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Probing the signature of axions through the quasinormal modes of black holes
Antonio De Felice, Shinji Tsujikawa
The axion-photon coupling allows the existence of a magnetically and electrically charged black hole (BH) solution endowed with a pseudo-scalar hair. For the Reissner-Nordstrom BH…
Can we distinguish black holes with electric and magnetic charges from quasinormal modes?
Antonio De Felice, Shinji Tsujikawa
We compute the quasinormal modes of static and spherically symmetric black holes (BHs) with electric and magnetic charges. For the electrically charged case, the dynamics of pertur…
Starobinsky inflation with a quadratic Weyl tensor
Antonio De Felice, Ryodai Kawaguchi, Kotaro Mizui +1
In Starobinsky inflation with a Weyl squared Lagrangian , where is a coupling constant, we study the linear stability of cosmological perturbations on a spatially flat F…
Excluding static and spherically symmetric black holes in Einsteinian cubic gravity with unsuppressed higher-order curvature terms
Antonio De Felice, Shinji Tsujikawa
Einsteinian cubic gravity is a higher-order gravitational theory in which the linearized field equations of motion match Einstein's equations on a maximally symmetric background. T…
Black holes in a new gravitational theory with trace anomalies
Shinji Tsujikawa
In a new gravitational theory with the trace anomaly recently proposed by Gabadadze, we study the existence of hairy black hole solutions on a static and spherically symmetric back…
Coupled vector Gauss-Bonnet theories and hairy black holes
Katsuki Aoki, Shinji Tsujikawa
We study vector-tensor theories in which a 4-dimensional vector field is coupled to a vector quantity , which is expressed in terms of and a metric tensor $…
Black hole perturbations in Maxwell-Horndeski theories
Ryotaro Kase, Shinji Tsujikawa
We study the linear stability of black holes in Maxwell-Horndeski theories where a gauge-invariant vector field is coupled to a scalar field with the Lagrangian of full Horn…
Cosmological stability in gravity
Shinji Tsujikawa
In gravitational theories where a canonical scalar field with a potential is coupled to a Gauss-Bonnet (GB) term with the Lagrangian , we study…
Cosmology in theories with spontaneous scalarization of neutron stars
Ratchaphat Nakarachinda, Sirachak Panpanich, Shinji Tsujikawa +1
In a model of spontaneous scalarization of neutron stars proposed by Damour and Esposite-Farese, a general relativistic branch becomes unstable to trigger tachyonic growth of a sca…
Inspiral gravitational waveforms from compact binary systems in Horndeski gravity
Yurika Higashino, Shinji Tsujikawa
In a subclass of Horndeski theories with the speed of gravity equivalent to that of light, we study gravitational radiation emitted during the inspiral phase of compact binary syst…
Symmetry restoration in the vicinity of neutron stars with a nonminimal coupling
Masato Minamitsuji, Shinji Tsujikawa
We propose a new model of scalarized neutron stars (NSs) realized by a self-interacting scalar field nonminimally coupled to the Ricci scalar of the form . The scala…
Stability of neutron stars in Horndeski theories with Gauss-Bonnet couplings
Masato Minamitsuji, Shinji Tsujikawa
In Horndeski theories containing a scalar coupling with the Gauss-Bonnet (GB) curvature invariant , we study the existence and linear stability of neutron star (NS) s…
Instability of hairy black holes in regularized 4-dimensional Einstein-Gauss-Bonnet gravity
Shinji Tsujikawa
In regularized 4-dimensional Einstein-Gauss-Bonnet (EGB) gravity derived from a Kaluza-Klein reduction of higher-dimensional EGB theory, we study the existence and stability of bla…
Linear stability of black holes with static scalar hair in full Horndeski theories: generic instabilities and surviving models
Masato Minamitsuji, Kazufumi Takahashi, Shinji Tsujikawa
In full Horndeski theories, we show that the static and spherically symmetric black hole (BH) solutions with a static scalar field~ whose kinetic term~ is nonvanishing on the…
Linear stability of black holes in shift-symmetric Horndeski theories with a time-independent scalar field
Masato Minamitsuji, Kazufumi Takahashi, Shinji Tsujikawa
We study linear perturbations about static and spherically symmetric black holes with a time-independent background scalar field in shift-symmetric Horndeski theories, whose Lagran…
Relativistic star perturbations in Horndeski theories with a gauge-ready formulation
Ryotaro Kase, Shinji Tsujikawa
We present a general framework for studying the relativistic star perturbations on a static and spherically symmetric background in full Horndeski theories. We take a perfect fluid…
Odd-parity stability of black holes in Einstein-Aether gravity
Shinji Tsujikawa, Chao Zhang, Xiang Zhao +1
In Einstein-Aether theory, we study the stability of black holes against odd-parity perturbations on a spherically symmetric and static background. For odd-parity modes, there are…
Spontaneous scalarization of charged stars
Masato Minamitsuji, Shinji Tsujikawa
We study static and spherically symmetric charged stars with a nontrivial profile of the scalar field in Einstein-Maxwell-scalar theories. The scalar field is coupled to a $U(1…
Instability of compact stars with a nonminimal scalar-derivative coupling
Ryotaro Kase, Shinji Tsujikawa
For a theory in which a scalar field has a nonminimal derivative coupling to the Einstein tensor of the form , it is known that there exis…
Stability of relativistic stars with scalar hairs
Ryotaro Kase, Rampei Kimura, Seiga Sato +1
We study the stability of relativistic stars in scalar-tensor theories with a nonminimal coupling of the form , where depends on a scalar field and is the Ricci…
Current status of space gravitational wave antenna DECIGO and B-DECIGO
Seiji Kawamura, Masaki Ando, Naoki Seto +84
Deci-hertz Interferometer Gravitational Wave Observatory (DECIGO) is the future Japanese space mission with a frequency band of 0.1 Hz to 10 Hz. DECIGO aims at the detection of pri…
General formulation of cosmological perturbations in scalar-tensor dark energy coupled to dark matter
Ryotaro Kase, Shinji Tsujikawa
For a scalar field coupled to cold dark matter (CDM), we provide a general framework for studying the background and perturbation dynamics on the isotropic cosmological backgro…
Suppressed cosmic growth in coupled vector-tensor theories
Antonio De Felice, Shintaro Nakamura, Shinji Tsujikawa
We study a coupled dark energy scenario in which a massive vector field with broken gauge symmetry interacts with the four-velocity of cold dark matter (CDM) t…
Scaling solutions and weak gravity in dark energy with energy and momentum couplings
Luca Amendola, Shinji Tsujikawa
We argue that the CDM tensions of the Hubble-Lemaitre expansion rate and the clustering normalization can be eased, at least in principle, by considering an interact…