arXiv subjects

Ching-Ming Chen

Publications and source records attributed to Ching-Ming Chen.

18 recordsLinked to original sources

arXiv2011

Type IIB Supersymmetric Flux Vacua

On the Type IIB toroidal T^6 orientifolds with generic flux compactifications, we conjecture that in generic supsersymmetric Minkowski vacua, at least one of the flux contributions to the seven-brane and D3-brane tadpoles is positive if the moduli are stabilized properly, and then the tadpole cancellation conditions can not be relaxed. To study the supsersymmetric Minkowski flux vacua, we simplify the fluxes reasonably and discuss the corresponding superpotential. We show that we can not have simultaneously the positive real parts of all the moduli and the negative/zero flux contributions to all the seven-brane and D3-brane tadpoles. Therefore, we can not construct realistic flux models with the relaxed tadpole cancellation conditions. When studying the supsersymmetric AdS vacua, we obtain flux models with the seven-brane and D3-brane tadpole cancellation conditions relaxed elegantly, and we present a semi-realistic Pati-Salam model as well as its particle spectrum. The lifting from the AdS vacua to the Minkowski/dS vacua remains a great challenge in flux model buildings on toroidal orientifolds.

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arXiv2011

MSSM-like AdS Flux Vacua with Frozen Open-string Moduli

We construct supersymmetric Pati-Salam flux vacua in AdS from intersecting D6-branes on T^6/(Z_2 x Z_2'). The models constructed have three generations of MSSM matter plus right-handed neutrinos. Because the cycles wrapped by the D-branes are rigid there are no extra massless fields in the adjoint representation, arising as open-string moduli. However, we find that it is problematic to break the Pati-Salam gauge symmetry to the Standard Model (SM) while keeping the SM hypercharge massless.

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arXiv2011

On F-theory E_6 GUTs

We approach the Minimum Supersymmetric Standard Model (MSSM) from an E_6 GUT by using the spectral cover construction and non-abelian gauge fluxes in F-theory. We start with an E_6 singularity unfolded from an E_8 singularity and obtain E_6 GUTs by using an SU(3) spectral cover. By turning on SU(2) X U(1)^2 gauge fluxes, we obtain a rank 5 model with the gauge group SU(3) X SU(2) X U(1)^2. Based on the well-studied geometric backgrounds in the literature, we demonstrate several models and discuss their phenomenology.

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arXiv2011

Flipped SU(5) GUTs from E_8 Singularities in F-theory

In this paper we construct supersymmetric flipped SU(5) GUTs from E_8 singularities in F-theory. We start from an SO(10) singularity unfolded from an E_8 singularity by using an SU(4) spectral cover. To obtain realistic models, we consider (3,1) and (2,2) factorizations of the SU(4) cover. After turning on the massless U(1)_X gauge flux, we obtain the SU(5) X U(1)_X gauge group. Based on the well-studied geometric backgrounds in the literature, we demonstrate several models and discuss their phenomenology.

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arXiv2010

Global SO(10) F-theory GUTs

Making use of toric geometry we construct a class of global F-theory GUT models. The base manifolds are blowups of Fano threefolds and the Calabi-Yau fourfold is a complete intersection of two hypersurfaces. We identify possible GUT divisors and construct SO(10) models on them using the spectral cover construction. We use a split spectral cover to generate chiral matter on the 10 curves in order to get more degrees of freedom in phenomenology. We use abelian flux to break SO(10) to SU(5)\times U(1) which is interpreted as a flipped SU(5) model. With the GUT Higgses in the SU(5)\times U(1) model it is possible to further break the gauge symmetry to the Standard Model. We present several phenomenologically attractive examples in detail.

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arXiv2009

A Note on Local GUT Models in F-Theory

We construct non-minimal GUT local models in the F-theory configuration. The gauge group on the bulk G_S is one rank higher than the GUT gauge group. The line bundles on the curves are non-trivial to break G_S down to the GUT gauge groups. We demonstrate examples of SU(5) GUT from G_S=SU(6) and G_S=SO(10), the flipped SU(5) from G_S=SO(10), and the SO(10) GUT from G_S=SO(12) and G_S=E_6. We obtain complete GUT matter spectra and couplings, with minimum exotic matter contents. GUT gauge group breaking to MSSM is achievable by instanton configurations.

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arXiv2008

Realistic Type IIB Supersymmetric Minkowski Flux Models without the Freed-Witten Anomaly

We show that there exist supersymmetric Minkowski vacua on Type IIB toroidal orientifold with general flux compactifications where the RR tadpole cancellation conditions can be relaxed and the Freed-Witten anomaly can be cancelled elegantly. We present a realistic Pati-Salam like flux model without the Freed-Witten anomaly. At the string scale, we can break the gauge symmetry down to the Standard Model (SM) gauge symmetry, achieve the gauge coupling unification naturally, and decouple all the extra chiral exotic particles. Thus, we have the supersymmetric SMs with/without SM singlet(s) below the string scale. Also, we can explain the SM fermion masses and mixings. In addition, the unified gauge coupling and the real parts of the dilaton and Kähler moduli are functions of the four-dimensional dilaton. The complex structure moduli and one linear combination of the imaginary parts of the Kähler moduli can be determined as functions of the fluxes and the dilaton.

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arXiv2008

Yukawa Corrections from Four-Point Functions in Intersecting D6-Brane Models

We discuss corrections to the Yukawa matrices of the Standard Model (SM) fermions in intersecting D-brane models due to four-point interactions. Recently, an intersecting D-brane model has been found where it is possible to obtain correct masses and mixings for all quarks as well as the tau lepton. However, the masses for the first two charged leptons come close to the right values but are not quite correct. Since the electron and muon are quite light, it is likely that there are additional corrections to their masses which cannot be neglected. With this in mind, we consider contributions to the SM fermion mass matrices from four-point interactions. In an explicit model, we show that it is indeed possible to obtain the SM fermion masses and mixings which are a better match to those resulting from experimental data extrapolated at the unification scale when these corrections are included. These corrections may have broader application to other models.

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arXiv2008

Realistic Yukawa Textures and SUSY Spectra from Intersecting Branes

We study the possible phenomenology of a three-family Pati-Salam model constructed from intersecting D6-branes in Type IIA string theory on the T^6/(Z2 x Z2) orientifold with some desirable semi-realistic features. In the model, tree-level gauge coupling unification is achieved automatically at the string scale, and the gauge symmetry may be broken to the Standard Model (SM) close to the string scale. The small number of extra chiral exotic states in the model may be decoupled via the Higgs mechanism and strong dynamics. We calculate the possible supersymmetry breaking soft terms and the corresponding low-energy supersymmetric particle spectra which may potentially be tested at the Large Hadron Collider (LHC). We find that for the viable regions of the parameter space the lightest CP-even Higgs boson mass usually satisfies m_H < 120 GeV, and the observed dark matter density may be generated. Finally, we find that it is possible to obtain correct SM quark masses and mixings, and the tau lepton mass at the unification scale. Additionally, neutrino masses and mixings may be generated via the seesaw mechanism. Mechanisms to stabilize the open and closed-string moduli, which are necessary for the model to be truly viable and to make definite predictions are discussed.

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arXiv2008

Flux Parameter Spaces in Type II Vacua

We study the flux parameter spaces for semi-realistic supersymmetric Pati-Salam models in the AdS vacua on Type IIA orientifold and realistic supersymmetric Pati-Salam models in the Minkowski vacua on Type IIB orientifold. Because the fluxes can be very large, we show explicitly that there indeed exists a huge number of semi-realistic Type IIA and realistic Type IIB flux models. In the Type IIA flux models, in the very large flux limit, the theory can become weakly coupled and the AdS vacua can approach to the Minkowski vacua. In a series of realistic Type IIB flux models, at the string scale, the gauge symmetry can be broken down to the Standard Model (SM) gauge symmetry, the gauge coupling unification can be achieved naturally, all the extra chiral exotic particles can be decoupled, and the observed SM fermion masses and mixings can be obtained as well. In particular, the real parts of the dilaton, Kähler moduli, and the unified gauge coupling are independent of the very large fluxes. The very large fluxes only affect the real and/or imaginary parts of the complex structure moduli, and/or the imaginary parts of the dilaton and Kähler moduli. However, these semi-realistic Type IIA and realistic Type IIB flux models can not be populated in the string landscape.

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arXiv2007

Realistic Type IIB Supersymmetric Minkowski Flux Vacua

We show that there exist supersymmetric Minkowski vacua on Type IIB toroidal orientifold with general flux compactifications where the RR tadpole cancellation conditions can be relaxed elegantly. Then we present a realistic Pati-Salam like model. At the string scale, the gauge symmetry can be broken down to the Standard Model (SM) gauge symmetry, the gauge coupling unification can be achieved naturally, and all the extra chiral exotic particles can be decoupled so that we have the supersymmetric SMs with/without SM singlet(s) below the string scale. The observed SM fermion masses and mixings can also be obtained. In addition, the unified gauge coupling, the dilaton, the complex structure moduli, the real parts of the Kähler moduli and the sum of the imaginary parts of the Kähler moduli can be determined as functions of the four-dimensional dilaton and fluxes, and can be estimated as well.

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arXiv2007

Variations of the Hidden Sector in a Realistic Intersecting Brane Model

Recently, we discussed the first example of a phenomenologically realistic intersecting D6-brane model. In this model, the gauge symmetry in the hidden sector is USp(2)_1 x USp(2)_2 x USp(2)_3 x USp(2)_4. However, we find that the USp(2)_1 x USp(2)_2 gauge symmetry can be replaced by an U(2)_{12} gauge symmetry, and/or the USp(2)_3 x USp(2)_4 gauge symmetry can be replaced by an U(2)_{34} gauge symmetry since the USp(2)^2 stacks of D6-branes contribute to the same Ramond-Ramond tadpoles as those of the U(2) stacks. Thus, there are three non-equivalent variations of the hidden sector, and the corresponding gauge symmetries are U(2)_{12} x USp(2)_3 x USp(2)_4, U(2)_{34} x USp(2)_1 x USp(2)_2, and U(2)_{12} x U(2)_{34}, respectively. Moreover, we study the hidden sector gauge symmetry breaking, discuss how to decouple the additional exotic particles, and briefly comment on the phenomenological consequences.

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arXiv2007

A Realistic World from Intersecting D6-Branes

We briefly describe a three-family intersecting D6-brane model in Type IIA theory on the T^6/(Z_2 x Z_2) orientifold with a realistic phenomenology. In this model, the gauge symmetry can be broken down to the Standard Model (SM) gauge symmetry close to the string scale, and the gauge coupling unification can be achieved. We calculate the supersymmetry breaking soft terms, and the corresponding low energy supersymmetric particle spectrum, which may be tested at the Large Hadron Collider (LHC). The observed dark matter density may also be generated. Finally, we can explain the SM quark masses and CKM mixings, and the tau lepton mass. The neutrino masses and mixings may be generated via the seesaw mechanism as well.

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arXiv2007

MSSM via Pati-Salam from Intersecting Branes on $T^6/(\mathbf{\Z_2} \times \mathbf{\Z_2'})$

We construct an MSSM-like model via Pati-Salam from intersecting D-branes in Type IIA theory on the $\Z_2 \times \Z_2'$ orientifold where the D-branes wrap rigid 3-cycles. Because the 3-cycles are rigid, there are no extra massless fields in the adjoint representation, arising as open-string moduli. The presence of these unobserved fields would create difficulties with asymptotic freedom as well as the prediction of gauge unification. The model constructed has four generations of MSSM matter plus right-handed neutrinos, as well as additional vector-like representations. In addition, we find that all of the required Yukawa couplings are allowed by global symmetries which arise from U(1)'s which become massive via a generalized Green-Schwarz mechanism. Furthermore, we find that the tree-level gauge couplings are unified at the string scale.

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arXiv2006

Flipped and Unflipped SU(5) as Type IIA Flux Vacua

On Type IIA orientifolds with flux compactifications in supersymmetric AdS vacua, we for the first time construct SU(5) models with three anti-symmetric {\bf 10} representations and without symmetric {\bf 15} representations. We show that all the pairs of the anti-fundamental {\bf \bar 5} and fundamental {\bf 5} representations can obtain GUT/string-scale vector-like masses after the additional gauge symmetry breaking via supersymmetry preserving Higgs mechanism. Then we have exact three {\bf \bar 5}, and no other chiral exotic particles that are charged under SU(5) due to the non-abelian anomaly free condition. Moreover, we can break the SU(5) gauge symmetry down to the SM gauge symmetry via D6-brane splitting, and solve the doublet-triplet splitting problem. Assuming that the extra one (or several) pair(s) of Higgs doublets and adjoint particles obtain GUT/string-scale masses via high-dimensional operators, we only have the MSSM in the observable sector below the GUT scale. Then the observed low energy gauge couplings can be generated via RGE running if we choose the suitable grand unified gauge coupling by adjusting the string scale. Furthermore, we construct the first flipped SU(5) model with exact three {\bf 10}, and the first flipped SU(5) model in which all the Yukawa couplings are allowed by the global U(1) symmetries.

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arXiv2006

Type IIA Pati-Salam Flux Vacua

We show that for supersymmetric AdS vacua on Type IIA orientifolds with flux compactifications, the RR tadpole cancellation conditions can be completely relaxed, and then the four-dimensional N=1 supersymmetry conditions are the main constraints on consistent intersecting D6-brane model building. We construct two kinds of three-family Pati-Salam models. In the first kind of models, the suitable three-family SM fermion masses and mixings can be generated at the stringy tree level, and then the rank one problem for the SM fermion Yukawa matrices can be solved. In the second kind of models, only the third family of the SM fermions can obtain masses at tree level. In these models, the complex structure parameters can be determined by supersymmetric D6-brane configurations, and all the moduli may be stabilized. The initial gauge symmetries U(4)_C \times U(2)_L \times U(2)_R and U(4)_C \times USp(2)_L \times U(2)_R can be broken down to the SU(3)_C \times SU(2)_L \times U(1)_{B-L} \times U(1)_{I_{3R}} due to the Green-Schwarz mechanism and D6-brane splittings, and further down to the SM gauge symmetry around the string scale via the supersymmetry preserving Higgs mechanism. Comparing to the previous model building, we have less bidoublet Higgs fields. However, there generically exist some exotic particles.

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arXiv2005

Flipped SU(5) From D-branes With Type IIB Fluxes

We construct flipped SU(5) GUT models as Type IIB flux vacua on $\Z_2\times \Z_2$ orientifolds. Turning on supergravity self-dual NSNS and RR three-form fluxes fixes the toroidal complex structure moduli and the dilaton. We give a specific example of a three-generation flipped SU(5) model with a complete Higgs sector where supersymmetry is softly broken by the supergravity fluxes in the closed string sector. All of the required Yukawa couplings are present if global U(1) factors resulting from a generalized Green-Schwarz mechanism are broken spontaneously or by world-sheet instantons. In addition, the model contains extra chiral and vector-like matter, potentially of mass $\mathcal{O}(M_{string})$ via trilinear superpotential couplings.

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arXiv2005

Standard-Like Model Building on Type II Orientifolds

We construct new Standard-like models on Type II orientifolds. In Type IIA theory on $\mathbf{T^6/(\Z_2\times \Z_2)}$ orientifold with intersecting D6-branes, we first construct a three-family trinification model where the $U(3)_C\times U(3)_L\times U(3)_R$ gauge symmetry can be broken down to the $SU(3)_C\times SU(2)_L\times U(1)_{Y_L}\times U(1)_{I_{3R}}\times U(1)_{Y_R}$ gauge symmetry by the Green-Schwarz mechanism and D6-brane splittings, and further down to the SM gauge symmetry at the TeV scale by Higgs mechanism. We also construct a Pati-Salam model where we may explain three-family SM fermion masses and mixings. Furthermore, we construct for the first time a Pati-Salam like model with $U(4)_C \times U(2)_L \times U(1)' \times U(1)''$ gauge symmetry where the $U(1)_{I_{3R}}$ comes from a linear combination of U(1) gauge symmetries. In Type IIB theory on $\mathbf{T^6/(\Z_2\times \Z_2)}$ orientifold with flux compactifications, we construct a new flux model with $U(4)_C \times U(2)_L \times U(2)_R$ gauge symmetry where the magnetized D9-branes with large negative D3-brane charges are introduced in the hidden sector. However, we can not construct the trinification model with supergravity fluxes because the three SU(3) groups already contribute very large RR charges. The phenomenological consequences of these models are briefly discussed as well.

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