Makoto Narita
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Research Subjects
Makoto Narita has a total of 11 co-authors. Here are the top co-authors by number of shared publications:
- Takashi Torii
Department of Physics Tokyo Institute of Technology Oh-Okayama Meguro-ku 152 Tokyo Japan
8 shared publications - Kengo Maeda
Department of Physics, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-0033, Japan
5 shared publications - Takashi Torii
Research Center for the Early Universe, University of Tokyo, Hongo, Bunkyo, Tokyo 113-0033, Japan
4 shared publications - Kei-Ichi Maeda
Department of Physics Waseda University Okubo 3-4-1 169-8555 Shinjuku Tokyo Japan
2 shared publications - Kengo Maeda
Department of Physics, Waseda University, Shinjuku-ku, Tokyo 169-8555, Japan
2 shared publications - Akihiro Ishibashi
Department of Physics, Tokyo Institute of Technology, Oh-Okayama, Meguro, Tokyo 152, Japan
1 shared publication
Latest Publications
- 23 July 2001
- Published by American Physical Society (APS) in Physical Review D
- Vol. 64 (4) , 044007
Scalar hair on the black hole in asymptotically anti–de Sitter spacetime
We examine the no-hair conjecture in asymptotically anti–de Sitter (AdS) spacetime. First, we consider a real scalar field as the matter field and assume static spherically symmetric spacetime. Analysis of the asymptotics shows that the scalar field must approach the extremum of its potential. Using this fact, it is proved that there is no regular black hole solution when the scalar field is massless or has a “convex” potential. Surprisingly, while the scalar field has a growing mode around the local minimum of the potential, there is no growing mode around the local maximum. This implies that the local maximum is a kind of “attractor” of the asymptotic scalar field. We give two examples of the new black hole solutions with a nontrivial scalar field configuration numerically in the symmetric or asymmetric double well potential models. We study the stability of these solutions by using the linear perturbation method in order to examine whether or not the scalar hair is physical. In the symmetric double well potential model, we find that the potential function of the perturbation equation is positive semidefinite in some wide parameter range and that the new solution is stable. This implies that the black hole no-hair conjecture is violated in asymptotically AdS spacetime.
- 23 July 2001
- Published by American Physical Society (APS) in Physical Review D
- Vol. 64 (4) , 044007
Scalar hair on the black hole in asymptotically anti–de Sitter spacetime
We examine the no-hair conjecture in asymptotically anti–de Sitter (AdS) spacetime. First, we consider a real scalar field as the matter field and assume static spherically symmetric spacetime. Analysis of the asymptotics shows that the scalar field must approach the extremum of its potential. Using this fact, it is proved that there is no regular black hole solution when the scalar field is massless or has a “convex” potential. Surprisingly, while the scalar field has a growing mode around the local minimum of the potential, there is no growing mode around the local maximum. This implies that the local maximum is a kind of “attractor” of the asymptotic scalar field. We give two examples of the new black hole solutions with a nontrivial scalar field configuration numerically in the symmetric or asymmetric double well potential models. We study the stability of these solutions by using the linear perturbation method in order to examine whether or not the scalar hair is physical. In the symmetric double well potential model, we find that the potential function of the perturbation equation is positive semidefinite in some wide parameter range and that the new solution is stable. This implies that the black hole no-hair conjecture is violated in asymptotically AdS spacetime.
- Open Access
The excitation of a charged string passing through a shock wave in a charged Aichelburg-Sexl spacetime
We investigate how much a first-quantized charged bosonic test string gets excited after crossing a shock wave generated by a charged particle with mass $\tilde{M}$ and charge $\tilde{Q}$. On the basis of Kaluza-Klein theory, we pay attention to a closed string model where charge is given by a momentum along a compactified extra-dimension. The shock wave is given by a charged Aichelburg-Sexl (CAS) spacetime where $\tilde{Q}=0$ corresponds to the ordinary Aichelburg-Sexl one. We first show that the CAS spacetime is a solution to the equations of motion for the metric, the gauge field, and the axion field in the low-energy limit. Secondly, we compute the mass expectation value of the charged test string after passing through the shock wave in the CAS spacetime. In the case of small $\tilde{Q}$, gravitational and Coulomb forces are canceled out each other and hence the excitation of the string remains very small. This is independent of the particle mass $\tilde{M}$ or the strength of the shock wave. In the case of large $\tilde{Q}$, however, every charged string gets highly excited by quantum fluctuation in the extra-dimension caused by both the gauge and the axion fields. This is quite different from classical "molecule", which consists of two electrically charged particles connected by a classical spring.Open AccessThe excitation of a charged string passing through a shock wave in a charged Aichelburg-Sexl spacetime
We investigate how much a first-quantized charged bosonic test string gets excited after crossing a shock wave generated by a charged particle with mass $\tilde{M}$ and charge $\tilde{Q}$. On the basis of Kaluza-Klein theory, we pay attention to a closed string model where charge is given by a momentum along a compactified extra-dimension. The shock wave is given by a charged Aichelburg-Sexl (CAS) spacetime where $\tilde{Q}=0$ corresponds to the ordinary Aichelburg-Sexl one. We first show that the CAS spacetime is a solution to the equations of motion for the metric, the gauge field, and the axion field in the low-energy limit. Secondly, we compute the mass expectation value of the charged test string after passing through the shock wave in the CAS spacetime. In the case of small $\tilde{Q}$, gravitational and Coulomb forces are canceled out each other and hence the excitation of the string remains very small. This is independent of the particle mass $\tilde{M}$ or the strength of the shock wave. In the case of large $\tilde{Q}$, however, every charged string gets highly excited by quantum fluctuation in the extra-dimension caused by both the gauge and the axion fields. This is quite different from classical "molecule", which consists of two electrically charged particles connected by a classical spring. - 24 October 2000
- Published by IOP Publishing in Classical and Quantum Gravity
- Vol. 17 (22) , 4597-4613
Asymptotic singular behaviour of Gowdy spacetimes in string theory
We study T3 Gowdy spacetimes in the Einstein-Maxwell-dilaton-axion system and show by the Fuchsian algorithm that they have, in general, asymptotically velocity-term-dominated singularities. The families of the corresponding solutions depend on the maximum number of arbitrary functions. Although coupling of the dilaton field with the Maxwell and/or the axion fields corresponds to the `potential' which appears in the Hamiltonian of vacuum Bianchi IX spacetimes, our result means that the spacetimes do not become Mixmaster necessarily.
- 24 October 2000
- Published by IOP Publishing in Classical and Quantum Gravity
- Vol. 17 (22) , 4597-4613
Asymptotic singular behaviour of Gowdy spacetimes in string theory
We study T3 Gowdy spacetimes in the Einstein-Maxwell-dilaton-axion system and show by the Fuchsian algorithm that they have, in general, asymptotically velocity-term-dominated singularities. The families of the corresponding solutions depend on the maximum number of arbitrary functions. Although coupling of the dilaton field with the Maxwell and/or the axion fields corresponds to the `potential' which appears in the Hamiltonian of vacuum Bianchi IX spacetimes, our result means that the spacetimes do not become Mixmaster necessarily.
- Open Access
Asymptotic singular behavior of Gowdy spacetimes in string theory
We study $T^{3}$ Gowdy spacetimes in the Einstein-Maxwell-dilaton-axion system and show by the Fuchsian algorithm that they have in general asymptotically velocity-term dominated singularities. The families of the corresponding solutions depend on the maximum number of arbitrary functions. Although coupling of the dilaton field with the Maxwell and/or the axion fields corresponds to the ``potential'' which appears in the Hamiltonian of vacuum Bianchi IX spacetimes, our result means that the spacetimes do not become Mixmaster necessarily.Open AccessAsymptotic singular behavior of Gowdy spacetimes in string theory
We study $T^{3}$ Gowdy spacetimes in the Einstein-Maxwell-dilaton-axion system and show by the Fuchsian algorithm that they have in general asymptotically velocity-term dominated singularities. The families of the corresponding solutions depend on the maximum number of arbitrary functions. Although coupling of the dilaton field with the Maxwell and/or the axion fields corresponds to the ``potential'' which appears in the Hamiltonian of vacuum Bianchi IX spacetimes, our result means that the spacetimes do not become Mixmaster necessarily. - 23 February 2000
- Published by American Physical Society (APS) in Physical Review D
- Vol. 61 (6)
Violation of the cosmic no hair conjecture in the Einstein-Maxwell-dilaton system
The cosmic no hair conjecture is tested in the spherically symmetric Einstein-Maxwell-dilaton~(EMD) system with a positive cosmological constant $\Lambda$. Firstly, we analytically show that once gravitational collapse occurs in the massless dilaton case, the system of field equations breaks down inevitably in outer communicating regions or at the boundary provided that a future null infinity ${\cal I}^+$ exists. Next we find numerically the static black hole solutions in the massive dilaton case and investigate their properties for comparison with the massless case. It is shown that their Abbott-Deser~(AD) mass are infinite, which implies that a spacetime with finite AD mass does not approach a black hole solution after the gravitational collapse. These results suggest that ${\cal I}^+$ cannot appear in the EMD system once gravitational collapse occurs and hence the cosmic no hair conjecture is violated in both the massless and the massive cases, in contrast to general relativity.Comment: 9 pages, REVtex, 5 figures, to appear in Phys. Rev.- 23 February 2000
- Published by American Physical Society (APS) in Physical Review D
- Vol. 61 (6)
Violation of the cosmic no hair conjecture in the Einstein-Maxwell-dilaton system
The cosmic no hair conjecture is tested in the spherically symmetric Einstein-Maxwell-dilaton~(EMD) system with a positive cosmological constant $\Lambda$. Firstly, we analytically show that once gravitational collapse occurs in the massless dilaton case, the system of field equations breaks down inevitably in outer communicating regions or at the boundary provided that a future null infinity ${\cal I}^+$ exists. Next we find numerically the static black hole solutions in the massive dilaton case and investigate their properties for comparison with the massless case. It is shown that their Abbott-Deser~(AD) mass are infinite, which implies that a spacetime with finite AD mass does not approach a black hole solution after the gravitational collapse. These results suggest that ${\cal I}^+$ cannot appear in the EMD system once gravitational collapse occurs and hence the cosmic no hair conjecture is violated in both the massless and the massive cases, in contrast to general relativity.Comment: 9 pages, REVtex, 5 figures, to appear in Phys. Rev.- Open Access
Violation of the cosmic no hair conjecture in Einstein-Maxwell-dilaton system
The cosmic no hair conjecture is tested in the spherically symmetric Einstein-Maxwell-dilaton~(EMD) system with a positive cosmological constant $\Lambda$. Firstly, we analytically show that once gravitational collapse occurs in the massless dilaton case, the system of field equations breaks down inevitably in outer communicating regions or at the boundary provided that a future null infinity ${\cal I}^+$ exists. Next we find numerically the static black hole solutions in the massive dilaton case and investigate their properties for comparison with the massless case. It is shown that their Abbott-Deser~(AD) mass are infinite, which implies that a spacetime with finite AD mass does not approach a black hole solution after the gravitational collapse. These results suggest that ${\cal I}^+$ cannot appear in the EMD system once gravitational collapse occurs and hence the cosmic no hair conjecture is violated in both the massless and the massive cases, in contrast to general relativity.Open AccessViolation of the cosmic no hair conjecture in Einstein-Maxwell-dilaton system
The cosmic no hair conjecture is tested in the spherically symmetric Einstein-Maxwell-dilaton~(EMD) system with a positive cosmological constant $\Lambda$. Firstly, we analytically show that once gravitational collapse occurs in the massless dilaton case, the system of field equations breaks down inevitably in outer communicating regions or at the boundary provided that a future null infinity ${\cal I}^+$ exists. Next we find numerically the static black hole solutions in the massive dilaton case and investigate their properties for comparison with the massless case. It is shown that their Abbott-Deser~(AD) mass are infinite, which implies that a spacetime with finite AD mass does not approach a black hole solution after the gravitational collapse. These results suggest that ${\cal I}^+$ cannot appear in the EMD system once gravitational collapse occurs and hence the cosmic no hair conjecture is violated in both the massless and the massive cases, in contrast to general relativity. - Open Access
String excitation inside generic black holes
We calculate how much a first-quantized string is excited after crossing the inner horizon of charged Vaidya solutions, as a simple model of generic black holes. To quantize a string suitably, we first show that the metric is approximated by a {\it plane-wave} metric near the inner horizon when the surface gravity of the horizon $\kappa_I$ is small enough. Next, it is analytically shown that the string crossing the inner horizon is excited infinitely in an asymptotically flat spacetime, while it is finite in an asymptotically de Sitter spacetime and the string can pass across the inner horizon when $\kappa_I<2\kappa:= 2 {min}\{\kappa_B,\kappa_C \}$, where $\kappa_B$~($\kappa_C$) is the surface gravity of the black hole~(cosmological) event horizon. This implies that the strong cosmic censorship holds in an asymptotically flat spacetime, while it is violated in an asymptotically de Sitter spacetime from the point of view of string theory.Open AccessString excitation inside generic black holes
We calculate how much a first-quantized string is excited after crossing the inner horizon of charged Vaidya solutions, as a simple model of generic black holes. To quantize a string suitably, we first show that the metric is approximated by a {\it plane-wave} metric near the inner horizon when the surface gravity of the horizon $\kappa_I$ is small enough. Next, it is analytically shown that the string crossing the inner horizon is excited infinitely in an asymptotically flat spacetime, while it is finite in an asymptotically de Sitter spacetime and the string can pass across the inner horizon when $\kappa_I<2\kappa:= 2 {min}\{\kappa_B,\kappa_C \}$, where $\kappa_B$~($\kappa_C$) is the surface gravity of the black hole~(cosmological) event horizon. This implies that the strong cosmic censorship holds in an asymptotically flat spacetime, while it is violated in an asymptotically de Sitter spacetime from the point of view of string theory. - 26 March 1999
- Published by American Physical Society (APS) in Physical Review D
- Vol. 59 (10) , 104002
Can the cosmological constant support a scalar field?
Static spherically symmetric gravitational equilibria of the real scalar field are discussed in the presence of the cosmological constant. We find nontrivial solutions if we take the self-interaction of the field into account while there is no such equilibria in the noninteracting case. The system has critical parameters beyond which new solutions disappear. They are determined by the ratio of the cosmological horizon to the “Compton radius” of the scalar field. We also discuss the stability of the solutions by means of a linear perturbation method and find that the number of unstable modes depends on the node number of the scalar field.
- 26 March 1999
- Published by American Physical Society (APS) in Physical Review D
- Vol. 59 (10) , 104002
Can the cosmological constant support a scalar field?
Static spherically symmetric gravitational equilibria of the real scalar field are discussed in the presence of the cosmological constant. We find nontrivial solutions if we take the self-interaction of the field into account while there is no such equilibria in the noninteracting case. The system has critical parameters beyond which new solutions disappear. They are determined by the ratio of the cosmological horizon to the “Compton radius” of the scalar field. We also discuss the stability of the solutions by means of a linear perturbation method and find that the number of unstable modes depends on the node number of the scalar field.
- 17 February 1999
- Published by American Physical Society (APS) in Physical Review D
- Vol. 59 (6) , 064027
Toward the no-scalar-hair conjecture in asymptotically de Sitter spacetime
We discuss the no-hair conjecture in the presence of a cosmological constant. For the first step the real scalar field is considered as the matter field and the spacetime is assumed to be static spherically symmetric. If the scalar field is massless or has a convex potential such as a mass term, it is proved that there is no regular black hole solution. For a general positive potential, we search for black hole solutions which support the scalar field with a double well potential, and find them by numerical calculations. The existence of such solutions depends on the values of the vacuum expectation value and the self-coupling constant of the scalar field. When we take the zero horizon radius limit, the solution becomes a boson star like solution which we found before. However new solutions are found to be unstable against the linear perturbation. As a result we can conclude that the no-scalar-hair conjecture holds in the case of scalar fields with a convex or double well potential.
- 17 February 1999
- Published by American Physical Society (APS) in Physical Review D
- Vol. 59 (6) , 064027
Toward the no-scalar-hair conjecture in asymptotically de Sitter spacetime
We discuss the no-hair conjecture in the presence of a cosmological constant. For the first step the real scalar field is considered as the matter field and the spacetime is assumed to be static spherically symmetric. If the scalar field is massless or has a convex potential such as a mass term, it is proved that there is no regular black hole solution. For a general positive potential, we search for black hole solutions which support the scalar field with a double well potential, and find them by numerical calculations. The existence of such solutions depends on the values of the vacuum expectation value and the self-coupling constant of the scalar field. When we take the zero horizon radius limit, the solution becomes a boson star like solution which we found before. However new solutions are found to be unstable against the linear perturbation. As a result we can conclude that the no-scalar-hair conjecture holds in the case of scalar fields with a convex or double well potential.
- 14 December 1998
- Published by American Physical Society (APS) in Physical Review Letters
- Vol. 81 (24) , 5270-5273
Do Naked Singularities Generically Occur in Generalized Theories of Gravity?
A new mechanism for causing naked singularities is found in an effective superstring theory. We investigate the gravitational collapse in a spherically symmetric Einstein-Maxwell-dilaton system in the presence of a pure cosmological-constant “potential,” where the system has no static black hole solution. We show that once gravitational collapse occurs in the system, naked singularities necessarily appear in the sense that the field equations break down in the domain of outer communications. This suggests that in generalized theories of gravity, the nonminimally coupled fields generically cause naked singularities in the process of gravitational collapse if the system has no static or stationary black-hole solution.
- 14 December 1998
- Published by American Physical Society (APS) in Physical Review Letters
- Vol. 81 (24) , 5270-5273
Do Naked Singularities Generically Occur in Generalized Theories of Gravity?
A new mechanism for causing naked singularities is found in an effective superstring theory. We investigate the gravitational collapse in a spherically symmetric Einstein-Maxwell-dilaton system in the presence of a pure cosmological-constant “potential,” where the system has no static black hole solution. We show that once gravitational collapse occurs in the system, naked singularities necessarily appear in the sense that the field equations break down in the domain of outer communications. This suggests that in generalized theories of gravity, the nonminimally coupled fields generically cause naked singularities in the process of gravitational collapse if the system has no static or stationary black-hole solution.