Results 51 to 60 of about 58,534 (245)

Back Reaction of Cosmological Perturbations [PDF]

, 2000
The presence of cosmological perturbations affects the background metric and matter configuration in which the perturbations propagate. This effect, studied a long time ago for gravitational waves, also is operational for scalar gravitational ...
Brandenberger, Robert H.
core   +2 more sources

Photon‐Sphere Modes in Curved Optical Microcavities: A Black‐Hole Analogue Laser

Advanced Science, EarlyView.
An optical analogue of a Schwarzschild black hole is realized using curved microcavities that preserve light‐like geodesics. A new family of laser modes confined around the photon sphere is identified alongside conventional whispering‐gallery modes. Analytical theory, numerical simulations, and experiments reveal curvature‐induced confinement, enabling
Chenni Xu, Aswathy Sundaresan, Nazire‐Begüm Kazkal, Clement Lafargue, Lior Zarfaty, Li‐Gang Wang, Ofek Birnholtz, Dominique Decanini, Melanie Lebental, Patrick Sebbah   +9 more
wiley   +1 more source

Appearances are deceptive: can graviton have a mass?

Journal of High Energy Physics
We study the dynamics of linear gravitational perturbations on cosmological backgrounds of massive fermionic fields. We observe that, when gravitational and matter action are expanded to quadratic order in gravitational perturbations on cosmological ...
Leihua Liu, Tomislav Prokopec
doaj   +1 more source

Scalar perturbations in cosmological f(R) models: the cosmic screening approach

European Physical Journal C: Particles and Fields, 2018
We investigate cosmological perturbations for nonlinear f(R) models within the cosmic screening approach. Matter is considered both in the form of a set of discrete point-like massive bodies and in the form of a continuous pressureless perfect fluid.
Özgür Akarsu, Ruslan Brilenkov, Maxim Eingorn, Valerii Shulga, Alexander Zhuk   +4 more
doaj   +1 more source

‘Turkeys Cannot Vote for Christmas’: Why Epistemic Disobedience in an Anti‐Black World Matters

Australian Journal of Social Issues, EarlyView.
ABSTRACT Never in the history of global coloniality has the idea of epistemic disobedience been as important as in the 21st century. This is not only because the struggle for decolonisation has shifted from physical confrontation between the coloniser and the colonised into a battle of ideas but also because the former has deployed the idea of ...
Morgan Ndlovu
wiley   +1 more source

DENSITY PERTURBATIONS IN A REALISTIC UNIVERSE

Odessa Astronomical Publications, 2017
We analyze evolution of density perturbations in a flat or open universe filled in with matter, relativistic particles and possibly cosmological constant. Density perturbations grow very slowly in a universe filled in with low mass neutrinos.
M. Demianski, Z. Golda, A. Woszczyna
doaj   +1 more source

Generating cosmological perturbations in non-singular Horndeski cosmologies

Journal of High Energy Physics, 2023
We construct a concrete model of Horndeski bounce with strong gravity in the past. Within this model we show that the correct spectra of cosmological perturbations may be generated at early contracting epoch, with mild fine-tuning ensuring that the ...
Yulia Ageeva, Pavel Petrov, Valery Rubakov   +2 more
doaj   +1 more source

Cosmological Perturbations in Ho\v{r}ava-Lifshitz Gravity

, 2009
We study cosmological perturbations in Ho\v{r}ava-Lifshitz Gravity. We consider scalar metric fluctuations about a homogeneous and isotropic space-time.
Brandenberger, R., Gao, Xian, Riotto, A., Wang, Yi   +3 more
core   +1 more source

PERTURBATIONS IN BOUNCING COSMOLOGICAL MODELS [PDF]

International Journal of Modern Physics D, 2004
I describe the features and general properties of bouncing models and the evolution of cosmological perturbations on such backgrounds. I will outline possible observational consequences of the existence of a bounce in the primordial Universe and I will make a comparison of these models with standard long inflationary scenarios.
openaire   +3 more sources

Analytical and Numerical Soliton Solutions of the Shynaray II‐A Equation Using the G′G,1G$$ \left(\frac{G^{\prime }}{G},\frac{1}{G}\right) $$‐Expansion Method and Regularization‐Based Neural Networks

Mathematical Methods in the Applied Sciences, EarlyView.
ABSTRACT Nonlinear differential equations play a fundamental role in modeling complex physical phenomena across solid‐state physics, hydrodynamics, plasma physics, nonlinear optics, and biological systems. This study focuses on the Shynaray II‐A equation, a relatively less‐explored parametric nonlinear partial differential equation that describes ...
Aamir Farooq, H. W. A. Riaz, Sadique Rehman, M. Mamun Miah, Wen Xiu Ma   +4 more
wiley   +1 more source