Article
Astronomy & Astrophysics
Cristian Erices, Pantelis Filis, Eleftherios Papantonopoulos
Summary: The study demonstrates the avoidance of the no-hair theorem in scalar-tensor theories with bimetric structure by introducing an electric charge, leading to black hole solutions with rich thermodynamic behavior. The interplay of stability and phase transitions between different black hole configurations resembles a solid-liquid-gas system, with an electric potential acting as pressure and a triple point where three phases coexist equally probable.
Article
Physics, Multidisciplinary
Xian Gao
Summary: The authors made a comprehensive classification of scalar monomials and covariant derivatives up to the third order, emphasizing their importance in effective field theory and exploring their complementarity; through systematic classification and derivation, a complete basis of monomials was derived with the potential for novel ghostfree Lagrangians; in addition, diagrammatic representations were developed to simplify the analysis process.
SCIENCE CHINA-PHYSICS MECHANICS & ASTRONOMY
(2021)
Article
Astronomy & Astrophysics
Valerio Faraoni, Theo B. Franconnet
Summary: This article investigates a puzzle in the recent thermodynamics of scalar-tensor gravity, where general relativity is a zero-temperature equilibrium state and scalar-tensor gravity is the nonequilibrium configuration of an effective dissipative fluid. A stealth solution of Brans-Dicke gravity with constant positive temperature is shown to be analogous to a metastable state for the effective fluid and to suffer from an instability. The stability analysis utilizes a modified gravity version of the Bardeen-Ellis-Bruni-Hwang gauge-invariant formalism for cosmological perturbations. The metastable state is destroyed by tensor perturbations.
Article
Astronomy & Astrophysics
Da Huang, Chao-Qiang Geng, Hao-Jui Kuan
Summary: Spontaneous scalarization in massive scalar-tensor theories introduces extra polarizations in gravitational waves, offering valuable probes into gravity theories. Self-coupling effects suppress scalarization magnitude and reduce gravitational wave signals' amplitude. Self-interacting effects are negligible in gravitational waveforms, resulting in characteristic inverse-chirp patterns observed on Earth. Detection of scalarization-induced gravitational waves may be possible with future detectors at a signal-to-noise ratio level of O(100).
CLASSICAL AND QUANTUM GRAVITY
(2021)
Article
Multidisciplinary Sciences
Tomohiro Inagaki, Masahiko Taniguchi
Summary: This paper investigates the Cartan formalism in F(R) gravity. The Cartan F(R) gravity is described based on the Riemann-Cartan geometry and the vierbein-associated local Lorenz symmetry. By assuming the spin connection-independent matter action, the action of Cartan F(R) gravity can be successfully rewritten into the Einstein-Hilbert action and a scalar field without any conformal transformations, while maintaining the symmetries. The resulting scalar-tensor theory is useful in applications of the usual slow-roll scenario.
Article
Astronomy & Astrophysics
Masato Minamitsuji, Antonio De Felice, Shinji Mukohyama, Michele Oliosi
Summary: In this study, static and spherically symmetric solutions are investigated in the minimal theory of bigravity (MTBG). It is found that a pair of Schwarzschild-de Sitter spacetimes with different cosmological constants and black hole masses is a solution in the self-accelerating branch of MTBG, but not in the normal branch. It is also shown that the Schwarzschild-de Sitter solutions can become compatible with the normal branch by using different coordinates. Furthermore, it is confirmed that the self-accelerating branch of MTBG admits static and spherically symmetric general relativity solutions with matter written in the spatially flat coordinates, including neutron stars with arbitrary matter equations of state. Finally, it is demonstrated that nontrivial solutions in the self-accelerating branch are given by the Schwarzschild-de Sitter metrics written in nonstandard coordinates.
Article
Astronomy & Astrophysics
David Langlois, Karim Noui, Hugo Roussille
Summary: A novel and remarkably simple formulation of degenerate higher-order scalar-tensor (DHOST) theories is presented, which can be simplified to the usual Einstein-Hilbert term through disformal transformations. This classification of all quadratic DHOST theories becomes transparent in a geometric reformulation that applies also to scalar-tensor theories degenerate only in the unitary gauge.
Article
Physics, Particles & Fields
Borna Salehian, Hong-Yi Zhang, Mustafa A. Amin, David Kaiser, Mohammad Hossein Namjoo
Summary: This paper systematically derives the SP equations and relativistic corrections from the nonlinear and fully relativistic KGE equations in an expanding universe, providing insights into deviations and applicability beyond the SP system. The method presented simplifies the analysis of scalar dark matter dynamics and accurately captures deviations from the SP system towards the full KGE case, particularly in calculating the mass-radius relationship of solitons.
JOURNAL OF HIGH ENERGY PHYSICS
(2021)
Article
Astronomy & Astrophysics
David Benisty, Moshe M. Chaichian, Markku Oksanen
Summary: This passage studies the phenomenological implications of the Mimetic Tensor-Vector-Scalar theory (MiTeVeS). The theory extends the vector field model of mimetic dark matter by incorporating a scalar field, which is known to be ghost instability-free. When there is no interaction between the scalar field and the vector field, the obtained cosmological solution corresponds to the General Theory of Relativity (GR) with a minimally-coupled scalar field. However, introducing an interaction term between the scalar field and the vector field results in interesting dynamics.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Physics, Nuclear
Tong-Zheng Wang, Wei-Liang Qian, Juan Fernando Zapata Zapata, Kai Lin
Summary: This study investigates the modes of scalar-tensor-Gauss-Bonnet theory black hole solutions and examines the characteristics of complex frequencies and the stability of the metric.
Article
Physics, Multidisciplinary
Jose Edgar Madriz Aguilar, M. Montes, A. Bernal
Summary: In this paper, we present cosmological solutions that represent the current accelerating expansion of the Universe using a geometrical gauge scalar-tensor theory of gravity. The background geometry is Weyl integrable, and we find a class of power law solutions for the Weyl scalar field in a power law expanding universe with an invariant metric. For specific parameters of the model, we obtain a deceleration parameter and equation of state parameters (EoS) that are consistent with PLANCK 2018 observational data. The deceleration parameter asymptotically approaches -1/2, and the EoS parameter can cross the phantom divide line in this model.
Article
Astronomy & Astrophysics
Erik Jimenez-Vazquez, Miguel Alcubierre
Summary: We study the critical gravitational collapse of a massless scalar field nonminimally coupled to gravity and determine the values of critical amplitude, critical exponent, and echoing exponent. We find that the behavior is similar to that of a minimally coupled scalar field for small coupling, but becomes more violent and rich in high coupling. A special slicing condition is introduced to avoid gauge pathologies in the strong-coupling regime.
Article
Astronomy & Astrophysics
Yolbeiker Rodriguez Baez, Manuel Gonzalez-Espinoza
Summary: In a scalar-vector-tensor theory, the stability of static spherically symmetric black holes under linear odd-parity perturbations is studied. The action is calculated to second order in the linear perturbations to obtain a master equation for these perturbations. No-ghost and Laplacian instability conditions are derived for this general class of models. The stability conditions for particular cases are examined using the generalized Regge-Wheeler potential.
CLASSICAL AND QUANTUM GRAVITY
(2023)
Article
Physics, Particles & Fields
Alvaro de la Cruz-Dombriz, Francisco Jose Maldonado Torralba, Anupam Mazumdar
Summary: This manuscript presents a theoretical framework of the infinite derivative theory of gravity with a non-symmetric connection. The field equations are explicitly derived at the linear level, resulting in new solutions with a non-trivial form of the torsion tensor in the presence of a fermionic source. It is shown that these solutions are both ghost and singularity-free.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
Sebastian Garcia-Saenz
Summary: Our analysis shows that coupling between vector fields described by the generalized Proca class of theories and a gravitational sector defined by a scalar-tensor theory of the degenerate type leads to the loss of at least one constraint associated with the scalar-tensor sector.
Article
Astronomy & Astrophysics
Sourav Sur, Arshdeep Singh Bhatia
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2017)
Article
Astronomy & Astrophysics
Debaprasad Maity, Soumitra SenGupta, Sourav Sur
CLASSICAL AND QUANTUM GRAVITY
(2009)
Article
Astronomy & Astrophysics
Sourav Sur, Arshdeep Singh Bhatia
CLASSICAL AND QUANTUM GRAVITY
(2014)
Review
Astronomy & Astrophysics
Sourav Sur, Saurya Das
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
(2009)
Article
Astronomy & Astrophysics
Hiyang Ramo Chothe, Ashim Dutta, Sourav Sur
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2019)
Article
Physics, Particles & Fields
Sourav Sur, Ashim Dutta, Hiyang Ramo Clothe
Summary: The theory extends the basic formalism of mimetic-metric-torsion gravity theory, showing geometrically how the mimetic scalar field acts as the source of both the trace and axial modes of torsion. It maintains conformal symmetry and spatial parity symmetry, demonstrating a geometric unification of the cosmological dark sector and the feasibility of a super-accelerating regime during the universe's evolution. The theory also predicts a smooth crossing of the phantom barrier at low red-shift and determines the extent of super-acceleration by examining the evolution of relevant torsion parameters.
EUROPEAN PHYSICAL JOURNAL C
(2021)
Article
Astronomy & Astrophysics
Mohit Kumar Sharma, Sourav Sur
Summary: This paper investigates the modifications in cosmic perturbations caused by the interaction between dark energy and dust-like matter. The study focuses on the late-time cosmic evolution and shows that such an interaction can significantly affect the perturbative spectrum. The matter density contrast is influenced by the interaction as well as the perturbation in dark energy induced by the scalar field. The standard parametrization for the matter density growth factor is found to be inadequate and is suitably modified. The paper also presents a numerical fit of the growth index in terms of the background parameters for an improved estimation.
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2022)
Article
Astronomy & Astrophysics
Saurya Das, Sourav Sur
Summary: The essay explains how gravity is an emergent phenomenon and should be quantized at the fundamental degrees of freedom level.
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2021)
Article
Physics, Multidisciplinary
Saurya Das, Sourav Sur
Summary: The dynamics of a quantum particle is determined by its wavefunction, which is influenced by both classical and quantum potentials. The particle experiences the combined effects of these potentials, making it impossible to distinguish between them, so observed potentials may be a result of both classical and quantum influences.
EUROPEAN PHYSICAL JOURNAL PLUS
(2021)
Article
Astronomy & Astrophysics
Saurya Das, Sourav Sur
Summary: This essay demonstrates that augmenting Newton's gravitational potential with a logarithmic term can partly or wholly mitigate the need for dark matter, and also provides an explanation for the effectiveness of MOND at galactic scales.
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2022)
Article
Astronomy & Astrophysics
Saurya Das, Sourav Sur
Summary: Recent research has shown that any observed potential can be generated by a suitable wave function. This study focuses on the gravitational potential and determines the wave function that produces it, suggesting that the observed gravitational interaction at all length scales can be explained by an underlying wave function. The implications of this result are discussed.
INTERNATIONAL JOURNAL OF MODERN PHYSICS D
(2022)
Article
Astronomy & Astrophysics
Mohit Kumar Sharma, Sourav Sur
Summary: We analyze the dynamical system of interacting dark energy-matter scenarios and study the critical points and stability at both the background level and the level of density perturbations. We find a double degeneracy in the critical point spectrum in the inhomogeneous picture due to the possible growth and decay of matter density perturbations. By analyzing the dynamics of the growth factor, we show that it initially surpasses unity at one of the critical points and leads to a stable configuration as the matter density fluctuations diminish. As for the growth index, we find that the only physically plausible trajectory is one that evolves mildly at high redshifts and becomes steeper with time, with an average value close to 6/11.
PHYSICS OF THE DARK UNIVERSE
(2023)
Article
Physics, Multidisciplinary
Saurya Das, Sourav Sur
Summary: The mass of an astrophysical object can be estimated by gravitational lensing, assuming the validity of the inverse square law of gravity. However, introducing a logarithmic potential at galactic length scales predicts a larger deflection angle, suggesting that the true mass of the object is less than estimated. This finding may lessen the significance of dark matter in explaining various observations.
Article
Astronomy & Astrophysics
Saurya Das, Sourav Sur
Summary: We examine the possibility of describing a unified picture of the dark side of the universe using a Bose-Einstein condensate (BEC) of light bosons. The energy density and quantum potential of the BEC can account for the emergence of cold dark matter and dark energy from the same source. However, even visible baryons have a quantum mechanical back-reaction on the effective dark energy and dark matter contents, which crucially determines the mass of the BEC.
PHYSICS OF THE DARK UNIVERSE
(2023)