arXiv subjects

Jorge Noronha

Publications and source records attributed to Jorge Noronha.

At least 181 records · Page 10Linked to original sources

arXiv2011

Hagedorn States and Thermalization in Heavy Ion Collisions

In recent years, Hagedorn states have been used to explain the equilibrium and transport properties of a hadron gas close to the QCD critical temperature. These massive resonances are shown to lower $η/s$ to near the AdS/CFT limit close to the phase transition. A comparison of the Hagedorn model to recent lattice results is made and it is found that the hadrons can reach chemical equilibrium almost immediately, well before the chemical freeze-out temperatures found in thermal fits for a hadron gas without Hagedorn states.

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arXiv2010

Heavy quarks and the collective properties of hot QCD

After reviewing the evidence that QCD matter at ultrarelativistic energies behaves as a very good fluid, we describe the connection of QCD fluidity to heavy quark observables. We review the way in which heavy quark spectra can place tighter limits on the viscosity of QCD matter. Finally, we show that correlations between flow observables and the event-by-event charm quark abundance ("flavoring") can shed light on the system's equation of state.

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arXiv2010

Universal Flow-Driven Conical Emission in Ultrarelativistic Heavy-Ion Collisions

The double-peak structure observed in soft-hard hadron correlations is commonly interpreted as a signature for a Mach cone generated by a supersonic jet interacting with the hot and dense medium created in ultrarelativistic heavy-ion collisions. We show that it can also arise due to averaging over many jet events in a transversally expanding background. We find that the jet-induced away-side yield does not depend on the details of the energy-momentum deposition in the plasma, the jet velocity, or the system size. Our claim can be experimentally tested by comparing soft-hard correlations induced by heavy-flavor jets with those generated by light-flavor jets.

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arXiv2010

Flavoring the Quark-Gluon Plasma with Charm

We demonstrate that a Quark-Gluon Plasma (QGP) with a dilute admixture of heavy quarks has, in general, a lower speed of sound than a "pure" QGP without effects from heavy flavors. The change in the speed of sound is sensitive to the details of the theory, making the hydrodynamic response to "flavoring" a sensitive probe of the underlying microscopic dynamics. We suggest that this effect may be measured in ultrarelativistic heavy ion collisions by relating the event-by-event number of charm quarks to flow observables such as the average transverse momentum.

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arXiv2010

The Heavy Quark Free Energy in QCD and in Gauge Theories with Gravity Duals

We show that the Polyakov loop approaches its asymptotic value at high temperatures {\it from below} in any strongly-coupled gauge theory at large $N_c$ with a dual supergravity description. In these theories the Polyakov loop can be used to define a quantity that behaves as a free energy of a heavy quark in the medium. This should be compared to the recent lattice results in pure glue SU(3) theory at high temperatures where the Polyakov loop approaches its non-interacting limit {\it from above}. We show that the "heavy quark free energy" obtained from the renormalized loop computed on the lattice does not behave as a true thermodynamic free energy. We conjecture that this should always be the case in asymptotically free gauge theories.

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arXiv2010

Transport Properties of QCD at Large $N_c$ and the Gauge/String Duality

Below the deconfinement phase transition large $N_c$ QCD is expected to be a very viscous hadronic fluid because both the shear and bulk viscosity to entropy density ratio, $η/s,ζ/s \sim N_c^2$. In this letter I show that $η/s \sim N_c^2$ in the confined phase of holographic models of QCD at large $N_c$ defined in the supergravity approximation. Our results show that the gauge/string duality can be used to describe not only nearly perfect fluids but also extremely viscous systems such as a cold gas of glueballs.

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arXiv2010

Connecting Polyakov Loops to the Thermodynamics of $SU(N_c)$ Gauge Theories Using the Gauge-String Duality

We show that in four-dimensional gauge theories dual to five-dimensional Einstein gravity coupled to a single scalar field in the bulk the derivative of the single heavy quark free energy in the deconfined phase is $dF_{Q}(T)/dT \sim -1/c_s^2(T)$, where $c_s(T)$ is the speed of sound. This general result provides a direct link between the softest point in the equation of state of strongly-coupled plasmas and the deconfinement phase transition described by the expectation value of the Polyakov loop. We give an explicit example of a gravity dual with black hole solutions that can reproduce the lattice results for the expectation value of the Polyakov loop and the thermodynamics of SU(3) Yang-Mills theory in the (non-perturbative) temperature range between $T_c$ and $3T_c$.

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arXiv2010

Polyakov Loops in Strongly-Coupled Plasmas with Gravity Duals

We study the properties of the Polyakov loop in strongly-coupled gauge plasmas that are conjectured to be dual to five dimensional theories of gravity coupled to a nontrivial single scalar field. We find a gravity dual that can describe the thermodynamic properties and also the expectation value of the Polyakov loop in the deconfined phase of quenched SU(3) QCD up to $3T_c$.

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arXiv2009

Transport Coefficients of Hadronic Matter near $T_c$

A hadron resonance gas model including all known particles and resonances with masses $m<2$ GeV and an exponentially rising density of Hagedorn states for $m>2$ GeV is used to obtain an upper bound on the shear viscosity to entropy density ratio, $η/s\approx1/(4π)$, of hadronic matter near $T_c$. We found a large trace anomaly and small speed of sound near $T_c$, which agree well with recent lattice calculations. We comment on the bulk viscosity to entropy density ratio close to $T_c$.

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arXiv2009

Thermal Width of the $Υ$ at Large t' Hooft Coupling

We use the AdS/CFT correspondence to show that the heavy quark (static) potential in a strongly-coupled plasma develops an imaginary part at finite temperature. Thus, deeply bound heavy quarkonia states acquire a small nonzero thermal width when the t'Hooft coupling $λ=g^2 N_c \gg 1$ and the number of colors $N_c \to \infty$. In the dual gravity description, this imaginary contribution comes from thermal fluctuations around the bottom of the classical sagging string in the bulk that connects the heavy quarks located at the boundary. We predict a strong suppression of $Υ$'s in heavy-ion collisions and discuss how this may be used to estimate the initial temperature.

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arXiv2009

The effect of quark coalescence on conical signals

We explore the effect of hadronization by partonic coalescence on a "conical" signal at the partonic level. We show that, by transferring partons from a lower to a higher $p_T$, coalescence makes the conical signal stronger and hence less susceptible to thermal smearing, provided the signal is integrated over a large momentum bin and effects such as non-collinearity and a finite Wigner function width are taken into account. We explore the role of this effect in baryon/meson scaling and calculate the effect of resonances decays on such a conical signal.

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arXiv2009

Conical Correlations, Bragg Peaks, and Transverse Flow Deflections in Jet Tomography

We use (3+1)-dimensional ideal hydrodynamics to describe a variety of different jet energy loss scenarios for a jet propagating through an opaque medium. The conical correlations obtained for fully stopped jets, revealing a Bragg peak, are discussed as well as results from pQCD and AdS/CFT. Moreover, we investigate transverse flow deflection. It is demonstrated that a double-peaked away-side structure can be formed due to the different contributions of several possible jet trajectories through an expanding medium.

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arXiv2009

The Heavy Quark Potential as a Function of Shear Viscosity at Strong Coupling

We determine finite temperature corrections to the heavy-quark (static) potential as a function of the shear viscosity to entropy density ratio in a strongly coupled, large-$N_c$ conformal field theory dual to five-dimensional Gauss-Bonnet gravity. We find that these corrections are even smaller than those predicted by perturbative QCD at distances relevant for small bound states in a deconfined plasma. Obtaining the dominant temperature and viscosity dependence of quarkonium binding energies will require a theory where conformal invariance is broken in such a way that the free energy associated with a single heavy quark is not just a pure entropy contribution.

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arXiv2009

Constraints on AdS/CFT Gravity Dual Models of Heavy Ion Collisions

We show that the five-fold constraints due to (1) the observed nuclear modification of heavy quark jets measured via non-photonic electrons $R_{AA}^e(p_T \sim 6 {\rm GeV})$ in central Au+Au collisions at 200 AGeV, (2) the "perfect fluid' elliptic transverse flow of low transverse momenta pions, $v_2(p_T\sim 1 {\rm GeV})$ reported for noncentral collisions, (3) the global pion rapidity density $dN_π/dy$, (4) the lattice QCD entropy density deficiency, $S/S_{SB}$, of strongly coupled Quark-Gluon Plasmas (sQGP), and (5) a causal requirement are analytically correlated in a class of gauge/string gravity dual models of sQGP dynamics. Current RHIC/BNL and lattice QCD data are found to be remarkably compatible with these models if the t'Hooft and Gauss-Bonnet coupling parameters lie in the range $λ\approx 10-25$ and $0< λ_{GB}< 0.09$. In addition, the observed five-fold correlation appears to favor color glass condensate over Glauber initial conditions within current systematic errors.

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arXiv2009

Anomalous Conical Di-jet Correlations in pQCD vs AdS/CFT

We propose an identified heavy quark jet observable to discriminate between weakly coupled pQCD and strongly coupled AdS/CFT models of quark gluon plasma dynamics in ultra-relativistic nuclear collisions at RHIC and LHC energies. These models are shown to predict qualitatively different associated hadron correlations with respect to tagged heavy quark jets. While both models feature similar far zone Mach and diffusion wakes, the far zone stress features are shown to be too weak to survive thermal broadening at hadron freeze-out. However, these models differ significantly in a near zone "Neck" region where strong chromo-fields sourced by the heavy quark jet couple to the polarizable plasma. Conical associated correlations, if any, are shown to be dominated by the jet induced transverse flow in the Neck zone and unrelated to the weak far zone wakes. Unlike in AdS/CFT, we show that the induced transverse flow in the Neck zone is too weak in pQCD to produce conical correlations after Cooper-Frye freeze-out. The observation of conical correlations violating Mach's law would favor the strongly-coupled AdS/CFT string drag dynamics, while their absence would favor weakly-coupled pQCD-based chromo-hydrodynamics.

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arXiv2009

Di-Jet Conical Correlations Associated with Heavy Quark Jets in anti--de Sitter Space/Conformal Field Theory Correspondence

We show that far zone Mach and diffusion wake ``holograms'' produced by supersonic strings in anti--de Sitter space/conformal field theory (AdS/CFT) correspondence do not lead to observable conical angular correlations in the strict $N_c\to\infty$ supergravity limit if Cooper-Frye hadronization is assumed. However, a special {\em nonequilibrium} ``neck'' zone near the jet is shown to produce an apparent sonic boom azimuthal angle distribution that is roughly independent of the heavy quark's velocity. Our results indicate that a measurement of the dependence of the away-side correlations on the velocity of associated identified heavy quark jets at the BNL Relativistic Heavy Ion Collider and CERN LHC will provide a direct test of the nonperturbative dynamics involved in the coupling between jets and the strongly-coupled Quark-Gluon Plasma (sQGP) implied by AdS/CFT correspondence.

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arXiv2009

Universality of the Diffusion Wake from Stopped and Punch-Through Jets in Heavy-Ion Collisions

We solve (3+1)-dimensional ideal hydrodynamical equations with source terms that describe punch-through and fully stopped jets in order to compare their final away-side angular correlations in a static medium. For fully stopped jets, the backreaction of the medium is described by a simple Bethe-Bloch-like model which leads to an explosive burst of energy and momentum (Bragg peak) close to the end of the jet's evolution through the medium. Surprisingly enough, we find that the medium's response and the corresponding away-side angular correlations are largely insensitive to whether the jet punches through or stops inside the medium. This result is also independent of whether momentum deposition is longitudinal (as generally occurs in pQCD energy loss models) or transverse (as the Bethe-Bloch formula implies). The existence of the diffusion wake is therefore shown to be universal to all scenarios where momentum as well as energy is deposited into the medium, which can readily be understood in ideal hydrodynamics through vorticity conservation. The particle yield coming from the strong forward moving diffusion wake that is formed in the wake of both punch-through and stopped jets largely overwhelms their weak Mach cone signal after freeze-out.

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arXiv2009

Mach cones in heavy ion collisions

We study the fate of the energy deposited by a jet in a heavy ion collision assuming that the medium created is opaque (jets quickly lose energy) and its viscosity is so low that the energy lost by the jet is quickly thermalized. The expectation is that under these conditions the energy deposited gives rise to a Mach cone. We argue that, in general, the behavior of the system is different from the naive expectation and it depends strongly on the assumptions made about the energy and momentum deposited by the jet into the medium. We compare our phenomenological hydrodynamic calculations performed in a static medium for a variety of energy-momentum sources (including a pQCD-based calculation) with the exact strong coupling limit obtained within the AdS/CFT correspondence. We also discuss the observability of hydrodynamical features triggered by jets in experimentally measured two-particle correlations at RHIC.

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