Dynamics Of Perturbations Research Articles

On chromonatural inflation in string theory

Sourced gravitational waves in chromonatural inflation (CNI) can give rise to a chiral spectrum of tensor fluctuations that is considerably enhanced relative to the vacuum fluctuations. If the field content of CNI acts purely as a spectator (SCNI), the inflationary sector can be consistent with current data making SCNI very appealing in view of future observations. We investigate the prospects of embedding SCNI in string theory, in the framework of Kähler inflation in type IIB large volume string compactifications, with a spectator sector associated with gaugino condensation on multiply magnetised D7-branes. We first introduce a generalised field theory framework that describes non-trivial multifield inflation coupled to gauge fields of the form generically arising in supergravity and string theory. We then use these results to study numerically and analytically both the background evolution and the dynamics of cosmological perturbations. We show that a successful inflationary background evolution with a large enhancement of the gravitational wave spectrum and a controllable backreaction from the amplified tensor fluctuations can be achieved by considering suitable values of three parameters present in our scenario: the magnetic flux, the degree of the condensing gauge group and the wrapping number of the D7-brane. On the other hand, the required values for these quantities may present a challenge for its successful realisation within string theory. We also discuss these challenges and the model from the viewpoint of the weak gravity conjecture.

Perturbation of the human gastrointestinal tract microbial ecosystem by oral drugs to treat chronic disease results in a spectrum of individual specific patterns of extinction and persistence of dominant microbial strains.

BackgroundOral drugs can have side effects such as diarrhea that indicate the perturbation of the gut microbial community. To further understand the dynamics of perturbation, we have assessed the strain relatedness of samples from previously published data sets from pre and post bowel evacuation, episodes of diarrhea, and administration of oral drugs to treat diabetes and rheumatoid arthritis.MethodsWe analyzed a total of published five data sets using our strain-tracking tool called Window-based Single Nucleotide Variant (SNV) Similarity (WSS) to identify related strains from the same individual.ResultsStrain-tracking analysis using the first data set from 8 individuals pre and 21–50 days post iso-osmotic bowel wash revealed almost all microbial strains were related in an individual between pre and post samples. Similarly, in a second study, strain-tracking analysis of 4 individuals pre and post sporadic diarrhea revealed the majority of strains were related over time (up to 44 weeks). In contrast, the analysis of a third data set from 22 individuals pre and post 3-day exposure of oral metformin revealed that no individuals had a related strain. In a fourth study, the data set taken at 2 and 4 months from 38 individuals on placebo or metformin revealed individual specific sharing of pre and post strains. Finally, the data set from 18 individuals with rheumatoid arthritis given disease-modifying antirheumatic drugs methotrexate or glycosides of the traditional Chinese medicinal component Tripterygium wilfordii showed individual specific sharing of pre and post strains up to 16 months.ConclusionOral drugs used to treat chronic disease can result in individual specific microbial strain change for the majority of species. Since the gut community provides essential functions for the host, our study supports personalized monitoring to assess the status of the dominant microbial strains after initiation of oral drugs to treat chronic disease.

Dynamics of Disturbances Caused by Local Sources of Heat Release in the Earth’s Damp Atmosphere

The stability of a layer of moist air above a heated surface of land or ocean is studied under the sudden influence of internal sources of heat release, which depend on the pressure and density. A dispersion equation is obtained for small 3D perturbations in a rotating atmosphere. It contains the previously known waves (acoustic, internal waves, and Brunt–​​Vaisala waves) and makes it possible to obtain a modified criterion for the onset of convective instability. This dispersion equation also makes it possible to study the effect of internal heat release on the dynamics of perturbation in these waves, including the conditions for the occurrence of instability generated by an atmospheric electric discharge. Taking into account new considered effects can lead to the identification of new instabilities and the modification of the previously known ones. The proposed system of equations allows numerical calculations of vortex flows in moist air in the near-surface layer and a more detailed study of the mechanisms of the beginning of hurricanes and tornadoes.

General formulation of cosmological perturbations in scalar-tensor dark energy coupled to dark matter

For a scalar field ϕ coupled to cold dark matter (CDM), we provide a general framework for studying the background and perturbation dynamics on the isotropic cosmological background. The dark energy sector is described by a Horndeski Lagrangian with the speed of gravitational waves equivalent to that of light, whereas CDM is dealt as a perfect fluid characterized by the number density nc and four-velocity ucμ. For a very general interacting Lagrangian f(nc, ϕ, X, Z), where f depends on nc, ϕ, X=−∂μ ϕ ∂μ ϕ/2, and Z=ucμ ∂μ ϕ, we derive the full linear perturbation equations of motion without fixing any gauge conditions. To realize a vanishing CDM sound speed for the successful structure formation, the interacting function needs to be of the form f=−f1(ϕ, X, Z)nc+f2(ϕ, X, Z). Employing a quasi-static approximation for the modes deep inside the sound horizon, we obtain analytic formulas for the effective gravitational couplings of CDM and baryon density perturbations as well as gravitational and weak lensing potentials. We apply our general formulas to several interacting theories and show that, in many cases, the CDM gravitational coupling around the quasi de-Sitter background can be smaller than the Newton constant G due to a momentum transfer induced by the Z-dependence in f2.

Structure formation in generalized Rastall gravity

Recently, a modified version of Rastall theory of gravity has been introduced in which a varying coupling parameter could act as dark energy (DE) and thus, it can be held responsible for the current accelerated expansion of the Universe. Motivated by this modification, we study here the evolution of linear and nonlinear perturbations in the matter content of the Universe, utilizing spherically symmetric top-hat collapse scenario. The exact solutions we obtain in linear regime show that as the Universe evolves, matter density perturbations grow and reach a maximum value at a certain redshift after which these perturbations start decreasing toward a finite positive value at the present time. Depending on model parameters, exact oscillatory solutions can be also found representing that matter perturbations could experience either overdense and underdense regions during the dynamical evolution of the Universe. Numerical solutions in nonlinear regime show that the amplitude of perturbations grows much faster than the linear one and diverges at a critical redshift. However, the formation of collapsed structures is delayed as compared to \(\Lambda \)CDM model. It is found that the running mutual interaction between matter and geometry, encoded in the variable Rastall coupling parameter, could drastically affect the dynamics of matter perturbations and their growth rate during the evolution of the Universe.

Solutal convection in horizontal porous layer with immobilization and clogging

The paper is devoted to the investigation of the solutal convection in a horizontal layer of porous media with horizontal seepage of the mixture and solute immobilization. The flow through porous media is modelled within the standard Darcy–Bousinesq model and immobilization is described by the mobile/immobile media (MIM) approach. The high concentrations of solute are considered which lead to taking into account the dependence of media permeability on porosity. The variation of porosity is modelled as a linear function of solute concentration in the immobile phase. It is shown that immobilisation leads to the stabilization of homogeneous filtration regime and to slow down of the perturbation dynamics. The increasing of critical parameters with the intensification of sorption is not monotonous due to saturation of porous matrix with the adsorbed solute.

Note on de Sitter vacua from perturbative and non-perturbative dynamics in type IIB/F-theory compactifications

The properties of the effective scalar potential are studied in the framework of type IIB string theory, taking into account perturbative and non-perturbative corrections. The former modify the Kähler potential and include α′ and logarithmic corrections generated when intersecting D7 branes are part of the internal geometric configuration. The latter add exponentially suppressed Kähler moduli dependent terms to the fluxed superpotential. The possibility of partial elimination of such terms which may happen for particular choices of world volume fluxes is also taken into account. That being the case, a simple set up of three Kähler moduli is considered in the large volume regime, where only one of them is assumed to induce non-perturbative corrections. It is found that the shape of the F-term potential crucially depends on the parametric space associated with the perturbative sector and the volume modulus. De Sitter vacua can be obtained by implementing one of the standard mechanisms, i.e., either relying on D-terms related to U(1) symmetries associated with the D7 branes, or introducing D3‾ branes. In general it is observed that the combined effects of non-perturbative dynamics and the recently introduced logarithmic corrections lead to an effective scalar potential displaying interesting cosmological and phenomenological properties.

The time-dependent mass of cosmological perturbations in loop quantum cosmology: Dapor–Liegener regularization

In this work, we compute the time-dependent masses that govern the dynamics of scalar and tensor perturbations propagating on an effective flat, homogeneous, and isotropic background within the framework of loop quantum cosmology (LQC), regularized according to the procedure put forward by Dapor and Liegener. To do so, we follow the two main approaches that, in the field of LQC, lead to hyperbolic equations for the perturbations in the ultraviolet sector: the hybrid and dressed metric formalisms. This allows us to compare the masses resulting from both proposals and analyze their positivity in regimes of physical interest: the big bounce and the contracting de Sitter phase in the asymptotic past that is a defining feature of the model under consideration.

Complex dynamics in a quasi-periodic plasma perturbations model

<p style='text-indent:20px;'>In this paper, the complex dynamics of a quasi-periodic plasma perturbations (QPP) model, which governs the interplay between a driver associated with pressure gradient and relaxation of instability due to magnetic field perturbations in Tokamaks, are studied. The model consists of three coupled ordinary differential equations (ODEs) and contains three parameters. This paper consists of three parts: (1) We study the stability and bifurcations of the QPP model, which gives the theoretical interpretation of various types of oscillations observed in [Phys. Plasmas, 18(2011):1-7]. In particular, assuming that there exists a finite time lag <inline-formula><tex-math id="M1">\begin{document}$ \tau $\end{document}</tex-math></inline-formula> between the plasma pressure gradient and the speed of the magnetic field, we also study the delay effect in the QPP model from the point of view of Hopf bifurcation. (2) We provide some numerical indices for identifying chaotic properties of the QPP system, which shows that the QPP model has chaotic behaviors for a wide range of parameters. Then we prove that the QPP model is not rationally integrable in an extended Liouville sense for almost all parameter values, which may help us distinguish values of parameters for which the QPP model is integrable. (3) To understand the asymptotic behavior of the orbits for the QPP model, we also provide a complete description of its dynamical behavior at infinity by the Poincaré compactification method. Our results show that the input power <inline-formula><tex-math id="M2">\begin{document}$ h $\end{document}</tex-math></inline-formula> and the relaxation of the instability <inline-formula><tex-math id="M3">\begin{document}$ \delta $\end{document}</tex-math></inline-formula> do not affect the global dynamics at infinity of the QPP model and the heat diffusion coefficient <inline-formula><tex-math id="M4">\begin{document}$ \eta $\end{document}</tex-math></inline-formula> just yield quantitative, but not qualitative changes for the global dynamics at infinity of the QPP model.

Dynamics of Perturbations under Diffusion in a Porous Medium

We consider the dynamics of finite perturbations of a plane phase transition surface in the problem of evaporation of a fluid inside a low-permeability layer of a porous medium. In the case of a nonwettable porous medium, the problem has two stationary solutions, each containing a discontinuity. These discontinuities correspond to plane stationary phase transition surfaces located inside the low-permeability porous layer. One of these surfaces is unstable with respect to long-wavelength perturbations, while the other is stable. We study the evolution of perturbations of the stable plane phase transition surface. It is known that when two phase transition surfaces are located close enough to each other, the dynamics of a weakly nonlinear and weakly unstable wave packet is described by the Kolmogorov–Petrovskii–Piskunov (KPP) diffusion equation. As traveling wave solutions, this equation has heteroclinic solutions with either oscillating or monotonic structure of the front. The boundary value problem in the full statement, which should be considered if the distance between the stable and unstable plane phase transition surfaces is not small, also has similar solutions. We formulate a sufficient condition for the decrease of finite perturbations of the stable plane phase transition surface. This condition depends on their position with respect to the standing wave type and traveling front type solutions of the model equations in the model description when the KPP equation holds.

Primordial universe with the running cosmological constant

Theoretically, the running of the cosmological constant in the IR region is not ruled out. On the other hand, from the QFT viewpoint, the energy released due to the variation of the cosmological constant in the late Universe cannot go to the matter sector. For this reason, the phenomenological bounds on such a running are not sufficiently restrictive. The situation can be different in the early Universe when the gravitational field was sufficiently strong to provide an efficient creation of particles from the vacuum. We develop a framework for systematically exploring this possibility. It is supposed that the running occurs in the epoch when the Dark Matter already decoupled and is expanding adiabatically, while the usual matter should be regarded approximately massless and can be abundantly created from vacuum due to the decay of vacuum energy. By using the handy model of Reduced Relativistic Gas for describing the warm Dark Matter, we consider the dynamics of both cosmic background and linear perturbations and evaluate the impact of the vacuum decay on the matter power spectrum and to the first CMB peak. Additionally, using the combined SNIa+BAO data, we find the best-fit values for the free parameters of the model.

Phase transitions in perturbative walking dynamics

In this paper, we investigate the dynamics of the confinement-deconfinement phase transition in a toy model where the walking dynamics is realized perturbatively. We study the properties of the phase transition focusing on the possible cosmological signatures it can provide. Interestingly the model is well under perturbative control only when the mass of the lightest field — the dilaton/scalon is much lighter than the rest of the fields and the phase transition proceeds slowly leading to strong signals in the stochastic gravitational wave spectrum.

Resolvent analysis of an airfoil laminar separation bubble at Re=500000

The perturbation dynamics over an airfoil laminar separation bubble (LSB) is examined via resolvent analysis. The computational burden of singular value decomposition (SVD) is relieved through the randomized method, and the local energy amplification mechanisms of the LSB are extracted from the global resolvent operator with the discounting approach. With the applications of input and output windows, it is shown that the Kelvin-Helmholtz instability dominates the energy amplification over the LSB, and the optimal momentum-based forcing aligns with the tangential direction of the surface.

State-Transition Analysis of Time-Sequential Gene Expression Identifies Critical Points That Predict Development of Acute Myeloid Leukemia.

Temporal dynamics of gene expression inform cellular and molecular perturbations associated with disease development and evolution. Given the complexity of high-dimensional temporal genomic data, an analytic framework guided by a robust theory is needed to interpret time-sequential changes and to predict system dynamics. Here we model temporal dynamics of the transcriptome of peripheral blood mononuclear cells in a two-dimensional state-space representing states of health and leukemia using time-sequential bulk RNA-seq data from a murine model of acute myeloid leukemia (AML). The state-transition model identified critical points that accurately predict AML development and identifies stepwise transcriptomic perturbations that drive leukemia progression. The geometry of the transcriptome state-space provided a biological interpretation of gene dynamics, aligned gene signals that are not synchronized in time across mice, and allowed quantification of gene and pathway contributions to leukemia development. Our state-transition model synthesizes information from multiple cell types in the peripheral blood and identifies critical points in the transition from health to leukemia to guide interpretation of changes in the transcriptome as a whole to predict disease progression. SIGNIFICANCE: These findings apply the theory of state transitions to model the initiation and development of acute myeloid leukemia, identifying transcriptomic perturbations that accurately predict time to disease development.See related commentary by Kuijjer, p. 3072 GRAPHICAL ABSTRACT: http://cancerres.aacrjournals.org/content/canres/80/15/3157/F1.large.jpg.

Onset of thermal convection in a horizontal porous layer saturated by a power–law fluid

A horizontal porous layer saturated by a non–Newtonian fluid is taken into account. The fluid is a Ostwald–De Waele type of fluid. The layer is heated from below while the upper boundary is isothermal. The lower boundary is impermeable and the upper one is free. A fully developed basic throughflow is considered. The basic state is perturbed by employing small amplitude perturbations such that a linear stability analysis is performed. The disturbances are assumed to be normal modes and a system of ordinary differential equations governing the perturbation dynamics is obtained. These ODEs form an eigenvalue problem that is solved numerically: both the neutral stability curves and the threshold values for the onset of convection are presented.

Satellite Remote Sensing of Forest Degradation using NDFI and the BFAST Algorithm

In this paper, results related with the assessment of the capabilityto detect forest degradation by analyzing NDFI time series through the BFAST algorithm are presented. Recent studies have shown the potential of the BFAST algorithm applied to a time-series of satellite-derived spectral indices such as NDVI or EVI to detect unambiguous and subtle perturbations of the forest cover canopy both positive (e.g. regeneration) and negative (e.g. deforestation). Similarly, these results suggest the feasibility to distinguish between several types of forest degradation and their causal agents such as selective logging and forest fire. In this context, the results derived from this research show that using NDFI as a data source in the BFAST algorithm improves the detection of forest degradation, and additionally provides information to understand both temporal and spatial approaches related with the dynamics of perturbations of the forest canopy.

Hydrodynamic Instability of Vertical Motions Excited by Spatially Periodic Distributions of Heat Sources

The hydrodynamic instability of a system of vertical motions initiated by spatially periodic distributions of heat sources is investigated. The Galerkin method with three basis trigonometric functions is used to describe the perturbation dynamics. The nonlinear system of equations for finding the expansion coefficients is formulated. It is found that the vertical motions are unstable in the absence of dissipation if the Richardson number is less than one eighth. A weakly nonlinear model of inviscid instability is developed. It is shown that the loss of stability in the presence of dissipation can lead to formation of either steady-state or time-oscillating secondary flow with nontrivial streamline topology.

Constraints on the spacetime dynamics of an early dark energy component

We consider an Early Dark Energy (EDE) cosmological model, and perform an analysis which takes into account both background and perturbation effects via the parameters c2eff and c2vis, representing effective sound speed and viscosity, respectively. By using the latest available data we derive constraints on the amount of dark energy at early times and the present value of the equation of state. Our focus is on the effect that early dark energy has on the Cosmic Microwave Background (CMB) data, including polarization and lensing, in a generalized parameter space including a varying total neutrino mass, and tensor to scalar ratio, besides the 6 standard parameters of the minimal cosmological model. We find that the inclusion of Baryonic Acoustic Oscillations (BAO) data and CMB lensing significantly improves the constraints on the EDE parameters, while other high redshift data like the Quasar Hubble diagram and the Lyman-α forest BAO have instead a negligible impact. We find ΩeDE < 0.0039 and w0 < −0.95 at the 95 % C.L. for EDE accounting for its clustering through the inclusion of perturbation dynamics. This limit becomes weaker ΩeDE < 0.0034 if perturbations are neglected. The constraints on the EDE parameters are remarkably stable even when Σ mν, and r parameters are varied, with weak degeneracies between ΩeDE and r or Σ mν. In general we expect smaller values for the upper limits on the total amount of EDE with an increasing neutrino mass, while with a decreasing value of the tensor to scalar ratio we expect the 2σ upper limits on EDE to increase. We compare this EDE model with a simple wCDM with zero dark energy at early times and we find ∼1–2% different upper limits on total neutrino mass and ∼0.1–0.2% difference on the equation of state at the present time. Perturbation parameters are not constrained with current data sets, and tensions between the CMB derived H0 and σ8 values and those measured with local probes are not eased. This work demonstrates the capability of CMB probes to constrain the total amount of EDE well below the percent level.

Spectral Features of Systems With Chaotic Dynamics

Using the Lorentz model and Hamiltonian systems without dissipation as an example, spectral methods for analyzing the dynamics of systems with chaotic behavior are considered. The insufficiency of the traditional approach to the study of perturbation dynamics based on an analysis of the roots of the classical spectral equation is discussed. It is proposed to study nonlinear systems using the method of constructing spectral equations with different eigenvalues, which allows one to take into account the randomness and multiplicity of states. The spectral features of instability and chaos for systems without dissipation are shown by the example of short-wave perturbations of a flow of a weakly ionized plasma gas.

Normal modes of vibrations around Hubble flow in jellium

A macroscopic Coulomb system of identical charged particles with or without a compensating background charge can evolve maintaining spatial homogeneity and isotropy that mimic the cosmological evolution of a universe with repulsive gravity. Here we study dynamics of small perturbations on the background of the corresponding Hubble flow by analyzing its normal modes of vibrations. Arbitrary disturbance of the flow can be resolved into two electroacoustic, two vortical, and one entropic modes whose dynamics is investigated. Specifically, in the zero pressure or long-wavelength limits perturbations of density and velocity evolve in a manner that is independent of the form of the initial disturbance. The same conclusion applies to vortical perturbations of the velocity for arbitrary pressure while entropic perturbations are advected by the Hubble flow. Without the background charge the underlying Hubble flow describes a Coulomb explosion whose stability with respect to small disturbances is also demonstrated.