On a journey to the beginning of time, puzzle over puzzle ask to be solved. Letâ€™s take on the challenge and enjoy the ride.

WelcomeI am an associate professor in physics at the Faculty of Science and Technology at the University of Stavanger. My research area is theoretical high energy nuclear physics with a focus on **real-time dynamics from lattice QCD**. Broadly speaking, I am working on devising a thermometer for the relativistic-heavy-ion collisions carried out at the LHC, RHIC and upcoming FAIR facility via a better understanding of the bound states of heavy quarks, so called heavy quarkonium.

As an associate member, I am actively involved in the collaborative research center SFB1225 ISOQUANT at the University of Heidelberg. Before taking up my current position in Stavanger I have been both a principal investigator in and the scientific manager of SFB1225.

I am delighted by having been awarded the **Nuclear Physics A Young Scientists Award** at the XXV International Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2015) in Kobe, Japan

With family ties to South Korea and having obtained my doctorate at The University of Tokyo in Japan, East Asia is on my radar. When time permits I enjoy listening to recorder music of the baroque and rennaissence era as well as the occasional electronica.

Elucidating the real-time dynamics of quantum fields and particles at the microspcopic scale is a key ingredient towards an understanding of the physics of relativistic heavy-ion collisions. One class of particle, the bound states of a $c\bar{c}$ or $b\bar{b}$ quark are of particular interest, as their constituent are heavy enough to survive the extreme environment of a collision but at the same time are susceptible to the evolution of their surroundings. Combining both first principles methods, such as lattice QCD with effective field theories I am working on a comprehensive description of heavy quarkonium properties under extreme conditions.

A lecture that combines theory education with hands-on programming tutorials that give students the skills to become active in forefront research in QCD. (Together with Denes Sexty at ITP Heidelberg in 2015)

Sommer school lectures with the aim to introduce students to two effective field theories NRQCD and pNRQCD used in current research on in-medium heavy quarkonium. One of the four lectures contains an in-depth description of the Bayesian approach to spectral function reconstruction that is central to understanding in-medium modification of hadrons.

Lecture 2: NRQCD [PDF]

Lecture 3: Bayesian Spectral Reconstructions [PDF]

Lecture 4: pNRQCD - Schrödinger Equation [PDF]

with chiral fermions on the lattice

In arXiv:1512.02374 we report on an exploratory lattice study on the phenomenon of chiral instabilities in non-Abelian gauge theories at high temperature. It is based on a recently constructed anomalous Langevin-type effective theory of classical soft gauge fields in the presence of a chiral number density $n_5=n_{\rm R}-n_{\rm L}$. Evaluated in thermal equilibrium using classical lattice techniques it reveals that the fluctuating soft fields indeed exhibit a rapid energy increase at early times and we observe a clear dependence of the diffusion rate of topological charge (sphaleron rate) on the the initial $n_5$, relevant in both early universe baryogenesis and relativistic heavy-ion collisions. The topological charge furthermore shows a drift among distinct vacuum sectors, roughly proportional to the initial $n_5$ and in turn the chiral imbalance is monotonously reduced as required by helicity conservation.

Download aEFT v1.0 [GZIP]

as used in the publication arXiv:1512.02374

Download runscript Yang-Mills [BASH]

Download runscript EFT n0=25 [BASH]

with extended search space

The standard implementation of the Maximum Entropy Method (MEM) follows Bryan and deploys a Singular Value Decomposition (SVD) to limit the dimensionality of the underlying solution space apriori. In arXiv:1110.6285 (J.Comput.Phys. 238 (2013) 106-114) we have presented arguments based on the shape of the SVD basis functions and numerical evidence from a mock data analysis, which show that the correct Bayesian solution is not in general recovered with this approach. As a remedy we propose to extend the search basis systematically, which will eventually recover the full solution space and the correct solution. In order to adequately approach problems where an exponentially damped kernel is used, we provide an open-source implementation, using the C/C++ language that utilizes high precision arithmetic adjustable at run-time. The LBFGS algorithm is included in the code in order to attack problems without the need to resort to a particular search space restriction.

Download ExtMEM v3.0 [BZIP2]

as used in the publication arXiv:1108.1579 (Phys.Rev.Lett. 108 (2012) 162001)

Download ExtMEM v3.11 with Fourier basis[GZIP]

as used in the proceeding arXiv:1208.5162 (PoS LATTICE2012 (2012) 100)

In arXiv:1607.04049 (Phys.Rev. D95 (2017) 054511) we improve and extend our study of the complex in-medium heavy quark potential and its Debye mass $m_D$ in a gluonic medium with a finer scan around the deconfinement transition and newly generated ensembles closer to the thermodynamic limit. On the lattices with larger physical volume, Re[V] shows signs of screening, i.e. a finite mD, only in the deconfined phase, reminiscent of a genuine phase transition. Consistently Im[V] exhibits nonzero values also only above $T_C$.

Downloads for quenched QCD ($\beta=6.1, \xi=3.2108, 32^3\times N_\tau$)

Re[V] datasets [TXT], Im[V] datasets [TXT]

In arXiv:1410.2546 (Phys.Rev.Lett. 114 (2015) 8, 082001) we presented a state-of-the-art determination of the complex valued static quark-antiquark potential at phenomenologically relevant temperatures around the deconfinement phase transition. Its values were obtained from non-perturbative lattice QCD simulations using spectral functions extracted via a novel Bayesian inference prescription. Among our finding were that the real part, both in a gluonic medium as well as in realistic QCD with light $u, d$ and $s$ quarks, lies close to the color singlet free energies in Coulomb gauge and shows Debye screening above the (pseudo) critical temperature $T_c$.

Downloads for quenched QCD (anisotropic Wilson action)

Re[V] datasets [GZIP], Im[V] datasets [GZIP]

and F1 datasets [GZIP], as well as the raw

Polyakov Loop correlators [GZIP] (for access contact me)

as shown in arXiv:1410.2546 (Phys.Rev.Lett. 114 (2015) 8, 082001) and used in arXiv:1506.08684

Downloads for $N_f=2+1$ flavor QCD (asqtad action, HotQCD)

Re[V] datasets [GZIP] and F1 datasets [GZIP], as well as the raw

Polyakov Loop correlators [GZIP] (for access contact me)

as shown in arXiv:1410.2546 (Phys.Rev.Lett. 114 (2015) 8, 082001) and used in arXiv:1509.07366

For a complete list of my publications see

the high energy physics information system
INSPIRE

Work

rothkopf @thphys.uni-heidelberg.de

Institute for Theoretical Physics

Department of Physics and Astronomy

Heidelberg University

Office: 108

Philosophenweg 12

D-Heidelberg 69120 Germany

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