arXiv subjects

Ichiro Oda

Publications and source records attributed to Ichiro Oda.

At least 73 records · Page 4Linked to original sources

arXiv2011

Superluminal Neutrinos from Gauge Field

We consider a possibility that the recent OPERA results on neutrinos' superluminality could be caused by a local effect of a new gauge field sourced by the earth. If neutrinos couple to this gauge field via a gauge-invariant but non-renormalizable interaction, the coupling effectively changes a background metric, thereby leading to superluminality of neutrinos. This possibility naturally might explain why neutrinos from CERN CNGS beam to Gran Sasso Laboratory become superluminal while those from SN1987A to Earth become subluminal.

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arXiv2011

A Resolution to Cherenkov-like Radiation of OPERA Neutrinos

The OPERA collabotation has reported evidence of superluminal neutrinos with a mean energy 17.5 GeV ranging up to 50 GeV. However, the superluminal interpretation of the OPERA results has been recently refuted theoretically by Cherenkov-like radiation. We discuss a loophole of this argument from the kinematical viewpoint and find it possible to avoid the Cherenkov-like radiation of the OPERA neutrinos. The key idea of our argument is to admit the fact that the neutrinos travel faster than the observed speed of light while they do slower than the true speed of light in vacuum so strictly speaking they are not superluminal but subluminal. Moreover, we present a model where these two velocities of light can be constructed by taking account of influences from dark matters near the earth.

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arXiv2011

Emergence of Superstring from Pure Spinor

Starting with a classical action where a pure spinor $λ^α$ is only a fundamental and dynamical variable, the pure spinor formalism for superparticle and superstring is derived by following the BRST formalism. In this formalism, not only the string variable $x^m$ but also the space-time spinor $θ^α$ are emerged as the Faddeev-Popov (FP) ghosts of a topological symmetry and its reducible symmetry. This study suggests that the fundamental theory behind the pure spinor formalism of the superstring might be a topological field theory.

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arXiv2011

Free Differential Algebras and Pure Spinor Action in IIB Superstring Sigma Models

In this paper we extend to the case of IIB superstring sigma models the method proposed in hep-th/10023500 to derive the pure spinor approach for type IIA sigma models. In particular, starting from the (Free) Differential Algebra and superspace parametrization of type IIB supergravity, extended to include the BRST differential and all the ghosts, we derive the BRST transformations of fields and ghosts as well as the standard pure spinor constraints for the ghosts $λ$ related to supersymmetry. Moreover, using the method first proposed by us, we derive the pure spinor action for type IIB superstrings in curved supergravity backgrounds (on shell), in full agreement with the action first obtained by Berkovits and Howe.

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arXiv2010

Remarks on Higgs Mechanism for Gravitons

We construct two kinds of model exhibiting Higgs mechanism for gravitons in potentials of scalar fields. One class of the model is based on a potential which is a generic function of the induced internal metric $H^{AB}$, and the other involves a potential which is a generic function of the usual metric tensor $g_{μν}$ and the induced curved metric $Y_{μν}$. In the both models, we derive conditions on the scalar potential in such a way that gravitons acquire mass in a flat Minkowski space-time without non-unitary propagating modes in the process of spontaneous symmetry breaking of diffeomorphisms through the condensation of scalar fields. We solve the conditions and find a general solution for the potential. As an interesting specific solution, we present a simple potential for which the Higgs mechanism for gravitons holds in any value of cosmological constant.

hep-th↗

arXiv2010

Higgs Mechanism for Gravitons

Just like the vector gauge bosons in the gauge theories, it is now known that gravitons acquire mass in the process of spontaneous symmetry breaking of diffeomorphisms through the condensation of scalar fields. The point is that we should find the gravitational Higgs mechanism such that it results in massive gravity in a flat Minkowski space-time without non-unitary propagating modes. This is usually achieved by including higher-derivative terms in scalars and tuning the cosmological constant to be a negative value in a proper way. Recently, a similar but different gravitational Higgs mechanism has been advocated by Chamseddine and Mukhanov where one can relax the negative cosmological constant to zero or positive one. In this work, we investigate why the non-unitary ghost mode decouples from physical Hilbert space in a general space-time dimension. Moreover, we generalize the model to possess an arbitrary potential and clarify under what conditions the general model exhibits the gravitational Higgs mechanism. By searching for solutions to the conditions, we arrive at two classes of potentials exhibiting gravitational Higgs mechanism. One class includes the model by Chamseddine and Mukhanov in a specific case while the other is completely a new model.

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arXiv2009

Renormalizability of Topologically Massive Gravity

We consider renormalizability of topologically massive gravity in three space-time dimensions. With a usual parametrization of the metric tensor, we establish the statement that topologically massive gravity is in fact renormalizable. In this proof, we make use of not only a recently found, new infrared regularization method of scalar mode but also a covariant ultraviolet regulator with a specific combination of higher derivative terms which is motivated by the new massive gravity in three dimensions.

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arXiv2009

Renormalizability of Massive Gravity in Three Dimensions

We discuss renormalizability of a recently established, massive gravity theory with particular higher derivative terms in three space-time dimensions. It is shown that this massive gravity is certainly renormalizable as well as unitary, so it gives us a physically interesting toy model of perturbative quantum gravity in three dimensions.

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arXiv2009

On Unitarity of Massive Gravity in Three Dimensions

We examine a unitarity of a particular higher-derivative extension of general relativity in three space-time dimensions, which has been recently shown to be equivalent to the Pauli-Fierz massive gravity at the linearized approximation level, and explore a possibility of generalizing the model to higher space-time dimensions. We find that the model in three dimensions is indeed unitary in the tree-level, but the corresponding model in higher dimensions is not so due to the appearance of non-unitary massless spin-2 modes.

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arXiv2009

Massive Gravity with Mass Term in Three Dimensions

We analyze the effect of the Pauli-Fierz mass term on a recently established, new massive gravity theory in three space-time dimensions. We show that the Pauli-Fierz mass term makes the new massive gravity theory non-unitary. Moreover, although we add the gravitational Chern-Simons term to this model, the situation remains unchanged and the theory stays non-unitary in spite that structure of the graviton propagator is greatly changed. Thus, the Pauli-Fierz mass term is not allowed to coexist with mass-generating higher-derivative terms in the new massive gravity.

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arXiv2008

Massive Gravity in Curved Cosmological Backgrounds

We study the physical propagating modes in a massive gravity model in curved cosmological backgrounds, which we have found as classical solutions in our previous paper. We show that, generically, there exist such the cosmological background solutions consistent with the equations of motion where we assume the ghost condensation ansatzes. Using the (1+3)-parametrization of the metric fluctuations with 'unitary' gauge, we find that there is neither a scalar ghost nor a tachyon in the spectrum of the propagating modes, the tensor modes become massive owing to gravitational Higgs mechanism, and the model is free of the Boulware-Deser instability. The price we have to pay is that the scalar sector breaks the Lorentz-invariance, but there are no pathologies in the spectrum and lead to interesting phenomenology. Moreover, we present a proof of the absence of non-unitary modes for a specific ghost condensation model in a cosmological background.

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arXiv2008

Y-Formalism and Curved Beta-Gamma Systems

We adopt the Y-formalism to study beta-gamma systems on hypersurfaces. We compute the operator product expansions of gauge-invariant currents and we discuss some applications of the Y-formalism to model on Calabi-Yau spaces.

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arXiv2008

Classical Solutions of Ghost Condensation Models

Motivated by ideas obtained from both ghost condensation and gravitational Higgs mechanism, we attempt to find classical solutions in the unitary gauge in general ghost condensation models. It is shown that depending on the form of scalar fields in an action, there are three kinds of exact solutions, which are (anti-) de Sitter space-time, polynomially expanding universes and flat Minkowski space-time. We briefly comment on gravitational Higgs mechanism in these models where we have massive gravitons of 5 degrees of freedom and 1 unitary scalar field (Nambu-Goldstone boson) after spontaneous symmetry breakdown of general coordinate reparametrization invariance. The models at hand are free from the problem associated with the non-unitary propagating mode.

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arXiv2007

Gravitational Higgs Mechanism with a Topological Term

We investigate the Higgs mechanism for gravity, which has been recently put forward by 't Hooft, when the Polyakov-type action for scalar fields is added to the original action. We find that from the Polyakov-type action, it is very natural to derive an 'alternative' metric tensor composed of the scalar fields. The positivity condition on the determinant can be also derived easily by requiring that this term does not change the dynamics at all and becomes a topological number, that is, the wrapping number. It turns out that the gauge conditions adopted by 't Hooft are nothing but the restriction on a sector with unit wrapping number.

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arXiv2007

Y-formalism and $b$ ghost in the Non-minimal Pure Spinor Formalism of Superstrings

We present the Y-formalism for the non-minimal pure spinor quantization of superstrings. In the framework of this formalism we compute, at the quantum level, the explicit form of the compound operators involved in the construction of the $b$ ghost, their normal-ordering contributions and the relevant relations among them. We use these results to construct the quantum-mechanical $b$ ghost in the non-minimal pure spinor formalism. Moreover we show that this non-minimal $b$ ghost is cohomologically equivalent to the non-covariant $b$ ghost.

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arXiv2005

The b-Field in Pure Spinor Quantization of Superstrings

In the framework of the pure spinor approach of superstring theories, we describe the Y-formalism and use it to compute the picture raised b-field. At the end we discuss briefly the new, non-minimal formalism of Berkovits and the related non-minimal b-field.

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arXiv2005

Worldline Approach of Topological BF Theory

We present a worldline description of topological non-abelian BF theory in arbitrary space-time dimensions. It is shown that starting with a trivial classical action defined on the worldline, the BRST cohomology has a natural representation as the sum of the de Rham cohomology. Based on this observation, we construct a second-quantized action of the BF theory. Interestingly enough, this theory naturally gives us a minimal solution to the Batalin-Vilkovisky master equation of the BF theory. Our formalism sheds some light not only on an interplay between the Witten-type and the Schwarz-type topological quantum field theories but also on the role of the Batalin-Vilkovisky antifields and ghosts as geometrical and elementary objects.

hep-th↗

arXiv2004

On the b-antighost in the Pure Spinor Quantization of Superstrings

Recently Berkovits has constructed a picture raised, compound field $b_B$ which is used to compute higher loop amplitudes in the pure spinor approach of superstrings. On the other hand, in the twisted and gauge fixed, superembedding approach with $n=2$ world-sheet (w.s.) supersymmetry that reproduces the pure spinor formulation, a field $b$ appears quite naturally as the current of one of the two twisted charges of the w.s. supersymmetry, the other being the BRST charge. In this paper we study the relation between $b$ and $b_B$. We shall show that $bZ$, where $Z$ is a picture raising operator, and $b_B$ belong to the same BRST cohomological class. This result is of importance since it implies that the cumbersome singularity which is present in $b$, is in fact harmless if $b$ is combined with $Z$.

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