arXiv subjects

Kunihito Uzawa

Publications and source records attributed to Kunihito Uzawa.

42 records · Page 3Linked to original sources

arXiv2005

Effective Potential in PP-Wave Geometry

We calculate effective potentials in scalar field theories on the maximally supersymmetric pp-wave background in ten dimensions. For this purpose we have to work in the light-cone formulation, and hence we introduce two methods to compute them in the light-cone frame. One is to use the Yan's formula for evaluating one-loop correction terms. The other is to introduce a cut-off for the light-cone momentum. These methods are also confirmed in the case of Minkowski spacetime.

hep-th↗

arXiv2005

Discrete Light-Cone Quantization in PP-Wave Background

We discuss the discrete light-cone quantization (DLCQ) of a scalar field theory on the maximally supersymmetric pp-wave background in ten dimensions. It has been shown that the DLCQ can be carried out in the same way as in the two-dimensional Minkowski spacetime. Then, the vacuum energy is computed by evaluating the vacuum expectation value of the light-cone Hamiltonian. The results are consistent with the effective potential obtained in our previous work [hep-th/0402028].

hep-th↗

arXiv2003

Dilaton Stabilization in (A)dS Spacetime with Compactified Dimensions

We investigate dilaton stabilization in a higher-dimensional theory. The background geometry is based on an eleven-dimensional Kaluza-Klein/supergravity model, which is assumed to be a product of four-dimensional de Sitter (dS_4) spacetime and a seven sphere. The dilaton potential has a local minimum resulting from contributions of the cosmological constant, the curvature of the internal spacetime and quantum effects of the background scalar, vector, spinor, and tensor fields. The dilaton settles down to the local minimum, and the scale of the extra dimensions eventually become time independent. Our four-dimensional universe evolves from dS_4 into AdS_4 after stabilization of the extra dimension.

hep-th↗

arXiv2003

Dilaton Dynamics in (A)dS_5 x S^5

We investigate a stabilization of extra dimensions in a ten-dimensional Kaluza-Klein theory and IIB supergravity. We assume (A)dS_5 x S^5 compactifcation, and calculate quantum effects to find an effective potential for the radius of internal space. The effective potential has a minimum, and if the universe is created on the top of the potential hill, the universe evolves from dS_5 to AdS_5 after exponential expansion. The internal space S^5 stays to be small and its radius becomes constant. Our model in IIB supergravity contains the 4-form gauge field with classically vacuum expectation value, which is role of ten-dimensional cosmological constant. If the universe evolves into AdS, the five-dimensional Randall & Sundrum setup with stabilized dilaton is obtained from the type IIB supergravity model.

hep-th↗

arXiv2000

Excitation of Kaluza-Klein modes of U(1) field by parametric resonance

In this paper, based on the theory of parametric resonance, we propose a cosmological criterion on ways of compactification: we rule out such a model of compactification that there exists a Kaluza-Klein mode satisfying $2m_{KK}=ω_b$, where $m_{KK}$ is mass of the Kaluza-Klein mode and $ω_b$ is the frequency of oscillation of the radius of the compact manifold on which extra dimensions are compactified. This is a restatement of the criterion proposed previously [S. Mukohyama, Phys. Rev. {\bf D57}, 6191 (1998)]. As an example, we consider a model of compactification by a sphere and investigate Kaluza-Klein modes of U(1) field. In this case the parametric resonance is so mild that the sphere model is not ruled out.

gr-qc↗

arXiv2000

Excitation of Kaluza-Klein gravitational mode

We investigate excitation of Kaluza-Klein modes due to the parametric resonance caused by oscillation of radius of compactification. We consider a gravitational perturbation around a D-dimensional spacetime, which we compactify on a (D-4)-sphere to obtain a 4-dimensional theory. The perturbation includes the so-called Kaluza-Klein modes, which are massive in 4-dimension, as well as zero modes, which is massless in 4-dimension. These modes appear as scalar, vector and second-rank symmetric tensor fields in the 4-dimensional theory. Since Kaluza-Klein modes are troublesome in cosmology, quanta of these Kaluza-Klein modes should not be excited abundantly. However, if radius of compactification oscillates, then masses of Kaluza-Klein modes also oscillate and, thus, parametric resonance of Kaluza-Klein modes may occur to excite their quanta. In this paper we consider part of Kaluza-Klein modes which correspond to massive scalar fields in 4-dimension and investigate whether quanta of these modes are excited or not in the so called narrow resonance regime of the parametric resonance. We conclude that at least in the narrow resonance regime quanta of these modes are not excited so catastrophically.

gr-qc↗