Publications
Explore my research articles and preprints below, followed by conference proceedings. Each entry includes a short description and links to the publication. For further details, visit my Google Scholar profile or INSPIRE profile.
Finite-volume scheme for first-order viscoresistive relativistic magnetohydrodynamics
Simulating relativistic plasmas without losing causality
We develop a finite-volume method for simulating relativistic plasmas with viscosity and electrical resistance. Based on a causal first-order theory, it tracks the coupled dissipation of energy, momentum and magnetic fields, and is tested against analytical results and two-dimensional simulations. The work provides numerical tools for exploring plasma dynamics in extreme environments.
Ruben Lier, Jay Armas, and Oliver Porth.
arXiv:2606.22691 (2026) · under review in Phys. Rev. D
Hyperscaling of spatial fluctuations constrains the development of urban populations
Finding the patterns that connect urban geometry and population fluctuations
How does the uneven distribution of people within a city change with the scale at which we look? Using population maps from the Netherlands and hundreds of cities worldwide, we identify a relationship between urban geometry and spatial fluctuations. Its evolution over time reveals the importance of spatial correlations and constrains models of urban growth.
Wout Merbis, Fernando A. N. Santos, Jay Armas, Frank Pijpers, and Mike Lees.
arXiv:2604.01969 (2026) · under review in PNAS Nexus
Null fluid/gravity correspondence
Connecting lightlike fluid motion with the geometry of spacetime
We establish a correspondence between null fluids and gravitational wave geometries in Anti-de Sitter spacetime. This extends the fluid/gravity connection into a regime where temperature approaches zero and fluid motion approaches the speed of light. We also develop the corresponding description for asymptotically flat gravitational backgrounds using the blackfold approach.
Jay Armas, Emil Have, and Gianbattista-Piero Nicosia.
JHEP 08 (2026), 220 · arXiv:2602.20268
Thermodynamics of ideal spin fluids and pseudo-gauge ambiguity
Putting the thermodynamics of spinning fluids on a consistent footing
Fluids whose constituents carry spin raise a subtle question: how should energy, momentum and angular momentum be assigned locally? We identify choices of conserved currents that satisfy standard thermodynamic relations, quantify the remaining ambiguities, and derive relations valid across these choices. Free fermions and scalar fields provide concrete applications.
Jay Armas and Akash Jain.
arXiv:2601.14421 (2026) · under review in Phys. Rev. X
Null matter and the ultrarelativistic origin of hydrodynamics at zero temperature
Discovering a hydrodynamic regime at zero temperature
We uncover a universal limit of relativistic fluid dynamics in which temperature tends to zero while the flow approaches the speed of light. The resulting theory describes null matter and can remain stable and causal in any hydrodynamic frame. It opens a route to understanding extreme flows and aspects of black-hole horizon dynamics.
Jay Armas, Emil Have, and Gianbattista-Piero Nicosia.
arXiv:2509.25320 (2025) · under review in Phys. Rev. Lett
Temperature of an active nematic
Tracing the thermal signature of self-driven matter
Active nematics are fluids of aligned, energy-consuming constituents. We show how their spontaneous flows can generate distinctive temperature patterns through local shearing and twisting. These patterns offer a thermal signature of activity, even though small temperature fluctuations around a homogeneous steady state can remain insensitive to that activity.
Jay Armas, Akash Jain, and Ruben Lier.
Phys. Rev. Research 8, L022011 (2026) · arXiv:2506.20602
Chiral anomaly from anomalous spin hydrodynamics
Linking quantum anomalies to the geometry of spinning fluids
We connect the dynamics of spinning black branes to a theory of fluids carrying angular momentum. In a holographic setting, a chiral anomaly in four dimensions acquires a geometric interpretation through spinning fluids and a gravitational anomaly in ten dimensions. This provides a new bridge between spin hydrodynamics, gravity and anomalous quantum transport.
Jay Armas and Giorgos Batzios.
Phys. Rev. D 114, L021901 (2026) · arXiv:2505.01843
Polarization in increasingly connected societies
Why more connections need not bring people closer together
Can a society become more polarized as its members become more connected? We introduce an opinion-formation model in which involvement shapes how people respond to others. Analytical results and different network structures show that increasing connectivity can strengthen polarization, offering a mechanism beyond explanations based only on social isolation or like-minded interactions.
Tuan Minh Pham, Sidney Redner, Lourens Waldorp, Jay Armas, and Han L. J. van der Maas.
Phys. Rev. E 113, 054303 (2026) · arXiv:2503.24098
Resistive relativistic magnetohydrodynamics without Ampere's law
A new route to simulating electrically resistive plasmas
Simulating highly conducting relativistic plasmas is difficult because the usual electromagnetic equations can become numerically stiff. We reformulate resistive magnetohydrodynamics using higher-form symmetry and a dual description of the electromagnetic field. This avoids evolving Ampere’s law directly while providing a causal framework for studying phenomena such as black-hole flares and neutron-star magnetospheres.
Ruben Lier, Akash Jain, Jay Armas, and Oliver Porth.
Phys. Rev. D 112, 083059 (2025) · arXiv:2501.04638
New asymptotically (Anti)-de Sitter black holes in (super)gravity
Expanding the landscape of higher-dimensional black holes
We use the blackfold approach to construct new approximate black-hole solutions in curved cosmological backgrounds and supergravity. The solutions carry multiple spins and charges and include higher-dimensional generalizations of familiar black holes and black rings. Some also describe new thermal states of strongly interacting quantum field theories through holography.
Jay Armas and Gianbattista-Piero Nicosia.
JHEP 09 (2024), 047 · arXiv:2406.17489
Hydrodynamics of thermal active matter
Bringing energy, temperature and fluctuations into active hydrodynamics
Living and self-driven systems continually consume fuel and exchange energy with their surroundings. We develop a hydrodynamic framework that includes this energy balance, local temperature and fluctuations. Applied to active nematics and superfluids, it connects activity-induced transport and phase transitions to the symmetries of driven systems.
Jay Armas, Akash Jain, and Ruben Lier.
Phys. Rev. E 112, 055401 (2025) · arXiv:2405.11023
Higher-group global symmetry and the bosonic M5 brane
Understanding branes through intertwined symmetries
We investigate higher-group symmetries, which link different kinds of extended conserved quantities. These symmetries organize the low-energy phases of matter and offer a new interpretation of the theories living on branes in string theory and M-theory. The bosonic M5 brane provides an explicit example, including a finite-temperature description that incorporates self-duality.
Jay Armas, Giorgos Batzios, and Akash Jain.
JHEP 08 (2024), 003 · arXiv:2402.19458
Topological plasma oscillations in the solar tachocline
Exploring the robust waves hidden inside the Sun
The solar tachocline is a thin transition region where rotation, magnetic fields and plasma motion interact. We study its oscillations using shallow-water magnetohydrodynamics and identify topologically protected wave modes near the equator. Their robustness may help interpret observations of the Sun’s interior and its activity.
Ruben Lier, Richard Green, Jan de Boer, and Jay Armas.
arXiv:2401.07622 (2024) · under review in ApJ
Probe particles in odd active viscoelastic fluids: how activity and dissipation determine linear stability
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.
Charlie Duclut, Stefano Bo, Ruben Lier, Jay Armas, Piotr Surówka, and Frank Jülicher.
Phys. Rev. E 109, 044126 (2024) · arXiv:2310.08640
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.
Jay Armas and Emil Have.
Phys. Rev. Lett. 132, 161606 (2024) · arXiv:2308.10594
Risk aversion can promote 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.
Jay Armas, Wout Merbis, Janusz Meylahn, Soroush Rafiee Rad, and Mauricio J. del Razo.
J. Phys. Complex. 6, 015010 (2025) · arXiv:2306.05971
Ideal 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.
Jay Armas and Emil Have.
SciPost Phys. 16, 039 (2024) · arXiv:2304.09596
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.
Jay Armas and Akash Jain.
Phys. Rev. D 109, 045019 (2024) · arXiv:2301.09628
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.
Jay Armas, Giorgos Batzios, and Jan Pieter van der Schaar.
JHEP 04 (2023), 021 · arXiv:2212.02777
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.
Jay Armas, Erik van Heumen, Akash Jain, and Ruben Lier.
Phys. Rev. B 107, 155108 (2023) · arXiv:2211.02117
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.
Ruben Lier, Charlie Duclut, Stefano Bo, Jay Armas, Frank Jülicher, and Piotr Surówka.
Phys. Rev. E 108, L023101 (2023) · arXiv:2205.12704
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.
Jay Armas and Filippo Camilloni.
JCAP 10 (2022), 039 · arXiv:2201.06847
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.
Jay Armas, Akash Jain, and Ruben Lier.
Phys. Rev. D 108, 086011 (2023) · arXiv:2112.14373
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.
Ruben Lier, Jay Armas, Stefano Bo, Charlie Duclut, Frank Jülicher, and Piotr Surówka.
Phys. Rev. E 105, 054607 (2022) · arXiv:2109.06606
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.
Richard Green, Jay Armas, Jan de Boer, and Luca Giomi.
arXiv:2011.12271 (2020) · under review in Phys. Rev. X
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.
Jay Armas and Akash Jain.
SciPost Phys. 11, 054 (2021) · arXiv:2010.15782
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.
Jay Armas, Yangyang Cai, Geoffrey Compère, David Garfinkle, and Samuel E. Gralla.
JCAP 04 (2020), 009 · arXiv:2002.01972
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.
Jay Armas and Akash Jain.
Phys. Rev. D 101, 121901 (2020) · arXiv:2001.07357
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.
Jay Armas, Jelle Hartong, Emil Have, Bjarke Frost Nielsen, and Niels A. Obers.
Phys. Rev. E 101, 062803 (2020) · arXiv:1912.01613
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.
Jay Armas and Akash Jain.
JHEP 01 (2020), 126 · arXiv:1908.01175
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.
Jay Armas, Nam Nguyen, Vasilis Niarchos, and Niels A. Obers.
JHEP 08 (2019), 128 · arXiv:1904.13283
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.
Jay Armas and Enrico Parisini.
JHEP 04 (2019), 169 · arXiv:1901.09369
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.
Jay Armas, Nam Nguyen, Vasilis Niarchos, Niels A. Obers, and Thomas Van Riet.
Phys. Rev. Lett. 122, 181601 (2019) · arXiv:1812.01067
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.
Jay Armas and Akash Jain.
JHEP 01 (2020), 041 · arXiv:1811.04913
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.
Jay Armas and Akash Jain.
Phys. Rev. Lett. 122, 141603 (2019) · arXiv:1808.01939
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.
Jay Armas, Jakob Gath, Akash Jain, and Andreas Vigand Pedersen.
JHEP 05 (2018), 192 · arXiv:1803.00991
Extremal Black Hole Horizons
Exploring black holes at the edge of extremality
We use an effective theory of extremal black branes to find evidence for new higher-dimensional black holes. The configurations include spinning rings and systems with several disconnected horizons, such as black saturns and paired rings. They extend the possible shapes and arrangements of zero-temperature horizons in vacuum gravity.
Jay Armas, Troels Harmark, and Niels A. Obers.
JHEP 03 (2018), 099 · arXiv:1712.09364
On actions for (entangling) surfaces and DCFTs
A common geometric language for membranes, interfaces and entanglement
We develop a variational framework for surfaces and interfaces, connecting their geometry to elastic response and spacetime stress. The same tools apply to fluid membranes, entangling surfaces and defects in quantum field theory. They reveal constraints on surface dynamics, boundary effects and conformal anomalies, including an unusual parity-odd elastic response.
Jay Armas and Javier Tarrio.
JHEP 04 (2018), 100 · arXiv:1709.06766
On the surface of superfluids
Discovering the physics at the boundary of a superfluid
A superfluid’s surface carries its own thermodynamics and transport, shaped by the fluid beneath it. We derive these surface properties for relativistic and non-relativistic superfluids and identify new contributions tied to bulk transport. Studying small disturbances also reveals distinctive waves that can propagate along the boundary.
Jay Armas, Jyotirmoy Bhattacharya, Akash Jain, and Nilay Kundu.
JHEP 06 (2017), 090 · arXiv:1612.08088
Forced Fluid Dynamics from Blackfolds in General Supergravity Backgrounds
Describing charged black branes as fluids driven by external fields
We derive the large-scale equations governing charged black branes in general gravitational backgrounds. Their collective motion takes the form of fluid dynamics on flexible surfaces, driven by external fields and fluxes. This brings a wide class of supergravity interactions into a unified effective description.
Jay Armas, Jakob Gath, Vasilis Niarchos, Niels A. Obers, and Andreas Vigand Pedersen.
JHEP 10 (2016), 154 · arXiv:1606.09644
Gravitational Tension, Spacetime Pressure and Black Hole Volume
Asking what pressure and volume mean for a black hole
We study how a black hole’s thermodynamics changes when its surrounding gravitational field changes. Gravitational tension and binding energy provide a natural way to describe these effects and clarify their relationship to pressure and volume. The analysis also exposes limits to treating black-hole volume as a universal physical quantity.
Jay Armas, Niels A. Obers, and Marco Sanchioni.
JHEP 09 (2016), 124 · arXiv:1512.09106
Surface transport in plasma-balls
Understanding transport at the edge of a plasma droplet
Finite droplets of relativistic fluid have surface properties that cannot be inferred from their bulk alone. We derive constraints on their surface transport, including the effects of temperature-dependent surface tension and bending rigidity. Through holography, these results also illuminate the physics of certain black-hole configurations.
Jay Armas, Jyotirmoy Bhattacharya, and Nilay Kundu.
JHEP 06 (2016), 015 · arXiv:1512.08514
New Geometries for Black Hole Horizons
Finding new shapes for higher-dimensional horizons
We extend the blackfold approach by integrating out parts of a black brane’s geometry to obtain new effective theories. This reveals previously unexplored horizon shapes, including helicoids, helicoidal rings and tori. The construction connects fluid and elastic response to the remarkable geometric variety allowed by higher-dimensional gravity.
Jay Armas and Matthias Blau.
JHEP 07 (2015), 048 · arXiv:1504.01393
Blackfolds, Plane Waves and Minimal Surfaces
Using the geometry of soap films to discover black holes
Minimal surfaces provide a geometric starting point for constructing unusual black-hole horizons. We explore how rotation and curved backgrounds turn these surfaces into viable blackfold configurations, uncovering helicoids, catenoids and other shapes. The results reveal connections between apparently different families of higher-dimensional black holes.
Jay Armas and Matthias Blau.
JHEP 07 (2015), 156 · arXiv:1503.08834
Uniqueness of Black Holes with Bubbles in Minimal Supergravity
Determining what uniquely identifies a black hole with spacetime bubbles
In five-dimensional supergravity, a black hole’s exterior can contain nontrivial bubbles supported by magnetic flux. We extend uniqueness theorems to these richer geometries and to configurations with several horizons. Alongside charges and geometric data, the fluxes threading the bubbles are essential to identifying the spacetime.
Jay Armas.
Class. Quantum Grav. 32, 045001 (2015) · arXiv:1408.4567
Constraints on the effective fluid theory of stationary branes
Constraining the fluid and elastic dynamics of stationary branes
We refine the effective description of stationary branes by including finite thickness, bending and transverse spin. Consistency between thermodynamics and conserved currents constrains the allowed corrections, including how spin couples to the surrounding spacetime. Black tori and charged black rings provide applications and comparisons with gravitational solutions.
Jay Armas and Troels Harmark.
JHEP 10 (2014), 063 · arXiv:1406.7813
Black Probes of Schrödinger Spacetimes
Probing holographic worlds with strings and membranes
We use thermal black strings and membranes to explore Anti-de Sitter and Schrödinger spacetimes in string theory and M-theory. These probes construct new approximate gravitational configurations and represent extended observables in the corresponding quantum theories. Comparing the backgrounds reveals how different spacetime symmetries affect the probes’ behaviour.
Jay Armas and Matthias Blau.
JHEP 08 (2014), 140 · arXiv:1405.1301
Black Holes and Biophysical (Mem)-branes
A shared effective theory for black holes and biological membranes
Black branes and biophysical membranes appear to belong to very different worlds, yet their long-wavelength dynamics can follow the same effective theory. We use this connection to incorporate finite-thickness effects in higher-dimensional black rings. The resulting predictions agree strikingly with numerical gravity calculations and expose a bridge between elasticity and gravitation.
Jay Armas and Troels Harmark.
Phys. Rev. D 90, 124022 (2014) · arXiv:1402.6330
(Non)-Dissipative Hydrodynamics on Embedded Surfaces
Following fluids that live on flexible surfaces
We formulate hydrodynamics for fluids confined to surfaces that can themselves bend and fluctuate. Combining fluid motion with elastic response and the second law of thermodynamics constrains the allowed transport coefficients. The framework applies to fluid membranes and helps characterize the effective elasticity of black branes.
Jay Armas.
JHEP 09 (2014), 047 · arXiv:1312.0597
Electroelasticity of Charged Black Branes
How charged black branes respond when bent
We develop an effective description of charged branes that combines fluid motion, elasticity and electrical polarization. Constructing bent black-brane solutions allows us to measure their bending and electric dipole responses. These gravitational systems obey a form of classical electroelasticity, with response coefficients analogous to those of ordinary materials.
Jay Armas, Jakob Gath, and Niels A. Obers.
JHEP 10 (2013), 035 · arXiv:1307.0504
Null-Wave Giant Gravitons from Thermal Spinning Brane Probes
Adding heat, spin and traveling waves to giant gravitons
We construct thermal giant gravitons from spherical black branes and investigate the effects of internal spin. Their temperature and rotation reveal a rich landscape of states in string theory and M-theory. A special zero-temperature limit produces new giant gravitons carrying null waves, beyond the usual worldvolume description.
Jay Armas, Niels A. Obers, and Andreas Vigand Pedersen.
JHEP 10 (2013), 109 · arXiv:1306.2633
How Fluids Bend: the Elastic Expansion for Higher-Dimensional Black Holes
Building an elastic theory of curved fluids and black holes
A fluid living on a flexible surface can bend as well as flow. We construct its effective free energy, generalizing membrane bending theories to rotating relativistic systems. The resulting elastic, hydrodynamic and spin responses provide higher-order corrections to the blackfold description of higher-dimensional black holes.
Jay Armas.
JHEP 09 (2013), 073 · arXiv:1304.7773
Relativistic Elasticity of Stationary Fluid Branes
Revealing elasticity within relativistic fluid mechanics
We show that a stationary fluid confined to a dynamical surface can respond elastically when that surface is slightly deformed. Under appropriate thermodynamic conditions, this behaviour is independent of spacetime dimension or a gravitational interpretation. It explains why black branes can exhibit elastic and electroelastic properties.
Jay Armas and Niels A. Obers.
Phys. Rev. D 87, 044058 (2013) · arXiv:1210.5197
Black Branes as Piezoelectrics
When bending a black brane creates electrical polarization
Piezoelectric materials develop electrical polarization when deformed. We uncover an analogous response in charged black branes and calculate elastic and piezoelectric coefficients for charged black strings. The results also yield predictions for the equilibrium of higher-dimensional charged black rings, connecting gravitational physics with a familiar material phenomenon.
Jay Armas, Jakob Gath, and Niels A. Obers.
Phys. Rev. Lett. 109, 241101 (2012) · arXiv:1209.2127
Thermal Giant Gravitons
Heating up giant gravitons
Giant gravitons are expanded brane configurations in string theory. We study how they change at finite temperature, finding a minimum angular momentum and radius as well as stable and unstable branches. Their thermodynamics provides a way to investigate how these gravitational objects relate to thermal states in the dual quantum theory.
Jay Armas, Troels Harmark, Niels A. Obers, Marta Orselli, and Andreas Vigand Pedersen.
JHEP 11 (2012), 123 · arXiv:1207.2789
Domain Structure of Black Hole Space-Times with a Cosmological Constant
Classifying black-hole geometry in curved cosmological backgrounds
We extend the domain-structure description of stationary black holes to spacetimes with a cosmological constant. The resulting geometric and topological data help characterize horizons in de Sitter and Anti-de Sitter backgrounds. This reveals important differences between the two settings and constrains possible horizon topologies.
Jay Armas, Pawel Caputa, and Troels Harmark.
Phys. Rev. D 85, 084019 (2012) · arXiv:1111.1163
The Young Modulus of Black Strings and the Fine Structure of Blackfolds
Measuring the elasticity of black strings
Thin black branes have an internal structure that becomes visible when they bend. We calculate a relativistic analogue of Young’s modulus, the quantity that measures a material’s elastic stiffness. These finite-thickness corrections improve the blackfold description and lead to new predictions for higher-dimensional black rings.
Jay Armas, Joan Camps, Troels Harmark, and Niels A. Obers.
JHEP 02 (2012), 110 · arXiv:1110.4835
Blackfolds in (Anti)-de Sitter Backgrounds
Constructing blackfolds in cosmological spacetimes
We construct approximate black-hole solutions in Anti-de Sitter and de Sitter backgrounds using the blackfold approach. Their horizons include products of spheres, with thermodynamic stability and rapid rotation playing important roles. The work shows how simple effective geometries capture limits of more complicated gravitational solutions.
Jay Armas and Niels A. Obers.
Phys. Rev. D 83, 084039 (2011) · arXiv:1012.5081
Maximal Analytic Extension and Hidden Symmetries of the Dipole Black Ring
Looking beyond the horizons of a dipole black ring
We extend the spacetime description of dipole black rings across their horizons to explore their global causal structure. The extended geometries contain multiple asymptotic regions and share features with charged four-dimensional black holes. We also identify hidden symmetries that simplify the motion of special lightlike trajectories.
Jay Armas.
Class. Quantum Grav. 28, 235014 (2011) · arXiv:1011.5618
Uniqueness Theorem for Black Hole Space-Times with Multiple Disconnected Horizons
Identifying spacetimes with several separate black-hole horizons
We prove a uniqueness result for stationary black-hole spacetimes with multiple disconnected horizons in five-dimensional minimal supergravity. Charges measured near individual horizons and local magnetic fluxes complement the quantities measured at infinity. Together with geometric boundary data, they specify configurations that a single set of global charges cannot distinguish.
Jay Armas and Troels Harmark.
JHEP 05 (2010), 093 · arXiv:0911.4654
Conference proceedings
Geometries for black hole horizons
Surveying the surprising shapes of higher-dimensional black holes
This proceedings contribution reviews how the blackfold effective theory constructs higher-dimensional black holes. It highlights horizons with nontrivial geometry and topology, including helicoidal configurations, and shows how an effective description makes this broader landscape accessible.
Jay Armas.
The Fourteenth Marcel Grossmann Meeting, pp. 1822–1827 (2017)
Membrane Hydrodynamics and Black Soap Bubbles
Connecting membrane dynamics with black-hole physics
This proceedings contribution explores the connection between fluid membranes and black holes through the blackfold approach. It presents the membrane perspective on gravitational dynamics, bringing together the physics of bending surfaces, hydrodynamics and black-hole geometry.
Jay Armas.
Fortschr. Phys. 64 (4–5), 408–411 (2016)