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 $t\sim40(\eta/s)^{4/3}/T$ [1], with $T$ the temperature at that time and $\eta/s$ 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 $0.41/T$. A recent extension found corrections to this result for finite values of the coupling, when $\eta/s$ is bigger than the canonical value of $1/4\pi$, which leads to $t\sim(0.41+1.6(\eta/s-1/4\pi))/T$ [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

Holographic thermalization with radial flow

Recently, a lot of effort has been put into describing the thermalization of the quark-gluon plasma using the gauge/gravity duality. In this context we here present a full numerical solution of the early far-from-equilibrium formation of the plasma, which is expanding radially in the transverse plane and is boost invariant along the collision axis. This can model the early stage of a head-on relativistic heavy ion collision. The resulting momentum distribution quickly reaches local equilibrium, after which they can be evolved using ordinary hydrodynamics. We comment on general implications for these hydrodynamic simulations, both for central and non-central collisions, and including fluctuations in the initial state.Comment: 4 pages, 6 figures, comparison with a paper by Pratt and Vredevoogd added in version

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

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

Absence of a local rest frame in far from equilibrium quantum matter

In a collision of strongly coupled quantum matter we find that the dynamics of the collision produces regions where a local rest frame cannot be defined because the energy-momentum tensor does not have a real time-like eigenvector. This effect is purely quantum mechanical, since for classical systems, a local rest frame can always be defined. We study the relation with the null and weak energy condition, which are violated in even larger regions, and compare with previously known examples. While no pathologies or instabilities arise, it is interesting that regions without a rest frame are possibly present in heavy ion collisions.Comment: 5 pages, 4 figures; v2: fixed typo, v3: added references, matches published versio

A fully dynamical simulation of central nuclear collisions

We present a fully dynamical simulation of central nuclear collisions around mid-rapidity at LHC energies. Unlike previous treatments, we simulate all phases of the collision, including the equilibration of the system. For the simulation, we use numerical relativity solutions to AdS/CFT for the pre-equilibrium stage, viscous hydrodynamics for the plasma equilibrium stage and kinetic theory for the low density hadronic stage. Our pre-equilibrium stage provides initial conditions for hydrodynamics, resulting in sizable radial flow. The resulting light particle spectra reproduce the measurements from the ALICE experiment at all transverse momenta.Comment: 4 pages, 6 figures; v2: minor changes; v3: major changes, including a new section comparing to free streaming, matches published versio

3D and 4D Simulations for Landscape Reconstruction and Damage Scenarios. GIS Pilot Applications

The project 3D and 4D Simulations for Landscape Reconstruction and Damage Scenarios: GIS Pilot Applications has been devised with the intention to deal with the demand for research, innovation and applicative methodology on the part of the international programme, requiring concrete results to increase the capacity to know, anticipate and respond to a natural disaster. This project therefore sets out to develop an experimental methodology, a wide geodatabase, a connected performant GIS platform and multifunctional scenarios able to profitably relate the added values deriving from different geotechnologies, aimed at a series of crucial steps regarding landscape reconstruction, event simulation, damage evaluation, emergency management, multi-temporal analysis. The Vesuvius area has been chosen for the pilot application owing to such an impressive number of people and buildings subject to volcanic risk that one could speak in terms of a possible national disaster. The steps of the project move around the following core elements: creation of models that reproduce the territorial and anthropic structure of the past periods, and reconstruction of the urbanized area, with temporal distinctions; three-dimensional representation of the Vesuvius area in terms of infrastructuralresidential aspects; GIS simulation of the expected event; first examination of the healthcareepidemiological consequences; educational proposals. This paper represents a proactive contribution which describes the aims of the project, the steps which constitute a set of specific procedures for the methodology which we are experimenting, and some thoughts regarding the geodatabase useful to “package” illustrative elaborations. Since the involvement of the population and adequate hazard preparedness are very important aspects, some educational and communicational considerations are presented in connection with the use of geotechnologies to promote the knowledge of risk

Universal hydrodynamic flow in holographic planar shock collisions

We study the collision of planar shock waves in AdS$_5$ as a function of shock profile. In the dual field theory the shock waves describe planar sheets of energy whose collision results in the formation of a plasma which behaves hydrodynamically at late times. We find that the post-collision stress tensor near the light cone exhibits transient non-universal behavior which depends on both the shock width and the precise functional form of the shock profile. However, over a large range of shock widths, including those which yield qualitative different behavior near the future light cone, and for different shock profiles, we find universal behavior in the subsequent hydrodynamic evolution. Additionally, we compute the rapidity distribution of produced particles and find it to be well described by a Gaussian.Comment: 23 pages, 15 figures, published versio

Творчество Дж. Дагджи в зеркале современной крымскотатарской литературы

Процесс возвращения крымских татар на свою историческую родину не только создал благоприятную почву для возрождения культуры в широком ее понимании, но и актуализировал вопросы ее изучения, развития и пропаганды. То же самое можно сказать о крымскотатарской литературе, пережившей на своем веку взлеты и падения, ставшей жертвой общественно-политических, социально-экономических потрясений последних сто лет. Литература, не потерявшее свое достоинство ни в годы тоталитаризма, ни в годы депортации, сегодня с новой силой, с новым вдохновением стала на путь развития. Возвращение из небытия титанов литературы, «засекреченных» до недавнего времени их произведений, появлению новых имен, усиления роли и места литературы в интеграционных процессах, их научное осмысление дают основания для такой констатации. Ярким примером тому может послужить творчество крупнейшего романиста, титана художественной мысли крымских татар ХХ столетия Дженгиз Дагджи, ныне проживающего в Лондоне, и, к сожалению, малоизвестного для некрымскотатарского читателя