STShinji Tsujikawa
Shinji Tsujikawa
*This is an algorithmically generated author record based on publicly available information.
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Shinji Tsujikawa has a total of 6 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
6 shared publications - Kei-Ichi Maeda
Department of Physics Waseda University Okubo 3-4-1 169-8555 Shinjuku Tokyo Japan
5 shared publications - Hiroki Yajima
Department of Physics Waseda University Shinjuku-ku 169-8555 Tokyo Japan
3 shared publications - Bruce A. Bassett
Institute for Machine Intelligence and Neural Discovery (MIND), University of the Witwatersrand
1 shared publication - Fermin Viniegra
Oxford University OX1 3NP Oxford England
1 shared publication - Takashi Torii
Research Center for the Early Universe, University of Tokyo, Hongo, Bunkyo, Tokyo 113-0033, Japan
1 shared publication
Latest Publications
- Open Access
Massive fermion production in nonsingular superstring cosmology
We study massive spin-1/2 fermion production in nonsingular superstring cosmology, taking into account one-loop quantum corrections to a superstring effective action with dilaton and modulus fields. While no creation occurs in the massless limit, massive fermions can be produced by the existence of a time-dependent frequency. Due to the increase of the Hubble expansion rate during the modulus-driven phase, the occupation of number of fermions continues to grow until the point of the graceful exit, after which fermion creation ceases with the decrease of the Hubble rate.
Open AccessMassive fermion production in nonsingular superstring cosmology
We study massive spin-1/2 fermion production in nonsingular superstring cosmology, taking into account one-loop quantum corrections to a superstring effective action with dilaton and modulus fields. While no creation occurs in the massless limit, massive fermions can be produced by the existence of a time-dependent frequency. Due to the increase of the Hubble expansion rate during the modulus-driven phase, the occupation of number of fermions continues to grow until the point of the graceful exit, after which fermion creation ceases with the decrease of the Hubble rate.
- 27 November 2000
- Published by American Physical Society (APS) in Physical Review D
- Vol. 62 (12) , 123512
New constraints on multifield inflation with nonminimal coupling
We study the dynamics and perturbations during inflation and reheating in a multifield model where a second scalar field is nonminimally coupled to the scalar curvature When is positive, the usual inflationary prediction for large-scale anisotropies is hardly altered while the fluctuation in sub-Hubble modes can be amplified during preheating for large For negative values of however, long-wave modes of the fluctuation exhibit exponential increase during inflation, leading to the strong enhancement of super-Hubble metric perturbations even when is less than unity. This is because the effective mass becomes negative during inflation. We constrain the strength of and the initial by the amplitude of produced density perturbations. One way to avoid nonadiabatic growth of super-Hubble curvature perturbations is to stabilize the mass through a coupling to the inflaton. Preheating may thus be necessary in these models to protect the stability of the inflationary phase.- 27 November 2000
- Published by American Physical Society (APS) in Physical Review D
- Vol. 62 (12) , 123512
New constraints on multifield inflation with nonminimal coupling
We study the dynamics and perturbations during inflation and reheating in a multifield model where a second scalar field is nonminimally coupled to the scalar curvature When is positive, the usual inflationary prediction for large-scale anisotropies is hardly altered while the fluctuation in sub-Hubble modes can be amplified during preheating for large For negative values of however, long-wave modes of the fluctuation exhibit exponential increase during inflation, leading to the strong enhancement of super-Hubble metric perturbations even when is less than unity. This is because the effective mass becomes negative during inflation. We constrain the strength of and the initial by the amplitude of produced density perturbations. One way to avoid nonadiabatic growth of super-Hubble curvature perturbations is to stabilize the mass through a coupling to the inflaton. Preheating may thus be necessary in these models to protect the stability of the inflationary phase.- Open Access
New constraints on multi-field inflation with nonminimal coupling
We study the dynamics and perturbations during inflation and reheating in a multi-field model where a second scalar field $\chi$ is nonminimally coupled to the scalar curvature $(\frac12 \xi R\chi^2$). When $\xi$ is positive, the usual inflationary prediction for large-scale anisotropies is hardly altered while the $\chi$ fluctuation in sub-Hubble modes can be amplified during preheating for large $\xi$. For negative values of $\xi$, however, long-wave modes of the $\chi$ fluctuation exhibit exponential increase during inflation, leading to the strong enhancement of super-Hubble metric perturbations even when $|\xi|$ is less than unity. This is because the effective $\chi$ mass becomes negative during inflation. We constrain the strength of $\xi$ and the initial $\chi$ by the amplitude of produced density perturbations. One way to avoid nonadiabatic growth of super-Hubble curvature perturbations is to stabilize the $\chi$ mass through a coupling to the inflaton. Preheating may thus be necessary in these models to protect the stability of the inflationary phase.Open AccessNew constraints on multi-field inflation with nonminimal coupling
We study the dynamics and perturbations during inflation and reheating in a multi-field model where a second scalar field $\chi$ is nonminimally coupled to the scalar curvature $(\frac12 \xi R\chi^2$). When $\xi$ is positive, the usual inflationary prediction for large-scale anisotropies is hardly altered while the $\chi$ fluctuation in sub-Hubble modes can be amplified during preheating for large $\xi$. For negative values of $\xi$, however, long-wave modes of the $\chi$ fluctuation exhibit exponential increase during inflation, leading to the strong enhancement of super-Hubble metric perturbations even when $|\xi|$ is less than unity. This is because the effective $\chi$ mass becomes negative during inflation. We constrain the strength of $\xi$ and the initial $\chi$ by the amplitude of produced density perturbations. One way to avoid nonadiabatic growth of super-Hubble curvature perturbations is to stabilize the $\chi$ mass through a coupling to the inflaton. Preheating may thus be necessary in these models to protect the stability of the inflationary phase. - 24 July 2000
- Published by American Physical Society (APS) in Physical Review D
- Vol. 62 (4) , 043512
Power-law inflation with a nonminimally coupled scalar field
We consider the dynamics of power-law inflation with a nonminimally coupled scalar field It is well known that multiple scalar fields with exponential potentials lead to an inflationary solution even if each scalar field is not capable to sustain inflation. In this paper, we show that inflation can be assisted even in the one-field case by the effect of nonminimal coupling. When is positive, since an effective potential which arises by a conformal transformation becomes flatter compared with the case of for we have an inflationary solution even when the Universe evolves as noninflationary in the minimally coupled case. For negative the assisted inflation can take place when evolves in the region of- 24 July 2000
- Published by American Physical Society (APS) in Physical Review D
- Vol. 62 (4) , 043512
Power-law inflation with a nonminimally coupled scalar field
We consider the dynamics of power-law inflation with a nonminimally coupled scalar field It is well known that multiple scalar fields with exponential potentials lead to an inflationary solution even if each scalar field is not capable to sustain inflation. In this paper, we show that inflation can be assisted even in the one-field case by the effect of nonminimal coupling. When is positive, since an effective potential which arises by a conformal transformation becomes flatter compared with the case of for we have an inflationary solution even when the Universe evolves as noninflationary in the minimally coupled case. For negative the assisted inflation can take place when evolves in the region of- 20 July 2000
- Published by American Physical Society (APS) in Physical Review D
- Vol. 62 (4) , 043505
Spinodal effect in the natural inflation model
Recently, Cormier and Holman pointed out that fluctuations of an inflaton field are significantly enhanced in the model of spinodal inflation with a potential for which the second derivative changes sign. As an application of this model, we investigate particle production in the natural inflation model with a potential by making use of the Hartree approximation. For typical mass scales GeV and GeV, we find that the growth of fluctuations relevantly occurs for the initial value of inflaton Especially for maximum fluctuations are so large that secondary inflation takes place by produced fluctuations. In this case, the achieved number of e-foldings becomes much larger than in the case where an effect of spinodal instability is neglected.- 20 July 2000
- Published by American Physical Society (APS) in Physical Review D
- Vol. 62 (4) , 043505
Spinodal effect in the natural inflation model
Recently, Cormier and Holman pointed out that fluctuations of an inflaton field are significantly enhanced in the model of spinodal inflation with a potential for which the second derivative changes sign. As an application of this model, we investigate particle production in the natural inflation model with a potential by making use of the Hartree approximation. For typical mass scales GeV and GeV, we find that the growth of fluctuations relevantly occurs for the initial value of inflaton Especially for maximum fluctuations are so large that secondary inflation takes place by produced fluctuations. In this case, the achieved number of e-foldings becomes much larger than in the case where an effect of spinodal instability is neglected.- Open Access
Multi-field fermionic preheating
Fermion creation during preheating in the presence of multiple scalar fields exhibits a range of interesting behaviour relevant to estimating post-inflation gravitino abundances. We present non-perturbative analysis of this phenomenon over a 6-dimensional parameter space in an expanding background paying particular attention to the interplay between instant and direct fermion preheating. In the broad resonance regime we find that instant fermion production is sensitive to suppression of the long wavelength scalar field modes during inflation. Further, the standard scenario of resonant fermionic preheating through inflaton decay can be significantly modified by instant preheating, and may even lead to a decrease in the number of fermions produced. We explicitly include the effects of metric perturbations and demonstrate that they are important at small coupling but not at strong coupling, due to the rapid saturation of the Pauli bound.
Open AccessMulti-field fermionic preheating
Fermion creation during preheating in the presence of multiple scalar fields exhibits a range of interesting behaviour relevant to estimating post-inflation gravitino abundances. We present non-perturbative analysis of this phenomenon over a 6-dimensional parameter space in an expanding background paying particular attention to the interplay between instant and direct fermion preheating. In the broad resonance regime we find that instant fermion production is sensitive to suppression of the long wavelength scalar field modes during inflation. Further, the standard scenario of resonant fermionic preheating through inflaton decay can be significantly modified by instant preheating, and may even lead to a decrease in the number of fermions produced. We explicitly include the effects of metric perturbations and demonstrate that they are important at small coupling but not at strong coupling, due to the rapid saturation of the Pauli bound.
- Open Access
Preheating with extra dimensions
We investigate preheating in a higher-dimensional generalized Kaluza-Klein theory with a quadratic inflaton potential $V(\phi)=\frac12 m^2\phi^2$ including metric perturbations explicitly. The system we consider is the multi-field model where there exists a dilaton field $\sigma$ which corresponds to the scale of compactifications and another scalar field $\chi$ coupled to inflaton with the interaction $\frac12 g^2\phi^2\chi^2+\tilde{g}^2\phi^3\chi$. In the case of $\tilde{g}=0$, we find that the perturbation of dilaton does not undergo parametric amplification while the $\chi$ field fluctuation can be enhanced in the usual manner by parametric resonance. In the presence of the $\tilde{g}^2\phi^3\chi$ coupling, the dilaton fluctuation in sub-Hubble scales is modestly amplified by the growth of metric perturbations for the large coupling $\tilde{g}$. In super-Hubble scales, the enhancement of the dilaton fluctuation as well as metric perturbations is weak, taking into account the backreaction effect of created $\chi$ particles. We argue that not only is it possible to predict the ordinary inflationary spectrum in large scales but extra dimensions can be held static during preheating in our scenario.Open AccessPreheating with extra dimensions
We investigate preheating in a higher-dimensional generalized Kaluza-Klein theory with a quadratic inflaton potential $V(\phi)=\frac12 m^2\phi^2$ including metric perturbations explicitly. The system we consider is the multi-field model where there exists a dilaton field $\sigma$ which corresponds to the scale of compactifications and another scalar field $\chi$ coupled to inflaton with the interaction $\frac12 g^2\phi^2\chi^2+\tilde{g}^2\phi^3\chi$. In the case of $\tilde{g}=0$, we find that the perturbation of dilaton does not undergo parametric amplification while the $\chi$ field fluctuation can be enhanced in the usual manner by parametric resonance. In the presence of the $\tilde{g}^2\phi^3\chi$ coupling, the dilaton fluctuation in sub-Hubble scales is modestly amplified by the growth of metric perturbations for the large coupling $\tilde{g}$. In super-Hubble scales, the enhancement of the dilaton fluctuation as well as metric perturbations is weak, taking into account the backreaction effect of created $\chi$ particles. We argue that not only is it possible to predict the ordinary inflationary spectrum in large scales but extra dimensions can be held static during preheating in our scenario. - Open Access
Power-law inflation with a nonminimally coupled scalar field
We consider the dynamics of power-law inflation with a nonminimally coupled scalar field $\phi$. It is well known that multiple scalar fields with exponential potentials $V(\phi)=V_0 {\rm exp}(-\sqrt{16\pi/p m_{\rm pl}^2} \phi)$ lead to an inflationary solution even if the each scalar field is not capable to sustain inflation. In this paper, we show that inflation can be assisted even in the one-field case by the effect of nonminimal coupling. When $\xi$ is positive, since an effective potential which arises by a conformal transformation becomes flatter compared with the case of $\xi=0$ for $\phi>0$, we have an inflationary solution even when the universe evolves as non-inflationary in the minimally coupled case. For the negative $\xi$, the assisted inflation can take place when $\phi$ evolves in the region of $\phi<0$ \.Open AccessPower-law inflation with a nonminimally coupled scalar field
We consider the dynamics of power-law inflation with a nonminimally coupled scalar field $\phi$. It is well known that multiple scalar fields with exponential potentials $V(\phi)=V_0 {\rm exp}(-\sqrt{16\pi/p m_{\rm pl}^2} \phi)$ lead to an inflationary solution even if the each scalar field is not capable to sustain inflation. In this paper, we show that inflation can be assisted even in the one-field case by the effect of nonminimal coupling. When $\xi$ is positive, since an effective potential which arises by a conformal transformation becomes flatter compared with the case of $\xi=0$ for $\phi>0$, we have an inflationary solution even when the universe evolves as non-inflationary in the minimally coupled case. For the negative $\xi$, the assisted inflation can take place when $\phi$ evolves in the region of $\phi<0$ \. - Open Access
Particle production in the oscillating inflation model
We investigate the particle production of a scalar field $\chi$ coupled to an inflaton field $\phi$ ($g^2\phi^2\chi^2/2$) in the {\it oscillating inflation} model, which was recently proposed by Damour and Mukhanov. Although the fluctuation of the $\phi$ field can be effectively enhanced during a stage of the oscillating inflation, the maximum fluctuation is suppressed as the critical value $\phi_c$ which indicates the scale of the core part of the inflaton potential decreases, in taking into account the back reaction effect of created particles. As for the $\chi$ particle production, we find that larger values of the coupling constant $g$ are required to lead to an efficient parametric resonance with the decrease of $\phi_c$, because an effective mass of inflaton around the minimum of its potential becomes larger. However, it is possible to generate the superheavy $\chi$ particle whose mass is greater than $10^{14}$ GeV, which would result in an important consequence for the GUT baryogenesis.Open AccessParticle production in the oscillating inflation model
We investigate the particle production of a scalar field $\chi$ coupled to an inflaton field $\phi$ ($g^2\phi^2\chi^2/2$) in the {\it oscillating inflation} model, which was recently proposed by Damour and Mukhanov. Although the fluctuation of the $\phi$ field can be effectively enhanced during a stage of the oscillating inflation, the maximum fluctuation is suppressed as the critical value $\phi_c$ which indicates the scale of the core part of the inflaton potential decreases, in taking into account the back reaction effect of created particles. As for the $\chi$ particle production, we find that larger values of the coupling constant $g$ are required to lead to an efficient parametric resonance with the decrease of $\phi_c$, because an effective mass of inflaton around the minimum of its potential becomes larger. However, it is possible to generate the superheavy $\chi$ particle whose mass is greater than $10^{14}$ GeV, which would result in an important consequence for the GUT baryogenesis. - 24 March 2000
- Published by American Physical Society (APS) in Physical Review D
- Vol. 61 (8) , 083516
Particle production in the oscillating inflation model
We investigate the particle production of a scalar field coupled to an inflaton field in the oscillating inflation model, which was recently proposed by Damour and Mukhanov. Although the fluctuation of the field can be effectively enhanced during a stage of the oscillating inflation, the maximum fluctuation is suppressed as the critical value which indicates the scale of the core part of the inflaton potential decreases, in taking into account the back reaction effect of created particles. As for the particle production, we find that larger values of the coupling constant g are required to lead to an efficient parametric resonance with the decrease of because an effective mass of inflaton around the minimum of its potential becomes larger. However, it is possible to generate the superheavy particle whose mass is greater than GeV, which would result in an important consequence for the GUT baryogenesis.- 24 March 2000
- Published by American Physical Society (APS) in Physical Review D
- Vol. 61 (8) , 083516
Particle production in the oscillating inflation model
We investigate the particle production of a scalar field coupled to an inflaton field in the oscillating inflation model, which was recently proposed by Damour and Mukhanov. Although the fluctuation of the field can be effectively enhanced during a stage of the oscillating inflation, the maximum fluctuation is suppressed as the critical value which indicates the scale of the core part of the inflaton potential decreases, in taking into account the back reaction effect of created particles. As for the particle production, we find that larger values of the coupling constant g are required to lead to an efficient parametric resonance with the decrease of because an effective mass of inflaton around the minimum of its potential becomes larger. However, it is possible to generate the superheavy particle whose mass is greater than GeV, which would result in an important consequence for the GUT baryogenesis.