arXiv subjects

Jorge Casalderrey-Solana

Publications and source records attributed to Jorge Casalderrey-Solana.

At least 19 recordsLinked to original sources

arXiv2026

Computationally Efficient Description of Medium Response to Jets in Heavy Ion Collisions

We develop an Efficient Wake procedure for computing the distribution of hadrons originating from jet wakes in heavy ion collisions - the hydrodynamic response of a droplet of quark-gluon plasma to the energy and momentum deposited in it by high-energy partons propagating through it. The procedure employs the linearity of linearized hydrodynamics and takes account of the effects of both longitudinal expansion and transverse radial flow on the hydrodynamic evolution of the wakes and on the resulting particle production at the freezeout hypersurface. It makes repeated use of template solutions to linearized hydrodynamics in a Bjorken flow background with no transverse flow, templates that need only be computed once, and uses suitable rotations and boosts to map fluctuations from these templates to fluctuations at a point on the freezeout hypersurface in a way that incorporates the effects of the radial flow. We benchmark this procedure by comparing its results to results obtained from full $(3+1)$-dimensional nonlinear hydrodynamics calculations, find reasonable agreement, and find that our Efficient Wake procedure yields a much better description of the distribution of hadrons originating from jet wakes than does the older oversimplified procedure employed in the Hybrid Model. And, the Efficient Wake procedure is computationally efficient: it is at least tens of thousands of times faster than full nonlinear hydrodynamics calculations. Hence, we anticipate that when our new procedure is implemented in Monte Carlo analyses of jets in heavy ion collisions, for example in the Hybrid Model, it will greatly improve the description of the soft component of many jet and jet substructure observables as compared to experimental data.

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arXiv2026

Megahertz Gravitational Waves from Neutron Star Mergers

Neutron star mergers provide a unique laboratory for the study of strong-field gravity coupled to quantum chromodynamics in extreme conditions. The frequencies and amplitudes of the resulting gravitational waves encode invaluable information about the merger. Simulations to date have shown that these frequencies lie in the kilohertz range. They have also shown that, if quantum chromodynamics possesses a first-order phase transition at high baryon density, then this is likely to be accessed during the merger dynamics. Here we show that this would result in the nucleation of superheated and/or supercompressed bubbles whose subsequent dynamics would produce gravitational waves in the megahertz range. We estimate the amplitude of this signal and compare it to the sensitivity of planned future detectors.

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arXiv2026

Hydrodynamics of Relativistic Superheated Bubbles

Relativistic, charged, superheated bubbles may play an important role in neutron star mergers if first-order phase transitions are present in the phase diagram of Quantum Chromodynamics. We describe the properties of these bubbles in the hydrodynamic regime. We find two qualitative differences with supercooled bubbles. First, the pressure at the center of an expanding superheated bubble can be higher or lower than the pressure in the asymptotic, metastable phase. Second, some fluid flows develop metastable regions behind the bubble wall for any choice of the equation of state. We consider the possible role of a conserved charge akin to baryon number. The fluid flow profiles are unaffected by this charge if the speed of sound is constant in each phase, but they are modified for more general equations of state. We compute the efficiency factor relevant for gravitational wave production.

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arXiv2025

Self-sustained, out-of-equilibrium inflation

We use holography to study dS-invariant states of non-conformal, strongly coupled quantum field theories in four-dimensional de Sitter space. We show that out-of-equilibrium effects can sustain the exponential inflation within the regime of validity of semiclassical gravity, $H \ll M \ll M_\mathrm{sp}$, with $H$ the Hubble parameter, $M$ the characteristic scale of the quantum field theory, $M_\mathrm{sp} = M_\mathrm{p}/N$ the species scale, $M_\mathrm{p}$ the Planck scale, and $N^2$ the number of matter fields. In the holographic description, the required fine-tuning scales only logarithmically with the ratio $M_\mathrm{sp}/H$. The resulting solutions exhibit apparent horizons whose increasing area indicates a continuous growth of the comoving entropy density. We suggest that this inflationary regime can arise as the late-time limit of a dynamical evolution starting from an initial Friedmann-Lemaître-Robertson-Walker universe.

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arXiv2025

Spinodal Gravitational Waves

We uncover a new gravitational-wave production mechanism in cosmological, first-order, thermal phase transitions. These are usually assumed to proceed via the nucleation of bubbles of the stable phase inside the metastable phase. However, if the nucleation rate is sufficiently suppressed, then the Universe may supercool all the way down the metastable branch and enter the spinodal region. In this case the transition proceeds via the exponential growth of unstable modes and the subsequent formation, merging and relaxation of phase domains. We use holography to follow the real-time evolution of this process in a strongly coupled, four-dimensional gauge theory. The resulting gravitational wave spectrum differs qualitatively from that in transitions mediated by bubble nucleation. We discuss the possibility that the spinodal dynamics may be preceded by a period of thermal inflation.

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arXiv2023

Quantum Matter near a Cosmological Singularity

General Relativity predicts that the spacetime near a cosmological singularity undergoes an infinite number of chaotic oscillations between different Kasner epochs with rapid transitions between them. This so-called BKL behaviour persists in the presence of several types of classical matter. Little is known in the presence of quantum effects. A major obstacle is the fact that the fast metric oscillations inevitably drive the matter far from equilibrium. We use holography to determine the evolution of the quantum stress tensor of a non-conformal, strongly-coupled, four-dimensional gauge theory in a Kasner spacetime. The stress tensor near the singularity is solely controlled by the ultraviolet fixed point of the gauge theory, and it diverges in a universal way common to all theories with a gravity dual. We then compute the backreaction of the stress tensor on the Kasner metric to leading order in the gravitational coupling. The modification of the Kasner exponents that we find suggests that the BKL behaviour may be avoided in the presence of quantum matter.

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arXiv2023

Thermal Emission of Gravitational Waves from Weak to Strong Coupling

We study the production of gravitational waves by a thermalized plasma of $\mathcal N$=4 Supersymmetric Yang Mills matter. We focus on the large number of colors limit, $N_c\rightarrow \infty$, and compute the spectrum of gravitational waves both for infinitely large and infinitesimally small values of the 't Hooft coupling constant $λ$. In the $λ\rightarrow \infty$ limit we employ the gauge/gravity duality to compute the emission rate via the analysis of Energy-Momentum tensor thermal correlators. In the $λ\rightarrow 0$ limit we employ state-of-the-art perturbative analyses to calculate the complete leading order emission rate. By comparing these extreme limits, we bracket the magnitude of the spectrum induced by this source of gravitational waves. Embedding our results in a cosmological evolution model, we find qualitative and quantitative similarities between the strong coupling spectrum and the extrapolation of the perturbative results up to an intermediate value of the coupling, after an appropriate re-scaling of the effective number of degrees of freedom. We comment on how our results can help better understand the contribution of thermalized matter to the stochastic spectrum of gravitational waves.

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arXiv2023

Holographic Bubbles with Jecco: Expanding, Collapsing and Critical

Cosmological phase transitions can proceed via the nucleation of bubbles that subsequently expand and collide. The resulting gravitational wave spectrum depends crucially on the properties of these bubbles. We extend our previous holographic work on planar bubbles to circular bubbles in a strongly-coupled, non-Abelian, four-dimensional gauge theory. This extension brings about two new physical properties. First, the existence of a critical bubble, which we determine. Second, the bubble profile at late times exhibits a richer self-similar structure, which we verify. These results require a new 3+1 evolution code called Jecco that solves the Einstein equations in the characteristic formulation in asymptotically AdS spaces. Jecco is written in the Julia programming language and is freely available. We present an outline of the code and the tests performed to assess its robustness and performance.

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arXiv2022

Asymmetric transverse momentum broadening in an inhomogeneous medium

Gradient jet tomography in high-energy heavy-ion collisions utilizes the asymmetric transverse momentum broadening of a propagating parton in an inhomogeneous medium. Such broadening is studied within a path integral description of the evolution of the Wigner distribution for a propagating parton in medium. Going beyond the eikonal approximation of multiple scattering, the evolution operator in the transverse direction can be expressed as the functional integration over all classical trajectories of a massive particle with the light-cone momentum $ω$ as its mass. With a dipole approximation of the Wilson line correlation function, evolution with the light-cone time $t$ is determined by the jet transport coefficient $\hat q$ that can vary with space and time. In a uniform medium with a constant $\hat q_0$, the analytical solution to the Wigner distribution becomes a typical drifted Gaussian in both transverse momentum and coordinate with the diffusion width $\sqrt{\hat q_0t}$ and $\sqrt{\hat q_0t^3/3ω^2}$, respectively. In the case of a simple Gaussian-like transverse inhomogeneity with a spatial width $σ$ on top of a uniform medium, the final asymmetrical momentum distribution can be calculated semi-analytically. The transverse asymmetry defined for jet gradient tomography that characterizes the asymmetrical distribution is found to linearly correlate with the initial transverse position of the propagating parton within the domain of the inhomogeneity. It decreases with the parton energy $ω$, increases with the propagation time initially and saturates when the diffusion distance is much larger than the size of the inhomogeneity or $t^3\gg 3ω^2σ^2/\hat q_0$. The transverse momentum broadening due to the inhomogeneity also saturates at late time in contrast to the continued increase with time if the drifted diffusion in space is ignored.

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arXiv2022

Holographic Evolution with Dynamical Boundary Gravity

Holography has provided valuable insights into the time evolution of strongly coupled gauge theories in a fixed spacetime. However, this framework is insufficient if this spacetime is dynamical. We present a scheme to evolve a four-dimensional, strongly interacting gauge theory coupled to four-dimensional dynamical gravity in the semiclassical regime. As in previous work, we use holography to evolve the quantum gauge theory stress tensor, whereas the four-dimensional metric evolves according to Einstein's equations coupled to the expectation value of the stress tensor. The novelty of our approach is that both the boundary and the bulk spacetimes are constructed dynamically, one time step at a time. We focus on Friedmann-Lemaître-Robertson-Walker geometries and evolve far-from-equilibrium initial states that lead to asymptotically expanding, flat or collapsing Universes

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arXiv2022

Bubble Wall Velocity from Holography

Cosmological phase transitions proceed via the nucleation of bubbles that subsequently expand and collide. The resulting gravitational wave spectrum depends crucially on the bubble wall velocity. Microscopic calculations of this velocity are challenging even in weakly coupled theories. We use holography to compute the wall velocity from first principles in a strongly coupled, non-Abelian, four-dimensional gauge theory. The wall velocity is determined dynamically in terms of the nucleation temperature. We find an approximately linear relation between the velocity and the ratio $Δ\mathcal{P}/\mathcal{E}$, with $Δ\mathcal{P}$ the pressure difference between the inside and the outside of the bubble and $\mathcal{E}$ the energy density outside the bubble. Up to a rescaling, the wall profile is well approximated by that of an equilibrium, phase-separated configuration at the critical temperature. We verify that ideal hydrodynamics provides a good description of the system everywhere except near the wall.

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arXiv2021

Domain Collisions

We use holography to study collisions of phase domains formed in a four-dimensional, strongly-coupled gauge theory with a first-order, thermal phase transition. We find three qualitatively different dynamical regimes depending on the collision velocity. For low velocities the domains slow down before the collision and subsequently merge and relax to equilibrium. For intermediate velocities no slow down is present before the merger. For high enough velocities the domains can collide and break apart several times before they finally merge. These features leave an imprint on the time evolution of the entropy of the system, which we compute from the area of the dual horizon on the gravity side.

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arXiv2021

Jet Wake from Linearized Hydrodynamics

We explore how to improve the hybrid model description of the particles originating from the wake that a jet produced in a heavy ion collision leaves in the droplet of quark-gluon plasma (QGP) through which it propagates, using linearized hydrodynamics on a background Bjorken flow. Jet energy and momentum loss described by the hybrid model become currents sourcing linearized hydrodynamics. By solving the linearized hydrodynamic equations numerically, we investigate the development of the wake in the dynamically evolving droplet of QGP, study the effect of viscosity, scrutinize energy-momentum conservation, and check the validity of the linear approximation. We find that linearized hydrodynamics works better in the viscous case because diffusive modes damp the energy-momentum perturbation produced by the jet. We calculate the distribution of particles produced from the jet wake by using the Cooper-Frye prescription and find that both the transverse momentum spectrum and the distribution of particles in azimuthal angle are similar in shape in linearized hydrodynamics and in the hybrid model. Their normalizations are different because the momentum-rapidity distribution in the linearized hydrodynamics analysis is more spread out, due to sound modes. Since the Bjorken flow has no transverse expansion, we explore the effect of transverse flow by using local boosts to add it into the Cooper-Frye formula. After including the effects of transverse flow in this way, the transverse momentum spectrum becomes harder: more particles with transverse momenta bigger than $2$ GeV are produced than in the hybrid model. Although we defer implementing this analysis in a jet Monte Carlo, as would be needed to make quantitative comparisons to data, we gain a qualitative sense of how the jet wake may modify jet observables by computing proxies for two example observables: the lost energy recovered in a cone of varying open angle, and the fragmentation function. We find that linearized hydrodynamics with transverse flow effects added improves the description of the jet wake in the hybrid model in just the way that comparison to data indicates is needed. Our study illuminates a path to improving the description of the wake in the hybrid model, highlighting the need to take into account the effects of both transverse flow and the broadening of the energy-momentum perturbation in spacetime rapidity on particle production.

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arXiv2020

Strong-coupling dynamics and entanglement in de Sitter space

We use holography to study the dynamics of a strongly-coupled gauge theory in four-dimensional de Sitter space with Hubble rate $H$. The gauge theory is non-conformal with a characteristic mass scale $M$. We solve Einstein's equations numerically and determine the time evolution of homogeneous gauge theory states. If their initial energy density is high compared with $H^4$ then the early-time evolution is well described by viscous hydrodynamics with a non-zero bulk viscosity. At late times the dynamics is always far from equilibrium. The asymptotic late-time state preserves the full de Sitter symmetry group and its dual geometry is a domain-wall in AdS$_5$. The approach to this state is characterised by an emergent relation of the form $\mathcal{P}=w\,\mathcal{E}$ that is different from the equilibrium equation of state in flat space. The constant $w$ does not depend on the initial conditions but only on $H/M$ and is negative if the ratio $H/M$ is close to unity. The event and the apparent horizons of the late-time solution do not coincide with one another, reflecting its non-equilibrium nature. In between them lies an "entanglement horizon" that cannot be penetrated by extremal surfaces anchored at the boundary, which we use to compute the entanglement entropy of boundary regions. If the entangling region equals the observable universe then the extremal surface coincides with a bulk cosmological horizon that just touches the event horizon, while for larger regions the extremal surface probes behind the event horizon.

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arXiv2020

Jet substructure modification probes the QGP resolution length

We show the sensitivity of groomed jet substructure measurements to the finite resolution power of the QGP to disentangle multiple energetic partons, as produced by QCD jets, that traverse it simultaneously. We illustrate these effects by studying Soft Dropped observables within a hybrid strong/weak coupling model for jet-medium interactions. By analysing Monte-Carlo-generated jet data in heavy ion collisions, we show that the angular structure of these type of observables is sensitive to the value of the QGP resolution length.

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arXiv2020

Dynamics of Phase Separation from Holography

We use holography to develop a physical picture of the real-time evolution of the spinodal instability of a four-dimensional, strongly-coupled gauge theory with a first-order, thermal phase transition. We numerically solve Einstein's equations to follow the evolution, in which we identify four generic stages: A first, linear stage in which the instability grows exponentially; a second, non-linear stage in which peaks and/or phase domains are formed; a third stage in which these structures merge; and a fourth stage in which the system finally relaxes to a static, phase-separated configuration. On the gravity side the latter is described by a static, stable, inhomogeneous horizon. We conjecture and provide evidence that all static, non-phase separated configurations in large enough boxes are dynamically unstable. We show that all four stages are well described by the constitutive relations of second-order hydrodynamics that include all second-order gradients that are purely spatial in the local rest frame. In contrast, a Müller-Israel-Stewart-type formulation of hydrodynamics fails to provide a good description for two reasons. First, it misses some large, purely-spatial gradient corrections. Second, several second-order transport coefficients in this formulation, including the relaxation times $τ_π$ and $τ_Π$, diverge at the points where the speed of sound vanishes.

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arXiv2019

Effective long distance $q\bar{q} $ potential in holographic RG flows

We study the $q\bar{q}$ potential in strongly coupled non-conformal field theories with a non-trivial renormalization group flow via holography. We focus on the properties of this potential at an inter-quark separation $L$ large compared to the characteristic scale of the field theory. These are determined by the leading order IR physics plus a series of corrections, sensitive to the properties of the RG-flow. To determine those corrections, we propose a general method applying holographic Wilsonian renormalization to a dual string. We apply this method to examine in detail two sets of examples, $3+1$-dimensional theories with an RG flow ending in an IR fixed point; and theories that are confining in the IR, in particular, the Witten QCD and Klebanov-Strassler models. In both cases, we find corrections with a universal dependence on the inter-quark separation. When there is an IR fixed point, that correction decays as a power $\sim 1/L^4$. We explain that dependence in terms of a double-trace deformation in a one-dimensional defect theory. For a confining theory, the decay is exponential $\sim e^{-ML}$, with $M$ a scale of the order of the glueball mass. We interpret this correction using an effective flux tube description as produced by a background internal mode excitation induced by sources localized at the endpoints of the flux tube. We discuss how these results could be confronted with lattice QCD data to test whether the description of confinement via the gauge/gravity is qualitatively correct.

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arXiv2019

Holographic Collisions across a Phase Transition

We use holography to analyse relativistic collisions in a one-parameter family of strongly coupled gauge theories with thermal phase transitions. For a critical value of the parameter the transition is second order, for subcritical values it is first order, and for super-critical values it is a smooth crossover. We extract the gauge theory stress tensor from collisions of gravitational shock waves on the dual geometries. Regardless of the nature of the transition, for values of the parameter close to the critical value almost all the energy of the projectiles is deposited into a long-lived, quasi-static blob of energy at mid-rapidity. This configuration is well described by the constitutive relations of second-order hydrodynamics that include all second-order gradients that are purely spatial in the local rest frame. In contrast, a Müller-Israel-Stewart-type formulation of hydrodynamics fails to provide a good description. We discuss possible implications for searches of the QCD critical point.

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