scholarly journals Splitting Into Two Isotropic Subspaces as a Result of Cosmological Evolution in Einstein—Gauss—Bonnet Gravity

2019 ◽  
Vol 25 (3) ◽  
pp. 243-249 ◽  
Author(s):  
D. Chirkov ◽  
A. Toporensky
Keyword(s):  
Cosmological Evolution ◽  
Bonnet Gravity ◽  
Isotropic Subspaces

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.

scholarly journals Gravitational lensing in 4-D Einstein–Gauss–Bonnet gravity in the presence of plasma

2021 ◽  
Vol 32 ◽  
pp. 100798
Author(s):  
Gulmina Zaman Babar ◽  
Farruh Atamurotov ◽  
Abdullah Zaman Babar
Keyword(s):  
Gravitational Lensing ◽  
Bonnet Gravity

scholarly journals Quantum extremal islands made easy. Part III. Complexity on the brane

2021 ◽  
Vol 2021 (2) ◽  
Author(s):  
Juan Hernandez ◽  
Robert C. Myers ◽  
Shan-Ming Ruan
Keyword(s):  
Holographic Model ◽  
Bonnet Gravity ◽  
Higher Curvature Gravity ◽  
Theories Of Gravity

Abstract We examine holographic complexity in the doubly holographic model introduced in [1, 2] to study quantum extremal islands. We focus on the holographic complexity=volume (CV) proposal for boundary subregions in the island phase. Exploiting the Fefferman-Graham expansion of the metric and other geometric quantities near the brane, we derive the leading contributions to the complexity and interpret these in terms of the generalized volume of the island derived from the induced higher-curvature gravity action on the brane. Motivated by these results, we propose a generalization of the CV proposal for higher curvature theories of gravity. Further, we provide two consistency checks of our proposal by studying Gauss-Bonnet gravity and f(ℛ) gravity in the bulk.

scholarly journals Cosmological Evolution of Supermassive Black Holes: Mass Functions and Spins

2012 ◽  
Vol 8 (S290) ◽  
pp. 259-260 ◽  
Author(s):  
Yan-Rong Li ◽  
Jian-Min Wang ◽  
Luis C. Ho
Keyword(s):  
Black Holes ◽  
Mass Function ◽  
Supermassive Black Holes ◽  
Cosmological Evolution ◽  
Radiative Efficiency ◽  
Bolometric Luminosity ◽  
History Of ◽  
Minor Mergers ◽  
Mass Dependent ◽  
Mass Functions

AbstractWe derive the mass function of supermassive black holes (SMBHs) over the redshift range 0 > z ≲ 2, using the latest deep luminosity and mass functions of field galaxies. Applying this mass function, combined with the bolometric luminosity function of active galactic nuclei (AGNs), into the the continuity equation of SMBH number density, we explicitly obtain the mass-dependent cosmological evolution of the radiative efficiency for accretion. We suggest that the accretion history of SMBHs and their spins evolve in two distinct regimes: an early phase of prolonged accretion, plausibly driven by major mergers, during which the black hole spins up, then switching to a period of random, episodic accretion, governed by minor mergers and internal secular processes, during which the hole spins down. The transition epoch depends on mass, mirroring other evidence for “cosmic downsizing” in the AGN population.

scholarly journals The Hot Universe with XRISM and Athena

2018 ◽  
Vol 14 (S342) ◽  
pp. 29-36
Author(s):  
M. Guainazzi ◽  
M. S. Tashiro
Keyword(s):  
Electromagnetic Radiation ◽  
Large Scale ◽  
Cosmological Evolution ◽  
X Ray ◽  
Hot Gas ◽  
Cosmic Vision ◽  
Esa Cosmic Vision ◽  
The Universe

AbstractX-ray spectroscopy is key to address the theme of “The Hot Universe”, the still poorly understood astrophysical processes driving the cosmological evolution of the baryonic hot gas traceable through its electromagnetic radiation. Two future X-ray observatories: the JAXA-led XRISM (due to launch in the early 2020s), and the ESA Cosmic Vision L-class mission Athena (early 2030s) will provide breakthroughs in our understanding of how and when large-scale hot gas structures formed in the Universe, and in tracking their evolution from the formation epoch to the present day.

Bounds on subspace codes based on totally isotropic subspace in symplectic spaces and extended symplectic spaces

2019 ◽  
Vol 12 (05) ◽  
pp. 1950069
Author(s):  
Mahdieh Hakimi Poroch
Keyword(s):  
Sphere Packing ◽  
Symplectic Space ◽  
Isotropic Subspace ◽  
Subspace Codes ◽  
Singleton Bound ◽  
Symplectic Spaces ◽  
Isotropic Subspaces ◽  
Totally Isotropic Subspace ◽  
Totally Isotropic Subspaces

In this paper, we propose the Sphere-packing bound, Singleton bound and Gilbert–Varshamov bound on the subspace codes [Formula: see text] based on totally isotropic subspaces in symplectic space [Formula: see text] and on the subspace codes [Formula: see text] based on totally isotropic subspace in extended symplectic space [Formula: see text].

scholarly journals LARGE SCALE ANISOTROPY DUE TO PRE-INFLATIONARY PHASE OF COSMIC EVOLUTION

2012 ◽  
Vol 27 (04) ◽  
pp. 1250014 ◽  
Author(s):  
PAVAN K. ALURI ◽  
PANKAJ JAIN
Keyword(s):  
Large Scale ◽  
Cosmological Evolution ◽  
Cosmic Evolution ◽  
Cosmological Observations ◽  
Inflationary Phase ◽  
The Universe ◽  
Dipole Modulation

We show that perturbations generated during the anisotropic pre-inflationary stage of cosmic evolution may affect cosmological observations today for a certain range of parameters. Due to the anisotropic nature of the universe during such early times, it might explain some of the observed signals of large scale anisotropy. In particular, we argue that the alignment of CMB quadrupole and octopole may be explained by the Sachs–Wolfe effect due to the large scale anisotropic modes from very early times of cosmological evolution. We also comment on how the observed dipole modulation of CMB power may be explained within this framework.

scholarly journals Magnetic-field effects on p-wave phase transition in Gauss–Bonnet gravity

2014 ◽  
Vol 29 (20) ◽  
pp. 1450094 ◽  
Author(s):  
Ya-Bo Wu ◽  
Jun-Wang Lu ◽  
Yong-Yi Jin ◽  
Jian-Bo Lu ◽  
Xue Zhang ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Phase Transition ◽  
P Wave ◽  
Vector Model ◽  
Magnetic Field Effects ◽  
Complex Vector ◽  
Bonnet Gravity ◽  
Yang Mills ◽  
Wave Phase ◽  
Lowest Landau Level

In the probe limit, we study the holographic p-wave phase transition in the Gauss–Bonnet gravity via numerical and analytical methods. Concretely, we study the influences of the external magnetic field on the Maxwell complex vector model in the five-dimensional Gauss–Bonnet–AdS black hole and soliton backgrounds, respectively. For the two backgrounds, the results show that the magnetic field enhances the superconductor phase transition in the case of the lowest Landau level, while the increasing Gauss–Bonnet parameter always hinders the vector condensate. Moreover, the Maxwell complex vector model is a generalization of the SU(2) Yang–Mills model all the time. In addition, the analytical results backup the numerical results. Furthermore, this model might provide a holographic realization for the QCD vacuum instability.

Bulk viscosity and cosmological evolution

1996 ◽  
Vol 111 (12) ◽  
pp. 1481-1486
Author(s):  
A. Beesham
Keyword(s):  
Bulk Viscosity ◽  
Cosmological Evolution
Sign in / Sign up

Export Citation Format

Share Document