A5067428193- Cosmology and Gravitation Theories
- Galaxies: Formation, Evolution, Phenomena
- Black Holes and Theoretical Physics
- Astrophysical Phenomena and Observations
- Astrophysics and Cosmic Phenomena
- Gamma-ray bursts and supernovae
- Astronomy and Astrophysical Research
- Astronomical Observations and Instrumentation
- Pulsars and Gravitational Waves Research
- Stellar, planetary, and galactic studies
- Solar and Space Plasma Dynamics
- Geophysics and Gravity Measurements
- Nuclear Materials and Properties
- Astrophysics and Star Formation Studies
- Nuclear Engineering Thermal-Hydraulics
- Dark Matter and Cosmic Phenomena
- Nuclear reactor physics and engineering
- Particle physics theoretical and experimental studies
- Astro and Planetary Science
- X-ray Spectroscopy and Fluorescence Analysis
- Radio Astronomy Observations and Technology
- High-pressure geophysics and materials
- Relativity and Gravitational Theory
- Nuclear Physics and Applications
- Atomic and Molecular Physics
University of Portsmouth
2015-2024
National Research Institute of Brewing
2022-2024
Josai University
2024
Kyushu Institute of Technology
2024
Juntendo University
2024
Hokkaido University
2023
Centre de Recerca Matemàtica
2023
Mitsubishi Group (Japan)
2014-2022
Western Region Agricultural Research Center
2022
Institute of Fruit Tree and Tea Science
2022
We present all scalar-tensor Lagrangians that are cubic in second derivatives of a scalar field, and degenerate, hence avoiding Ostrogradsky instabilities. Thanks to the existence constraints, they propagate no more than three degrees freedom, despite having higher order equations motion. also determine viable combinations previously identified quadratic degenerate newly established ones. Finally, we study whether new theories connected known such as Horndeski beyond Horndeski, through...
We review recent progress in the construction of modified gravity models as alternatives to dark energy well development cosmological tests gravity. Einstein's theory general relativity (GR) has been tested accurately within local universe i.e. Solar System, but this leaves possibility open that it is not a good description at largest scales Universe. This being said, standard model cosmology assumes GR on all scales. In 1998, astronomers made surprising discovery expansion Universe...
We introduce a new code, ECOSMOG, to run N-body simulations for wide class of modified gravity and dynamical dark energy theories. These theories generally have one or more degrees freedom, the dynamics which are governed by their (usually rather nonlinear) equations motion. Solving these non-linear has been great challenge in cosmology. Our code is based on RAMSES solves Poisson equation adaptively refined meshes gain high resolutions high-density regions. added solver extra degree(s)...
We study new consistent scalar-tensor theories of gravity recently introduced by Langlois and Noui with potentially interesting cosmological applications. derive the conditions for existence a primary constraint that prevents propagation an additional dangerous mode associated higher order equations motion. then classify most general, are at quadratic in second derivatives scalar field. In addition, we investigate possible connection between these (beyond) Horndeski through conformal...
We present a model of Early Modified Gravity (EMG) consisting in scalar field $\sigma$ with non-minimal coupling to the Ricci curvature type $M^2_{\rm pl}+\xi \sigma^2$ plus cosmological constant and small effective mass demonstrate its ability alleviate $H_0$ tension while providing good fit Cosmic Microwave Background (CMB) anisotropies Baryon Acoustic Oscillations (BAO) data. In this field, frozen deep radiation era, grows around redshift matter-radiation equality because non-relativistic...
Abstract We present a non-perturbative method for calculating the abundance of primordial black holes given an arbitrary one-point probability distribution function curvature perturbation, <?CDATA $P(\zeta)$ ?> . A is essential when considering non-Gaussianities that cannot be treated using conventional perturbative expansion. To determine full statistics density field, we relate ζ to Gaussian field by equating cumulative functions. consider two examples: specific local-type non-Gaussian...
Abstract The separate-universe approach gives an intuitive way to understand the evolution of cosmological perturbations in long-wavelength limit. It uses solutions spatially-homogeneous equations motion model inhomogeneous universe on large scales. We show that fails a finite range super-Hubble scales at sudden transition from slow roll ultra-slow during inflation very early universe. Such transitions are feature models giving enhancement primordial power spectrum small scales, necessary...
We study spherically symmetric solutions in a covariant massive gravity model, which is candidate for ghost-free non-linear completion of the Fierz-Pauli theory. There branch that exhibits Vainshtein mechanism, recovering General Relativity below radius given by $(r_g m^2)^{1/3}$, where $m$ graviton mass and $r_g$ Schwarzschild matter source. Another exact exists, corresponding to Schwarzschild-de Sitter spacetimes curvature scale de space proportional squared graviton.
We investigate strong coupling effects in a covariant massive gravity model, which is candidate for ghost free non-linear completion of Fierz-Pauli. analyse the conditions to recover general relativity via Vainshtein mechanism weak field limit, and find three main cases depending on choice parameters. In first case, potential such that all non-linearities disappear vDVZ discontinuity cannot be avoided. second allows within macroscopic radius from source. last scalar graviton completely...
It is shown by an explicit calculation that the excitations about self-accelerating cosmological solution of Dvali-Gabadaze-Porrati model contain a ghost mode. This raises serious doubts viability this solution. Our analysis reveals similarity between quadratic theory for perturbations around universe and Abelian gauge with two St\"uckelberg fields.
We present a cosmological model with solution that self-accelerates at late-times without signs of ghost instabilities on small scales. The is natural extension the Brans-Dicke (BD) theory including non-linear derivative interaction, which appears in Galilean shift symmetry. existence self-accelerating universe requires negative BD parameter but, thanks to term, fluctuations around are stable General relativity recovered early times and scales by this interaction via Vainshtein mechanism. At...
We perform high resolution N-body simulations for f(R) gravity based on a self-adaptive particle- mesh code MLAPM. The Chameleon mechanism that recovers General Relativity small scales is fully taken into account by self-consistently solving the non-linear equation scalar field. independently confirm previous simulation results, including matter power spectrum, halo mass function and density profiles, obtained Oyaizu et al. (Phys.Rev.D 78, 123524, 2008) Schmidt 79, 083518, 2009), extend up...
The DGP brane-world model provides an alternative to the standard LCDM cosmology, in which late universe accelerates due a modification of gravity rather than vacuum energy. cosmological constant Λ is replaced by single parameter, crossover scale rc, DGP. supernova redshift observations can be fitted both models, with ∼ H02 and rc H0−1. This degeneracy broken structure formation, suppressed different ways two models. There some confusion literature about how linear growth factor modified...
We consider brane world models, which can be constructed in the five-dimensional Brans-Dicke theory with bulk scalar field potentials suggested by supergravity theory. For different choices of and parameters we get: (i) an unstabilized model Randall-Sundrum solution for metric constant field; (ii) models flat background tension-full branes; (iii) stabilized one reproduces gives exponential field. also discuss relationship between solutions frames - non-minimal minimal coupling
The next generation of weak lensing surveys will trace the growth large scale perturbations through a sequence epochs, offering an opportunity to test general relativity on cosmological scales. We review in detail parametrization used MGCAMB describe modified expected alternative theories gravity and generalized dark energy models. highlight its advantages examine several theoretical aspects. In particular, we show that same set equations can be consistently superhorizon subhorizon linear...
In standard cosmologies, dark energy (DE) interacts only gravitationally with matter (DM). There could be a nongravitational interaction in the sector, leading to changes effective DE equation of state, redshift dependence DM density and structure formation. We use cosmic microwave background, baryon acoustic oscillation supernova data constrain model where transfer sector is proportional density. are two subclasses, defined by vanishing momentum either or frame. conduct Markov-Chain Monte...
We test general relativity (GR) using current cosmological data: the CMB from WMAP5 [E. Komatsu et al. (WMAP Collaboration), Astrophys. J. Suppl. Ser. 180, 330 (2009)], integrated Sachs-Wolfe (ISW) effect cross correlation of with six galaxy catalogs [T. Giannantonio al., Phys. Rev. D 77, 123520 (2008)], a compilation supernovae (SNe) type Ia including latest Sloan Digital Sky Survey SNe [R. Kessler 185, 32 (2009).], and part weak lensing (WL) data Canada-Franco-Hawaii Telescope Legacy [L....
Starting from the general Horndeski action, we derive most effective theory for scalar perturbations around flat space that allows us to screen fifth forces via Vainshtein mechanism. The is described by a generalization of Galileon Lagrangian, which use study stability spherically symmetric configurations exhibiting effect. In particular, discuss phenomenological consequences scalar-tensor coupling absent in standard Lagrangian. This controls superluminality and fluctuations inside radius...
We study primordial fluctuations generated during inflation in a class of models motivated by the DBI Galileons, which are extensions action that yield second order field equations. This generalises Galileons similar way with K-inflation. calculate non-Gaussianity from bispectrum curvature perturbations at leading slow-varying approximations. show estimator for equilateral-type non-Gaussianity, $f_{\rm NL} ^{equil}$, can be applied to measure amplitude even presence Galileon-like term...
The almost simultaneous detection of gravitational waves and a short gamma-ray burst from neutron star merger has put tight constraint on the difference between speed gravity light. In four-dimensional scalar-tensor theory with second-order equations motion, Horndeski theory, this translates into significant reduction viable parameter space theory. Recently, extensions which are free Ostrogradsky ghosts despite presence higher-order derivatives in have been identified classified exploiting...