“Bulletin Board”

 School of Physics - January 27, 2018

NEWS title: A paper from school of physics in PRL.

Hesam Soltanpanahi, a postdoc at school of physics and his Polish collaborators have recently published a paper in Physical Review Letters.


Non-equilibrium physics in strongly coupled field theories is an open and active area of research for instance in physics of hadrons and QCD. Traditional tools, namely, perturbation theory and lattice QCD method are not applicable to study the real time evolution of these systems for various reasons. Nonetheless, AdS/CFT and holography which bridges between problems from the strongly coupled field theories and methods from General Relativity, provides tools to tackle such problems. The intriguing aspect of studying dynamical phenomena in AdS/CFT, apart from the intrinsic interest in developing computational techniques to facilitate investigation of strong coupling physics, is the natural mapping of these dynamics into the time dependent phenomena in a classical bulk spacetime. In particular, phase transitions within the AdS/CFT correspondence are typically studied in equilibrium by comparing the free energies of two candidate dual equilibrium geometries which correspond to the two phases. The new paper published in PRL in which Dr. Soltanpanahi is a coauthor, studies a holographic system with a first order phase transition in real time and establishes that domains of the two coexisting phases with identical free energies arise dynamically through nonlinear real time evolution. This result opens up numerous avenues of further research for the study of real time phase transition dynamics. The holographic computation allows for the study of the whole process of the build up of the instability and subsequent dynamics of phase separation. It is this information which was not be easily accessible from the field theory perspective. Depending on the initial configuration, the authors observe two patterns of behaviour and isolate two distinct regimes in the temporal evolution: first an exponential growth and then subsequent linear expansion, and a collision of transient bubbles (associated with each phase). The holographic computation allows for such insight into the full temporal dynamics from the onset of the spinodal instability to final equilibration into the two separated phases. These phenomena would be very difficult, if not impossible, to study quantitatively in the conventional field theory framework.

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