arXiv subjects

Ken-ji Hamada

Publications and source records attributed to Ken-ji Hamada.

At least 37 records · Page 2Linked to original sources

arXiv2007

Baryogenesis by Quantum Gravity

A novel mechanism of baryogenesis is proposed on the basis of the phase transition from the conformal invariant space-time to the Einstein space-time in quantum gravity. Strong-coupling gravitational excitations with dynamical mass about 10^17 GeV are generated at the transition. They eventually decay into ordinary matters. As a realization of unparticle physics we show that the low energy effective interactions between the gravitational potential describing the excitation and the non-conserving matter currents by the axial anomalies can explain matter asymmetry out of thermal equilibrium.

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arXiv2007

Analyzing WMAP Observation by Quantum Gravity

The angular power spectra of cosmic microwave background are analyzed under the light of the evolutional scenario of the universe based on the renormalizable quantum theory of gravity in four dimensions. The equation of evolution is solved numerically fixing the power law spectrum predicted by the conformal gravity for the initial condition. The equation requires to introduce a dynamical energy scale about 10^{17}GeV, where the inflationary space-time evolution makes a transition to the big-bang of the conventional Friedmann universe. The quality of fit to the three-year data of WMAP implies the possibility to understand the observation by quantum gravity.

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arXiv2006

Space-time Evolution and CMB Anisotropies from Quantum Gravity

We propose an evolutional scenario of the universe which starts from quantum states with conformal invariance, passing through the inflationary era, and then makes transition to the conventional Einstein space-time. The space-time dynamics is derived from the renormalizable higher-derivative quantum gravity developed on the basis of a renormalizable conformal gravity in four dimensions. Based on the linear perturbation theory in the inflationary background, we simulate evolutions of gravitational scalar, vector and tensor perturbations, and evaluate the spectra at the transition point located at the beginning of the big bang. The obtained spectra cover the range of the primordial spectra for explaining the tiny anisotropy in the homogeneous CMB.

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arXiv2004

Quantum Gravity Scenario of Inflation based on the CMB Anisotropies

Inflationary scenario based on a renormalizable model of conformal gravity is proposed and primordial spectrum is derived. The sharp fall off of the angular power spectra at low multipoles in the COBE and WMAP observations are explained by a dynamical scale of quantum gravity. At this scale, the universe would make a sharp transition from the quantum spacetime with conformal invariance to the classical spacetime.

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arXiv2004

Building Blocks of Physical States in a Non-Critical 3-Brane on R*S^3

The physical states in a world-volume model of a non-critical 3-brane are systematically constructed using techniques of four-dimensional conformal field theories on R*S^3 developed recently. Invariant combinations of creation modes under a special conformal transformation provide building blocks of physical states. Any state can be created by acting with such building blocks on a conformally invariant vacuum in an invariant way under the other conformal charges: the Hamiltonian and rotation generators on S^3. We explicitly construct building blocks for scalar, vector and gravitational fields, and classify them as finite types.

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arXiv2004

Conformal Algebra and Physical States in Non-critical 3-brane on R*S^3

A world-volume model of non-critical 3-brane is quantized in a strong coupling phase where fluctuations of the conformal mode become dominant. This phase, called the conformal-mode dominant phase, is realized at the very high energy far beyond the Planck mass scale. We separately treat the conformal mode and the traceless mode and quantize the conformal mode "non-perturbatively", while the traceless mode is treated in the perturbation which is renormalizable and asymptotically free. In the conformal-mode dominant phase, the coupling of the traceless mode vanishes and the world-volume dynamics is described as a four dimensional conformal field theory (CFT_4). We canonically quantize this model on R*S^3 where the dynamical metric fields are expanded using spherical tensor harmonics on S^3. Conformal charges and conformal algebra are constructed. They give strong constraints on physical states. We find that all negative-metric modes are related to positive-metric modes through the charges so that they are not independent physical modes themselves. An infinite number of physical states satisfying the conformal invariance conditions are constructed. In appendix, we construct spherical vector, tensor harmonics on S^3 in the useable form using Wigner D-functions and Clebsch-Gordan coefficients and calculate integrals of their products.

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arXiv2004

CMB Anisotropies Reveal Quantized Gravity

A novel primordial spectrum with a dynamical scale of quantum gravity origin is proposed to explain the sharp fall off of the angular power spectra at low multipoles in the COBE and WMAP observations. The spectrum is derived from quantum fluctuations of the scalar curvature in a renormalizable model of induced gravity. This model describes the very early universe by the conformal field fluctuating about an inflationary background with the expansion time constant of order of the Planck mass.

astro-ph↗

arXiv2002

Resummation and Higher Order Renormalization in 4D Quantum Gravity

Higher order renormalization in 4D quantum gravity is carried out using dimensional regularization with great care concerning the conformal-mode dependence. In this regularization, resummation can be automatically carried out without making an assumption like that of David, Distler and Kawai. In this paper we consider a model of 4D quantum gravity coupled to QED. Resummation inevitably implies a four-derivative quantum gravity. The renormalizability is directly checked up to $O(e_r^6)$ and $O(t_r^2)$, where $e_r$ and $t_r$ are the running coupling constants of QED and the traceless gravitational mode. There is no other running coupling constant in our model. The conformal mode is treated exactly, which means it is unrenormalized. It is found that Hathrell's results are included in our results. As a by-product, it is found that a higher-order gravitational correction to the beta function of QED is negative. An advantage of our model is that in the very high-energy regime, it closely resembles exactly solvable 2D quantum gravity. Thus, we can study physical states of 4D quantum gravity in this regime in parallel to those of 2D quantum gravity, which can be described with diffeomorphism invariant composite fields.

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arXiv2001

Note on Quantum Diffeomorphism Invariance, Physical States and Unitarity

Recently, using a local action satisfying the Wess-Zumino condition as a kinetic term of the conformal mode, we formulated a four-dimensional quantum geometry (4DQG). The conformal mode can be treated exactly, and it was shown that the part of the effective action related to this mode is given by the scale-invariant non-local Riegert action. As for the traceless mode, we introduce dimensionless coupling, which is a unique gravitational coupling of this theory satisfying the conditions of renormalizability and asymptotic freedom. Although this theory is asymptotically free, the physical states are non-trivial, which should be described as composite fields, like the spectrum of 2DQG. The possibility that the physical state conditions representing background-metric independence conceal ghosts is pointed out. The usual graviton state would be realized when the physical state condition breaks down dynamically.

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arXiv2001

Integrability and Scheme-Independence of Even Dimensional Quantum Geometry Effective Action

We investigate how the integrability conditions for conformal anomalies constrain the form of the effective action in even-dimensional quantum geometry. We show that the effective action of four-dimensional quantum geometry (4DQG) satisfying integrability has a manifestly diffeomorphism invariant and regularization scheme-independent form. We then generalize the arguments to six dimensions and propose a model of 6DQG. A hypothesized form of the 6DQG effective action is given.

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arXiv2001

A Dynamical Solution of Stable Starobinsky-Type Inflation Model in Quantum Geometry

Quantum geometry gives a regularization scheme-independent effective action, whoes equation of motion for the conformal mode has a stable de Sitter solution at the high-energy region where the coupling of the self-interactions of the traceless mode can be neglected because of the asymptotic freedom. However, the dynamics of the traceless mode suggests that inflation ends at the low-energy region.

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arXiv2000

A Candidate for Renormalizable and Diffeomorphism Invariant 4D Quantum Theory of Gravity

We present evidence that there is a 4D model that satisfies the conditions of renormalizability and diffeomorphism invariance simultaneously at the 2-loop level. The traceless mode is treated perturbatively, while the conformal mode can be managed exactly. The two conditions constrain the theory strongly and determine the measure of the gravitational field uniquely. Quantum corrections of the cosmological constant are computed in part to 3-loop diagrams. The method to remove the negative-metric states is also discussed from the viewpoint of diffeomorphism invariance in analogy to the $R_ξ$ gauge in spontaneously broken gauge theory. The model may be a candidate for a continuum version of 4D simplicial quantum geometry realized in recent numerical simulations.

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arXiv2000

On The BRST Formulation of Diffeomorphism Invariant 4D Quantum Gravity

In this note we give some remarks on the BRST formulation of a renormalizable and diffemorphism invariant 4D quantum gravity recently proposed by the author, which satisfies the integrability condition by Riegard, Fradkin and Tseytlin at the 2-loop level. Diffeomorphism invariance requires an addition of the Wess-Zumino action, from which the Weyl action can be induced by expanding around a vacuum expectation value of the conformal mode. This fact suggests the theory has in itself a mechanism to remove extra negative-metric states dynamically.

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arXiv1999

Background-metric Independent Formulation of 4D Quantum Gravity

Using the background-metric independence for the traceless mode as well as the conformal mode, 4D quantum gravity is described as a quantum field theory defined on a non-dynamical background-metric. The measure then induces an action with 4 derivatives. So we think that 4-th order gravity is essential and the Einstein-Hilbert term should be treated like a mass term. We introduce the dimensionless self-coupling constant t for the traceless mode. In this paper we study a model where the measure can be evaluated in the limit $t \to 0$ exactly, using the background-metric independence for the conformal mode. The t-dependence of the measure is determined perturbatively using the background-metric independence for the traceless mode.

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arXiv1997

Supersymmetric Wilson Loops in IIB Matrix Model

We show that the supersymmetric Wilson loops in IIB matrix model give a transition operator from reduced supersymmetric Yang-Mills theory to supersymmetric space-time theory. In comparison with Green-Schwarz superstring we identify the supersymmetric Wilson loops with the asymptotic states of IIB superstring. It is pointed out that the supersymmetry transformation law of the Wilson loops is the inverse of that for the vertex operators of massless modes in the U(N) open superstring with Dirichlet boundary condition.

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arXiv1996

W_infty Structures of 2D String Theory

The Ward identities of the $W_{\infty}$ symmetry in 2D string theory in the tachyon background are studied in the continuum approach. Comparing the solutions with the matrix model results, it is verified that 2D string amplitudes are different from the matrix model amplitudes only by the external leg factors even in higher genus. This talk is based on the recent work [1] and also [2] for the $c_M <1$ model. (Talk given at the workshop on ``Frontiers in Quantum Field Theory'', Osaka, Japan, December 1995.)

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arXiv1995

Ward Identities of W_{\infty} Symmetry and Higher Genus Amplitudes in 2D String Theory

The Ward identities of the $W_{\infty}$ symmetry in two dimensional string theory in the tachyon background are studied in the continuum approach. We consider amplitudes different from 2D string ones by the external leg factor and derive the recursion relations among them. The recursion relations have non-linear terms which give relations among the amplitudes defined on different genus. The solutions agree with the matrix model results even in higher genus. We also discuss differences of roles of the external leg factor between the $c_M = 1$ model and the $c_M <1$ model.

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arXiv1994

Non-linear Structures in Non-critical NSR String

We investigate the Ward identities of the $\W_{\infty}$ symmetry in the super-Liouville theory coupled to the super-conformal matter of central charge ${\hat c}_M = 1-2(p-q)^2 /pq$. The theory is classified into two chiralities. For the positive chirality, all gravitationally dressed scaling operators are generated from the $q-1$ gravitational primaries by acting one of the ring generators in the R-sector on them repeatedly. After fixing the normalizations of the dressed scaling operators, we find that the Ward identities are expressed in the form of the {\it usual} $\W_q$ algebra constraints as in the bosonic case: $\W^{(k+1)}_n τ=0$, $(k=1,\cdots,q-1 ;~ n \in {\bf Z}_{\geq 1-k})$, where the equations for even and odd $n$ come from the currents in the NS- and the R-sector respectively. The non-linear terms come from the anomalous contributions at the boundaries of moduli space. The negative chirality is defined by interchanging the roles of $p$ and $q$. Then we get the $\W_p $ algebra constraints.

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