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Tetsuya Shiromizu

Publications and source records attributed to Tetsuya Shiromizu.

At least 91 records · Page 5Linked to original sources
arXiv2005

Close-limit analysis for head-on collision of two black holes in higher dimensions: Brill-Lindquist initial data

Motivated by the TeV-scale gravity scenarios, we study gravitational radiation in the head-on collision of two black holes in higher dimensional spacetimes using a close-limit approximation. We prepare time-symmetric initial data sets for two black holes (the so-called Brill-Lindquist initial data) and numerically evolve the spacetime in terms of a gauge invariant formulation for the perturbation around the higher-dimensional Schwarzschild black holes. The waveform and radiated energy of gravitational waves emitted in the head-on collision are clarified. Also, the complex frequencies of fundamental quasinormal modes of higher-dimensional Schwarzschild black holes, which have not been accurately derived so far, are determined.

gr-qc↗
arXiv2005

Gravitational collapse disturbs the dS/CFT correspondence?

We study the gravitational collapse in five-dimensional de Sitter (dS) spacetime and discuss the existence of the conformal boundaries at future timelike infinity from the perspective of the dS/CFT correspondence. We investigate the motion of a spherical dust shell and the black hole area bounds. The latter includes the analysis of the trapping horizon and the initial data with spindle-shaped matter distribution. In all above analyses we find the evidences that guarantee the existence of the conformal boundaries at future timelike infinity which are essential to apply the dS/CFT correspondence.

gr-qc↗
arXiv2005

Baryon number violation due to brane dynamics

We derive the low energy effective theory for two brane system with bulk complex scalar fields. Then we find that higher order corrections to the effective equation for scalar fields on the brane lead us to the baryon number(B) violating process if the complex scalar field is regarded as a particle carrying the baryon number current. We see that the motion of the brane leads us the baryon number violation via the current-curvature coupling even if the potential for scalar fields do not exist. We also estimate the net baryon number assuming a C/CP violating interaction.

hep-ph↗
arXiv2005

Kaluza-Klein bubble like structure and celestial sphere in inflationary universe

We consider five dimensional deSitter spacetimes with a deficit angle due to the presence of a closed 2-brane and identify one dimension as an extra dimension. From the four dimensional viewpoint we can see that the spacetime has a structure similar to a Kaluza-Klein bubble of nothing, that is, four dimensional spacetime ends at the 2-brane. Since a spatial section of the full deSitter spacetime has the topology of a sphere, the boundary surface surrounds the remaining four dimensional spacetime, and can be considered as the celestial sphere. After the spacetime is created from nothing via an instanton which we describe, some four dimensional observers in it see the celestial sphere falling down, and will be in contact with a 2-brane attached on it.

hep-th↗
arXiv2005

Galaxy clustering constraints on deviations from Newtonian gravity at cosmological scales

In spite of the growing observational evidence for dark matter and dark energy in the universe, their physical nature is largely unknown. In fact, several authors have proposed modifications of Newton's law of gravity at cosmological scales to account for the apparent acceleration of the cosmic expansion. Inspired by such suggestions, we attempt to constrain possible deviations from Newtonian gravity by means of the clustering of SDSS (Sloan Digital Sky Survey) galaxies. To be specific, we assume a simple modification of Newton's law with an additional Yukawa-type term characterized by the amplitude αand the length scale λ. Adopting spatially-flat universes dominated by cold dark matter and/or dark energy, we solve a linear perturbation equation for the growth of density fluctuations. In particular, we find an exact analytic solution for the Einstein -- de Sitter case. Following the Peacock-Dodds prescription, we compute the nonlinear power spectra of mass fluctuations, perform a statistical comparison with the SDSS galaxy data, and derive constraints in the α-λplane; for instance, we obtain the constraints of -0.5<α<0.6 and -0.8<α<0.9 (99.7% confidence level) for λ=5h^{-1}Mpc and 10h^{-1}Mpc, respectively. We also discuss several future possibilities for improving our analysis.

astro-ph↗
arXiv2005

Gravity is controlled by cosmological constant

We discuss a Randall-Sundrum-type two D-braneworld model in which D-branes possess different values of the tensions from those of the charges, and derive an effective gravitational equation on the branes. As a consequence, the Einstein-Maxwell theory is realized together with the non-zero cosmological constant. Here an interesting point is that the effective gravitational constant is proportional to the cosmological constant. If the distance between two D-branes is appropriately tuned, the cosmological constant can have a consistent value with the current observations. From this result we see that, in our model, the presence of the cosmological constant is naturally explained by the presence of the effective gravitational coupling of the Maxwell field on the D-brane.

hep-th↗
arXiv2004

Positivity Bounds for the Y-ADM Mass Density

Killing-Yano tensors are natural generalizations of Killing vectors to arbitrary rank anti-symmetric tensor fields. It was recently shown that Killing-Yano tensors lead to conserved gravitational charges, called Y-ADM charges. These new charges are interesting because they measure, for example, the mass density of a p-brane, rather than the total ADM mass which may be infinite. In this paper, we show that the spinorial techniques used by Witten, in his proof of the positive energy theorem, may be straightforwardly extended to study the positivity properties of the Y-ADM mass density for p-brane spacetimes. Although the resulting formalism is quite similar to the ADM case, we show that establishing a positivity bound in the higher rank Y-ADM case requires imposing a condition on the Weyl tensor in addition to an energy condition. We find appropriate energy conditions for spacetimes that are conformally flat or algebraically special, and for spacetimes that have an exact Killing vector along the brane. Finally we discuss our expression for the Y-ADM mass density from the Hamiltonian point of view.

hep-th↗
arXiv2004

Asymmetric D-braneworld

In recent papers on Randall-Sundrum D-braneworld model with Z_2 symmetry, it was shown that the effective gravity does not work as usual, that is, the gravity does not couple to the gauge field localised on the brane in a usual way. At first glance there are two possibilities to avoid this serious problem. One is to remove the Z_2 symmetry and another is to consider a non-BPS state. In this paper we analyze the Randall-Sundrum D-braneworld model without Z_2 symmetry by long wave approximation. The result is unexpected one, that is, the gauge field does not couple to the gravity on the brane in the leading order again. Therefore the remaining possibility to recover the conventional gravitational theory would be non-BPS cases.

hep-th↗
arXiv2004

Gravity in Randall-Sundrum two D-brane model

We analyse Randall-Sundrum two D-brane model by linear perturbation and then consider the linearised gravity on the D-brane. The qualitative contribution from the Kaluza-Klein modes of gauge fields to the coupling to the gravity on the brane will be addressed. As a consequence, the gauge fields localised on the brane are shown not to contribute to the gravity on the brane at large distances. Although the coupling between gauge fields and gravity appears in the next order, the ordinary coupling cannot be realised.

hep-th↗
arXiv2004

Twist of stationary black hole/ring in five dimensions

It is unlikely that uniqueness theorem holds for stationary black holes in higher dimensional spacetimes. However, we will examine the possibility that the higher multipole moments classify vacuum solutions uniquely. Especially, we compute the potentials associated with rotational Killing vectors and look at the dependence on the total mass M and angular momentum J. Consequently, there is a potential $σ$ which we cannot write down in terms of integer power of M and J explicitly. This may be regarded as an evidence for the uniqueness using multipole moments generated by $σ$.

gr-qc↗
arXiv2004

Randall-Sundrum two D-brane model

In Randall-Sundrum two D-brane system we derive the gravitational theory on the branes. It is turned out from the consistency that one D-brane has the negative tension brane under Randall-Sundrum tuning and both gauge fields on the brane are related by scale transformation through the bulk RR/NS-NS fields. As same with the single D-brane case, the gauge field which is supposed to be localised on the brane does not couple to the gravity on the branes.

hep-th↗
arXiv2004

Spacetime dynamics and baryogenesis in braneworld

We point out that the effective theory for the Randall-Sundrum braneworld models with bulk fields contains the baryon number violation process depending on the spacetime dynamics. Combining to the curvature-current interaction, the net baryon number observed today may be explained. The resultant baryon to entropy ratio is determined by the ratio of the Planck scales in four dimensional and five dimensional spacetime except for the parameter for CP violation.

hep-ph↗
arXiv2004

Spatial infinity in higher dimensional spacetimes

Motivated by recent studies on the uniqueness or non-uniqueness of higher dimensional black hole spacetime, we investigate the asymptotic structure of spatial infinity in n-dimensional spacetimes($n \geq 4$). It turns out that the geometry of spatial infinity does not have maximal symmetry due to the non-trivial Weyl tensor {}^{(n-1)}C_{abcd} in general. We also address static spacetime and its multipole moments P_{a_1 a_2 ... a_s}. Contrasting with four dimensions, we stress that the local structure of spacetimes cannot be unique under fixed a multipole moments in static vacuum spacetimes. For example, we will consider the generalized Schwarzschild spacetimes which are deformed black hole spacetimes with the same multipole moments as spherical Schwarzschild black holes. To specify the local structure of static vacuum solution we need some additional information, at least, the Weyl tensor {}^{(n-2)}C_{abcd} at spatial infinity.

gr-qc↗
arXiv2004

Low energy effective action on a self-gravitating D-brane

Recently the study of braneworld on the self-gravitating D-brane has been initiated and derived the gravitational equation on the brane by holographic and geometrical projection methods. Surprisingly, in common with these two methods, the matter on the brane cannot be the source of the gravity on the brane at leading order. In this paper we will propose the low energy effective action on the D-brane coupled with gravity which derives the same results.

hep-th↗
arXiv2003

D-braneworld cosmology II: Higher order corrections

We investigate braneworld cosmology based on the D-brane initiated in our previous paper. The brane is described by a Born-Infeld action and the gauge field is contained. The higher order corrections of an inverse string tension will be addressed. The results obtained by the truncated argument are altered by the higher order corrections. The equation of state of the gauge field on the brane is radiation-like in low energy scales and almost dust-like fluid in high energy scales. Our model is, however, limited below a critical finite value of the energy density. For the description of full history of our universe the presence of a S-brane might be essential.

hep-th↗
arXiv2003

Cosmological constant and gravitational theory on D-brane

In a toy model we derive the gravitational equation on a self-gravitating curved D-brane. The effective theory on the brane is drastically changed from the ordinal Einstein equation. The net cosmological constant on the brane depends on a tuning between the brane tension and the brane charges. Moreover, non-zero matter stress tensor exists if the net cosmological constant is not zero. This fact indicates a direct connection between matters on the brane and the dark energy.

hep-th↗
arXiv2003

Steep Inflation followed by Born-Infeld Reheating

We discuss a model in which high energy brane corrections allow a single scalar field to describe inflation at early epochs and quintessence at late times. The reheating mechanism in the model originates from Born-Infeld matter whose energy density mimics cosmological constant at very early times and manifests itself as radiation subsequently. For most of the inflationary evolution the Born-Infeld matter remains subdominant to the the scalar field. Shortly before the end of inflation driven by the scalar field, the energy density of Born-Infeld matter starts scaling as radiation and drops by several orders of magnitudes at the epoch inflation ends. The problem of over production of gravity wave background in scenarios based upon reheating through gravitational particle production is successfully resolved by suitably fixing the initial value of radiation energy density at the end of inflation. No additional fine tuning of the parameters is required for a viable evolution.

hep-th↗