arXiv subjects

Shun'ya Mizoguchi

Publications and source records attributed to Shun'ya Mizoguchi.

At least 37 records · Page 2Linked to original sources

arXiv2015

Anomaly-free Multiple Singularity Enhancement in F-theory

We study global Calabi-Yau realizations of multiple singularity enhancement relevant for family-unification model building in F-theory. We examine the conditions under which the generation of extra chiral matter at multiple singularities on 7-branes in six-dimensional F-theory can be consistent with anomaly cancellation. It is shown that the generation of extra matter is consistent only if it is accompanied by simultaneous degenerations of loci of the leading polynomial of the discriminant so that the total number of chiral matter does not change. We also show that the number of singlets expected to arise matches the decrease of the complex structure moduli for the restricted geometry.

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arXiv2015

Supersymmetric heterotic solutions via non-SU(3) standard embedding

A supersymmetric solution to type II supergravity is constructed by superposing two hyperkählers with torsion metrics. The solution is given by a Käler with torsion metric with $SU(3)$ holonomy. The metric is embedded into a heterotic solution obeying the Strominger system, together with a Yang-Mills instanton obtained by the standard embedding. T dualities lead to an $SO(6)$ instanton describing a symmetry breaking from $E_8$ to $SO(10)$. The compactification by taking a periodic array yields a supersymmetric domain wall solution of heterotic supergravity.

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arXiv2014

Large Lepton-flavor Mixings from E8 Kodaira Singularity: Lopsided Texture via F-theory Family Unification

We show that a special type of colliding 7-brane configuration of a codimension-two singularity realizes not only a six-dimensional spectrum with exactly the same quantum numbers as that of the three-generation E7/(SU(5) x U(1)^3) coset family unification model, but also the three sets of nonchiral singlet pairs with precisely the correct U(1) charges needed for explaining the Yukawa hierarchies and large lepton-flavor mixings in a well-known seesaw scenario.

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arXiv2014

F-theory Family Unification

We propose a new geometric mechanism for naturally realizing unparallel three families of flavors in string theory, using the framework of F-theory. We consider a set of coalesced local 7-branes of a particular Kodaira singularity type and allow some of the branes to bend and separate from the rest, so that they meet only at an intersection point. Such a local configuration can preserve supersymmetry. Its matter spectrum is investigated by studying string junctions near the intersection, and shown to coincide, after an orbifold projection, with that of a supersymmetric coset sigma model whose target space is a homogeneous Kahler manifold associated with a corresponding painted Dynkin diagram. In particular, if one starts from the E7 singularity, one obtains the E7/(SU(5)xU(1)^3) model yielding precisely three generations with an unparallel family structure. Possible applications to string phenomenology are also discussed.

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arXiv2012

Family Unification via Quasi-Nambu-Goldstone Fermions in String Theory

Some of the supersymmetric nonlinear sigma models on exceptional groups (E7 or E8) are known to yield almost minimal necessary content of matter fields for phenomenological model building, including three chiral families and a Higgs multiplet. We explore a possible realization of such a family unification in heterotic string theory, where the spontaneously broken symmetry that we focus on is the one associated with the change of global orientation of the spin bundle embedded in the gauge bundle, which cannot be ignored in the presence of a magnetic source of the B field. We show in a simple model that it indeed gives rise to chiral matter fields on the defect similarly to the domain-wall fermions, and compare the chiral zero mode spectrum with the sigma model. The setup is reduced to a system similar to that postulated in the orbifold GUT or the grand gauge-Higgs unification model, where the origin of Z2 identification is accounted for as arising from the bolt of the Atiyah-Hitchin manifold.

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arXiv2012

General Kaluza-Klein black holes with all six independent charges in five-dimensional minimal supergravity

Using the SL(2,R)-duality in a dimensionally reduced spacetime in (the bosonic sector of) five-dimensional minimal supergravity, we construct general Kaluza-Klein black hole solutions which carry six independent charges, its mass, angular momentum along four dimensions, electric and magnetic charges of the Maxwell fields in addition to Kaluza-Klein electric and magnetic monopole charges.

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arXiv2012

"Flip" of SL(2,R)-duality in five-dimensional supergravity

The dimensional reduction of the bosonic sector of five-dimensional minimal supergravity to a Lorentzian four-dimensional spacetime leads to a theory with a massless axion and a dilaton coupled to gravity and two U(1) gauge fields and the dimensionally reduced equations of motion have SL(2,R)/SO(2)-duality invariance. In our previous work, utilizing the duality invariance, we formulated solution-generation techniques within five-dimensional minimal supergravity. In this work, by choosing a timelike Killing vector, we consider dimensional reduction to a four-dimensional Euclidean space, in which the field equations have SL(2,R)/SO(1,1) invariance. In the timelike case, we develop a new duality transformation technique, while in the spacelike case we have done that in the previous work. As an example, by applying it to the Rasheed solutions, we obtain rotating Kaluza-Klein black hole solutions in five-dimensional minimal supergravity. In general, in contrast to the spacelike case, the resulting dimensionally reduced solution includes the so-called NUT parameter and therefore from a four-dimensional point of view, such a spacetime is not asymptotically flat. However, it is shown that in some special cases, it can describe ordinary Kaluza-Klein black holes.

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arXiv2011

New approach to solution generation using SL(2,R)-duality of a dimensionally reduced space in five-dimensional minimal supergravity and new black holes

The dimensional reduction of (the bosonic sector of) five-dimensional minimal supergravity to four dimensions leads to a theory with a massless axion and a dilaton coupled to gravity and two U(1) gauge fields (one of which has Chern-Simons coupling), whose field equations have SL(2,R)-invariance. Utilizing this SL(2,R)-duality, we provide a new formalism for solution generation. As an example, applying it to the Rasheed solution, which are known to describe dyonic rotating black holes (from the four-dimensional point of view) of five-dimensional pure gravity, we obtain rotating Kaluza-Klein black hole solutions in five-dimensional minimal supergravity. We also show that the solutions have six charges: mass, angular momentum, Kaluza-Klein electric/magnetic charges and electric/magnetic charges of the Maxwell field, four of which are related by a constraint.

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arXiv2011

Taub-NUT Crystal

We consider the Gibbons-Hawking metric for a three-dimensional periodic array of multi-Taub-NUT centers, containing not only centers with a positive NUT charge but also ones with a negative NUT charge. The latter are regarded as representing the asymptotic form of the Atiyah-Hitchin metric. The periodic arrays of Taub-NUT centers have close parallels with ionic crystals, where the Gibbons-Hawking potential plays the role of the Coulomb static potential of the ions, and are similarly classified according to their space groups. After a periodic identification and a Z2 projection, the array is transformed by T-duality to a system of NS5-branes with the SU(2) structure, and a further standard embedding yields, though singular, a half-BPS heterotic 5-brane background with warped compact transverse dimensions. A discussion is given of the possibility of probing the singular geometry by two-dimensional gauge theories.

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arXiv2010

Note on Anomaly Cancellation on SO(32) heterotic 5-brane

We show that the gauge, gravitational (tangent-bundle) and their mixed anomalies arising from the localized modes near a 5-brane in the SO(32) heterotic string theory cancel with the anomaly inflow from the bulk with the use of the Green-Schwarz mechanism on the brane, similarly to the E_8 x E_8 5-brane case. We also compare our result with Mourad's analysis performed in the small-instanton limit.

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arXiv2009

Chiral Generations on Intersecting 5-branes in Heterotic String Theory

We show that there exist two 27 and one 27 bar of E6, net one D=4, N=1 chiral matter supermultiplet as zero modes localized on the intersection of two 5-branes in the E8 x E8 heterotic string theory. The smeared intersecting 5-brane solution is used via the standard embedding to construct a heterotic background, which provides, after a compactification of some of the transverse dimensions, a five-dimensional Randall-Sundrum II like brane-world set-up in heterotic string theory. As a by-product, we present a new proof of anomaly cancellation between those from the chiral matter and the anomaly inflow onto the brane without small instanton.

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arXiv2009

Chiral Zero Modes on Intersecting Heterotic 5-branes

We show that there exist two 27 and one 27bar of E6, net one chiral supermultiplet as zero modes localized on the intersecting 5-branes in the E8 x E8 heterotic string theory. A heterotic background is constructed by the standard embedding in the smeared solution, and the Dirac equation is solved explicitly on this background. It provides, after a compactification of some of the transverse dimensions, a Randall-Sundrum II like brane-world set-up in heterotic string theory.

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arXiv2008

Warped String Compactification via Singular Calabi-Yau Conformal Field Theory

We construct spacetime supersymmetric, modular invariant partition functions of strings on the conifold-type singularities which include contributions from the discrete-series representations of SL(2, R). The discrete spectrum is automatically consistent with the GSO projection in the continuous sector, and contains massless matter fields localized on a four-dimensional submanifold at the tip of a cigar. In particular, they are in the 27+1 of E6 for the E8 x E8 heterotic string. We speculate about a possible realization of local E6 GUT by using this framework.

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arXiv2008

Localized Modes in Type II and Heterotic Singular Calabi-Yau Conformal Field Theories

We consider type II and heterotic string compactifications on an isolated singularity in the noncompact Gepner model approach. The conifold-type ADE noncompact Calabi-Yau threefolds, as well as the ALE twofolds, are modeled by a tensor product of the SL(2,R)/U(1) Kazama-Suzuki model and an N=2 minimal model. Based on the string partition functions on these internal Calabi-Yaus previously obtained by Eguchi and Sugawara, we construct new modular invariant, space-time supersymmetric partition functions for both type II and heterotic string theories, where the GSO projection is performed before the continuous and discrete state contributions are separated. We investigate in detail the massless spectra of the localized modes. In particular, we propose an interesting three generation model, in which each flavor is in the 27+1 representation of E6 and localized on a four-dimensional space-time residing at the tip of the cigar.

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arXiv2007

Lower-dimensional superstrings in the double-spinor formalism

We study lower-dimensional superstrings in the double-spinor formalism introduced by Aisaka and Kazama. These superstrings can be consistently quantized and are equivalent to the lower-dimensional pure-spinor superstrings proposed by Grassi and Wyllard. The unexpected physical spectrum of the pure-spinor superstrings may thus be regarded as a manifestation of noncriticality. We also discuss how to couple these covariant superstrings to the compactified degrees of freedom described by the N=2 superconformal field theory.

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arXiv2006

Progress toward the Determination of Complete Vertex Operators for The IIB Matrix Model

We report on progress in determining the complete form of vertex operators for the IIB matrix model. The exact expressions are obtained for those emitting massless IIB supergravity fields up to sixth order in the light-cone superfield, in which the conjugate gravitino and conjugate two-form vertex operators are newly determined. We also provide a consistency check by computing the kinematical factor of a four-point graviton amplitude in a D-instanton background. We conjecture that the low-energy effective action of the IIB matrix model at large N is given by tree-level supergravity coupled to the vertex operators.

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arXiv2006

Little IIB Matrix Model

We study the zero-dimensional reduced model of D=6 pure super Yang-Mills theory and argue that the large N limit describes the (2,0) Little String Theory. The one-loop effective action shows that the force exerted between two diagonal blocks of matrices behaves as 1/r^4, implying a six-dimensional spacetime. We also observe that it is due to non-gravitational interactions. We construct wave functions and vertex operators which realize the D=6, (2,0) tensor representation. We also comment on other "little" analogues of the IIB matrix model and Matrix Theory with less supercharges.

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arXiv2006

Nonlocal charges of T-dual strings

We obtain sets of infinite number of conserved nonlocal charges of strings in a flat space and pp-wave backgrounds, and compare them before and after T-duality transformation. In the flat background the set of nonlocal charges is the same before and after the T-duality transformation with interchanging odd and even-order charges. In the IIB pp-wave background an infinite number of nonlocal charges are independent, contrast to that in a flat background only the zero-th and first order charges are independent. In the IIA pp-wave background, which is the T-dualized compactified IIB pp-wave background, the zero-th order charges are included as a part of the set of nonlocal charges in the IIB background. To make this correspondence complete a variable conjugate to the winding number is introduced as a Lagrange multiplier in the IIB action a la Buscher's transformation.

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