scholarly journals A viable compactification scenario in Gauss-Bonnet gravity

2018 ◽  
Vol 168 ◽  
pp. 02003 ◽  
Author(s):  
Alexey Toporensky ◽  
Sergey Pavluchenko
Keyword(s):  
Extra Dimensions ◽  
Initial Conditions ◽  
Cosmological Evolution ◽  
Spatial Curvature ◽  
Bonnet Gravity ◽  
Curvature Effects ◽  
Exponential Expansion ◽  
Initial Anisotropy ◽  
Spatial Dimensions

In this talk we address two important issues which could affect reaching the exponential and Kasner asymptotes in Einstein-Gauss-Bonnet cosmologies – spatial curvature and anisotropy in both three- and extra-dimensional subspaces. In the first part we consider cosmological evolution of spaces being the product of two isotropic and spatially curved subspaces. We consider all possible number of spatial dimensions and provide description of the curvature effects in these dimensions. It is demonstrated that the dynamics in D = 2 (the number of extra dimensions) and D ≥ 3 is different. In particular, the regime with the “stabilization” of extra dimensions could be reached only if D ≥ 3. In the second part we study the influence of initial anisotropy. Our study of reveals that transition from Gauss-Bonnet Kasner regime to anisotropic exponential expansion (with expanding three and contracting extra dimensions) is stable with respect to breaking the symmetry within both three- and extra-dimensional subspaces in any number of extra dimensions. This allows us to construct a scenario where isotropisation of outer and inner subspaces is reached dynamically from rather general anisotropic initial conditions.

Research on a complete model of cosmological evolution a classical scalar field with a Higgs potential. II. Numerical simulation

2021 ◽  
pp. 147-151
Author(s):  
Yu.G. Ignat’ev ◽  
◽  
A.R. Samigullina ◽  
Keyword(s):  
Numerical Simulation ◽  
Computer Simulation ◽  
Scalar Field ◽  
Initial Conditions ◽  
Higgs Field ◽  
Hubble Constant ◽  
Cosmological Evolution ◽  
Higgs Potential ◽  
Complete Model ◽  
Expansion Stage

A study and computer simulation of a complete model of the cosmological evolution of a classical scalar field with a Higgs potential is carried out without the assumption that the Hubble constant is nonnegative. It is shown that in most cases of initial conditions the cosmological model passes from the expansion stage to the compression stage. Thus, cosmological models based on the classical Higgs field are unstable with respect to finite perturbations.

DETECTION OF THE SPATIAL CURVATURE EFFECTS THROUGH PHYSICAL PHENOMENA: THE NONLINEAR COHERENT STATES APPROACH

2012 ◽  
Vol 09 (01) ◽  
pp. 1250009 ◽  
Author(s):  
A. MAHDIFAR ◽  
R. ROKNIZADEH ◽  
M. H. NADERI
Keyword(s):  
Hilbert Space ◽  
Geometric Phase ◽  
Coherent States ◽  
Transition Probability ◽  
Physical Space ◽  
Spatial Curvature ◽  
Curved Space ◽  
Curvature Effects ◽  
Projective Hilbert Space ◽  
Physical Phenomena

In this paper, by using the nonlinear coherent states approach, we find a relation between the geometric structure of the physical space and the geometry of the corresponding projective Hilbert space. To illustrate the approach, we explore the quantum transition probability and the geometric phase in the curved space.

scholarly journals Geography of fields in extra dimensions: String theory lessons for particle physics

2015 ◽  
Vol 30 (10) ◽  
pp. 1530008 ◽  
Author(s):  
Hans Peter Nilles ◽  
Patrick K. S. Vaudrevange
Keyword(s):  
String Theory ◽  
Particle Physics ◽  
Extra Dimensions ◽  
Model Building ◽  
Unified Theory ◽  
Fundamental Interactions ◽  
Spatial Dimensions ◽  
Physics Model ◽  
String Theories

String theoretical ideas might be relevant for particle physics model building. Ideally one would hope to find a unified theory of all fundamental interactions. There are only a few consistent string theories in D = 10 or 11 spacetime dimensions, but a huge landscape in D = 4. We have to explore this landscape to identify models that describe the known phenomena of particle physics. Properties of compactified six spatial dimensions are crucial in that respect. We postulate some useful rules to investigate this landscape and construct realistic models. We identify common properties of the successful models and formulate lessons for further model building.

scholarly journals COSMOLOGY FROM MODULI DYNAMICS

2004 ◽  
Vol 19 (31) ◽  
pp. 5443-5454 ◽  
Author(s):  
TIRTHABIR BISWAS ◽  
PRASHANTH JAIKUMAR
Keyword(s):  
String Theory ◽  
Extra Dimensions ◽  
Initial Conditions ◽  
Turn On ◽  
Quintessence Field ◽  
M Theory

We investigate moduli field dynamics in supergravity/M-theory like set ups where we turn on fluxes along some or all of the extra dimensions. As has been argued in the context of string theory, we observe that the fluxes tend to stabilize the squashing (or shape) modes. Generically we find that at late times the shape is frozen while the radion evolves as a quintessence field. At earlier times we have a phase of radiation domination where both the volume and the shape moduli are slowly evolving. However, depending on the initial conditions and the parameters of the theory, like the value of the fluxes, curvature of the internal manifold and so on, the dynamics of the internal manifold can be richer with interesting cosmological consequences, including inflation.

NÖTHER’S SYMMETRIES IN (n+1)-DIMENSIONAL NONMINIMALLY COUPLED COSMOLOGIES

1993 ◽  
Vol 02 (04) ◽  
pp. 463-476 ◽  
Author(s):  
SALVATORE CAPOZZIELLO ◽  
RUGGIERO DE RITIS ◽  
PAOLO SCUDELLARO
Keyword(s):  
Scalar Field ◽  
General Solution ◽  
Effective Action ◽  
The Other ◽  
Spatial Curvature ◽  
General Transformation ◽  
Systematic Analysis ◽  
Induced Gravity ◽  
Constant Of Motion ◽  
Spatial Dimensions

We perform a systematic analysis of nonminimally coupled cosmologies in (n+1)-dimensional homogeneous and isotropic spacetimes, searching for Nöther’s symmetries and generalizing the results of our previous works. We obtain (i) the absence of symmetries when the spatial curvature constant k is nonzero and n=2, 3, but their existence for all the other n; (ii) the existence of such symmetries for every number of spatial dimensions (except n=1) when k=0. In this latter case, we are able to find a general transformation through which we recover the string-dilaton effective action in (n+1) dimensions and the major peculiarity of string cosmology: the scale factor duality. Furthermore, the symmetry fixes a relation among the coupling F(ϕ), the potential V(ϕ) of the scalar field ϕ, the number of spatial dimensions and the spatial curvature constant. When this is the case, it is possible to find a constant of motion and then get the general solution of the dynamics. Finally, in the framework of the so-called Induced Gravity Theories, we are able to obtain the Newton constant at the present time (t→∞) depending on the number of spatial dimensions and directly related to the constant of motion existing in such a model.

Cosmological evolution of homogeneous universal extra dimensions

2003 ◽  
Vol 68 (6) ◽  
Author(s):  
Torsten Bringmann ◽  
Martin Eriksson ◽  
Michael Gustafsson
Keyword(s):  
Extra Dimensions ◽  
Cosmological Evolution

A Timeless, Boundless, Equilibrium Universe

1982 ◽  
Vol 4 (4) ◽  
pp. 482-483 ◽  
Author(s):  
Grote Reber
Keyword(s):  
Steady State ◽  
Relative Motion ◽  
Big Bang ◽  
The Other ◽  
Expanding Universe ◽  
Spatial Curvature ◽  
Doppler Shifts ◽  
Spatial Dimensions ◽  
State Models ◽  
The Universe

For more than half a century the theory that the universe is expanding has dominated cosmology. All current cosmological theories, from the various Big Bang models to the various Steady State models, explicitly assume an expanding universe. The evidence in favour of an expanding universe is purely circumstantial, and is based on a “sheer assumption”, (Hubble 1936a) that red-shifts in the light received by an observer on Earth from distant objects are caused by relative motion and hence may be interpreted as Doppler shifts. Hubble (1936b) continues: “…the ever expanding model … seems rather dubious”, and “On the other hand, if the recession factor is dropped, if red-shifts are not primarily velocity-shifts, the picture is simple and plausible. There is no evidence of expansion and no restriction of time-scale, no trace of spatial curvature and no limitations of spatial dimensions.” (Hubble 1936c). These statements are as true today as they were in 1936.

scholarly journals Pattern Formation in a Model Oxygen-Plankton System

Computation ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 59 ◽  
Author(s):  
Yadigar Sekerci ◽  
Sergei Petrovskii
Keyword(s):  
Dissolved Oxygen ◽  
Initial Conditions ◽  
Tipping Point ◽  
Ecological Problem ◽  
Marine Fauna ◽  
Important Indicator ◽  
Spatial Dimensions ◽  
Parameter Values ◽  
Oxygen Dynamics ◽  
System Approaches

Decreasing level of dissolved oxygen has recently been reported as a growing ecological problem in seas and oceans around the world. Concentration of oxygen is an important indicator of the marine ecosystem’s health as lack of oxygen (anoxia) can lead to mass mortality of marine fauna. The oxygen decrease is thought to be a result of global warming as warmer water can contain less oxygen. Actual reasons for the observed oxygen decay remain controversial though. Recently, it has been shown that it may as well result from a disruption of phytoplankton photosynthesis. In this paper, we further explore this idea by considering the model of coupled plankton-oxygen dynamics in two spatial dimensions. By means of extensive numerical simulations performed for different initial conditions and in a broad range of parameter values, we show that the system’s dynamics normally lead to the formation of a rich variety of patterns. We reveal how these patterns evolve when the system approaches the tipping point, i.e., the boundary of the safe parameter range beyond which the depletion of oxygen is the only possibility. In particular, we show that close to the tipping point the spatial distribution of the dissolved oxygen tends to become more regular; arguably, this can be considered as an early warning of the approaching catastrophe.

scholarly journals On Minimisation of Earthing System Touch Voltages

Energies ◽  
2019 ◽  
Vol 12 (20) ◽  
pp. 3838 ◽  
Author(s):  
Vaclav Vycital ◽  
Michal Ptacek ◽  
David Topolanek ◽  
Petr Toman
Keyword(s):  
Sensitivity Analysis ◽  
System Design ◽  
Initial Conditions ◽  
Optimal Solution ◽  
Solution Space ◽  
Specific Situation ◽  
Double Ring ◽  
Spatial Dimensions ◽  
Cost Efficient ◽  
Optimisation Methods

Finding cost efficient earthing system design with acceptable level of safety might be quite tedious work. Thus, many earthing system engineers try to find the most suitable design either by employing only their best experience or taking advantage of some more complex optimisation programs. Although both approaches might work well under certain circumstances, they might fail either due to counter-intuitiveness of the specific situation or by misunderstanding of the applied optimisation method, its limitations etc. Thus, in this paper, the earthing system design optimisation problem was addressed by analysing optimisation simulation results together with conducted sensitivity analysis. In the paper, a simple double ring earthing system was optimised while using five different optimisation methods. The earthing system was placed in different horizontally stratified soil models and the earthing system was optimised by minimising touch voltages instead of commonly minimised earth potential rise. The earthing system was modelled by Ansys Maxwell software. Apart from using Ansys Maxwell built-in optimisers, the possible solution space has also been mapped by performing sensitivity analysis with changing the earthing system design dimensions and the results of optimisation were compared and validated. It was found out that the Sequential Non-Linear Programming Optimisation technique was quite superior to the other techniques. Additionally, in most cases, the Ansys Maxwell optimiser was able to found optimal solution; however, in some cases, based on the initial conditions, it might get stuck in local minima or the results might be influenced by the solution noise. Additionally, some quite non intuitive dependencies of earthing system electrodes positions had been found when different spatial dimensions constraints are used.

Sign in / Sign up

Export Citation Format

Share Document