93 citations · 651 across the 35 of their papers we have counts for
36 papers
Technically Natural Suppression of Fifth Force
Kensuke Homma, Taishi Katsuragawa, Shinya Matsuzaki
Light scalars generically mediate a fifth force incompatible with local tests of gravity unless their couplings are parametrically suppressed or screening mechanisms are introduced…
Stimulated radiation from superradiant scalar cloud in scalar-tensor theory
Wenyi Wang, Sousuke Noda, Taishi Katsuragawa
Scalar-tensor theories predict fundamental scalar fields of considerable interest in astrophysics and cosmology. We investigate the superradiant instability of scalar clouds around…
Wormhole spacetimes in an expanding universe: Energy conditions and future singularities
Taishi Katsuragawa, Shin'ichi Nojiri, Sergei D. Odintsov
We study wormhole geometries embedded in an expanding universe within a four-scalar non-linear model, where the target-space metric is identified with the spacetime Ricci tenso…
Cosmological Perturbation in New General Relativity: Propagating mode from the violation of local Lorentz invariance
Kyosuke Tomonari, Taishi Katsuragawa, Shin'ichi Nojiri
We investigate the propagating modes of New General Relativity (NGR) in second-order linear perturbations in the Lagrangian density (first-order in field equations). The Dirac-Berg…
Revisiting Coincident GR in Internal STEGR Formulation
Kyosuke Tomonari, Taishi Katsuragawa, Shin'ichi Nojiri
We revisit Coincident General Relativity (CGR) in the gauge approach to gravity based on Symmetric Teleparallel Equivalent to General Relativity (STEGR) in the \textit{internal-spa…
Solar system tests in covariant f(Q) gravity
Wenyi Wang, Kun Hu, Taishi Katsuragawa
We study the Solar System constraints on covariant gravity. The covariant theory is described by the metric and affine connection, where both the torsion and curvatur…
Scalar-Induced Electromagnetic Radiation: Comparison with Axion-Like Particles and Implications for Modified Gravity
Wenyi Wang, Sousuke Noda, Taishi Katsuragawa
The scalar-tensor theory of gravity, a modified gravity theory, introduces a fundamental scalar field that can serve as dynamical dark energy, driving the late-time accelerated exp…
Compact star in noninteger power model of gravity
Yong-Xiang Cui, Zu Yan, Kota Numajiri +2
We investigate compact stars in the noninteger power (NIP) model of gravity theory, which includes the higher-curvature correction to the Einstein-Hilbert action. The mass-r…
Future singularity in an anisotropic universe
Taishi Katsuragawa, Shin'ichi Nojiri, Sergei D. Odintsov
We investigate future singularities originating from the anisotropy in the Universe. We formulate a new class of singularities in the homogeneous and anisotropic universe, comparin…
Theoretical and observational constraints on early dark energy in gravity
Hua Chen, Taishi Katsuragawa, Shin'ichi Nojiri +1
This work examines an early dark energy (EDE) scenario in the context of gravity. EDE is introduced to alleviate the Hubble tension by temporarily injecting approximately $1…
Nonpropagating ghost in covariant gravity
Kun Hu, Makishi Yamakoshi, Taishi Katsuragawa +2
gravity is an extension of the symmetric teleparallel equivalent to general relativity (STEGR). This work shows that based on the scalar-nonmetricity formulation, a scalar m…
Revisiting compact star in gravity: Roles of chameleon potential and energy conditions
Kota Numajiri, Yong-Xiang Cui, Taishi Katsuragawa +1
We reexamine the static and spherical symmetric compact star configuration in the model of the gravity theory. With asymptotic solutions for the additional scalar degr…
Cosmological gravity probes: connecting recent theoretical developments to forthcoming observations
Shun Arai, Katsuki Aoki, Yuji Chinone +20
Since the discovery of the accelerated expansion of the present Universe, significant theoretical developments have been made in the area of modified gravity. In the meantime, cosm…
Towards a unified interpretation of the early Universe in -corrected dark energy model of gravity
Hua Chen, Taishi Katsuragawa, Shinya Matsuzaki
-corrected dark energy (DE) models in gravity have been widely investigated in recent years, which not only removes the weak singularity potentially present in DE model…
ADM formulation and Hamiltonian analysis of gravity
Kun Hu, Taishi Katsuragawa, Taotao Qiu
gravity is an extension of the symmetric teleparallel equivalent to general relativity. We demonstrate the Hamiltonian analysis of gravity with fixing the coincident…
Compact Star in General Gravity: Inevitable Degeneracy Problem and Non-Integer Power Correction
Kota Numajiri, Taishi Katsuragawa, Shin'ichi Nojiri
We investigate a compact star in the general gravity. Developing a novel formulation in the spherically symmetric and static space-time with the matter, we confirm that an a…
Static and spherically symmetric solutions in f(Q) gravity
Wenyi Wang, Hua Chen, Taishi Katsuragawa
f(Q) gravity is the extension of symmetric teleparallel general relativity (STGR), in which both curvature and torsion vanish, and gravity is attributed to nonmetricity. This work…
Hunting dark energy with pressure-dependent photon-photon scattering
Taishi Katsuragawa, Shinya Matsuzaki, Kensuke Homma
Toward understanding of dark energy, we propose a novel method to directly produce a chameleon particle and force its decay under controlled gas pressure in a laboratory-based expe…
Confronting Inflation Models with the Coming Observations on Primordial Gravitational Waves
Taotao Qiu, Taishi Katsuragawa, Shulei Ni
The recent observations from CMB have imposed a very stringent upper-limit on the tensor/scalar ratio of inflation models, , which indicates that the primordial grav…
Dark matter candidate induced by Horndeski theory: dark matter halo and cosmological evolution
Jiaming Shi, Taishi Katsuragawa, Taotao Qiu
We study spherically symmetric solutions with a scalar field in the shift-symmetric subclass of the Horndeski theory. Constructing an effective energy-momentum tensor of the scalar…
Big Bang Nucleosynthesis Hunts Chameleon Dark Matter
Hua Chen, Taishi Katsuragawa, Shinya Matsuzaki +1
We study the chameleon field dark matter, dubbed \textit{scalaron}, in gravity in the Big Bang Nucleosynthesis (BBN) epoch. With an -correction term required to solve…
Gravitational Waves in Gravity: Scalar Waves and the Chameleon Mechanism
Taishi Katsuragawa, Tomohiro Nakamura, Taishi Ikeda +1
We discuss the scalar mode of gravitational waves emerging in the context of gravity by taking into account the chameleon mechanism. Assuming a toy model with a specific mat…
Screened and Unscreened Solutions for Relativistic Star in de Rham-Gabadadze-Tolley (dRGT) Massive Gravity
Masashi Yamazaki, Taishi Katsuragawa, Sergei D. Odintsov +1
We study the static and spherical symmetric (SSS) configurations in the non-minimal model of the de Rham-Gabadadze-Tolley (dRGT) massive gravity with a flat reference metric. Consi…
gravity in the early Universe: Electroweak phase transition and chameleon mechanism
Taishi Katsuragawa, Shinya Matsuzaki, Eibun Senaha
It is widely believed that the screening mechanism is an essential feature for the modified gravity theory. Although this mechanism has been examined thoroughly in the past decade,…