A5025905107- Cosmology and Gravitation Theories
- Black Holes and Theoretical Physics
- Pulsars and Gravitational Waves Research
- Gamma-ray bursts and supernovae
- Noncommutative and Quantum Gravity Theories
- Radio Astronomy Observations and Technology
- Solar and Space Plasma Dynamics
- Galaxies: Formation, Evolution, Phenomena
- Geophysics and Gravity Measurements
- Astrophysical Phenomena and Observations
- Advanced Thermodynamics and Statistical Mechanics
- Quantum Electrodynamics and Casimir Effect
- Seismic Imaging and Inversion Techniques
- Relativity and Gravitational Theory
- Particle physics theoretical and experimental studies
- Anomaly Detection Techniques and Applications
- Theoretical and Computational Physics
- Model Reduction and Neural Networks
- Computational Physics and Python Applications
- Statistical Methods and Inference
- Advanced Differential Geometry Research
- nanoparticles nucleation surface interactions
- Machine Learning in Materials Science
- Complex Systems and Time Series Analysis
- Stochastic processes and financial applications
Institute for Fundamental Physics of the Universe
2021-2024
California Institute of Technology
2024
University of Pisa
2024
Scuola Internazionale Superiore di Studi Avanzati
2021-2023
University of Trieste
2021-2023
Istituto Nazionale di Fisica Nucleare, Sezione di Trieste
2021-2023
Institut de Physique Théorique
2018-2020
Université Paris-Saclay
2013-2020
Centre National de la Recherche Scientifique
2018-2020
CEA Paris-Saclay
2018-2020
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 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...
Modifications of General Relativity leave their imprint both on the cosmic expansion history through a non-trivial dark energy equation state, and evolution cosmological perturbations in scalar tensor sectors. In particular, modification sector gives rise to notion gravitational-wave (GW) luminosity distance, different from standard electromagnetic that can be studied with sirens at GW detectors such as LISA or third-generation ground based experiments. We discuss predictions for modified...
The Laser Interferometer Space Antenna (LISA) has the potential to reveal wonders about fundamental theory of nature at play in extreme gravity regime, where gravitational interaction is both strong and dynamical. In this white paper, Fundamental Physics Working Group LISA Consortium summarizes current topics physics observations GWs can be expected provide key input. We briefest reviews then delineate avenues for future research directions discuss connections between working group, other...
The European Pulsar Timing Array (EPTA) and Indian (InPTA) collaborations have measured a low-frequency common signal in the combination of their second first data releases respectively, with correlation properties gravitational wave background (GWB). Such may its origin number physical processes including cosmic population inspiralling supermassive black hole binaries (SMBHBs); inflation, phase transitions, strings tensor mode generation by non-linear evolution scalar perturbations early...
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...
Recently, a class of theories massive gravity has been shown to be ghost-free. We study the spherically symmetric solutions in bigravity formulation such theories. In general, admit both Lorentz-invariant and Lorentz-breaking asymptotically flat behavior also fall into two branches. first branch, all can found analytically are Schwarzschild-like, with no modification as is for other classes second exact hard find, relying on perturbation theory, Yukawa-like modifications static potential...
We consider theories describing the dynamics of a four-dimensional metric, whose Lagrangian is diffeomorphism invariant and depends at most on second derivatives metric. Imposing degeneracy conditions we find set Lagrangians that, apart form Einstein-Hilbert one, are either trivial or contain more than 2 degrees freedom. Among partially degenerate theories, recover Chern-Simons gravity, endowed with constraints structure suggests presence instabilities. Then, enlarge class parity violating...
Determining the most general, consistent scalar tensor theory of gravity is important for building models inflation and dark energy. In this work we investigate number degrees freedom present in beyond Horndeski. We discuss how to construct from extrinsic curvature constant field hypersurface, find a simple expression action which guarantees existence primary constraint necessary avoid Ostrogradsky instability. Our analysis completely gauge-invariant. However confirm that, mixing together...
The recent simultaneous detection of gravitational waves and a gamma-ray burst from neutron star merger significantly shrank the space viable scalar-tensor theories by demanding that speed gravity is equal to light. survived belong class degenerate higher order theories. We study whether these are suitable as dark energy candidates. find scaling solutions in matter dominated universe lead de Sitter at late times without cosmological constant, realizing self-acceleration. evaluate quasistatic...
We develop a new technique for finding black hole solutions in modified gravity that have ``stealth'' hair, i.e., hair of which the only gravitational effect is to tune cosmological constant. consider scalar-tensor theories waves propagate at speed light and show that, subject parametric constraint we specify, Einstein metrics can be painted with stealth provided there exists family geodesics always normal spacelike surfaces. also present novel scalar-dressed rotating has finite scalar field...
We have conducted fully relativistic simulations in a class of scalar-tensor theories with derivative self-interactions and screening local scales. By using high-resolution shock-capturing methods nonvanishing shift vector, we managed to avoid issues plaguing similar attempts the past. first confirmed recent results by ourselves spherical symmetry, obtained an approximate approach pointing at partial breakdown black-hole collapse. Then, considered late inspiral merger binary neutron stars....
We analyze the ringdown phase of first detected black-hole merger, GW150914, using a simulation-based inference pipeline based on masked autoregressive flows. obtain approximate marginal posterior distributions for parameters, namely mass, spin, and amplitude phases dominant mode its overtone. Thanks to locally amortized nature our method, we are able calibrate posteriors with injected simulations, producing regions guaranteed (i.e. exact) frequentist coverage true values. For calibrated...
We study in a systematic way generic nonderivative (massive) deformation of general relativity using the Hamiltonian formalism. The number propagating degrees freedom is analyzed nonperturbative and background independent way. show that condition having only five can be cast set differential equations for deforming potential. Though conditions are rather restrictive, many solutions found.
Cosmological perturbations of Friedmann-Robertson-Walker solutions in ghost free massive bigravity, including also a second matter sector, are studied detail. At early time, we find that subhorizon exponential instabilities unavoidable and they lead to premature departure from the perturbative regime cosmological perturbations.
We study static spherically symmetric solutions of massive bigravity theory, free from the Boulware-Deser ghost. show recovery general relativity via Vainshtein mechanism, in weak limit physical metric. find a single polynomial equation determining behavior solution for distances smaller than inverse graviton mass. This is generically seventh order, while specific choice parameters theory it can be reduced to lower orders. The analytic different regimes: below radius (where recovered), and...
We study the screening mechanism in most general scalar-tensor theories that leave gravitational waves unaffected and are thus compatible with recent LIGO/Virgo observations. Using effective field theory of dark energy approach, we consider action for perturbations beyond linear order, focusing on quasistatic limit. When restricting to subclass satisfy wave constraints, fully nonlinear Lagrangian contains only three independent parameters. One these, ${\ensuremath{\beta}}_{1}$, is uniquely...
We consider $k$-essence, a scalar-tensor theory with first-order derivative self-interactions that can screen local scales from scalar fifth forces, while allowing for sizeable deviations general relativity on cosmological scales. construct fully nonlinear static stellar solutions show the presence of this screening mechanism, and we use them as initial data simulations oscillations gravitational collapse in spherical symmetry. find $k$-essence theories relevance cosmology, mechanism works...
The Laser Interferometer Space Antenna (LISA) has two scientific objectives of cosmological focus: to probe the expansion rate universe, and understand stochastic gravitational-wave backgrounds their implications for early universe particle physics, from MeV Planck scale. However, range potential applications gravitational wave observations extends well beyond these objectives. This publication presents a summary state art in LISA cosmology, theory methods, identifies new opportunities use...
Abstract We point out that the initial-value (Cauchy) problem for self-interacting vector fields presents same well-posedness issues as first-order derivative scalar (often referred to k -essence). For latter, suitable strategies have been employed in last few years successfully evolve Cauchy at level of infrared theory, without need an explicit ultraviolet completion. argue very techniques can also be applied fields, avoiding a number and “pathologies” recently found literature.