Regimes Of Parameter Space Research Articles

Dynamics of the osmotic lysis of mineral protocells and its avoidance at the origins of life.

The osmotic rupture of a cell, its osmotic lysis or cytolysis, is a phenomenon that active biological cell volume regulation mechanisms have evolved in the cell membrane to avoid. How then, at the origin of life, did the first protocells survive prior to such active processes? The pores of alkaline hydrothermal vents in the oceans form natural nanoreactors in which osmosis across a mineral membrane plays a fundamental role. Here, we discuss the dynamics of lysis and its avoidance in an abiotic system without any active mechanisms, reliant upon self-organized behaviour, similar to the first self-organized mineral membranes within which complex chemistry may have begun to evolve into metabolism. We show that such mineral nanoreactors could function as protocells without exploding because their self-organized dynamics have a large regime in parameter space where osmotic lysis does not occur and homeostasis is possible. The beginnings of Darwinian evolution in proto-biochemistry must have involved the survival of protocells that remained within such a safe regime.

Inertial active harmonic particle with memory induced spreading by viscoelastic suspension.

We investigate the self-propulsion of an inertial active particle confined in a two-dimensional harmonic trap. The particle is suspended in a non-Newtonian or viscoelastic suspension with a friction kernel that decays exponentially with a time constant characterizing the memory timescale or transient elasticity of the medium. By solving the associated non-Markovian dynamics, we identify two regimes in parameter space distinguishing the oscillatory and non-oscillatory behavior of the particle motion. By simulating the particle trajectories and exactly calculating the steady-state probability distribution functions and mean square displacement; interestingly, we observe that with an increase in the memory time scale, the effective temperature of the environment increases. As a consequence, the particle becomes energetic and spread away from the center, covering larger space inside the confinement. On the other hand, with an increase in the duration of the activity, the particle becomes trapped by the harmonic confinement.

Holographic duals of the mathcal{N} = 1* gauge theory

We use the long-wavelength effective theory of black branes (blackfold approach) to perturbatively construct holographic duals of the vacua of the mathcal{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 back-grounds corresponding to the high- and low-temperature phases of the gauge theory. Our approach recovers the results for the brane potentials and equilibrium configurations known in the literature in the extremal limit, while away from extremality we find metastable black D3-NS5 configurations with horizon topology ℝ3 × \U0001d54a2 × \U0001d54a3 in certain regimes of parameter space, which cloak potential brane singularities. We uncover novel features of the phase diagram of the mathcal{N} = 1* gauge theory in different ensembles and provide further evidence for the appearance of metastable states in holographic backgrounds dual to confining gauge theories.

Toward matter dynamics in spin foam quantum gravity

Any approach to pure quantum gravity must eventually face the question of coupling quantum matter to the theory. In the past, several ways of coupling matter to spin foam quantum gravity have been proposed, but the dynamics of the coupled matter-gravity system is challenging to explore. To take first steps towards uncovering the influence quantum matter has on spin foam models, we couple free, massive scalar lattice field theory to a restricted, semi-classical 4d spin foam model, called quantum cuboids. This model can be understood as a superposition of hypercuboidal (and thus irregular) lattices. Both theories are coupled by defining scalar lattice field theory on irregular lattices via discrete exterior calculus and then superimposing these theories by summing over spin foam configurations. We compute expectation values of geometric and matter observables using Markov Chain Monte Carlo techniques. From the observables, we identify a regime in parameter space, in which the spin foam possesses a finite total volume and looks on average like a regular lattice with an emergent lattice spacing dependent on the mass of the scalar field. We also measure the 2-point correlation function and correlation length of the scalar field in relation to the geodesic distance encoded in the spin foam. Our results are consistent with the correlation function of ordinary scalar lattice field theory defined on a fixed regular lattice with the emergent lattice spacing and the same mass. We conclude that in this regime of the model, the scalar field is not sensitive to the fluctuations of the spin foam and effectively behaves as if it is defined on a fixed regular lattice.

Skyrmions in Twisted Bilayer Graphene: Stability, Pairing, and Crystallization

We study the excitations that emerge upon doping the translationally invariant correlated insulating states in magic-angle twisted bilayer graphene at various integer filling factors ν. We identify parameter regimes where these are excitations associated with skyrmion textures in the spin or pseudospin degrees of freedom, and explore both short-distance pairing effects and the formation of long-range ordered skyrmion crystals. We perform a comprehensive analysis of the pseudospin skyrmions that emerge upon doping insulators at even ν, delineating the regime in parameter space where these are the lowest-energy charged excitations by means of self-consistent Hartree-Fock calculations on the interacting Bistritzer-MacDonald model. We explicitly demonstrate the purely electron-mediated pairing of skyrmions, a key ingredient behind a recent proposal of skyrmion superconductivity. Building upon this, we construct hopping models to extract the effective masses of paired skyrmions, and discuss our findings and their implications for skyrmion superconductivity in relation to experiments, focusing on the dome-shaped dependence of the transition temperature on the twist angle. We also investigate the properties of spin skyrmions about the quantized anomalous Hall insulator at ν=+3. In both cases, we demonstrate the formation of robust spin or pseudospin skyrmion crystals upon doping to a finite density away from integer filling.5 MoreReceived 20 January 2022Revised 13 June 2022Accepted 29 June 2022DOI:https://doi.org/10.1103/PhysRevX.12.031020Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasSkyrmionsSuperconductivityPhysical SystemsGrapheneStrongly correlated systemsTwisted bilayer grapheneTechniquesHartree-Fock methodsCondensed Matter, Materials & Applied Physics

Thermodynamic quasi-stability of super entropic BTZ black hole

We know that criteria for thermodynamic stability of a most general black hole appears in the form of a series of inequalities connecting second-order derivatives of the black hole mass with respect to its parameters. Quasi-stable black holes satisfy some of these stability criteria in a certain regime of parameter space, but they never satisfy all the criteria simultaneously. We also know that specific heat, by virtue of our general stability criteria, is not necessarily negative for quasi-stable black holes. We show here that ([Formula: see text])-dimensional charged super entropic BTZ black hole is thermodynamically quasi-stable if fluctuation in cosmological constant is taken into account. We in fact study the fluctuations of all the thermodynamic parameters of this black hole in detail, namely, its charge, horizon area and cosmological constant. This detailed study concludes that this BTZ black hole transforms into some other kind of black hole during its Hawking decay and becomes stable. We also show differences in thermodynamic properties between this charged super entropic BTZ black hole and other AdS black holes.

Comparison between fluid-gravity and membrane-gravity dualities for Einstein–Maxwell system

Derivative expansion and large-D expansion are two perturbation techniques, which are used to generate dynamical black-brane solutions to Einstein’s equations in presence of negative cosmological constant. In this paper we have compared these two techniques and established the equivalence of the gravity solutions generated by these two different techniques in appropriate regime of parameter space up to first non-trivial order in both the perturbation parameters for Einstein–Maxwell systems, generalizing the earlier works of [, ] for non-charged systems. An one-to-one map between dynamical black-brane geometry and AdS space, which also exists at finite number of dimensions, has also been established.

A study of quantum Berezinskii\u2013Kosterlitz\u2013Thouless transition for parity-time symmetric quantum criticality

The Berezinskii–Kosterlitz–Thouless (BKT) mechanism governs the critical behavior of a wide range of many-body systems. We show here that this phenomenon is not restricted to conventional many body system but also for the strongly correlated parity-time (PT) symmetry quantum criticality. We show explicitly behaviour of topological excitation for the real and imaginary part of the potential are different through the analysis of second order and third order renormalization group (RG). One of the most interesting feature that we observe from our study the presence of hidden QBKT and also conventional QBKT for the real part of the potential whereas there is no such evidence for the imaginary part of the potential. We also present the exact solution for the RG flow lines. We show explicitly how the physics of single field double frequencies sine-Gordon Hamiltonian effectively transform to the dual field double frequencies sine-Gordon Hamiltonian for a certain regime of parameter space. This is the first example in any quantum many body systems. We present the results of second order and third order RG flow results explicitly for the real and imaginary part of the potential. This PT symmetric system can be experimentally tested in ultra-cold atoms. This work provides a new perspective for the PT symmetric quantum criticality.

Constructing AdS2 flow geometries

We consider two-dimensional geometries flowing away from an asymptotically AdS2 spacetime. Macroscopically, flow geometries and their thermodynamic properties are studied from the perspective of dilaton-gravity models. We present a precise map constructing the fixed background metric from the boundary two-point function of a nearly massless matter field. We analyse constraints on flow geometries, viewed as solutions of dimensionally reduced theories, stemming from energy conditions. Microscopically, we construct computationally tractable RG flows in SYK-type models at vanishing and non-vanishing temperature. For certain regimes of parameter space, the flow geometry holographically encoding the microscopic RG flow is argued to interpolate between two (near) AdS2 spacetimes. The coupling between matter fields and the dilaton in the putative bulk is also discussed. We speculate on microscopic flows interpolating between an asymptotically AdS2 spacetime and a portion of a dS2 world.

Occurrence of Vibrational resonance in an oscillator with an asymmetric Toda potential

Vibrational resonance (VR) is a phenomenon wherein the response of a nonlinear oscillator driven by biharmonic forces with two different frequencies, ω and Ω, such that Ω≫ω, is enhanced by optimizing the parameters of high-frequency driving force. In this paper, an counterintuitive scenario in which a biharmonically driven nonlinear oscillator does not vibrate under the well known VR conditions is reported. This behaviour was observed in a system with an integrable and asymmetric Toda potential driven by biharmonic forces in the usual VR configuration. It is shown that with constant dissipation and in the presence of biharmonic forces, VR does not take place, whereas with nonlinear displacement-dependent periodic dissipation multiple VR can be induced at certain values of high-frequency force parameters. Theoretical analysis are validated using numerical computation and Simulink implementation in MATLAB. Finally, the regime in parameter space of the dissipation for optimum occurrence of multiple VR in the Toda oscillator was estimated. This result would be relevant for experimental applications of dual-frequency driven laser models where the Toda potential is extensively employed.

Multi-critical topological transition at quantum criticality

The investigation and characterization of topological quantum phase transition between gapless phases is one of the recent interest of research in topological states of matter. We consider transverse field Ising model with three spin interaction in one dimension and observe a topological transition between gapless phases on one of the critical lines of this model. We study the distinct nature of these gapless phases and show that they belong to different universality classes. The topological invariant number (winding number) characterize different topological phases for the different regime of parameter space. We observe the evidence of two multi-critical points, one is topologically trivial and the other one is topologically active. Topological quantum phase transition between the gapless phases on the critical line occurs through the non-trivial multi-critical point in the Lifshitz universality class. We calculate and analyze the behavior of Wannier state correlation function close to the multi-critical point and confirm the topological transition between gapless phases. We show the breakdown of Lorentz invariance at this multi-critical point through the energy dispersion analysis. We also show that the scaling theories and curvature function renormalization group can also be effectively used to understand the topological quantum phase transitions between gapless phases. The model Hamiltonian which we study is more applicable for the system with gapless excitations, where the conventional concept of topological quantum phase transition fails.

Dynamics of Colombo’s Top: Generating Exoplanet Obliquities from Planet–Disk Interactions

Abstract Large planetary spin–orbit misalignments (obliquities) may strongly influence atmospheric circulation and tidal heating in a planet. A promising avenue to generate obliquities is via spin–orbit resonances, where the spin and orbital precession frequencies of a planet cross each other as the system evolves in time. One such mechanism involves a dissipating (mass-losing) protoplanetary disk that drives orbital precession of an interior planet. We study this scenario analytically in this paper, and obtain the mapping between the general initial spin orientation and the final obliquity. We show that (i) under adiabatic evolution (i.e., the disk dissipates at a sufficiently slow rate), the final planetary obliquity as a function of the initial spin orientation bifurcates into distinct tracks governed by interactions with the resonance; and (ii) under nonadiabatic evolution, a broad range of obliquities can be excited. We obtain analytical expressions for the final obliquities for various regimes of parameter space. The dynamical system studied in this paper is an example of “Colombo’s top,” and our analysis and results can be adapted to other applications.

Dynamical persistence in high-diversity resource-consumer communities.

We show how highly-diverse ecological communities may display persistent abundance fluctuations, when interacting through resource competition and subjected to migration from a species pool. These fluctuations appear, robustly and predictably, in certain regimes of parameter space. Their origin is closely tied to the ratio of realized species diversity to the number of resources. This ratio is set by competition, through the balance between species being pushed out and invading. When this ratio is smaller than one, dynamics will reach stable equilibria. When this ratio is larger than one, the competitive exclusion principle dictates that fixed-points are either unstable or marginally stable. If they are unstable, the system is repelled from fixed points, and abundances forever fluctuate. While marginally-stable fixed points are in principle allowed and predicted by some models, they become structurally unstable at high diversity. This means that even small changes to the model, such as non-linearities in how resources combine to generate species’ growth, will result in persistent abundance fluctuations.

Slow heating in a quantum coupled kicked rotors system

We consider a finite-size periodically driven quantum system of coupled kicked rotors which exhibits two distinct regimes in parameter space: a dynamically-localized one with kinetic-energy saturation in time and a chaotic one with unbounded energy absorption (dynamical delocalization). We provide numerical evidence that the kinetic energy grows subdiffusively in time in a parameter region close to the boundary of the chaotic dynamically-delocalized regime. We map the different regimes of the model via a spectral analysis of the Floquet operator and investigate the properties of the Floquet states in the subdiffusive regime. We observe an anomalous scaling of the average inverse participation ratio (IPR) analogous to the one observed at the critical point of the Anderson transition in a disordered system. We interpret the behavior of the IPR and the behavior of the asymptotic-time energy as a mark of the breaking of the eigenstate thermalization in the subdiffusive regime. Then we study the distribution of the kinetic-energy-operator off-diagonal matrix elements. We find that in presence of energy subdiffusion they are not Gaussian and we propose an anomalous random matrix model to describe them.

Searching for Wide Companions and Identifying Circum(sub)stellar Disks through PSF Fitting of Spitzer/IRAC Archival Images

Abstract Direct imaging surveys have discovered wide-orbit planetary-mass companions that challenge existing models of both star and planet formation, but their demographics remain poorly sampled. We have developed an automated binary companion point-spread function (PSF) fitting pipeline to take advantage of Spitzer's infrared sensitivity to planetary-mass objects and circum(sub)stellar disks, measuring photometry across the four Infrared Array Camera (IRAC) channels of 3.6, 4.5, 5.8, and 8.0 μm. We present PSF fitting photometry of archival Spitzer/IRAC images for 11 young, low-mass (M ∼ 0.044–0.88 M ⊙; K3.5–M7.5) members of three nearby star-forming regions (Chameleon, Taurus, and Upper Scorpius; d ∼ 150 pc; τ ∼ 1–10 Myr) that host confirmed or candidate faint companions at ρ = 1.″68–7.″31. We recover all system primaries, six confirmed, and two candidate low-mass companions in our sample. We also measure nonphotospheric [3.6]–[8.0] colors for three of the system primaries, four of the confirmed companions, and one candidate companion, signifying the presence of circumstellar or circum(sub)stellar disks. We furthermore report the confirmation of a ρ = 4.″66 (540 au) companion to [SCH06] J0359+2009 which was previously identified as a candidate via imaging over five years ago, but was not studied further. Based on its brightness (M [3.6] = 8.53 mag), we infer the companion mass to be M = 20 ± 5 M Jup given the primary’s model-derived age of 10 Myr. Our framework is sensitive to companions with masses less than 10 M Jup at separations of ρ = 300 au in nearby star-forming regions, opening up a new regime of parameter space that has yet to be studied in detail, discovering planetary-mass companions in their birth environments and revealing their circum(sub)stellar disks.

Lock-in regimes for Vortex-Induced Vibrations of a cylinder attached to a bistable spring

We study Vortex-Induced Vibrations (VIV) of a cylinder placed in uniform flow, attached to bistable springs, with the goal of understanding the effect of the non-linearity of the spring on the size of the lock-in regime. A reduced order Wake Oscillator Model (WOM), used to numerically simulate this system, also forms the basis of our theoretical analysis. We first characterize the natural frequency of the bistable spring as a function of the distance between the potential minima of the spring potential and the maximum displacement amplitude. Using one-way coupled simulations of the wake variable, we also construct a model for oscillations of the wake variable as a function of the displacement amplitude and frequency of structure oscillations. The budget for the average kinetic energy of the structure, involving the balance of rate of energy production (via vortex shedding) with rate of energy dissipation (via fluid damping) implies a universal relationship between the oscillation amplitude and structure frequency, which we term as the ”Equilibrium Constraint” (EC). At high mass ratios, the lock-in condition, coupled with the EC, can be used to obtain a set of possible solutions for the oscillation amplitude of the cylinder, given a particular reduced velocity. We are able to then propose a theoretical model for dependence of oscillation amplitude on reduced velocity for VIV involving linear and bistable springs. For a given value of inter-well distance of the spring potential, the theory is able to predict the range of reduced velocity over which the structure undergoes double-well and single-well oscillations. The WOM simulations confirm that the regimes in parameter space corresponding to larger amplitudes can typically be attributed to the lock-in of the lift force acting on the cylinder with the natural frequency of the spring. We find that the lock-in characteristics of the linear and bistable springs are quite similar if the amplitude dependence of the natural frequency of the bistable spring is taken into account. The theory is able to accurately describe the qualitative behavior of the oscillation amplitude with respect to the spring potential and flow parameters. The theory is also able to successfully explain why the range of reduced velocities over which large amplitude VIV is observed increases for cases involving bistable springs. The results here are potentially useful towards designing systems involving VIV with non-linear springs, such as for enhancing the range of flow velocity where power extraction is achieved in VIV-based energy harvesting devices.

Metastable Nonextremal Antibranes

We find new and compelling evidence for the metastability of supersymmetry-breaking states in holographic backgrounds whose consistency has been the source of ongoing disagreements in the literature. As a concrete example, we analyze anti-D3 branes at the tip of the Klebanov-Strassler throat. Using the blackfold formalism we examine how temperature affects the conjectured metastable 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, in a regime of parameter space that was previously inaccessible. Away from extremality we uncover a metastable black Neveu-Schwarz five-brane (NS5) state that disappears near a geometric transition where black anti-D3 branes and black NS5 branes become indistinguishable. This is remarkably consistent with complementary earlier results based on the analysis of regularity conditions of backreacted solutions. We therefore provide highly nontrivial evidence for the metastability of antibranes in noncompact throat geometries since we find a consistent picture over different regimes in parameter space.

Fluid-gravity and membrane-gravity dualities. Comparison at subleading orders

In this note, we have compared two different perturbation techniques that could be used to generate solutions of Einstein’s equations in the presence of negative cosmological constant. One of these two methods is derivative expansion and the other is an expansion in inverse powers of dimension. Both the techniques generate space-time with a singularity shielded by a dynamical event horizon. We have shown that in the appropriate regime of parameter space and with an appropriate choice of coordinates, the metrics and corresponding horizon dynamics, generated by these two different techniques, are exactly equal to the order the solutions are known both sides. This work is essentially an extension of [1] where the authors have shown the equivalence of the two techniques up to the first non-trivial order.

Transport coherence and diffusion in a temporal asymmetric rocked ratchet model

We study the overdamped Brownian dynamics of a particle in a sawtooth potential along with a temporal asymmetric driving force. We observe that in the deterministic limit, the transport coherence which is determined by a dimensionless quantity, called Peclet number Pe, is quite high under certain circumstances. For all the regime of parameter space of this model, Pe in our model shows similar features of current like Stokes efficiency. Diffusion as a function of driving amplitude shows a nonmonotonic behavior and results a minimum exactly at which the current shows a maximum. Unlike the previously studied models, Pe in our model shows a peaking behavior with temperature. Moreover, the diffusion shows a nonlinear dependence of temperature in the long-time limit and it is sensitive to the potential asymmetry parameter.

Consistency in drift-ordered fluid equations

We address several concerns related to the derivation of drift-ordered fluid equations. Starting from a fully Galilean invariant fluid system, we show how consistent sets of perturbative drift-fluid equations in the case of an isothermal collisionless fluid can be obtained. Treating all the dynamical fields on equal footing in the singular-drift expansion, we show under what conditions a set of perturbative equations can have a non-trivial quasi-neutral limit. We give a suitable perturbative setup where we provide the full set of perturbative equations for obtaining the first-order corrected fields and show that all the constants of motion are preserved at each order. With the dynamical field variables under perturbative control, we subsequently provide a quantitative analysis by means of numerical simulations. With direct access to first-order corrections, the convergence properties are addressed for different regimes of parameter space and the validity of the first-order approximation is discussed in the three settings: cold ions, hot ions, and finite charge density.