A5083749517- Cosmology and Gravitation Theories
- Galaxies: Formation, Evolution, Phenomena
- Black Holes and Theoretical Physics
- Dark Matter and Cosmic Phenomena
- Astrophysics and Cosmic Phenomena
- Particle physics theoretical and experimental studies
- Solar and Space Plasma Dynamics
- Geophysics and Gravity Measurements
- Pulsars and Gravitational Waves Research
- Radio Astronomy Observations and Technology
- Relativity and Gravitational Theory
- Astronomy and Astrophysical Research
- Noncommutative and Quantum Gravity Theories
- Stellar, planetary, and galactic studies
- Advanced Differential Geometry Research
- Quantum Electrodynamics and Casimir Effect
- Gamma-ray bursts and supernovae
- Astrophysical Phenomena and Observations
- Advanced Thermodynamics and Statistical Mechanics
- Computational Physics and Python Applications
- Scientific Research and Discoveries
- Neutrino Physics Research
- History and Developments in Astronomy
- Geomagnetism and Paleomagnetism Studies
- Synthetic Aperture Radar (SAR) Applications and Techniques
University of Oslo
2015-2024
Physical Sciences (United States)
2024
Institute of Theoretical Physics
2024
Instituto Politécnico de Lisboa
2022
Hospitais da Universidade de Coimbra
2022
University of Coimbra
2022
Polytechnic Institute of Viseu
2021
Chinese Academy of Sciences
2020
National Astronomical Observatories
2020
Fraunhofer Center for International Management and Knowledge Economy
2013
Abstract The simplest ΛCDM model provides a good fit to large span of cosmological data but harbors areas phenomenology and ignorance. With the improvement number accuracy observations, discrepancies among key parameters have emerged. most statistically significant tension is 4 σ 6 disagreement between predictions Hubble constant, H 0 , made by early time probes in concert with ‘vanilla’ model, late time, model-independent determinations from local measurements distances redshifts. high...
We show that, as a result of nonlinear self-interactions, it is feasible, at least in light the bounds coming from terrestrial tests gravity, measurements Casimir force and those constraints imposed by physics compact objects, big-bang nucleosynthesis cosmic microwave background, for there to exist, our Universe, one or more scalar fields that couple matter much strongly than gravity does. These behave like chameleons: changing their properties fit surroundings. As these can be not only very...
We investigate the observational consequences of a novel class stable interacting dark energy (IDE) models, featuring interactions between matter (DM) and (DE). In first part our work, we start by considering two IDE models which are known to present early-time linear perturbation instabilities. Applying transformation depending on equation state (EoS) DM-DE coupling, then obtain models. Subsequently, derive robust accurate constraints parameters these assuming constant EoS wx for DE fluid,...
Non-linear electrodynamics (NLED) theories are well-motivated extensions of QED in the strong field regime, and have long been studied search for regular black hole (BH) solutions. We consider two well-studied NLED models coupled to General Relativity: Euler-Heisenberg model Bronnikov model. After carefully accounting effective geometry induced by corrections, we determine shadows BHs within these models. then compare shadow supermassive BH M87* recently imaged Event Horizon Telescope...
Searching for violations of the no-hair theorem (NHT) is a powerful way to test gravity, and more generally fundamental physics, particularly with regards existence additional scalar fields. The first observation black hole (BH) shadow by Event Horizon Telescope (EHT) has opened new direct window onto tests gravity in strong-field regime, including probes NHT. We consider two scenarios described Einstein-Maxwell equations General Relativity electromagnetism, which we add field. In case...
General Relativity and the $\Lambda$CDM framework are currently standard lore constitute concordance paradigm. Nevertheless, long-standing open theoretical issues, as well possible new observational ones arising from explosive development of cosmology last two decades, offer motivation lead a large amount research to be devoted in constructing various extensions modifications. All extended theories scenarios first examined under light consistency, then applied geometrical backgrounds, such...
Abstract A new degravitation mechanism within the framework of scalar tensor gravity is postulated and included by prescription. The eliminates all constant contributions from potential to Friedmann equation, leaving only kinematic dynamic terms drive cosmic acceleration. We explore a scenario involving density-triggered phase transition in late-time universe, argue that resulting effective energy density equation state parameter can explain cosmology when extrapolated region space.
We consider the cosmology where some function $f(G)$ of Gauss-Bonnet term $G$ is added to gravitational action account for late-time accelerating expansion universe. The covariant and gauge invariant perturbation equations are derived with a method which could also be applied general $f(R,{R}^{ab}{R}_{ab},{R}^{abcd}{R}_{abcd})$ theories. It pointed out that, despite their fourth-order character, such gravity models generally cannot reproduce arbitrary background cosmic evolutions; example,...
We investigate the consequences of an imperfect dark energy fluid on large scale structure. A phenomenological three parameter description is used to study effect cosmic microwave background radiation (CMBR) and matter power spectrum. In addition equation state sound speed, we allow a nonzero viscosity for fluid. Then anisotropic stress perturbations are generated in energy. general, find that this possibility not excluded by present day cosmological observations. simplest case when all...
A relativistic theory of modified gravity has been recently proposed by Bekenstein. The tensor field in Einstein's is replaced a scalar, vector, and which interact such way to give Newtonian dynamics (MOND) the weak-field nonrelativistic limit. We study evolution Universe theory, identifying its key properties comparing it with standard cosmology obtained Einstein gravity. scalar akin that tracker quintessence fields. expand linear order find perturbations on large scales. impact galaxy...
We consider several new classes of viable vector field alternatives to the inflaton and quintessence scalar fields. Spatial fields are shown be compatible with cosmological anisotropy bounds if only slightly displaced from potential minimum while dominant, or driving an anisotropic expansion nearly vanishing quadropole today. The Bianchi I model a spatial isotropic fluid is studied as dynamical system, types scaling solutions found. On other hand, time-like automatically large-scale...
We investigate theories of gravity within the Palatini approach and show how one can determine expansion history, , for an arbitrary choice . As example, we consider cosmological constraints on such arising from supernova type Ia, large-scale structure formation, cosmic microwave background observations. find that best fit to data is a non-null leading order correction Einstein gravity. However, current exhibits no significant trend toward corrections compared concordance ΛCDM model. Our...
We study the spherical collapse model in dark energy cosmologies, which is modelled as a minimally coupled scalar field.We first follow standard assumption that does not cluster on scales of interest.Investigating four different popular potentials detail, we show predictions depend potential used.We also investigate dependence initial conditions.Secondly, how far perturbations quintessence field affect model.In doing so, assume collapses along with matter.Although still subdominant at time...
We investigate a string-inspired dark energy scenario featuring scalar field with coupling to the Gauss-Bonnet invariant. discuss extensively cosmological and astrophysical implications of coupled field. Such can trigger onset late domination after scaling matter era. The universe may then cross phantom divide perhaps also exit from acceleration. evolution fluctuations in their impact on clustering are studied detail model independently. small-scale limit is derived for perturbations...
We study the space–time evolution of fine structure constant, α, inside evolving spherical overdensities in a lambda-CDM Friedmann universe using infall model. show that its value virialised regions will be significantly larger than low-density background universe. The consideration inhomogeneous is therefore essential for correct comparison extragalactic and solar system limits on, observations of, possible time variation α other constants. Time cosmological can give rise to no locally...
We show that, as a result of nonlinear self-interactions, scalar field theories that couple to matter much more strongly than gravity are not only viable but could well be detected by number future experiments provided they properly designed do so.
We investigate cosmologies where the accelerated expansion of universe is driven by a field with an anisotropic equation state. model such scenarios within Bianchi I framework, introducing two skewness parameters to quantify deviation pressure from isotropy. study dynamics background in these models. A special case cosmological constant analyzed detail. The then confronted redshift and angular distribution type Ia supernovae. In addition, we effects on cosmic microwave (CMB) anisotropies for...
It is shown that extensions to general relativity, which introduce a strongly coupled scalar field, can be viable if the interaction has nonconformal form. Such disformal coupling depends upon gradients of field. Thus, field locally static and smooth, becomes invisible in Solar System: this screening mechanism. A cosmological model considered where triggers onset accelerated expansion after scaling matter era, giving good fit wide range background observational data. Moreover, leaves...
Cosmological consequences of a coupling between massive neutrinos and dark energy are investigated. In such models, the neutrino mass is function scalar field, which plays role energy. The evolution background cosmological perturbations discussed. We find that mass-varying can leave significant imprint on anisotropies in cosmic microwave even lead to reduction power large angular scales.
If the dark energy equation of state is anisotropic, expansion rate universe becomes direction dependent at late times. We show that such models are not only cosmologically viable but they could explain some observed anomalies in cosmic microwave background. The possible anisotropy can then be constrained by studying its effects on luminosity distance-redshift relation inferred from several observations. A vector field action for also presented as an example a possibility.
The apparent alignment of the cosmic microwave background multipoles on large scales challenges standard cosmological model. Scalar field inflation is isotropic and cannot account for observed alignment. We explore imprints, a non-standard spinor driven would leave anisotropies. show it natural to expect an anisotropic inflationary expansion Universe which has effect suppressing low multipole amplitude primordial power spectrum, while at same time provide usual features.