Publications by Jorge Casalderrey-Solana


Holographic isotropisation in Gauss-Bonnet gravity

Journal of High Energy Physics Springer Verlag 2017 (2017)

T Andrade, J Casalderrey-Solana, A Ficnar

We study holographic isotropisation of homogeneous, strongly coupled, non-Abelian plasmas in Gauss-Bonnet gravity with a negative cosmological constant. We focus on small values of the Gauss-Bonnet coupling parameter λGB and linearise the equations of motion around a time-dependent background solution with λGB = 0. We numerically solve the linearised equations and show that the entire time evolution of the pressure anisotropy can be well approximated by the linear in λGB corrections to the quasinormal mode expansion, even in the cases of high anisotropy. We finally show that, quite generally, the time evolution of the pressure anisotropy with the Gauss-Bonnet term is approximately shifted with respect to the evolution without it, with the sign of the shift being directly related to the sign of the λGB parameter. Combined with the observation that negative λGB captures qualitative features of positive gauge coupling corrections, this suggests that the latter generically increase the isotropisation time of strongly coupled plasmas.


Paths to equilibrium in non-conformal collisions

Journal of High Energy Physics Springer Verlag 2017 (2017) 154

M Attems, J Casalderrey-Solana, D Mateos, D Santos-Oliván, CF Sopuerta, M Triana, M Zilhão

We extend our previous analysis of holographic heavy ion collisions in non-conformal theories. We provide a detailed description of our numerical code. We study collisions at different energies in gauge theories with different degrees of non-conformality. We compare four relaxation times: the hydrodynamization time (when hydrodynamics becomes applicable), the EoSization time (when the average pressure approaches its equilibrium value), the isotropization time (when the longitudinal and transverse pressures approach each other) and the condensate relaxation time (when the expectation value of a scalar operator approaches its equilibrium value). We find that these processes can occur in several different orderings. In particular, the condensate can remain far from equilibrium even long after the plasma has hydrodynamized and EoSized. We also explore the rapidity distribution of the energy density at hydrodynamization. This is far from boost-invariant and its width decreases as the non-conformality increases. Nevertheless, the velocity field at hydrodynamization is almost exactly boost-invariant regardless of the non-conformality. This result may be used to constrain the initialization of hydrodynamic fields in heavy ion collisions.


Phase transitions, inhomogeneous horizons and second-order hydrodynamics

Journal of High Energy Physics Springer 2017 (2017) 129-

M Attems, Y Bea, J Casalderrey-Solana, D Mateos, M Triana, M Zilhão

We use holography to study the spinodal instability of a four-dimensional, strongly-coupled gauge theory with a first-order thermal phase transition. We place the theory on a cylinder in a set of homogeneous, unstable initial states. The dual gravity configurations are black branes afflicted by a Gregory-Laflamme instability. We numerically evolve Einstein’s equations to follow the instability until the system settles down to a stationary, inhomogeneous black brane. The dual gauge theory states have constant temperature but non-constant energy density. We show that the time evolution of the instability and the final states are accurately described by second-order hydrodynamics. In the static limit, the latter reduces to a single, second-order, non-linear differential equation from which the inhomogeneous final states can be derived.


Holographic collisions in non-conformal theories

Journal of High Energy Physics Springer Verlag 2017 (2017) 1-12

M Attems, J Casalderrey-Solana, D Mateos, D Santos-Oliván, CF Sopuerta, M Triana, M Zilhão

We numerically simulate gravitational shock wave collisions in a holographic model dual to a non-conformal four-dimensional gauge theory. We find two novel effects associated to the non-zero bulk viscosity of the resulting plasma. First, the hydrodynamization time increases. Second, if the bulk viscosity is large enough then the plasma becomes well described by hydrodynamics before the energy density and the average pressure begin to obey the equilibrium equation of state. We discuss implications for the quark-gluon plasma created in heavy ion collision experiments.


Probing jet decoherence in heavy ion collisions

Nuclear Physics A Elsevier 967 (2017) 564-567

J Casalderrey-Solana, Y Mehtar-Tani, CA Salgado, K Tywoniuk

We suggest to use the SofDrop jet grooming technique to investigate the sensitivity of jet substructure to color decoherence in heavy ion collisions. We propose in particular to analyze the two-prong probability angular distribution as a probe of the transition between the coherent and incoherent energy loss regimes. We predict an increasing suppression of two-prong substructures with angle as the medium resolves more jet substructure.


Predictions for boson-jet observables and fragmentation function ratios from a hybrid strong/weak coupling model for jet quenching

Journal of High Energy Physics Springer Berlin Heidelberg 2016 (2016)

J Casalderrey-Solana, DC Gulhan, JG Milhano, D Pablos, K Rajagopal

We have previously introduced a hybrid strong/weak coupling model for jet quenching in heavy ion collisions in which we describe the production and fragmentation of jets at weak coupling, using Pythia, and describe the rate at which each parton in the jet shower loses energy as it propagates through the strongly coupled plasma, dE/dx, using an expression computed holographically at strong coupling. The model has a single free parameter that we fit to a single experimental measurement. We then confront our model with experimental data on many other jet observables, focusing in this paper on boson-jet observables, finding that it provides a good description of present jet data. Next, we provide the predictions of our hybrid model for many measurements to come, including those for inclusive jet, dijet, photon-jet and Z-jet observables in heavy ion collisions with energy (Formula presented.) ATeV coming soon at the LHC. As the statistical uncertainties on near-future measurements of photon-jet observables are expected to be much smaller than those in present data, with about an order of magnitude more photon-jet events expected, predictions for these observables are particularly important. We find that most of our pre- and post-dictions do not depend sensitively on the form we choose for the rate of energy loss dE/dx of the partons in the shower. This gives our predictions considerable robustness. To better discriminate between possible forms for the rate of energy loss, though, we must turn to intrajet observables. Here, we focus on ratios of fragmentation functions. We close with a suggestion for a particular ratio, between the fragmentation functions of inclusive and associated jets with the same kinematics in the same collisions, which is particularly sensitive to the x- and E-dependence of dE/dx, and hence may be used to learn which mechanism of parton energy loss best describes the quenching of jets.


A comprehensive analysis of jet quenching via a hybrid strong/weak coupling model for jet-medium interactions

Nuclear Physics A Elsevier 956 (2016) 613-616

J Casalderrey-Solana, DC Gulhan, JG Milhano, D Pablos, K Rajagopal

Within a hybrid strong/weak coupling model for jets in strongly coupled plasma, we explore jet modifications in ultra-relativistic heavy ion collisions. Our approach merges the perturbative dynamics of hard jet evolution with the strongly coupled dynamics which dominates the soft exchanges between the fast partons in the jet shower and the strongly coupled plasma itself. We implement this approach in a Monte Carlo, which supplements the DGLAP shower with the energy loss dynamics as dictated by holographic computations, up to a single free parameter that we fit to data. We then augment the model by incorporating the transverse momentum picked up by each parton in the shower as it propagates through the medium, at the expense of adding a second free parameter. We use this model to discuss the influence of the transverse broadening of the partons in a jet on intra-jet observables. In addition, we explore the sensitivity of such observables to the back-reaction of the plasma to the passage of the jet.


Boson-Jet Correlations in a Hybrid Strong/Weak Coupling Model for Jet Quenching in Heavy Ion Collisions

NUCLEAR AND PARTICLE PHYSICS PROCEEDINGS 276 (2016) 285-288

J Casalderrey-Solana, DC Gulhan, J Guilherme Milhano, D Pablos, K Rajagopal


Thermodynamics, transport and relaxation in non-conformal theories

Journal of High Energy Physics Springer Verlag 2016 (2016)

M Attems, J Casalderrey-Solana, D Mateos, I Papadimitriou, D Santos-Oliván, CF Sopuerta, M Triana, M Zilhão

We study the equilibrium and near-equilibrium properties of a holographic five-dimensional model consisting of Einstein gravity coupled to a scalar field with a non-trivial potential. The dual four-dimensional gauge theory is not conformal and, at zero temperature, exhibits a renormalisation group flow between two different fixed points. We quantify the deviations from conformality both in terms of thermodynamic observables and in terms of the bulk viscosity of the theory. The ratio of bulk over shear viscosity violates Buchel’s bound. We study relaxation of small-amplitude, homogeneous perturbations by computing the quasi-normal modes of the system at zero spatial momentum. In this approximation we identify two different relaxation channels. At high temperatures, the different pressures first become approximately equal to one another, and subsequently this average pressure evolves towards the equilibrium value dictated by the equation of state. At low temperatures, the average pressure first evolves towards the equilibrium pressure, and only later the different pressures become approximately equal to one another.


Two-gluon emission and interference in a thin QCD medium: insights into jet formation

Journal of High Energy Physics Springer Berlin Heidelberg 2016 (2016) 174

J Casalderrey-Solana, D Pablos, K Tywoniuk

In heavy-ion collisions, an abundant production of high-energy QCD jets allows to study how these multiparticle sprays are modified as they pass through the quark-gluon plasma. In order to shed new light on this process, we compute the inclusive two-gluon rate off a hard quark propagating through a color deconfined medium at first order in medium opacity. We explicitly impose an energy ordering of the two emitted gluons, such that the “hard” gluon can be thought of as belonging to the jet substructure while the other is a “soft” emission (which can be collinear or medium-induced). Our analysis focusses on two specific limits that clarify the modification of the additional angle- and formation time-ordering of splittings. In one limit, the formation time of the “hard” gluon is short compared to the “soft” gluon formation time, leading to a probabilistic formula for production of and subsequent radiation off a quark-gluon antenna. In the other limit, the ordering of formation is reverted, which automatically leads to the fact that the jet substructure is resolved by the medium. We observe in this case a characteristic delay: the jet radiates as one color current (quark) up to the formation of the “hard” gluon, at which point we observe the onset of radiation of the new color current (gluon). Within our kinematic constraints, our computation supports a picture in which the in-medium jet dynamics are described as a collection of subsequent antennas which are resolved by the medium according to their transverse extent.


Holographic 3-jet events

NUCLEAR AND PARTICLE PHYSICS PROCEEDINGS 276 (2016) 115-116

J Casalderrey-Solana, A Ficnar


Holographic heavy ion collisions with baryon charge

Journal of High Energy Physics Springer Verlag 2016 (2016)

J Casalderrey-Solana, D Mateos, W van der Schee, M Triana

We numerically simulate collisions of charged shockwaves in Einstein-Maxwell theory in anti-de Sitter space as a toy model of heavy ion collisions with non-zero baryon charge. The stress tensor and the baryon current become well described by charged hydrodynamics at roughly the same time. The effect of the charge density on generic observables is typically no larger than 15%. We find significant stopping of the baryon charge and compare our results with those in heavy ion collision experiments.


A hybrid strong/weak coupling approach to jet quenching (vol 10, pg, 2014)

JOURNAL OF HIGH ENERGY PHYSICS (2015) ARTN 175

J Casalderrey-Solana, DC Gulhan, JG Milhano, D Pablos, K Rajagopal


Jet quenching within a hybrid strong/weak coupling approach

NUCLEAR PHYSICS A 931 (2014) 487-492

J Casalderrey-Solana, D Can Gulhan, J Guilherme Milhano, D Pablos, K Rajagopal


Towards a hybrid strong/weak coupling approach to jet quenching

NUCLEAR PHYSICS A 932 (2014) 421-425

J Casalderrey-Solana, DC Gulhan, JG Milhano, D Pablos, K Rajagopal


A hybrid strong/weak coupling approach to jet quenching

JOURNAL OF HIGH ENERGY PHYSICS (2014)

J Casalderrey-Solana, DC Gulhan, JG Milhano, D Pablos, K Rajagopal


Longitudinal coherence in a holographic model of asymmetric collisions.

Physical review letters 112 (2014) 221602-

J Casalderrey-Solana, MP Heller, D Mateos, W van der Schee

As a model of the longitudinal structure in heavy ion collisions, we simulate gravitational shock wave collisions in anti-de Sitter space in which each shock is composed of multiple constituents. We find that all constituents act coherently, and their separation leaves no imprint on the resulting plasma, when this separation is ≲0.26/T_{hyd}, with T_{hyd} the temperature of the plasma at the time when hydrodynamics first becomes applicable. In particular, the center-of-mass of the plasma coincides with the center-of-mass of all the constituents participating in the collision, as opposed to the center-of-mass of the individual collisions. We discuss the implications for nucleus-nucleus and proton-nucleus collisions.


High-<inf>p T</inf> and jets. a summary of results from quark matter 2012

Nuclear Physics A 904-905 (2013) 326c-333c

J Casalderrey Solana, A Milov

A broad range of new experimental data and theoretical results on the properties of hadronic matter under extreme conditions have been reported at Quark Matter 2012 conference. At this conference the scientific community was presented with a variety of measurements from the 2011 lead-lead LHC run using hard probe observables. Many measurements, such as boson-jet correlations, production rates of the b-jets, high precision jet fragmentation and others were shown for the first time. The new data from the LHC was matched by new techniques and analyses coming from RHIC experiments. This proceedings article summarises the new measurements with high-p T particles and jets and attempts to provide a theoretical explanation for the novel results presented at the conference. © 2013.


From full stopping to transparency in a holographic model of heavy ion collisions.

Physical review letters 111 (2013) 181601-

J Casalderrey-Solana, MP Heller, D Mateos, W van der Schee

We numerically simulate planar shock wave collisions in anti-de Sitter space as a model for heavy ion collisions of large nuclei. We uncover a crossover between two different dynamical regimes as a function of the collision energy. At low energies the shocks first stop and then explode in a manner approximately described by hydrodynamics, in close similarity with the Landau model. At high energies the receding fragments move outwards at the speed of light, with a region of negative energy density and negative longitudinal pressure trailing behind them. The rapidity distribution of the energy density at late times around midrapidity is not approximately boost invariant but Gaussian, albeit with a width that increases with the collision energy.


New picture of jet quenching dictated by color coherence

PHYSICS LETTERS B 725 (2013) 357-360

J Casalderrey-Solana, Y Mehtar-Tani, CA Salgado, K Tywoniuk

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