arXiv subjects

Romulo Rougemont

Publications and source records attributed to Romulo Rougemont.

At least 37 records · Page 2Linked to original sources

arXiv2022

QCD Equation of State and Phase Diagram from Holographic Black Holes

By using the AdS/CFT correspondence, we construct an Einstein-Maxwell-Dilaton model to map the thermodynamics of strongly interacting matter. The holographic model, constrained to reproduce the lattice QCD equation of state at zero baryon chemical potential, predicts a critical end point and a first order phase transition line. We also obtain the equation of state of the model for a large region of the phase diagram. We characterize the crossover transition region by two lines, one associated to the inflection of the second order baryon susceptibility, and another one associated to the minimum of the square of the speed of sound along trajectories of constant entropy per baryon number. We observe that both lines merge at the critical point.

nucl-th↗

arXiv2022

QCD Equilibrium and Dynamical Properties from Holographic Black Holes

By using gravity/gauge correspondence, we employ an Einstein-Maxwell-Dilaton model to compute the equilibrium and out-of-equilibrium properties of a hot and baryon rich strongly coupled quark-gluon plasma. The family of 5-dimensional holographic black holes, which are constrained to mimic the lattice QCD equation of state at zero density, is used to investigate the temperature and baryon chemical potential dependence of the equation of state. We also obtained the baryon charge conductivity, and the bulk and shear viscosities with a particular focus on the behavior of these observables on top of the critical end point and the line of first order phase transition predicted by the model.

nucl-th↗

arXiv2022

Hydrodynamization times of a holographic fluid far from equilibrium

We investigate several hydrodynamization times for an ensemble of different far-from-equilibrium solutions of the strongly coupled $\mathcal{N}=4$ Supersymmetric Yang-Mills plasma undergoing Bjorken flow. For the ensemble of initial data analyzed in the present work, we find that, with typical tolerances between $3\%$ to $5\%$, the average hydrodynamization time associated with the late time convergence of the pressure anisotropy to the corresponding Borel resummed hydrodynamic attractor is approximately equal to the average hydrodynamization time associated with the Navier-Stokes result, while both are shorter than the average hydrodynamization time associated with second-order hydrodynamics. On the other hand, we find that the entropy density of the different solutions coalesces to second-order hydrodynamics long before entering in the Navier-Stokes regime. A clear hierarchy between the different average hydrodynamization times of the Bjorken expanding fluid is established for the set of analyzed initial data, comprising also some solutions which, whilst satisfying the dominant and the weak energy conditions at the initial time, evolve such as to transiently violate one or both conditions when the fluid is still far from equilibrium. In particular, solutions violating the weak energy condition are generally found to take a longer time to enter in the hydrodynamic regime than the other solutions.

nucl-th↗

arXiv2021

Violation of energy conditions and entropy production in holographic Bjorken flow

We demonstrate that a Bjorken expanding strongly coupled $\mathcal{N}=4$ Supersymmetric Yang-Mills plasma can display dynamically-driven violations of the dominant and also the weak energy condition during hydrodynamization. In addition, we find that a period of vanishing entropy production in far-from-equilibrium stages induces later violations of the dominant energy condition in the strongly coupled plasma. Such violations cannot occur in a classical description of hydrodynamization and suggest that the inclusion of quantum effects in transport can lead to new phenomena in these regimes, even for systems without anomalies or spin.

nucl-th↗

arXiv2021

Hot and dense quark-gluon plasma thermodynamics from holographic black holes

We present new results on the equation of state and transition line of hot and dense strongly interacting QCD matter, obtained from a bottom-up Einstein-Maxwell-Dilaton holographic model. We considerably expand the previous coverage in baryon densities in this model by implementing new numerical methods to map the holographic black hole solutions onto the QCD phase diagram. We are also able to obtain, for the first time, the first-order phase transition line in a wide region of the phase diagram. Comparisons with the most recent lattice results for the QCD thermodynamics are also presented.

nucl-th↗

arXiv2020

Jet quenching parameters in strongly coupled anisotropic plasmas in the presence of magnetic fields

I use the holographic gauge/gravity duality to systematically calculate the jet quenching parameters in strongly coupled anisotropic plasmas in the presence of external magnetic fields. The magnetic field breaks down spatial rotation symmetry from $SO(3)$ to $SO(2)$, leading to the presence of multiple anisotropic jet quenching parameters, which are evaluated here in two quite different holographic settings. One of them corresponds to a top-down deformation of the strongly coupled $\mathcal{N} = 4$ Super Yang-Mills plasma triggered by an external magnetic field, while the other one is a bottom-up Einstein-Maxwell-Dilaton model of phenomenological relevance for high energy peripheral heavy ion collisions, since it is able to provide a quantitative description of $(2+1)$-flavors lattice QCD thermodynamics with physical quark masses at zero and nonzero magnetic fields. I find for both models an overall enhancement of all the anisotropic jet quenching parameters with increasing magnetic fields. Moreover, I also conclude that for both models transverse momentum broadening is larger in transverse directions than in the direction of the magnetic field. Since these conclusions are shown to hold for two rather different holographic setups at finite temperature and magnetic fields, they are suggested as fairly robust features of strongly coupled anisotropic magnetized plasmas.

hep-ph↗

arXiv2020

Diagonal and Hall holographic conductivities dual to a bulk condensate of magnetic monopoles

By employing the holographic operator mixing technique to deal with coupled perturbations in the gauge/gravity duality, I numerically compute the real and imaginary parts of the diagonal and Hall AC conductivities in a strongly coupled quantum field theory dual to a bulk condensate of magnetic monopoles. The results obtained show that a conclusion previously derived in the literature, namely, the vanishing of holographic DC conductivities in 3-dimensional strongly coupled quantum field theories dual to a 4-dimensional bulk magnetic monopole condensate, also applies to the calculation of diagonal and Hall conductivities in the presence of a topological $θ$-term. Therefore, the condensation of magnetic monopoles in the bulk is suggested as a rather general and robust mechanism to generate dual strongly coupled quantum field theories with zero DC conductivities. The interplay between frequency, $θ$-angle and the characteristic mass scale of the monopole condensate on the results for the conductivities is also investigated.

hep-th↗

arXiv2018

Non-hydrodynamic quasinormal modes and equilibration of a baryon dense holographic QGP with a critical point

We compute the homogeneous limit of non-hydrodynamic quasinormal modes (QNM's) of a phenomenologically realistic Einstein-Maxwell-Dilaton (EMD) holographic model for the Quark-Gluon Plasma (QGP) that is able to: i) {\it quantitatively} describe state-of-the-art lattice results for the QCD equation of state and higher order baryon susceptibilities with $2+1$ flavors and physical quark masses up to highest values of the baryon chemical potential currently reached in lattice simulations; ii) describe the nearly perfect fluidity of the strongly coupled QGP produced in ultrarelativistic heavy ion collisions; iii) give a very good description of the bulk viscosity extracted via some recent Bayesian analyzes of hydrodynamical descriptions of heavy ion experimental data. This EMD model has been recently used to predict the location of the QCD critical point in the QCD phase diagram, which was found to be within the reach of upcoming low energy heavy ion collisions. The lowest quasinormal modes of the $SO(3)$ rotationally invariant quintuplet, triplet, and singlet channels evaluated in the present work provide upper bounds for characteristic equilibration times describing how fast the dense medium returns to thermal equilibrium after being subjected to small disturbances. We find that the equilibration times in the different channels come closer to each other at high temperatures, although being well separated at the critical point. Moreover, in most cases, these equilibration times decrease with increasing baryon chemical potential while keeping temperature fixed.

hep-ph↗

arXiv2017

Critical point in the phase diagram of primordial quark-gluon matter from black hole physics

Strongly interacting matter undergoes a crossover phase transition at high temperatures $T\sim 10^{12}$ K and zero net-baryon density. A fundamental question in the theory of strong interactions, Quantum Chromodynamics (QCD), is whether a hot and dense system of quarks and gluons displays critical phenomena when doped with more quarks than antiquarks, where net-baryon number fluctuations diverge. Recent lattice QCD work indicates that such a critical point can only occur in the baryon dense regime of the theory, which defies a description from first principles calculations. Here we use the holographic gauge/gravity correspondence to map the fluctuations of baryon charge in the dense quark-gluon liquid onto a numerically tractable gravitational problem involving the charge fluctuations of holographic black holes. This approach quantitatively reproduces ab initio results for the lowest order moments of the baryon fluctuations and makes predictions for the higher order baryon susceptibilities and also for the location of the critical point, which is found to be within the reach of heavy ion collision experiments.

nucl-th↗

arXiv2017

Dynamical vs. equilibrium properties of the QCD phase transition: a holographic perspective

We employ an Einstein-Maxwell-Dilaton (EMD) holographic model, which is known to be in good agreement with lattice results for the QCD equation of state with $(2+1)$ flavors and physical quark masses, to investigate the temperature and baryon chemical potential dependence of the susceptibilities, conductivities, and diffusion coefficients associated with baryon, electric, and strangeness conserved charges. We also determine how the bulk and shear viscosities of the plasma vary in the plane of temperature and baryon chemical potential. The diffusion of conserved charges and the hydrodynamic viscosities in a baryon rich quark-gluon plasma are found to be suppressed with respect to the zero net baryon case. The transition temperatures associated with equilibrium and non-equilibrium quantities are determined as a function of the baryon chemical potential for the first time. Because of the crossover nature of the QCD phase transition even at moderately large values of the chemical potential, we find that the transition temperatures associated with different quantities are spread in the interval between $130-200$ MeV and they all decrease with increasing baryon chemical potential.

hep-ph↗

arXiv2017

Momentum transport in strongly coupled anisotropic plasmas in the presence of strong magnetic fields

We present a holographic perspective on momentum transport in strongly coupled, anisotropic non-Abelian plasmas in the presence of strong magnetic fields. We compute the anisotropic heavy quark drag forces and Langevin diffusion coefficients and also the anisotropic shear viscosities for two different holographic models, namely, a top-down deformation of strongly coupled $\mathcal{N} = 4$ Super-Yang-Mills (SYM) theory triggered by an external Abelian magnetic field, and a bottom-up Einstein-Maxwell-dilaton (EMD) model which is able to provide a quantitative description of lattice QCD thermodynamics with $(2+1)$-flavors at both zero and nonzero magnetic fields. We find that, in general, energy loss and momentum diffusion through strongly coupled anisotropic plasmas are enhanced by a magnetic field being larger in transverse directions than in the direction parallel to the magnetic field. Moreover, the anisotropic shear viscosity coefficient is smaller in the direction of the magnetic field than in the plane perpendicular to the field, which indicates that strongly coupled anisotropic plasmas become closer to the perfect fluid limit along the magnetic field. We also present, in the context of the EMD model, holographic predictions for the entropy density and the crossover critical temperature in a wider region of the $(T,B)$ phase diagram that has not yet been covered by lattice simulations. Our results for the transport coefficients in the phenomenologically realistic magnetic EMD model could be readily used as inputs in numerical codes for magnetohydrodynamics.

hep-ph↗

arXiv2017

Critical behavior of non-hydrodynamic quasinormal modes in a strongly coupled plasma

We study the behavior of quasinormal modes in a top-down holographic dual corresponding to a strongly coupled $\mathcal{N} = 4$ super Yang-Mills plasma charged under a $U(1)$ subgroup of the global $SU(4)$ R-symmetry. In particular, we analyze the spectra of quasinormal modes in the external scalar and vector diffusion channels near the critical point and obtain the behavior of the characteristic equilibration times of the plasma as the system evolves towards the critical point of its phase diagram. Except close to the critical point, we observe that by increasing the chemical potential one generally increases the damping rate of the quasinormal modes, which leads to a reduction of the characteristic equilibration times in the dual strongly coupled plasma. However, as one approaches the critical point the typical equilibration time (as estimated from the lowest non-hydrodynamic quasinormal mode frequency) increases, although remaining finite, while its derivative with respect to the chemical potential diverges with exponent -1/2. We also find a purely imaginary non-hydrodynamical mode in the vector diffusion channel at nonzero chemical potential which dictates the equilibration time in this channel near the critical point.

hep-th↗

arXiv2016

Polyakov loop and heavy quark entropy in strong magnetic fields from holographic black hole engineering

We investigate the temperature and magnetic field dependence of the Polyakov loop and heavy quark entropy in a bottom-up Einstein-Maxwell-dilaton (EMD) holographic model for the strongly coupled quark-gluon plasma (QGP) that quantitatively matches lattice data for the $(2+1)$-flavor QCD equation of state at finite magnetic field and physical quark masses. We compare the holographic EMD model results for the Polyakov loop at zero and nonzero magnetic fields and the heavy quark entropy at vanishing magnetic field with the latest lattice data available for these observables and find good agreement for temperatures $T\gtrsim 150$ MeV and magnetic fields $eB\lesssim 1$ GeV$^2$. Predictions for the behavior of the heavy quark entropy at nonzero magnetic fields are made that could be readily tested on the lattice.

hep-ph↗

arXiv2016

Holographic black hole engineering at finite baryon chemical potential

This is a contribution for the Proceedings of the Conference Hot Quarks 2016, held at South Padre Island, Texas, USA, 12-17 September 2016. I briefly review some thermodynamic and baryon transport results obtained from a bottom-up Einstein-Maxwell-Dilaton holographic model engineered to describe the physics of the quark-gluon plasma at finite temperature and baryon density. The results for the equation of state, baryon susceptibilities, and the curvature of the crossover band are in quantitative agreement with the corresponding lattice QCD results with $2+1$ flavors and physical quark masses. Baryon diffusion is predicted to be suppressed by increasing the baryon chemical potential.

nucl-th↗

arXiv2016

Chern-Simons diffusion rate across different phase transitions

We investigate how the dimensionless ratio given by the Chern-Simons diffusion rate $Γ_{\textrm{CS}}$ divided by the product of the entropy density $s$ and temperature $T$ behaves across different kinds of phase transitions in the class of bottom-up non-conformal Einstein-dilaton holographic models originally proposed by Gubser and Nellore. By tuning the dilaton potential, one is able to holographically mimic a first order, a second order, or a crossover transition. In a first order phase transition, $Γ_{\textrm{CS}}/sT$ jumps at the critical temperature (as previously found in the holographic literature), while in a second order phase transition it develops an infinite slope. On the other hand, in a crossover, $Γ_{\textrm{CS}}/sT$ behaves smoothly, although displaying a fast variation around the pseudo-critical temperature. In all the cases, $Γ_{\textrm{CS}}/sT$ increases with decreasing $T$. The behavior of the Chern-Simons diffusion rate across different phase transitions is expected to play a relevant role for the chiral magnetic effect around the QCD critical end point, which is a second order phase transition point connecting a crossover band to a line of first order phase transition. Our findings in the present work add to the literature the first predictions for the Chern-Simons diffusion rate across second order and crossover transitions in strongly coupled non-conformal, non-Abelian gauge theories.

hep-ph↗

arXiv2016

Energy loss, equilibration, and thermodynamics of a baryon rich strongly coupled quark-gluon plasma

Lattice data for the QCD equation of state and the baryon susceptibility near the crossover phase transition (at zero baryon density) are used to determine the input parameters of a 5-dimensional Einstein-Maxwell-Dilaton holographic model that provides a consistent holographic framework to study both equilibrium and out-of-equilibrium properties of a hot and {\it baryon rich} strongly coupled quark-gluon plasma (QGP). We compare our holographic equation of state computed at nonzero baryon chemical potential, $μ_B$, with recent lattice calculations and find quantitative agreement for the pressure and the speed of sound for $μ_B \leq 400$ MeV. This holographic model is used to obtain holographic predictions for the temperature and $μ_B$ dependence of the drag force and the Langevin diffusion coefficients associated with heavy quark jet propagation as well as the jet quenching parameter $\hat{q}$ and the shooting string energy loss of light quarks in the baryon dense plasma. We find that the energy loss of heavy and light quarks generally displays a nontrivial, fast-varying behavior as a function of the temperature near the crossover. Moreover, energy loss is also found to generally increase due to nonzero baryon density effects even though this strongly coupled liquid cannot be described in terms of well defined quasiparticle excitations. Furthermore, to get a glimpse of how thermalization occurs in a hot and baryon dense QGP, we study how the lowest quasinormal mode of an external massless scalar disturbance in the bulk is affected by a nonzero baryon charge. We find that the equilibration time associated with the lowest quasinormal mode decreases in a dense medium.

hep-th↗

arXiv2016

Thermal photon and dilepton production and electric charge transport in a baryon rich strongly coupled QGP from holography

We obtain the thermal photon and dilepton production rates in a strongly coupled quark-gluon plasma (QGP) at both zero and nonzero baryon chemical potential using a bottom-up Einstein-Maxwell-Dilaton (EMD) holographic model that is in good quantitative agreement with the thermodynamics of $(2+1)$-flavor lattice QCD around the crossover transition for baryon chemical potentials up to 400 MeV, which may be reached in the beam energy scan (BES) at RHIC. We find that increasing the temperature $T$ and the baryon chemical potential $μ_B$ enhances the peak present in both spectra. We also obtain the electric charge susceptibility, the DC and AC electric conductivities and the electric charge diffusion as functions of $T$ and $μ_B$. We find that electric diffusive transport is suppressed as one increases $μ_B$. At zero baryon density, we compare our results for the DC electric conductivity and the electric charge diffusion with the latest lattice data available for these observables and find reasonable agreement around the crossover transition. Therefore, our holographic results may be used to constraint the magnitude of the thermal photon and dilepton production rates in a strongly coupled QGP, which we found to be at least one order of magnitude below perturbative estimates.

hep-ph↗

arXiv2016

Holographic calculation of the QCD crossover temperature in a magnetic field

Lattice data for the QCD equation of state and the magnetic susceptibility computed near the crossover transition at zero magnetic field are used to determine the input parameters of a five dimensional Einstein-Maxwell-Dilaton holographic model. Once the model parameters are fixed at zero magnetic field, one can use this holographic construction to study the effects of a magnetic field on the equilibrium and transport properties of the quark-gluon plasma. In this paper we use this model to study the dependence of the crossover temperature with an external magnetic field. Our results for the pressure of the plasma and the crossover temperature are in quantitative agreement with current lattice data for values of the magnetic field $0 \le eB \lesssim 0.3$ GeV$^2$, which is the relevant range for ultrarelativistic heavy ion collision applications.

hep-th↗