho\v{r}ava gravity. In such spacetimes, accretion structures
significantly different from those present in the standard black hole
spacetimes occur due to the "antigravity" effect causing existence of an
internal static sphere surrounded by Keplerian discs. We focus our attention on
the optical effects related to the Keplerian accretion discs, constructing the
optical appearance of the Keplerian discs, the spectral continuum due to their
thermal radiation, and spectral profiled lines generated in the innermost parts
of such discs. The KS naked singularity signature is strongly encoded in the
characteristics of predicted optical effects, especially in the case of the
spectral continuum and spectral lines profiled by the strong gravity of the
spacetimes, due to the region of the vanishing of the angular velocity gradient
influencing the effectivity of the viscosity mechanism. We can conclude that
optical signatures of the Kehagias-Sfetsos naked singularities can be well
distinguished from the signatures of the standard black holes
Silhouette and spectral line profiles in the special modification of the Kerr black hole geometry generated by quintessential fields
We study optical effects in quintessential Kerr black hole spacetimes
corresponding to the limiting case of the equation-of-state parameter
of the quintessence. In dependence on the dimensionless
quintessential field parameter , we determine the black hole silhouette and
the spectral line profiles of Keplerian disks generated in this special
quintessential Kerr geometry, representing an extension of the general
modifications of the Kerr geometry introduced recently by Ghasemi-Nodehi and
Bambi \cite{Gha-Bam:2016:EPJC:}. We demonstrate that due to the influence of
the parameter , the silhouette is almost homogeneously enlarged, and the
spectral line profiles are redshifted with almost conserved shape
Equilibration and hydrodynamics at strong and weak coupling
We give an updated overview of both weak and strong coupling methods to
describe the approach to a plasma described by viscous hydrodynamics, a process
now called hydrodynamisation. At weak coupling the very first moments after a
heavy ion collision is described by the colour-glass condensate framework, but
quickly thereafter the mean free path is long enough for kinetic theory to
become applicable. Recent simulations indicate thermalization in a time
[1], with the temperature at that time and
the shear viscosity divided by the entropy density. At (infinitely)
strong coupling it is possible to mimic heavy ion collisions by using
holography, which leads to a dual description of colliding gravitational shock
waves. The plasma formed hydrodynamises within a time of . A recent
extension found corrections to this result for finite values of the coupling,
when is bigger than the canonical value of , which leads to
[2]. Future improvements include the
inclusion of the effects of the running coupling constant in QCD.Comment: 7 pages, 4 figures, talk presented at Quark Matter 2017 (Chicago
Fluctuations of CMBR in accelerating universe
The influence of the observed relict vacuum energy on the fluctuations of
CMBR going through cosmological matter condensations is studied in the
framework of the Einstein-Strauss-de Sitter vakuola model. It is shown that
refraction of light at the matching surface of the vakuola and the expanding
Friedman universe can be very important during accelerated expansion of the
universe, when the velocity of the matching surface relative to static
Schwarzchildian observers becomes relativistic. Relevance of the refraction
effect for the temperature fluctuations of CMBR is given in terms of the
redshift and the angular extension of the fluctuating region
Coupling constant corrections in a holographic model of heavy ion collisions
We initiate a holographic study of coupling-dependent heavy ion collisions by
analysing for the first time the effects of leading-order, inverse coupling
constant corrections. In the dual description, this amounts to colliding
gravitational shock waves in a theory with curvature-squared terms. We find
that at intermediate coupling, nuclei experience less stopping and have more
energy deposited near the lightcone. When the decreased coupling results in an
80% larger shear viscosity, the time at which hydrodynamics becomes a good
description of the plasma created from high energy collisions increases by 25%.
The hydrodynamic phase of the evolution starts with a wider rapidity profile
and smaller entropy.Comment: V2: 6 pages, 5 figures. Second-order coupling constant corrections
added. Version appeared in PR
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