A5038956146- Cosmology and Gravitation Theories
- Black Holes and Theoretical Physics
- Galaxies: Formation, Evolution, Phenomena
- Pulsars and Gravitational Waves Research
- Dark Matter and Cosmic Phenomena
- Relativity and Gravitational Theory
- Solar and Space Plasma Dynamics
- Gamma-ray bursts and supernovae
- Geomagnetism and Paleomagnetism Studies
- Geophysics and Gravity Measurements
- Particle physics theoretical and experimental studies
- History and Developments in Astronomy
- Space Science and Extraterrestrial Life
- Atomic and Subatomic Physics Research
- International Science and Diplomacy
Karlsruhe Institute of Technology
2017
Stockholm University
2009-2016
AlbaNova
2010-2016
We obtain the general cosmological evolution equations for a classically consistent theory of bimetric gravity. Their analytic solutions are demonstrated to generically allow cosmic starting out from matter dominated FLRW universe while relaxing towards de Sitter (anti-de Sitter) phase at late time. In particular, we examine subclass models which contain that able reproduce expansion history concordance model inspite nonlinear couplings two metrics. This is explicitly by fitting these...
We perform cosmological perturbation theory in Hassan-Rosen bimetric gravity for general homogeneous and isotropic backgrounds. In the de Sitter approximation, we obtain decoupled sets of massless massive scalar gravitational fluctuations. Matter perturbations then evolve like Einstein gravity. perturb future regime by ratio matter to dark energy, producing quasi-de space. this more setting fluctuations mix. argue that regime, growth structure differs from
When Peccei-Quinn (PQ) symmetry breaking happens after inflation, the axion field takes random values in causally disconnected regions. This leads to fluctuations of order one energy density around QCD epoch. These over-densities eventually decouple from Hubble expansion and form so-called miniclusters. We present a semi-analytical method calculate average density, as well power spectrum, re-alignment mechanism this scenario. Furthermore, we develop modified Press & Schechter approach,...
We study the cosmic expansion history of massive bigravity with a viable matter coupling which treats both metrics on equal footing. derive Friedmann equation for effective metric through couples to two metrics, and its solutions. For certain parameter choices, background cosmology is identical that ΛCDM. More general parameters yield dynamical dark energy, can still be in agreement observations history. specific choices interest, including minimal models, maximally-symmetric candidate...
There is a no-go theorem forbidding flat and closed FLRW solutions in massive gravity on reference metric, while open are unstable. Recently it was shown that this can be overcome if at least some matter couples to hybrid metric composed of both the dynamical fixed metric. We show not compatible with standard description cosmological sources terms effective perfect fluids, predictions theory become sensitive either detailed field-theoretical modelling content or presence additional dark...
In this paper we study the phenomenology of stars and galaxies in massive bigravity. We give parameter conditions for existence viable star solutions when radius is much smaller than Compton wavelength graviton. If these are not met, constrain ratio between coupling constants two metrics, order to e.g. neutron stars. For galaxies, put constraints on both graviton conformal factor metrics. The relationship black holes stars, whether former can be formed from latter, discussed. argue that...
We study the integrated Sachs-Wolfe (ISW) effect in ghost-free, massive bigravity. focus on infinite-branch bigravity (IBB) model which exhibits viable cosmic expansion histories and stable linear perturbations, while cosmological constant is set to zero late-time accelerated of Universe due solely gravitational interaction terms. The ISW contribution CMB auto-correlation power spectrum predicted, as well cross-correlation between temperature anisotropies large-scale structure. use...
We investigate constraints on dark energy fluctuations using type Ia supernovae. If is not in the form of a cosmological constant, that if equation state w≠−1, we expect only temporal, but also spatial variations density. Such would cause local universal expansion rate and directional dependences redshift-distance relation. present scheme for relating power spectrum to an angular covariance function standard candle magnitude fluctuations. The predictions phenomenological model are compared...
We investigate the observational consequences of scalar instabilities in bimetric theory, under assumption that Vainshtein mechanism restores general relativity within a certain distance from gravitational sources. argue early time have negligible impact on observed structures. Assuming affect sub-horizon density fluctuations, we constrain redshift, z_i, below which are ruled out. For "minimal" beta_1-model, constraints close to theoretical expectations z_i = 0.5, potentially allowing model...
This white paper outlines the plans of History Philosophy Culture Working Group Next Generation Event Horizon Telescope Collaboration.