Quasi static evolution of compact objects in modified gravity

In this work, we have presented a detailed analysis of the event horizon of regular black holes (BHs) in modified gravity known as MOG, the so-called regular MOG BH. The motion of neutral particles around the BH has also been explored. The test particle motion study shows that the positive (negative) values of the MOG parameter mimic the spin of a rotating Kerr BH, providing the same values for the innermost stable pro-grade (retrograde) orbits of the particles in the range of the spin parameter a/M∈(−0.4125,0.6946). The efficiency of energy release from the accretion disk by the Novikov–Thorne model has been calculated, and the efficiency was shown to be linearly proportional to the increase of the MOG parameter α. Moreover, we have developed a new methodology to test gravity theories in strong-field regimes using precision data from twin-peaked quasiperiodic oscillations (QPOs) of objects calculating possible values of upper and lower frequencies. However, it is obtained that the positive MOG parameter can not mimic the spin of Kerr BHs in terms of the same QPO frequencies. We have provided possible ranges for upper and lower frequencies of twin-peak QPOs with the ratio of the upper and lower frequencies of 3:2 around regular MOG BHs in the different models. Moreover, as an example, we provide detailed numerical analysis of the QPO of GRS 1915+105 with the frequencies νU=168±5Hz and νL=113±3Hz. It is shown that the central BH of the QPO object can be a regular MOG BH when the value of the parameter is α=0.2844−0.1317+0.0074 and shines in the orbits located at the distance r/M=7.6322−0.0826+0.0768 from the central BH. It is also shown that the orbits where QPOs shine are located near the innermost stable circular orbit (ISCO) of the test particle. The correlation between the radii of ISCO and the QPO orbits is found, and it can be used as a new theoretical way to determine ISCO radius through observational data from the QPOs around various compact objects.

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Dark energy and modified gravity in degenerate higher-order scalar–tensor (DHOST) theories: A review

International Journal of Modern Physics D ◽

10.1142/s0218271819420069 ◽

2019 ◽

Vol 28 (05) ◽

pp. 1942006 ◽

Cited By ~ 48

Author(s):

David Langlois

Keyword(s):

Dark Energy ◽

Modified Gravity ◽

Higher Order ◽

Second Order ◽

Compact Objects ◽

Degree Of Freedom ◽

Scalar Mode

This paper reviews scalar–tensor theories characterized by a Lagrangian that, despite the presence of second-order derivatives, contains a single scalar degree of freedom. These theories, known as Degenerate Higher-Order Scalar–Tensor (DHOST) theories, include Horndeski and Beyond Horndeski theories. They propagate a single scalar mode as a consequence of the degeneracy of their Lagrangian and, therefore, are not plagued by an Ostrogradsky instability. They have been fully classified up to cubic order in second-order derivatives. The study of their phenomenological consequences restricts the subclass of DHOST theories that are compatible with observations. In cosmology, these theories can be described in the language of the unified effective approach to dark energy and modified gravity. Compact objects in the context of DHOST theories are also discussed.

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Electromagnetic field and cylindrical compact objects in modified gravity

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stw423 ◽

2016 ◽

Vol 458 (2) ◽

pp. 1785-1802 ◽

Cited By ~ 55

Author(s):

Z. Yousaf ◽

M. Zaeem ul Haq Bhatti

Keyword(s):

Electromagnetic Field ◽

Modified Gravity ◽

Compact Objects

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Effects of modified gravity coupled with mechanical stimulation on molecular signal transduction and target gene transcription in 3D osteon cell network.

10.26226/morressier.59c106e8d462b80292389ad4 ◽

2017 ◽

Author(s):

Cassandra M. Juran

Keyword(s):

Signal Transduction ◽

Gene Transcription ◽

Mechanical Stimulation ◽

Modified Gravity ◽

Target Gene ◽

Cell Network ◽

Molecular Signal ◽

Target Gene Transcription

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Study of a Restricted Modified Gravity on astrophysical and cosmological scales

Iranian Journal of Physics Research ◽

10.29252/ijpr.19.2.447 ◽

2019 ◽

Vol 19 (2) ◽

pp. 447-453

Author(s):

Nasim Derakhshanian ◽

Amir Ghalee ◽

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Keyword(s):

Modified Gravity

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Editorial [Dark Energy and Modified Gravity]

The Open Astronomy Journal ◽

10.2174/1874381101003020012 ◽

2010 ◽

Vol 3 (2) ◽

pp. 12-12

Author(s):

S. Nojiri ◽

S. D. Odintsov

Keyword(s):

Dark Energy ◽

Modified Gravity

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Spin effects in the effective field theory approach to Post-Minkowskian conservative dynamics

Journal of High Energy Physics ◽

10.1007/jhep06(2021)012 ◽

2021 ◽

Vol 2021 (6) ◽

Author(s):

Zhengwen Liu ◽

Rafael A. Porto ◽

Zixin Yang

Keyword(s):

Field Theory ◽

Effective Field Theory ◽

Scattering Problem ◽

Finite Size ◽

Effective Field ◽

Compact Objects ◽

Scattering Data ◽

Theory Approach ◽

Spin Effects ◽

Radial Action

Abstract Building upon the worldline effective field theory (EFT) formalism for spinning bodies developed for the Post-Newtonian regime, we generalize the EFT approach to Post-Minkowskian (PM) dynamics to include rotational degrees of freedom in a manifestly covariant framework. We introduce a systematic procedure to compute the total change in momentum and spin in the gravitational scattering of compact objects. For the special case of spins aligned with the orbital angular momentum, we show how to construct the radial action for elliptic-like orbits using the Boundary-to-Bound correspondence. As a paradigmatic example, we solve the scattering problem to next-to-leading PM order with linear and bilinear spin effects and arbitrary initial conditions, incorporating for the first time finite-size corrections. We obtain the aligned-spin radial action from the resulting scattering data, and derive the periastron advance and binding energy for circular orbits. We also provide the (square of the) center-of-mass momentum to $$ \mathcal{O}\left({G}^2\right) $$ O G 2 , which may be used to reconstruct a Hamiltonian. Our results are in perfect agreement with the existent literature, while at the same time extend the knowledge of the PM dynamics of compact binaries at quadratic order in spins.

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Horizon radiation reaction forces

Journal of High Energy Physics ◽

10.1007/jhep10(2020)026 ◽

2020 ◽

Vol 2020 (10) ◽

Author(s):

Walter D. Goldberger ◽

Ira Z. Rothstein

Keyword(s):

Black Hole ◽

Equations Of Motion ◽

Finite Size ◽

Radiation Reaction ◽

Effective Field ◽

Compact Objects ◽

Finite Size Effect ◽

Binary Black Holes ◽

Dissipative Effects ◽

Reaction Forces

Abstract Using Effective Field Theory (EFT) methods, we compute the effects of horizon dissipation on the gravitational interactions of relativistic binary black hole systems. We assume that the dynamics is perturbative, i.e it admits an expansion in powers of Newton’s constant (post-Minkowskian, or PM, approximation). As applications, we compute corrections to the scattering angle in a black hole collision due to dissipative effects to leading PM order, as well as the post-Newtonian (PN) corrections to the equations of motion of binary black holes in non-relativistic orbits, which represents the leading order finite size effect in the equations of motion. The methods developed here are also applicable to the case of more general compact objects, eg. neutron stars, where the magnitude of the dissipative effects depends on non-gravitational physics (e.g, the equation of state for nuclear matter).

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