Paul Romatschke's homepage

Nuclear Physics Group
Department of Physics
390 UCB
University of Colorado
Boulder, CO 80309-0390

Phone: +1-303-492-1578
Fax: +1-303-492-3352
E-Mail: paul DOT romatschke AT colorado DOT edu

Hydrodynamic Simulation of a Au+Au Collision: Temperature Profile


I am currently an assistant professor in the Physics Department of the University of Colorado, Boulder. See below for a short summary of my recent research interests or view a list of my articles at inSPIRES. If you came here looking for the the homepage of my wife Ulrike Romatschke, follow this link.

Students: see below under "Teaching".


Recent Events

03/2013: Link to Mathematica 8 Notebook on Shock Wave Collisions in AdS5 with radial flow (Website)

Cold Dense Matter

The determination of the equation of state for cold, dense nuclear matter e.g. in neuton stars has been a vexing problem for decades. Since QCD cannot be accurately solved for densities of interest in neutron star physics (because of the infamous sign problem plaguing lattice QCD and the fact that the QCD coupling becomes sizeable there), a common approach has been to use phenomenological models. My collaborators and I have taken a different approach: use microscopic calculations at low densities (variational, BHF) and very high densities (pQCD with running coupling and mass) and match those at some density. The results are encouraging inasfar as uncertainties are comparatively small and results are in agreement with present-day neutron star observations. Below is a list of my contributions to this topic:
  1. A. Kurkela, P. Romatschke, A. Vuorinen and B. Wu, Looking inside neutron stars: Microscopic calculations confront observations, PDF, Abstract, (2010).
    Comments: Applying our matched EoS to rotating neutron stars and comparing to neutron star observations on mass, frequency and radii.
    Results available here.
  2. A. Kurkela, P. Romatschke and A. Vuorinen, Cold Quark Matter, PDF, Abstract, Phys.Rev.D81:105021 (2010).
    Comments: Perturbation theory to O(alpha_s^2) for cold and dense QCD matter with full strange quark mass effects included (supersedes Freedman/McLerran/Baluni's result). Constraints on strange quark matter, strangelets, and hybrid quark stars.
    Results available here.
  3. Eduardo S. Fraga, Paul Romatschke, The Role of quark mass in cold and dense perturbative QCD, PDF, Abstract, Phys.Rev.D71:105014 (2005).
    Comments: Strange stars, Quark stars, neutron stars?

Relativistic Viscous Hydrodynamics

The recent paradigm of the ideal fluid created at the relativistic heavy-ion collider (RHIC) has been embraced by many experimentalists and theorists alike. Strangely enough, much "evidence" to this notion has been based on the success of describing experimental data by non-viscous hydrodynamics. Work on the subject of viscous hydrodynamics evolved from studies in 0+1 dimensions ("Bjorken flow") over 1+1 dimensions ("Transverse flow") to 2+1 dimensions ("Elliptic flow"). More formal issues concern the allowed form of the relativistic viscous hydrodynamics equations and what effect fluid turbulence (if it develops) might have.
  1. P. Romatschke, Relativistic (Lattice) Boltzmann Equation with Non-Ideal Equation of State PDF, Abstract, Phys.Rev. D85 (2012) 065012.
    Comments: Relativistic Fluid Dynamics Algorithm for Non-Ideal Equations of State.
  2. P. Romatschke, M. Mendoza and S. Succi, A fully relativistic lattice Boltzmann algorithm, PDF, Abstract, Phys.Rev. C84 (2011) 034903.
    Comments: A new computational fluid dynamics (CDF) algorithm for relativistic hydrodynamics. Ideal equations of state only. Download code here
  3. P. Kovtun, G.D. Moore and P. Romatschke, The stickiness of sound: An absolute lower limit on viscosity and the breakdown of second order relativistic hydrodynamics, PDF, Abstract, Phys.Rev. D84 (2011) 025006.
    Comments: Effect of thermal noise on hydrodynamic transport coefficients.
  4. P. Romatschke, Relativistic Viscous Fluid Dynamics and Non-Equilibrium Entropy, PDF, Abstract, Class.Quant.Grav.27:025006 (2010).
    Comments: Most general form of 2nd order non-conformal fluid dynamic equations (at zero charge density). Also derived is the form of the non-equilibrium entropy current in the fluid dynamics regime.
  5. P. Romatschke, New Developments in Relativistic Viscous Hydrodynamics, PDF, Abstract, Int.J.Mod.Phys.E19:1-53 (2010).
    Comments: Review of recent progress in relativistic viscous hydrodynamics.
  6. M. Luzum and P. Romatschke, Viscous Hydrodynamic Predictions for Nuclear Collisions at the LHC PDF, Abstract, Phys.Rev.Lett.103:262302 (2009).
    Comments: Predictions for lead-lead and proton-proton collisions at the LHC. Download code and results here!
  7. M. Luzum and P. Romatschke, Conformal Relativistic Viscous Hydrodynamics: Applications to RHIC PDF, Abstract, Phys.Rev.C78:034915 (2008)
    Comments: Results from conformal viscous hydro on Au+Au collisions at RHIC, for Glauber and CGC initial conditions. Details of Setup. Dependence on 2nd order coefficients and Cooper-Frye ansatz discussed. Discussion of early thermalization and viscosity over entropy ratio. Download Results here!
    Update: we fixed a bug in the calculation for the resonances (see published erratum: Phys.Rev.C79:039903(E), 2008); revised plots/data will be made available soon.
  8. R. Baier, P. Romatschke, D.T. Son, A.O. Starinets, M.A. Stephanov, Relativistic viscous hydrodynamics, conformal invariance, and holography, PDF, Abstract, JHEP 0804:100, (2008).
    Comments: Fixing the form of second-order relativistic viscous hydrodynamic equations; supersedes Israel-Stewart theory
  9. Paul Romatschke, Fluid turbulence and eddy viscosity in relativistic heavy-ion collisions, PDF, Abstract, (2007).
    Comments: Thoughts about Fluid Turbulence
  10. Paul Romatschke, Ulrike Romatschke, How perfect is the RHIC fluid? PDF, Abstract, Phys. Rev. Lett.99, 172301 (2007).
    Comments: Viscous Hydrodynamics for Non-central Collisions, Elliptic flow, Comparison to Data
    Download Code here!
  11. Paul Romatschke, Causal Viscous Hydrodynamics for Central Heavy-Ion Collisions II: Meson Spectra and HBT Radii PDF, Abstract, Eur.Phys.J.C52:203-209 (2007).
    Comments: Viscous Hydrodynamics for Central Collisions, Freeze-Out and Comparison to Data
    Download Code+Results here!
  12. Rudolf Baier, Paul Romatschke, Causal Viscous Hydrodynamics for Central Heavy-Ion Collisions, PDF, Abstract, Eur.Phys.J.C51:677-687 (2007).
    Comments: Viscous Hydrodynamics for Central Collisions, Transverse flow, Code tests
  13. Rudolf Baier, Paul Romatschke, Urs Achim Wiedemann, Transverse flow in relativistic viscous hydrodynamics, PDF, Abstract, Nucl.Phys.A782:313-318 (2007).
    Comments: How not to Approximate Viscous Hydrodynamic Equations
  14. Rudolf Baier, Paul Romatschke, Urs Achim Wiedemann, Dissipative hydrodynamics and heavy ion collisions, PDF, Abstract, Phys.Rev.C73, 064903 (2006).
    Comments: Viscous Hydrodynamic Equations I, Bjorken flow.

Non-Abelian Plasma Instabilities

Plasma instabilities in QCD are a very interesting and rich phenomenon that may perhaps lead to fast equilibration in the context of heavy-ion collisions. Much progress has been made in recent years, but a thorough understanding of non-Abelian plasma instabilities in heavy-ion collisions is still missing.
Below is a list of my contributions to this topic,
  1. P. Romatschke, Momentum broadening in an anisotropic plasma, PDF, Abstract, Phys. Rev. C75, 014901 (2007).
    Comments: Jet broadening in an anisotropic QCD plasma: "the ridge"
    See arxiv source for numerics
  2. P. Romatschke and A. Rebhan, Plasma Instabilities in an Anisotropically Expanding Geometry, PDF, Abstract, Phys. Rev. Lett.97, 252301 (2006).
  3. P. Romatschke and R. Venugopalan, The Unstable Glasma, PDF, Abstract, Phys. Rev. D74, 045011 (2006)
  4. P. Romatschke and R. Venugopalan, A Weibel instability in the melting color glass condensate PDF, Abstract, Eur. Phys. J. A29:71-75 (2006).
  5. P. Romatschke and R. Venugopalan, Collective Non-Abelian Instabilities in a Melting Color Glass Condensate, PDF, Abstract, Phys. Rev. Lett.96, 062302 (2006).
    Comments: Full 3D simulation of classical chromodynamics in expanding space
    Download Code here!
  6. A. Rebhan, P. Romatschke and M. Strickland, Quark-Gluon-Plasma Instabilities in Discretized Hard-Loop Approximation, PDF, Abstract, JHEP 0509:041 (2005).
  7. A. Rebhan, P. Romatschke and M. Strickland, Hard-Loop dynamics of Non-Abelian Plasma Instabilities, PDF, Abstract, Phys. Rev. Lett.94, 102303 (2005).
  8. P. Romatschke and M. Strickland, Progress in Anisotropic Plasma Physics, PDF, Abstract (2004).
  9. P. Romatschke and M. Strickland, Collisional Energy Loss of a Heavy Quark in an Anisotropic Quark-Gluon Plasma, PDF, Abstract, Phys.Rev.D71, 125008 (2005).
    Numerics setup can be found here! Warning: unmaintained and not commented.
  10. P. Romatschke and M. Strickland, Collective Modes of an Anisotropic Quark-Gluon Plasma II, PDF, Abstract (2004), Phys. Rev. D70, 116006 (2004).
  11. P. Romatschke and M. Strickland, Energy Loss of a Heavy Fermion in an Anisotropic QED Plasma, PDF, Abstract, Phys. Rev. D 69, 065005 (2004).
    Numerics setup can be found here! Warning: unmaintained and not commented.
  12. P. Romatschke and M. Strickland, Collective Modes of an Anisotropic Quark-Gluon Plasma, PDF, Abstract, Phys. Rev. D 68, 036004 (2003).

Nonlinear Gravity

  1. Paul Romatschke and J. Drew Hogg, Pre-Equilibrium Radial Flow from Central Shock-Wave Collisions in AdS5 PDF, Abstract.
    Comments: A numerical solution to a toy model of a high energy particle collision in a strongly coupled gauge theory.
  2. Bin Wu and Paul Romatschke, Shock wave collisions in AdS5: approximate numerical solutions PDF, Abstract, Int.J.Mod.Phys. C22 (2011) 1317-1342.
    Comments: A numerical solution to a toy model of a high energy particle collision in a strongly coupled gauge theory.
  3. Daniel Grumiller, Paul Romatschke, On the collision of two shock waves in AdS5 PDF, Abstract, JHEP 0808:027 (2008).
    Comments: A (partial) solution to a toy model of a high energy particle collision in a strongly coupled gauge theory.

Various other projects

  1. P. Romatschke and D.T. Son, Spectral sum rules for the quark-gluon plasma, PDF, Abstract, Phys.Rev.D80:065021 (2009).
    Comments: Sum rules for Energy-Momentum Tensor Correlators in SU(N) and N=4 SYM.
    C++ code used to check sum rules for N=4 SYM is available here.
  2. M. Laine, O. Philipsen, P. Romatschke, M. Tassler, Real-time static potential in hot QCD, PDF, Abstract, JHEP 0703:054 (2007).
    Comments: Quarkonia
  3. Paul Romatschke, Quasiparticle description of the hot and dense quark gluon plasma. PDF, Abstract, (2003).
    Comments: PhD thesis
  4. Anton Rebhan, Paul Romatschke, HTL quasiparticle models of deconfined QCD at finite chemical potential, PDF, Abstract, Phys.Rev.D68:025022 (2003).
    Comments: The HTL Quasiparticle model
    Download results here !
  5. Paul Romatschke, Cold deconfined matter EOS through an HTL quasiparticle model, PDF, Abstract, (2002).
    Comments: My first preprint :-)
  6. Paul Romatschke, Thermal corrections to the sunset diagram, unpublished, ps (2001).
    Comments: Diploma thesis



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Last update: 05.03.2013