| 1. |
Kanno Sugumi, Soda Jiro, Infinite violation of Bell inequalities in inflation, Physical Review D, 10.1103/PhysRevD.96.083501, 96, 8, 83501-83501, 2017.05, We study the violation of Bell-Mermin-Klyshko (BMK) inequalities in initial quantum states of scalar fields in inflation. We show that the Bell inequality is maximally violated by the Bunch-Davies vacuum which is a two-mode squeezed state of a scalar field. However, we find that the violation of the BMK inequalities does not increase with the number of modes to measure. We then consider a non-Bunch-Davies vacuum expressed by a four-mode squeezed state of two scalar fields. Remarkably, we find that the violation of the BMK inequalities increases exponentially with the number of modes to measure. This shows that the BMK inequalities are useful to classify the initial quantum state of the Universe.. |
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KANNO Sugumi, SASAKI Misao, SODA Jiro, Institute of Cosmology Department of Physics and Astronomy Tufts University, Yukawa Institute for Theoretical Physics Kyoto University, Department of Physics Kyoto University, Destabilizing Tachyonic Vacua at or above the BF Bound(Astrophysics and Cosmology), Progress of theoretical physics, 10.1143/PTP.128.213, 128, 1, 213-226, 2012.03, It is well known that tachyonic vacua in an asymptotically Anti-de Sitter (AdS) spacetime are classically stable if the mass squared is at or above the Breitenlohner and Freedman (BF) bound. We study the quantum stability of these tachyonic vacua in terms of instantons. We find a, series of exact instanton solutions destabilizing tachyonic state at or above the BF bound in asymptotically AdS space. We also give an analytic formula for the decay rate and show that it is finite. Comparing our result with the well-known algebraic condition for the stability, we discuss stability conditions of tachyonic vacua at or above the BF bound.. |
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Watanabe Masa-aki, Kanno Sugumi, Soda Jiro, Department of Physics Kyoto University, Centre for Particle Theory Department of Mathematical Sciences Durham University Science Laboratories, Department of Physics Kyoto University, The Nature of Primordial Fluctuations from Anisotropic Inflation(Astrophysics and Cosmology), Progress of theoretical physics, 10.1143/PTP.123.1041, 123, 6, 1041-1068, 2010.02, We study the statistical nature of primordial fluctuations from an anisotropic inflation which is realized by a vector field coupled to an inflaton. We find a suitable gauge, which we call the canonical gauge, for anisotropic inflation by generalizing the flat slicing gauge in conventional isotropic inflation. Using the canonical gauge, we reveal the structure of the couplings between curvature perturbations, vector waves, and gravitational waves. We identify two sources of anisotropy, i.e. the anisotropy due to the anisotropic expansion of the universe and that due to the anisotropic couplings among variables. It turns out that the latter effect is dominant. Since the coupling between the curvature perturbations and vector waves is the strongest one, the statistical anisotropy in the curvature perturbations is larger than that in gravitational waves. We find the cross correlation between the curvature perturbations and gravitational waves which never occurs in conventional inflation. We also find the linear polarization of gravitational waves. Finally, we discuss cosmological implication of our results.. |
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Kanno Sugumi, Langlois David, Sasaki Misao, Jiro SODA, Department of Physics McGill University, APC Universite, Yukawa Institute for Theoretical Physics Kyoto University, Department of Physics Kyoto University, Kaluza-Klein Braneworld Cosmology with Static Internal Dimensions(Astrophysics and Relativity), Progress of theoretical physics, 10.1143/PTP.118.701, 118, 4, 701-713, 2007.07, We investigate the Kaluza-Klein braneworld cosmology from the point of view of observers on the brane. We first generalize the Shiromizu-Maeda-Sasaki (SMS) equations to higher dimensions. As an application, we study a (4+n)-dimensional brane with n dimensions compactified on the brane, in a (5+n)-dimensional bulk. By assuming that the size of the internal space is static, that the bulk energy-momentum tensor can be ignored, we determine the effect of the bulk geometry on the Kaluza-Klein braneworld. Then we derive the effective Friedmann equation on the brane. It turns out that the Friedmann equation explicitly depends on the equation of state, in contrast to the braneworld in a 5-dimensional bulk spacetime. In particular, in a radiation-dominated era, the effective Newton constant depends logarithmically on the scale factor. If we include a pressureless matter on the brane, this dependence disappears after the radiation-matter equality. This may be interpreted as stabilization of the Newton constant by the matter on the brane. Our findings imply that the Kaluza-Klein braneworld cosmology is quite different from the conventional Kaluza-Klein cosmology even at low energy.. |
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Tamaki T, Kanno S, Soda J, Radionic nonuniform black strings, PHYSICAL REVIEW D, 10.1103/PhysRevD.69.024010, 69, 2, 2003.07. |
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Kanno Sugumi, Sasaki Misao, Soda Jiro, Graduate School of Human and Environmental Studies Kyoto University, Department of Earth and Space Science Graduate School of Science Osaka University, Department of Fundamental Sciences FIHS Kyoto University, Born-Again Braneworld, Progress of theoretical physics, 10.1143/PTP.109.357, 109, 3, 357-369, 2002.10, We propose a cosmological braneworld scenario in which two branes collide and emerge as reborn branes whose tensions have signs opposite to the original tensions of the respective branes. In this scenario, gravity on each of the branes is described by a scalar-tensor-type theory in which the radion plays the role of the gravitational scalar, and the branes are assumed to be inflating. However, the whole dynamics are different from those of the usual inflation, due to the non-trivial dynamics of the radion field. Transforming the conformal frame to the Einstein frame, this born-again scenario resembles the pre-big-bang scenario. Thus, our scenario has features of both inflation and pre-big-bang scenarios. In particular, gravitational waves produced from vacuum fluctuations may have a very blue spectrum, while the inflaton field gives rise to a standard scale-invariant spectrum.. |
