scholarly journals A new f(R) gravity model and properties of gravitational waves in it

2020 ◽  
Vol 80 (12) ◽  
Author(s):  
Dhruba Jyoti Gogoi ◽  
Umananda Dev Goswami
Keyword(s):  
Gravitational Waves ◽  
Gravity Model ◽  
Longitudinal Mode ◽  
Mass Scale ◽  
Gravity Models ◽  
Jordan Frame ◽  
New Model ◽  
Existing Problems ◽  
Pulsar Timing ◽  
New Directions

AbstractIn this paper, we have introduced a new f(R) gravity model as an attempt to have a model with more parametric control, so that the model can be used to explain the existing problems as well as to explore new directions in physics of gravity, by properly constraining it with recent observational data. Here basic aim is to study the properties of Gravitational Waves (GWs) in this new model. In f(R) gravity metric formalism, the model shows the existence of scalar degree of freedom as like other f(R) gravity models. Due to this reason, there is a scalar mode of polarization of GWs present in the theory. This polarization mode exists in a mixed state, of which one is transverse massless breathing mode with non-vanishing trace and the other is massive longitudinal mode. The longitudinal mode being massive, travels at speed less than the usual tensor modes found in General Relativity (GR). Moreover, for a better understanding of the model, we have studied the potential and mass of scalar graviton in both Jordan frame and Einstein frame. This model can pass the solar system tests and can explain primordial and present dark energy. Also, we have put constraints on the model. It is found that the correlation function for the third mode of polarization under certain mass scale predicted by the model agrees well with the recent data of Pulsar Timing Arrays. It seems that this new model would be useful in dealing with different existing issues in the areas of astrophysics and cosmology.

Gravitational Waves

2018 ◽  
Author(s):  
Michele Maggiore
Keyword(s):  
Black Hole ◽  
Perturbation Theory ◽  
Gravitational Waves ◽  
Transfer Functions ◽  
Normal Modes ◽  
Cosmological Perturbation ◽  
Tests Of General Relativity ◽  
Pulsar Timing ◽  
Tensor Perturbations ◽  
Stochastic Backgrounds

A comprehensive and detailed account of the physics of gravitational waves and their role in astrophysics and cosmology. The part on astrophysical sources of gravitational waves includes chapters on GWs from supernovae, neutron stars (neutron star normal modes, CFS instability, r-modes), black-hole perturbation theory (Regge-Wheeler and Zerilli equations, Teukoslky equation for rotating BHs, quasi-normal modes) coalescing compact binaries (effective one-body formalism, numerical relativity), discovery of gravitational waves at the advanced LIGO interferometers (discoveries of GW150914, GW151226, tests of general relativity, astrophysical implications), supermassive black holes (supermassive black-hole binaries, EMRI, relevance for LISA and pulsar timing arrays). The part on gravitational waves and cosmology include discussions of FRW cosmology, cosmological perturbation theory (helicity decomposition, scalar and tensor perturbations, Bardeen variables, power spectra, transfer functions for scalar and tensor modes), the effects of GWs on the Cosmic Microwave Background (ISW effect, CMB polarization, E and B modes), inflation (amplification of vacuum fluctuations, quantum fields in curved space, generation of scalar and tensor perturbations, Mukhanov-Sasaki equation,reheating, preheating), stochastic backgrounds of cosmological origin (phase transitions, cosmic strings, alternatives to inflation, bounds on primordial GWs) and search of stochastic backgrounds with Pulsar Timing Arrays (PTA).

Formation of BIon by joining accretion disks

2019 ◽  
Vol 16 (01) ◽  
pp. 1950014
Author(s):  
Aroonkumar Beesham ◽  
Somayeh Shoorvazi
Keyword(s):  
Gravitational Waves ◽  
Accretion Disks ◽  
New Model

Recently, some authors have proposed a new model for the BIon which can be applied in both nanosystems and cosmology. A Bion is a configuration which has been constructed from two branes and a wormhole which connects them. In this paper, we consider the process of formation of a BIon by joining hexagonal accretion disks. These disks exchange gravitational waves with each other and produce some curvature. By increasing the number of connected disks and joining these waves, a wormhole emerges.

Limiting and Detecting Gravitational Waves with a Pulsar Timing Array

2011 ◽  
Author(s):  
D. R. B. Yardley ◽  
W. A. Coles ◽  
G. B. Hobbs ◽  
R. N. Manchester ◽  
Marta Burgay ◽  
...  
Keyword(s):  
Gravitational Waves ◽  
Pulsar Timing ◽  
Pulsar Timing Array

scholarly journals THE GRAVITY MODEL FORMALIZATION FOR THE INTERCITY PASSENGER’S CORRESPONDENCES PARAMETER’S ESTIMATION

2017 ◽  
Vol 16 (5) ◽  
pp. 437-443 ◽  
Author(s):  
C. V. Dolya
Keyword(s):  
Gravity Model ◽  
Transportation System ◽  
Gravity Models ◽  
Gravity Modeling ◽  
Passenger Transport ◽  
Passenger Transportation ◽  
The Given ◽  
Selection Of ◽  
Calibration Coefficients

he paper considers a possibility to apply gravity models for calculation of intercity passenger transport corres- pondences which are implemented with the help of public transport. The Ukraine transportation system has been selected as an object of investigation and this approach extends application possibilities of the obtained results. Calibration coefficients used in calculation of the indicated correspondences are rather important and significant in case of forecasting passenger transport correspondences. Formalization of these factors is necessary for every transportation system if a calculation of pas-senger transport correspondences has been made for it. In this case searching for actual calibration parameters and other coef-ficients as components of gravitational models is a relevant objective of the given paper. Selection of the gravity model va- riant plays rather significant role in solution of this problem. The developed methods for calculation of passenger transport correspondences are proposed for their application in respect of various transport and trip types. The executed research works have made it possible to investigate a process pertaining to providing of services for passenger transportation while using public routes. The obtained characteristics on functioning of the studied system have allowed to assess the possibility for ap-plication of the known methods for calculation of passenger correspondences and analyze the quality of their application. Calibration coefficients have been empirically selected for calculation of the indicated correspondences while using method of gravity modeling. Formalization of previously unexplored parameters of gravity model component provides the possibility to apply the considered approach for calculation of passenger correspondences within the framework of the investigated trans-portion system. This makes it possible to plan and arrange interaction of various transport types and provides new data and knowledge on the studied system.

Randomness in modified general relativity theory: The stochastic f(R) gravity model

2018 ◽  
Vol 96 (11) ◽  
pp. 1173-1177
Author(s):  
Tomer Shushi
Keyword(s):  
Gravity Field ◽  
Gravity Model ◽  
Gravity Models ◽  
Relativity Theory ◽  
Field Equations ◽  
Important Special Case ◽  
Proposed Model ◽  
Stochastic Space ◽  
Wavefunction Collapse ◽  
New Interpretation

We consider a stochastic modification of the f(R) gravity models, and provide its important properties, including the gravity field equations for the model. We show a prediction in which particles are localized by a system of random gravitational potentials. As an important special case, we investigate a gravity model in the presence of a small stochastic space–time perturbation and provide its gravity field equations. Using the proposed model we examine the stochastic quantum mechanics interpretation, and obtain a novel Schrödinger equation with gravitational potential that is based on diffusion in a gravitational field. Furthermore, we provide a new interpretation to the wavefunction collapse. It seems that the stochastic f(R) gravity model causes decoherence of the spatial superposition state of particles.

LIGO/Virgo Listens to Neutron Stars

2020 ◽  
pp. 137-145
Author(s):  
John W. Moffat
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Gravitational Waves ◽  
Gamma Ray ◽  
Accurate Determination ◽  
Hubble Constant ◽  
Gravitational Theory ◽  
Optical Signal ◽  
Gravity Models ◽  
Expansion Of The Universe

On August 8, 2017, LIGO/Virgo detected the merging of two neutron stars 130 million light years away. Just 1.7 seconds later, the Fermi Gamma Ray Space Telescope received an optical signal—a short gamma ray burst (GRB). Thus began a new era of “multimessenger astronomy.” The GRBs are very energetic explosions observed in galaxies. The neutron star merger offers the first evidence that heavy metals such as gold, platinum, and uranium were created by the collision of neutron stars in a “kilonova.” The resulting gravitational waves offer a new way of measuring the Hubble constant, which determines the rate of expansion of the universe. An important result from the neutron star merger is an extremely accurate determination of the speed of gravitational waves; they move at the speed of light. This has significant ramifications for gravitational theory. It falsifies many proposed modified gravity models.

scholarly journals A fast quadrature-based gravity model for the homogeneous polyhedron

2019 ◽  
Vol 492 (1) ◽  
pp. 420-430
Author(s):  
Jason M Pearl ◽  
Darren L Hitt
Keyword(s):  
Gravitational Field ◽  
Gravity Model ◽  
Approximate Model ◽  
Edge Length ◽  
Gravity Models ◽  
Surface Topology ◽  
Constant Density ◽  
Bulk Properties ◽  
Average Edge Length ◽  
Computationally Expensive

ABSTRACT To date several probes have been sent to explore the Solar system’s asteroids and comets. These bodies are often irregular in shape and to safely navigate probes in their vicinity accurate gravity models are required. For an arbitrarily shaped constant-density body, the gravitational field can be determined from the surface topology and bulk properties. This is achieved by replacing the body’s true geometry with a polyhedron that closely resembles it and for which analytic equations for the gravitational field exist. For some applications however, these equations are too computationally expensive and it can be beneficial to replace them with numerically amenable approximations. In this work, a numerical-quadrature-based model for the gravitational field of a polyhedron consisting of triangular facets is derived. The proposed approximate model is found to be faster than its analytic counterpart. The error of the approximation is found to be negligible for the potential and Laplacian calculations. The approximate model introduces singularities to the surface of the acceleration calculation degrading the solution at altitudes less than the average edge length of the polyhedron.

Sign in / Sign up

Export Citation Format

Share Document