arXiv subjects

Derek Teaney

Publications and source records attributed to Derek Teaney.

At least 55 records · Page 3Linked to original sources

arXiv2014

A scaling relation between proton-nucleus and nucleus-nucleus collisions

It is recently discovered that at high multiplicy, the proton-nucleus ($pA$) collisions give rise to two particle correlations that are strikingly similar to those of nucleus-nucleus ($AA$) collisions at the same multiplicity, although the system size is smaller in $pA$. Using an independent cluster model and a simple conformal scaling argument, where the ratio of the mean free path to the system size stays constant at fixed multiplicity, we argue that flow in $pA$ emerges as a collective response to the fluctuations in the position of clusters, just like in $AA$ collisions. With several physically motivated and parameter free rescalings of the recent LHC data, we show that this simple model captures the essential physics of elliptic and triangular flow in $pA$ collisions.

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arXiv2014

A scaling relation between pA and AA collisions

We compare the flow-like correlations in high multiplicity proton-nucleus ($p+A$) and nucleus-nucleus ($A+A$) collisions. At fixed multiplicity, the correlations in these two colliding systems are strikingly similar, although the system size is smaller in $p+A$. Based on an independent cluster model and a simple conformal scaling argument, where the ratio of the mean free path to the system size stays constant at fixed multiplicity, we argue that flow in $p+A$ emerges as a collective response to the fluctuations in the position of clusters, just like in $A+A$ collisions. With several physically motivated and parameter free rescalings of the recent LHC data, we show that this simple model captures the essential physics of elliptic and triangular flow in $p+A$ collisions. We also explore the implications of the model for jet energy loss in $p+A$, and predict slightly larger transverse momentum broadening in $p+A$ than in $A+A$ at the same multiplicity.

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arXiv2014

Plane correlations and hydrodynamic simulations of heavy ion collisions

We use a nonlinear response formalism to describe the event plane correlations measured by the ATLAS collaboration. With one exception ($\left\langle \cos(2Ψ_2 - 6Ψ_3 + 4 Ψ_4) \right\rangle$), the event plane correlations are qualitatively reproduced by considering the linear and quadratic response to the lowest cumulants. For the lowest harmonics such as $\left\langle \cos(2Ψ_2+3Ψ_3 - 5Ψ_5) \right\rangle$, the correlations are quantitatively reproduced, even when the naive Glauber model prediction has the wrong sign relative to experiment. The quantitative agreement for the higher plane correlations (especially those involving $Ψ_6$) is not as good. The centrality dependence of the correlations is naturally explained as an average of the linear and quadratic response.

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arXiv2013

Heavy ions and string theory

We review a selection of recent developments in the application of ideas of string theory to heavy ion physics. Our topics divide naturally into equilibrium and non-equilibrium phenomena. On the non-equilibrium side, we discuss generalizations of Bjorken flow, numerical simulations of black hole formation in asymptotically anti-de Sitter geometries, equilibration in the dual field theory, and hard probes. On the equilibrium side, we summarize improved holographic QCD, extraction of transport coefficients, inclusion of chemical potentials, and approaches to the phase diagram. We close with some possible directions for future research.

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arXiv2013

Second order viscous corrections to the harmonic spectrum in heavy ion collisions

We calculate the second order viscous correction to the kinetic distribution, $δf_{(2)}$, and use this result in a hydrodynamic simulation of heavy ion collisions to determine the complete second order correction to the harmonic spectrum, $v_n$. At leading order in a conformal fluid, the first viscous correction is determined by one scalar function, $χ_{0p}$. One moment of this scalar function is constrained by the shear viscosity. At second order in a conformal fluid, we find that $δf(\p)$ can be characterized by two scalar functions of momentum, $χ_{1p}$ and $χ_{2p}$. The momentum dependence of these functions is largely determined by the kinematics of the streaming operator. Again, one moment of these functions is constrained by the parameters of second order hydrodynamics, $τ_π$ and $λ_1$. The effect of $δf_{(2)}$ on the integrated flow is small (up to $v_4$), but is quite important for the higher harmonics at modestly-large $p_T$. Generally, $δf_{(2)}$ increases the value of $v_n$ at a given $p_T$, and is most important in small systems.

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arXiv2013

Next-to-leading order thermal photon production in a weakly coupled quark-gluon plasma

We compute the next-to-leading order O(g) correction to the thermal photon production rate in a QCD plasma. The NLO contributions can be expressed in terms of gauge invariant condensates on the light cone, which are amenable to novel sum rules and Euclidean techniques. We expect these technologies to be generalizable to other NLO calculations. For the phenomenologically interesting value of alpha_s=0.3, the NLO correction represents a 20% increase and has a functional form similar to the LO result.

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arXiv2012

Non-linear flow response and reaction plane correlations

We apply the non-linear flow response formalism to the recently measured event plane correlations. We find that as a result of the combined effects of linear and non-linear flow response, the observed event plane correlations can be understood as an effective average of the 'linear limit' and 'non-linear limit'.

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arXiv2012

Dilaton emission and absorption from far-from-equilibrium non-abelian plasma

Using gauge/gravity duality, we study emission and absorption rates of scalar quanta from far-from-equilibrium N = 4 supersymmetric Yang-Mills plasma. By comparing the emission and absorption rates to expectations from the Fluctuation-Dissipation Theorem, we study how the spectrum thermalizes and how the thermalization time depends on the four momentum of the emitted quanta.

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arXiv2012

Longitudinal fluctuations of the fireball density in heavy-ion collisions

We show that fluctuations of the fireball shape in the longitudinal direction generate nontrivial rapidity correlations that depend not only on the rapidity difference, y_{1} - y_{2}, but also on the rapidity sum, y_{1} + y_{2}. This is explicitly demonstrated in a simple wounded nucleon model, and the general case is also discussed. We show how to extract different components of the fluctuating fireball shape from the measured two-particle rapidity correlation function. The experimental possibility of studying the longitudinal initial conditions in heavy-ion and proton-proton collisions is emphasized.

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arXiv2012

Non linearities in the harmonic spectrum of heavy ion collisions with ideal and viscous hydrodynamics

We determine the non-linear hydrodynamic response to geometrical fluctuations in heavy ion collisions using ideal and viscous hydrodynamics. This response is characterized with a set of non-linear response coefficients that determine, for example, the $v_5$ that is produced by an $ε_2$ and an $ε_3$. We analyze how viscosity damps both the linear and non-linear response coefficients, and provide an analytical estimate that qualitatively explains most of the trends observed in more complete simulations. Subsequently, we use these nonlinear response coefficients to determine the linear and non-linear contributions to $v_1$, $v_4$ and $v_5$. For viscous hydrodynamics the nonlinear contribution is dominant for $v_4$, $v_5$ and higher harmonics. For $v_1$, the nonlinear response constitutes an important $\sim 25%$ correction in mid-central collisions. The nonlinear response is also analyzed as a function of transverse momentum for $v_1$, $v_4$ and $v_5$. Finally, recent measurements of correlations between event-planes of different harmonic orders are discussed in the context of non-linear response.

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arXiv2012

Study on initial geometry fluctuations via participant plane correlations in heavy ion collisions: part II

Further investigation of the participant plane correlations within a Glauber model framework is presented, focusing on correlations between three or four participant planes of different order. A strong correlation is observed for $\cos(2Φ_{2}^*+3Φ_{3}^*-5Φ_{5}^*)$ which is a reflection of the elliptic shape of the overlap region. The correlation between the corresponding experimental reaction plane angles can be easily measured. Strong correlations of similar geometric origin are also observed for $\cos(2Φ_{2}^*+4Φ_{4}^*-6Φ_{6}^*)$, $\cos(2Φ_2^*-3Φ_3^*-4Φ_4^*+5Φ_5^*)$, $\cos(6Φ_2^*+3Φ_3^*-4Φ_4^*-5Φ_5^*)$, $\cos(Φ_1^*-2Φ_2^*-3Φ_3^*+4Φ_4^*)$, $\cos(Φ_1^*+6Φ_2^*-3Φ_3^*-4Φ_4^*)$, and $\cos(Φ_1^*+2Φ_2^*+3Φ_3^*-6Φ_6^*)$, which are also measurable. Experimental measurements of the corresponding reaction plane correlators in heavy ion collisions at RHIC and the LHC may improve our understanding of the physics underlying the measured higher order flow harmonics.

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arXiv2012

The Wake of a Heavy Quark in Non-Abelian Plasmas : Comparing Kinetic Theory and the AdS/CFT Correspondence

We compute the non-equilibrium stress tensor induced by a heavy quark moving through weakly coupled QCD plasma at the speed of light and compare the result to N = 4 Super Yang Mills theory at strong coupling. The QCD Boltzmann equation is reformulated as a Fokker-Planck equation in a leading log approximation which is used to compute the induced stress. The transition from nonequilibrium at short distances to equilibrium at large distances is analyzed with first and second order hydrodynamics. Even after accounting for the obvious differences in shear lengths, the strongly coupled theory is significantly better described by hydrodynamics at sub-asymptotic distances. We argue that this difference between the kinetic and AdS/CFT theories is related to the second order hydrodynamic coefficient $τ_π$. $τ_π$ is numerically large in units of the shear length for theories based on the Boltzmann equation.

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arXiv2011

Dynamical Hawking radiation and holographic thermalization

Using gauge/gravity duality, we study the thermalization of strongly coupled N = 4 supersymmetric Yang-Mills plasma. We analyze the expectation value of the stress tensor and scalar correlation functions and the applicability of the fluctuation dissipation theorem. Via gauge/gravity duality, this maps into studying the equilibration of a black hole geometry and its Hawking radiation.

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arXiv2011

Fluctuation, dissipation, and thermalization in non-equilibrium AdS_5 black hole geometries

We give a simple recipe for computing dissipation and fluctuations (commutator and anti-commutator correlation functions) for non-equilibrium black hole geometries. The recipe formulates Hawking radiation as an initial value problem, and is suitable for numerical work. We show how to package the fluctuation and dissipation near the event horizon into correlators on the stretched horizon. These horizon correlators determine the bulk and boundary field theory correlation functions. In addition, the horizon correlators are the components of a horizon effective action which provides a quantum generalization of the membrane paradigm. In equilibrium, the analysis reproduces previous results on the Brownian motion of a heavy quark. Out of equilibrium, Wigner transforms of commutator and anti-commutator correlation functions obey a fluctuation-dissipation relation at high frequency.

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arXiv2010

Triangularity and Dipole Asymmetry in Heavy Ion Collisions

We introduce a cumulant expansion to parameterize possible initial conditions in relativistic heavy ion collisions. We show that the cumulant expansion converges and that it can systematically reproduce the results of Glauber type initial conditions. At third order in the gradient expansion, the cumulants characterize the triangularity $ $ and the dipole asymmetry $ $ of the initial entropy distribution. We show that for mid-peripheral collisions the orientation angle of the dipole asymmetry $ψ_{1,3}$ has a $20%$ preference out of plane. This leads to a small net $v_1$ out of plane. In peripheral and mid-central collisions the orientation angles $ψ_{1,3}$ and $ψ_{3,3}$ are strongly correlated. We study the ideal hydrodynamic response to these cumulants and determine the associated $v_1/ε_1$ and $v_3/ε_3$ for a massless ideal gas equation of state. $v_1$ and $v_3$ develop towards the edge of the nucleus, and consequently the final spectra are more sensitive to the viscous dynamics of freezeout. The hydrodynamic calculations for $v_3$ are compared to Alver and Roland fit of two particle correlation functions. Finally, we propose to measure the $v_1$ associated with the dipole asymmetry and the correlations between $ψ_{1,3}$ and $ψ_{3,3}$ by measuring a two particle correlation with respect to the participant plane, $<\cos(ϕ_a - 3ϕ_b + 2Ψ_{PP})>$. The hydrodynamic prediction for this correlation function is several times larger than a correlation currently measured by the STAR collaboration, $<\cos(ϕ_a + ϕ_\b - 2Ψ_{PP})>$.

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arXiv2010

Spectral densities for hot QCD plasmas in a leading log approximation

We compute the spectral densities of $T^{μν}$ and $J^μ$ in high temperature QCD plasmas at small frequency and momentum,\, $ω,k \sim g^4 T$. The leading log Boltzmann equation is reformulated as a Fokker Planck equation with non-trivial boundary conditions, and the resulting partial differential equation is solved numerically in momentum space. The spectral densities of the current, shear, sound, and bulk channels exhibit a smooth transition from free streaming quasi-particles to ideal hydrodynamics. This transition is analyzed with conformal and non-conformal second order hydrodynamics, and a second order diffusion equation. We determine all of the second order transport coefficients which characterize the linear response in the hydrodynamic regime.

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arXiv2010

Stochastic String Motion Above and Below the World Sheet Horizon

We study the stochastic motion of a relativistic trailing string in black hole AdS_5. The classical string solution develops a world-sheet horizon and we determine the associated Hawking radiation spectrum. The emitted radiation causes fluctuations on the string both above and below the world-sheet horizon. In contrast to standard black hole physics, the fluctuations below the horizon are causally connected with the boundary of AdS. We derive a bulk stochastic equation of motion for the dual string and use the AdS/CFT correspondence to determine the evolution a fast heavy quark in the strongly coupled $\N=4$ plasma. We find that the kinetic mass of the quark decreases by $ΔM=-\sqrt{γλ}T/2$ while the correlation time of world sheet fluctuations increases by $\sqrtγ$.

hep-th↗

arXiv2010

Radiative energy loss and v2 spectra for viscous hydrodynamics

This work investigates the first correction to the equilibrium phase space distribution and its effects on spectra and elliptic flow in heavy ion collisions. We show that the departure from equilibrium on the freezeout surface is the largest part of the viscous corrections to $v_2(p_T)$. However, the momentum dependence of the departure from equilibrium is not known {\it a priori}, and it is probably not proportional to $p_T^2$ as has been assumed in hydrodynamic simulations. At high momentum in weakly coupled plasmas it is determined by the rate of radiative energy loss and is proportional to $p_T^{3/2}$. The weaker $p_T$ dependence leads to straighter $v_2(p_T)$ curves at the same value of viscosity. Further, the departure from equilibrium is generally species dependent. A species dependent equilibration rate, with baryons equilibrating faster than mesons, can explain ``constituent quark scaling'' without invoking coalescence models.

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