Research
My research spans a wide variety of topics in theoretical physics. I work on various aspects of string theory and black holes but I also spend a significant amount of time understanding the emergent hydrodynamic descriptions of many-body systems including quantum matter, soft/active matter, high-energy and astrophysical plasmas. I also work on complex systems with applications to ecosystems and social systems.
I am part of the string theory group at the University of Amsterdam but I am also part of DIEP, where I engage in interdisciplinary (complexity) research aiming at bridging different disciplines such as chemistry, mathematics, logic, ecosystem dynamics and computer science.
You can find a list of my research in Google scholar.
Research group
At the University of Amsterdam I work with a group of exceptional reserchers.
Akash Jain
Postdoc and Marie-Curie Fellow
Ruben Lier
Postdoc
George Batzios
PhD student
Gian-Piero Nicosia
PhD student
Past members
A list of past members of my research group
Piotr Surówka
Visiting Professor from January to August 2022
Richard Green
Postdoc from September 2019 to 2021 (joint with Jan de Boer and Luca Giomi)
Publications
Below is a summary of my publications starting in 2018. For the full list of publications see my Google scholar profile or my Inspires profile.
Probe particles in odd active viscoelastic fluids
Understanding how activity and dissipation determine linear stability in active systems
Odd viscoelastic materials are constrained by fewer symmetries than their even counterparts. The breaking of these symmetries allow these materials to exhibit different features, which have attracted considerable attention in recent years. Immersing a bead in such complex fluids allows for probing their physical properties, highlighting signatures of their oddity and exploring consequences of these broken symmetries. We present the conditions under which the activity of an odd viscoelastic fluid can give rise to linear instabilities in the motion of the probe particle and unveil how the features of the probe particle dynamics depend on the oddity and activity of the viscoelastic medium in which it is immersed.
Carrollian fluids and spontaneous breaking of boost symmetry
Understanding fluids with Carrollian symmetry
In the hydrodynamic regime, field theories typically have their boost symmetry spontaneously broken due to the presence of a thermal rest frame although the associated Goldstone field does not acquire independent dynamics. We show that this is not the case for Carrollian field theories where the boost Goldstone field plays a central role. This allows us to give a first-principles derivation of the equilibrium currents and dissipative effects of Carrollian fluids. We also demonstrate that the limit of vanishing speed of light of relativistic fluids is a special case of this class of Carrollian fluids. Our results shine light on the thermodynamic properties and thermal partition functions of Carrollian field theories.
Risk aversion promotes cooperation
Understanding cooperation in living and complex systems
Cooperative dynamics are central to our understanding of many phenomena in living and complex systems, including the transition to multicellularity, the emergence of eusociality in insect colonies, and the development of full-fledged human societies. However, we lack a universal mechanism to explain the emergence of cooperation across length scales, across species, and scalable to large populations of individuals. We present a novel framework for modelling cooperation games with an arbitrary number of players by combining reaction networks, methods from quantum mechanics applied to stochastic complex systems, game theory and stochastic simulations of molecular reactions.
Fracton superfluids
Understanding the collective behaviour of hypothetical quasi-particles
We investigate the thermodynamics of equilibrium thermal states and their near-equilibrium dynamics in systems with fractonic symmetries in arbitrary curved space. We find distinctive features of each of these phases and regimes at ideal order in gradients, without introducing dissipative effects. In particular we note the appearance of a sound mode for s-wave fracton superfluids. We show that previous work on fracton hydrodynamics falls into these classes. Finally, we study ultra-dense p-wave fracton superfluids with a large kinetic mass in addition to studying the thermodynamics of ideal Aristotelian superfluids.
Approximate higher-form symmetries, topological defects, and dynamical phase transitions
Understanding phases of matter using exotic notions of symmetry
Higher-form symmetries are a valuable tool for classifying topological phases of matter. However, emergent higher-form symmetries in interacting many-body quantum systems are not typically exact due to the presence of topological defects. In this paper, we develop a systematic framework for building effective theories with approximate higher-form symmetries, i.e. higher-form symmetries that are weakly explicitly broken. We focus on a continuous U(1) q-form symmetry and study various patterns of symmetry breaking. We show that our framework is able to describe various phase transitions due to proliferation of vortices or defects. This includes the melting transition in smectic crystals, the plasma phase transition from polarised gases to magnetohydrodynamics, the spin-ice transition, the superfluid to neutral fluid transition and the Meissner effect in superconductors, among many others.
Holographic duals of the N=1* gauge theory
Using the Polchinski-Strassler mechanism to construct higher-dimensional black holes in string theory
We use the long-wavelength effective theory of black branes (blackfold approach) to perturbatively construct holographic duals of the vacua of the N=1* supersymmetric gauge theory. Employing the mechanism of Polchinski and Strassler, we consider wrapped black five-brane probes with D3-brane charge moving in the perturbative supergravity backgrounds corresponding to the high and low temperature phases of the gauge theory.
Full publication here.
Hydrodynamics of plastic deformations in electronic crystals
Understanding what plasticity is and its effects in electronic crystals.
We construct a new hydrodynamic framework describing plastic deformations in electronic crystals. The framework accounts for pinning, phase, and momentum relaxation effects due to translational disorder, diffusion due to the presence of interstitials and vacancies, and strain relaxation due to plasticity and dislocations. We obtain the hydrodynamic mode spectrum and correlation functions in various regimes in order to identify the signatures of plasticity in electronic crystal phases.
Full publication here.
Lift force in odd compressible fluids
Understanding active fluid with odd properties
We compute the response matrix for a tracer particle in a compressible fluid with odd viscosity living on a two-dimensional surface. Unlike the incompressible case, we find that an odd compressible fluid can produce an odd lift force on a tracer particle. Using a “shell localization” formalism, we provide analytic expressions for the drag and odd lift forces acting on the tracer particle in a steady state and also at finite frequency.
Full publication here.
A stable and causal model of magnetohydrodynamics
Understanding the hydrodynamics of high-energy particle physics and astrophysical plasmas
We formulate the theory of first-order dissipative magnetohydrodynamics in an arbitrary hydrodynamic frame under the assumption of parity-invariance and discrete charge symmetry. Together with a detailed analysis of transport, entropy production and Kubo formulae, the theory presented here is well suited for studying dissipative effects in various contexts ranging from heavy-ion collisions to astrophysics.
Full publication here.
Approximate symmetries, pseudo-Goldstones, and the second law of thermodynamics
Understanding the physics of approximately broken symmetries.
We propose a general hydrodynamic framework for systems with spontaneously broken approximate symmetries. We focus on systems with approximate U(1) and translation symmetries, with direct applications to pinned superfluids and charge density waves. We also comment on the implications for chiral perturbation theory.
Full publication here.
Passive odd viscoelasticity
Understanding the physics of odd elasto-viscoplastic materials
Active chiral viscoelastic materials exhibit elastic responses perpendicular to the applied stresses, referred to as odd elasticity. We use a covariant formulation of viscoelasticity combined with an entropy production analysis to show that odd elasticity is not only present in active systems but also in broad classes of passive chiral viscoelastic fluids.
Full publication here.
Topological waves in passive and active fluids on curved surfaces: a unified picture
Understanding the role of topology in geophysical and biophysical fluids.
We investigate the occurrence of topologically protected waves in classical fluids confined on curved surfaces. Using a combination of topological band theory and real space analysis, we demonstrate the existence of a system-independent mechanism behind topological protection in two-dimensional passive and active fluids. This allows us to formulate an index theorem linking the number of modes, determined by the topology of Fourier space, to the real space topology of the surface on which they are hosted.
Full publication here.
Effective field theory for hydrodynamics without boosts
Understanding fluids with broken boost symmetry
We formulate the Schwinger-Keldysh effective field theory of hydrodynamics without boost symmetry. This includes a spacetime covariant formulation of classical hydrodynamics without boosts with an additional conserved particle/charge current coupled to Aristotelian background sources. This provides a unified covariant stable approach for simultaneously treating Lorentzian, Galilean, and Lifshitz fluids within an effective field theory framework and sets the stage for future studies of non-relativistic intertwined patterns of symmetry breaking.
Full publication here.
Consistent Blandford-Znajek Expansion
Understanding the basic mechanism for black hole jets
The Blandford-Znajek mechanism is the continuous extraction of energy from a rotating black hole via plasma currents flowing on magnetic field lines threading the horizon. In the discovery paper, Blandford and Znajek demonstrated the mechanism by solving the equations of force-free electrodynamics in a perturbative expansion valid at small black hole spin. Attempts to extend this perturbation analysis to higher order have encountered inconsistencies.We overcome this problem using the method of matched asymptotic expansions, taking care to resolve all of the singular surfaces (light surfaces) in the problem.
Full publication here.
Hydrodynamics for charge density waves and their holographic duals
Formulating hydrodynamics of charge density waves
We formulate a theory of dissipative hydrodynamics with spontaneously broken translations, describing charge density waves in a clean isotropic electronic crystal. We identify a novel linear transport coefficient, lattice pressure, capturing the effects of background strain and thermal expansion in a crystal. We argue that lattice pressure is a generic feature of systems with spontaneously broken translations and must be accounted for while building and interpreting holographic models. We also provide the first calculation of the coefficients of thermal and chemical expansion in a holographic electronic crystal.
Full publication here.
Newton-Cartan Submanifolds and Fluid Membranes
Understanding biophysical membranes
We develop the geometric description of submanifolds in Newton-Cartan spacetime. This provides the necessary starting point for a covariant spacetime formulation of Galilean-invariant hydrodynamics on curved surfaces. We also find a generalisation of the Canham-Helfrich bending energy for lipid vesicles that takes into account the requirements of thermal equilibrium.
Full publication here.
Viscoelastic hydrodynamics and holography
Understanding viscoelasticty and its holographic description
We formulate the theory of nonlinear viscoelastic hydrodynamics of anisotropic crystals in terms of dynamical Goldstone scalars of spontaneously broken translational symmetries, under the assumption of homogeneous lattices and absence of plastic deformations. We reformulate classical elasticity effective field theory using surface calculus in which the Goldstone scalars naturally define the position of higher-dimensional crystal cores, covering both elastic and smectic crystal phases. We propose a new simple holographic model of viscoelastic hydrodynamics by adopting an alternative quantisation for the scalar fields.
Full publication here.
Thermal transitions of metastable M-branes
Constructing new bound-states in string theory backgrounds
We use blackfold methods to analyse the properties of putative supergravity solutions in M-theory that describe the backreaction of polarised anti-M2 branes (namely, M5 branes wrapping three-cycles with negative M2-brane charge) in the Cvetic-Gibbons-Lu-Pope background of eleven-dimensional supergravity. At zero temperature we recover the metastable state of Klebanov and Pufu directly in supergravity.
Full publication here.
Instabilities of Thin Black Rings: Closing the Gap
Understanding black rings in higher dimensions
We initiate the study of dynamical instabilities of higher-dimensional black holes using the blackfold approach, focusing on asymptotically flat boosted black strings and singly-spinning black rings in D≥5. We derive novel analytic expressions for the growth rate of the Gregory-Laflamme instability for boosted black strings and its onset for arbitrary boost parameter. In the case of black rings, we study their stability properties in the region of parameter space that has so far remained inaccessible to numerical approaches.
Full publication here.
Meta-stable non-extremal anti-branes
Understanding mechanisms for supersymmetry breaking
We find new and compelling evidence for the meta-stability of SUSY-breaking states in holographic backgrounds whose consistency has been the source of ongoing disagreements in the literature. As a concrete example, we analyse anti-D3 branes at the tip of the Klebanov-Strassler (KS) throat. Using the blackfold formalism we examine how temperature affects the conjectured meta-stable state and determine whether and how the existing extremal results generalize when going beyond extremality. In the extremal limit we exactly recover the results of Kachru, Pearson and Verlinde (KPV), in a regime of parameter space that was previously inaccessible.
Full publication here.
One-form superfluids and magnetohydrodynamics
Understanding the physics of plasmas
We use the framework of generalised global symmetries to study various hydrodynamic regimes of hot electromagnetism. We formulate the hydrodynamic theories with an unbroken or a spontaneously broken U(1) one-form symmetry. The latter of these describes a one-form superfluid, which is characterised by a vector Goldstone mode and a two-form superfluid velocity. Two special limits of this theory have been studied in detail: the string fluid limit where the U(1) one-form symmetry is partly restored, and the electric limit in which the symmetry is completely broken.
Full publication here.
Magnetohydrodynamics as superfluidity
Understanding the physics of plasmas
We show that relativistic magnetohydrodynamics (MHD) can be recast as a novel theory of superfluidity. This new theory formulates MHD just in terms of conservation equations, including dissipative effects, by introducing appropriate variables such as a magnetic scalar potential, and providing necessary and sufficient conditions to obtain equilibrium configurations. We show that this scalar potential can be interpreted as a Goldstone mode originating from the spontaneous breaking of a one-form symmetry, and present the most generic constitutive relations at one derivative order for a parity-preserving plasma in this new superfluid formulation.
Full publication here.
Dissipative hydrodynamics with higher-form symmetry
Understanding hydrodynamics with higher-form currents
A theory of parity-invariant dissipative fluids with q-form symmetry is formulated to first order in a derivative expansion. The fluid is anisotropic with symmetry SO(D−1−q)×SO(q) and carries dissolved q-dimensional charged objects that couple to a (q+1)-form background gauge field. The formalism developed here can be easily adapted to study hydrodynamics with multiple higher-form symmetries.
Full publication here.