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Ready for a new year !

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Lectures on spectral methods in numerical relativity by S.Grieninger

Sebastian Grieninger from IFT Madrid will give a set of 5 lectures about spectral methods in numerical relativity the week between Monday 25th of July and Friday 30th of July. The lectures will take place each day online (link will be shared beforehand) at 3 pm China time, they will be focused on the usage of spectral methods for applications of Holography and they will include explicit tutorials and examples.

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New paper in PRL!

Can fluids far from equilibrium display universal behaviors? Black holes may know the answer

Far from equilibrium systems display a plethora of interesting and new phenomena which are relevant for a diverse collection of research areas from ultra-cold gases to heavy ion collisions and quenched systems in material science and which can be directly tested in table-top experiments. Can fluids driven far from equilibrium display any degree of universality?

Recent findings by researchers from the Institute of Theoretical Physics (ITP) of the Chinese Academy of Sciences (CAS) and Shanghai Jiao Tong University (SJTU) have found that the answer might be “yes”. The study was published in PRL on the 27th of July (PhysRevLett.129.011602).

The dynamics of fluids near equilibrium can be well described by hydrodynamics whose history goes back more than 2000 years with the work On Floating Bodies by Archimedes. More recently, scientists discovered that strongly coupled fluids display very universal properties, the most famous of which is a universal minimum in the ratio between their shear viscosity and their entropy density given in terms of a few fundamental constants such as the speed of light and the Planck constant and known as the Kovtun-Son-Starinets (KSS) bound. Interestingly, this bound has been formally derived using the holographic duality, a powerful theoretical framework that is able to map commonly intractable problems, such as the shear dynamics of strongly coupled fluids, to simpler problems related to the dynamics of certain gravitational black holes.

Using precise numerical simulations for the time dependent dynamics of higher dimensional black holes driven far from equilibrium by external shear deformations, this recent work suggests that this universality could survive even far away from equilibrium, providing another case in favor of “the unreasonable effectiveness” of hydrodynamics beyond its naïve regime of applicability. The results of this study show that the viscosity-entropy ratio of strongly coupled fluids attains a constant value even when the system is driven far away from equilibrium by a time dependent external source. This outcome is completely independent of the form of the driving and holds even in the absence of conformal symmetry. Moreover, whenever the shear rate is small compared to the characteristic energy scale, this late time value corresponds exactly with that given by near-equilibrium hydrodynamics, suggesting the existence of an out-of-equilibrium attractor. On the contrary, when the late time state is kept far from equilibrium by a large shear rate (in energy units), this constant value can be parametrically smaller than the aforementioned near-equilibrium KSS value and novel phenomena appear. This research indicates the existence of universal mechanisms in the out-of-equilibrium behavior of strongly coupled fluids which might have important consequences on the dynamics of several systems such as quark-gluon plasma and complex fluids in general and which can be potentially tested in the lab in the near future.

Phys. Rev. Lett. 129, 011602 (2022) – Shear Flows in Far-From-Equilibrium Strongly Coupled Fluids (aps.org)

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New paper in Nature Communications

Our team found that the low-frequency scaling of the VDOS of nanoconfined solid systems goes faster than Debye law !!!

Check it out: The ω3 scaling of the vibrational density of states in quasi-2D nanoconfined solids | Nature Communications

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New paper in Science Advances

Our work on nonlinear elasticity, yielding and entropy in amorphous solids has been recently published in Science Advances. It was a great collaboration between Shanghai and Beijing and between high-energy physicists and soft-matter physicists. For a brief press release see here. Congratulations to all the members of the collaboration!!

An article about our paper has also appeared in Phys.org

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Our recent PRB letter Featured in Physics

Our recent paper “Superconducting dome in ferroelectric-type materials from soft mode instability” published as a letter in PRB is featured in Physics by APS. You can find the article about our paper here.

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The team is growing!

Xin-Meng, Masataka will join our group this year as postdoctoral fellows.

Xin-Meng Wu
Masataka Matsumoto

Cunyuan will join our group this year as a PhD student.

Cunyuan Jiang

WELCOME TO THE TEAM !!

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Matteo’s lectures on liquids dynamics are online!

If you missed Matteo’s lectures on liquids dynamics you can see them here:

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Matteo’s lectures at the Institute of Continuous Media Mechanics (Perm) next week !

Matteo will give a series of lectures next week about the theory of liquids dynamics @ the Institute of Continuous Media Mechanics of the Ural Branch of the Russian Academy of Science (ICMM UB RAS) Perm, Russia. The details are below.

Program:

16 ноября 2021
11:00 (9:00 МСК, 14:00 Shanghai)
Лекция 2 – Prof. M.Baggioli: The dynamics of (k-gapped) shear waves and their dispersion relation

17 ноября 2021
11:00 (9:00 МСК, 14:00 Shanghai)
Лекция 4 – Prof. M.Baggioli: The low frequency scaling of the vibrational density of states

19 ноября 2021
11:00 (9:00 МСК, 14:00 Shanghai)
Лекция 6 – Prof. M.Baggioli: The temperature dependence of the heat capacity.

Abstract. The vibrational, thermodynamically and mechanical properties of solids are well-understood since Debye’s work in 1912. On the contrary, the same understanding for amorphous systems (liquids and glasses) has remained elusive for more than a century and it is still a mystery. In these lectures, we will consider three distinctive properties of liquids which are drastically different from their solid counterpart and which remain largely unexplained: (I) the dynamics of (k-gapped) shear waves and their dispersion relation, (II) the low frequency scaling of the vibrational density of states and (III) the temperature dependence of the heat capacity. After reviewing these three problems, we will tackle them from a theoretical point of view using symmetries, effective field theory and hydrodynamics.
The lectures are mainly based on:
– “Gapped momentum states”, Physics Reports 2020 [arXiv:1904.01419]
– “Field Theory of Dissipative Systems with Gapped Momentum States”, PRD 2020 [arXiv:2004.13613]
– “Universal law for the vibrational density of states of liquids”, PNAS 2021 [arXiv:2101.01380]
– “Deformations, relaxation and broken symmetries in liquids, solids and glasses: a unified topological field theory” [arXiv:2101.05015]
– “Explaining the specific heat of liquids based on instantaneous normal modes”, PRE 2021 [arXiv:2101.07585 ]

More details @:

ИМСС УрО РАН – Цикл лекций (icmm.ru)

The link to follow them is below:

МИГ “Механизмы переноса импульса и диссипации… ” (icmm.ru)

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Giorgio gave his first talk in Ljubljana!

This week, Giorgio gave his first talk in the “Holography, transport and strings” seminar series in Ljubljana about his ongoing project. You can see the slides below.