Yoshinobu Habara | Searcharxiv

arXiv2015

A state description of pair production from Dirac sea in gravitational field --physical interpretation of Weyl anomaly--

We present the method that the pair production of particles is described as a Fock space state vector, where the pair production stems from receiving energy from, as an example, gravitational background field. At the same time we show a sort of new mechanism that in the diffeomorphism-invariant Dirac sea the Weyl symmetry is broken due to the pair production and this provides us a new physical interpretation of the origin of Weyl anomaly. In the present paper at the first place, we consider two kinds of background space-time which are connected each other by the Weyl transformation. It is shown that the vacuum, i.e. Dirac sea, in the "curved" space-time \underline{after} making Weyl transformation is nothing but the pair produced state provided we consider the state in terms of the Fock space basis in the "flat" space-time \underline{before} making the Weyl transformation. When summing up with respect to the time the contribution of pair production of each time-slice we obtain the Ricci scalar $R$ and then it is related to the trace part $\left\langle T^μ_{\> μ}\right\rangle$ of the energy-momentum tensor to produce Weyl anomaly.

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arXiv2014

A new mechanism of realizing inflationary universe with recourse to backreaction of quantized free fields -- Inflation without inflaton --

It is shown that the inflationary era in early universe is realized due to the effect of backreaction of quantized matter fields. In fact we start by quantizing a free scalar field in the Friedmann-Robertson-Walker space-time, and the field is fluctuating quantum mechanically around the bottom of the mass potential. We then obtain the vacuum expectation value of the energy density of the scalar field as a functional of the scale factor $a(t)$ of the universe. By plugging it into the Einstein equation, a self-consistent equation is established in which the matter fields determine the time evolution of the universe. We solve this equation by setting few conditions and find the following solution: the universe expands à la de Sitter with e-folding number $\gtrsim 60$ and then it turns to shrink with a decreasing Hubble parameter $H(t)$ which rapidly goes to zero.

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arXiv2012

Possible origin of CMB temperature fluctuations: Vacuum fluctuations of Kaluza-Klein and string states during inflationary era

We point out that the temperature fluctuations of cosmic microwave background (CMB) can be generated in a way that is different from the one usually assumed in slow-roll inflation. Our mechanism is based on vacuum fluctuations of fields which are at rest at the bottom of the potential, such as Kaluza-Klein modes or string excited states. When there are a large number (typically of order $N\sim 10^{14}$) of fields with small mass in unit of Hubble parameter during the inflationary era, this effect can give significant contributions to the CMB temperature fluctuations. This number $N$ makes it possible to enhance scalar perturbation relative to tensor perturbation. Comparison with the observed amplitudes suggests that models with string scale of order $10^{-5}$ of 4D Planck scale are favorable.

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arXiv2011

CMB Fluctuations and String Compactification Scales

We propose a mechanism for the generation of temperature fluctuations of cosmic microwave background. We consider a large number of fields, such as Kaluza-Klein modes and string excitations. Each field contributes to the gravitational potential by a small amount, but an observable level of temperature fluctuations is achieved by summing up the contribution of typically of order 10^{14} fields. Tensor fluctuations are hardly affected by these fields. Our mechanism is based on purely quantum effects, and is different from the "slow-roll" or "curvaton" scenario. Using the observed data, we find constraints on the parameters of this model, such as the size of the extra dimensions and the string scale. Our model predicts a particular pattern of non-gaussianity with a small magnitude.

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arXiv2007

Dirac Sea and Hole Theory for Bosons I -- A new formulation of quantum field theories --

Bosonic formulation of the negative energy sea, so called Dirac sea, is proposed by constructing a hole theory for bosons as a new formulation of the second quantization of bosonic fields. The original idea of Dirac sea for fermions, where the vacuum state is considered as a state completely filled by fermions of negative energy and holes in the sea are identified as anti-particles, is extended to boson case in a consistent manner. The bosonic vacuum consists of a sea filled by negative energy bosonic states, while physical probabilities become always positive definite. We introduce a method of the double harmonic oscillator to formulate the hole theory of bosons. Our formulation is also applicable to supersymmetric field theory. The sea for supersymmetric theories has an explicit supersymmetry. We suggest applications of our formulations to the anomaly theories and the string theories.

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arXiv2007

Dirac Sea and Hole Theory for Bosons II -- Renormalization Approach --

In bosonic formulation of the negative energy sea, so called Dirac sea presented in the preceding paper [arXiv:hep-th/0603242], one of the crucial points is how to construct a positive definite inner product in the negative energy states, since naive attempts would lead to non-positive definite ones. In the preceding paper the non-local method is used to define the positive definite inner product. In the present article we make use of a kind of $ε$-regularization and renormalization method which may clarify transparently the analytical properties of our formulation.

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arXiv2006

Gauge Theory and a Dirac Operator on a Noncommutative Space

As a tool to carry out the quantization of gauge theory on a noncommutative space, we present a Dirac operator that behaves as a line element of the canonical noncommutative space. Utilizing this operator, we construct the Dixmier trace, which is the regularized trace for infinite-dimensional matrices. We propose the possibility of solving the cosmological constant problem by applying our gauge theory on the noncommutative space.

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arXiv2006

Gauge Theory and Dirac Operator on Noncommutative Space II -Minkowskian and Euclidean Cases-

In the preceding paper [arXiv:hep-th/0604217], we construct the Dirac operator and the integral on the canonical noncommutative space. As a matter of fact, they are ones on the noncommutative torus. In the present article, we introduce the method to extend to the Minkowskian and Euclidean cases. As a concluding remark, we present a geometrical notion of our gauge theory.

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arXiv2005

Supersymmetric Relativistic Quantum Mechanics

We present an attempt to formulate the supersymmetric and relativistic quantum mechanics in the sense of realizing supersymmetry on the single particle level, by utilizing the equations of motion which is equivalent to the ordinary 2nd quantization of the chiral multiplet. The matrix formulation is used to express the operators such as supersymmtry generators and fields of the chiral multiplets. We realize supersymmetry prior to filling the Dirac sea.

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arXiv2005

Dirac Sea for Bosons also and SUSY for Single Particles

We consider the long standing problem in field theories of bosons that the boson vacuum does not consist of a `sea', unlike the fermion vacuum. We show with the help of supersymmetry considerations that the boson vacuum indeed does also consist of a sea in which the negative energy states are all "filled", analogous to the Dirac sea of the fermion vacuum, and that a hole produced by the annihilation of one negative energy boson is an anti-particle. This might be formally coped with by introducing the notion of a double harmonic oscillator, which is obtained by extending the condition imposed on the wave function. Next, we present an attempt to formulate the supersymmetric and relativistic quantum mechanics utilizing the equations of motion.

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arXiv2005

Hole Theory of Boson Sea

We propose a hole theory for bosons, in which, analogous to fermions, a hole produced by the annihilation of one negative energy boson is an anti-particle. We show that the boson vacuum indeed also consists of a sea in which all negative energy states are filled and the density of probability of the Klein-Gordon theory is positive definite also for the negative energy solution. This formalism is obtained by introducing the notion of a double harmonic oscillator, which is constructed by extending the condition imposed on the wave function. This double harmonic oscillator contains not only positive energy states but also negative energy ones. The physical result obtained from our method is consistent with that of the ordinary second quantization formalism. Our formulation is also consistent with the supersymmetric point of view. We finally suggest applications of our method to the anomalies of boson theories and the string theories.

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arXiv2005

Cyclic Universe à la string theory

We shall present a model of the "cyclic universe" that can be constructed only by assuming a minimal set of properties of string theory. We clarify our viewpoint of the cyclic universe and show some attempts to mateliarize the idea as field theoretical manner.

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arXiv2005

Negative Energy (Dirac-like) Sea for Bosons and Supersymmetry

We consider the long standing problem in field theories of bosons that the boson vacuum does not consist of a `sea', unlike the fermion vacuum. We show with the help of supersymmetry considerations that the boson vacuum indeed does also consist of a sea in which the negative energy states are all "filled", analogous to the Dirac sea of the fermion vacuum, and that a hole produced by the annihilation of one negative energy boson is an anti-particle. This might be formally coped with by introducing the notion of a double harmonic oscillator, which is obtained by extending the condition imposed on the wave function. Next, we present an attempt to formulate the supersymmetric and relativistic quantum mechanics utilizing the equations of motion.

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arXiv2004

Boson Sea versus Dirac Sea -- General formulation of boson sea through supersymmetry --

We consider the long standing problem in field theories of bosons that the boson vacuum does not consist of a `sea', unlike the fermion vacuum. We show with the help of supersymmetry considerations that the boson vacuum indeed does also consist of a sea in which the negative energy states are all "filled", analogous to the Dirac sea of the fermion vacuum, and that a hole produced by the annihilation of one negative energy boson is an anti-particle. Here, we must admit that it is only possible if we allow --as occurs in the usual formalism anyway-- that the "Hilbert space" for the single particle bosons is not positive definite. This might be formally coped with by introducing the notion of a double harmonic oscillator, which is obtained by extending the condition imposed on the wave function. This double harmonic oscillator includes not only positive energy states but also negative energy states. We utilize this method to construct a general formalism for a boson sea analogous to the Dirac sea, irrespective of the existence of supersymmetry. The physical result is consistent with that of the ordinary second quantization formalism. We finally suggest applications of our method to the string theories.

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arXiv2003

Unitary-Matrix Integration on 2D Yang-Mills Action

Using the idea of Itzykson-Zuber integral, unitary-matrix integration of 2D Yang-Mills action is presented. The uniqueness of the solution of heat equation enables us to integrate out the unitary-matrix parts of hermite matrices and to obtain the expression of integration over vectors, also in this case.

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arXiv2002

Supersymmetric Field Theories on Noncommutative Spaces

Supersymmetric field theories on noncommutative spaces are constructed. We present two different representations of noncommutative space, but we can obtain supersymmetry algebla and supersymmetric Yang-Mills action independent of its representation. As a result, we will see that the action has a close relationship with IIB matrix model.

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arXiv2001

A New Approach to Scalar Field Theory on Noncommutative Space

A new approach to constructing the noncommutative scalar field theory is presented. Not only between x_i and p_j, we impose commutation relations between x_is as well as p_js, and give a new representation of x_i,p_js. We carry out both first- and second-quantization explicitly. The second-quantization is performed in both the operator formalism and the functional integral one.

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