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Hyun Min Lee

Publications and source records attributed to Hyun Min Lee.

At least 163 records · Page 9Linked to original sources
arXiv2004

Brane solutions of a spherical sigma model in six dimensions

We explore solutions of six dimensional gravity coupled to a non-linear sigma model, in the presence of co-dimension two branes. We investigate the compactifications induced by a spherical scalar manifold and analyze the conditions under which they are of finite volume and singularity free. We discuss the issue of single-valuedness of the scalar fields and provide some special embedding of the scalar manifold to the internal space which solves this problem. These brane solutions furnish some self-tuning features, however they do not provide a satisfactory explanation of the vanishing of the effective four dimensional cosmological constant. We discuss the properties of this model in relation with the self-tuning example based on a hyperbolic sigma model.

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arXiv2004

Cosmology of intersecting brane world models in Gauss-Bonnet gravity

We study the cosmological properties of a codimension two brane world that sits at the intersection between two four branes, in the framework of six dimensional Einstein-Gauss-Bonnet gravity. Due to contributions of the Gauss-Bonnet terms, the junction conditions require the presence of localized energy density on the codimension two defect. The induced metric on this surface assumes a FRW form, with a scale factor associated to the position of the brane in the background; we can embed on the codimension two defect the preferred form of energy density. We present the cosmological evolution equations for the three brane, showing that, for the case of pure AdS$_6$ backgrounds, they acquire the same form of the ones for the Randall-Sundrum II model. When the background is different from pure AdS$_6$, the cosmological behavior is potentially modified in respect to the typical one of codimension one brane worlds. We discuss, in a particular model embedded in an AdS$_6$ black hole, the conditions one should satisfy in order to obtain standard cosmology at late epochs.

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arXiv2004

Double Suppression of FCNCs in Supersymmetric Models

A mechanism for double suppression of flavor-changing neutral currents (FCNCs) and CP violating phases in supersymmetric models is suggested. At M_{SUSY} they are suppressed due to a nonabelian discrete flavor symmetry, and the infrared attractive force of gauge interactions in extra dimensions are used to suppress them at the compactification scale. We present a concrete model, which is a simple extension of S_{3} invariant minimal supersymmetric standard model, where only SU(2)_{L} and SU(3)_{C} gauge multiplets are assumed to propagate in the bulk. We find that a disorder of two orders of magnitude in soft supersymmetry breaking parameters above the compactification scale may be allowed to satisfy experimental constraints on FCNC processes and CP violating phenomena.

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arXiv2003

Localized tadpoles and anomalies in 6D orbifolds

In this talk, we review the instability due to radiatively induced FI tadpoles in ${\cal N}=2$ supersymmetric gauge theories on orbifolds in six dimensions. Even with the localized FI tadpoles, we have the unbroken supersymmetry at the expense of having the spontaneous localization of bulk zero mode. We find the non-decoupling of massive modes unlike the 5D case. We also comment on the local anomaly cancellation.

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arXiv2003

Anomalies on orbifolds with gauge symmetry breaking

We embed two 4D chiral multiplets of opposite representations in the 5D N=2 $SU(N+K)$ gauge theory compactified on an orbifold $S^1/(Z_2\times Z'_2)$. There are two types of orbifold boundary conditions in the extra dimension to obtain the 4D N=1 $SU(N)\times SU(K)\times U(1)$ gauge theory from the bulk: in Type I, one has the bulk gauge group at $y=0$ and the unbroken gauge group at $y=πR/2$ while in Type II, one has the unbroken gauge group at both fixed points. In both types of orbifold boundary conditions, we consider the zero mode(s) as coming from a bulk $(K+N)$-plet and brane fields at the fixed point(s) with the unbroken gauge group. We check the consistency of this embedding of fields by the localized anomalies and the localized FI terms. We show that the localized anomalies in Type I are cancelled exactly by the introduction of a bulk Chern-Simons term. On the other hand, in some class of Type II, the Chern-Simons term is not enough to cancel all localized anomalies even if they are globally vanishing. We also find that for the consistent embedding of brane fields, there appear only the localized log FI terms at the fixed point(s) with a U(1) factor.

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arXiv2003

Spontaneous localization of bulk fields: the six-dimensional case

We study N=2 supersymmetric gauge theories with $d=6$ bulk and $d=4$ brane fields charged under a U(1) gauge symmetry. Radiatively induced Fayet-Iliopoulos terms lead to an instability of the bulk fields. We compute the profile of the bulk zero modes and observe the phenomenon of spontaneous localization towards the position of the branes. While this mechanism is quite similar to the $d=5$ case, the mass spectrum of the excited Kaluza-Klein modes shows a crucial difference.

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arXiv2003

Softness of Brane-localized Supersymmetry Breaking on Orbifolds

We consider the brane-localized supersymmetry breaking in 5D compactified on $S^1/Z_2$. In case of a bulk gaugino with arbitrary brane masses for its even and odd modes, we find the mass spectrum and the wave functions of gaugino. We show that the gaugino masses at the distant brane are soft in the usual sense in the effective field theory with zero modes of bulk gauge fields and they are also extremely soft in view of the one-loop finite mass of a brane scalar in the KK regularization.

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arXiv2003

Towards 5D Grand Unification without SUSY Flavor Problem

We consider the renormalization group approach to the SUSY flavor problem in the supersymmetric SU(5) model with one extra dimension. In higher dimensional SUSY gauge theories, it has been recently shown that power corrections due to the Kaluza-Klein states of gauge fields run the soft masses generated at the orbifold fixed point to flavor conserving values in the infra-red limit. In models with GUT breaking at the brane where the GUT scale can be larger than the compactification scale, we show that the addition of a bulk Higgs multiplet, which is necessary for the successful unification, is compatible with the flavor universality achieved at the compactification scale.

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arXiv2002

5D $SU(3)_W$ unification at TeV and cancellation of local gauge anomalies with split multiplets

We consider the 5D gauge unification of $SU(2)_L\times U(1)_Y$ into $SU(3)_W$ at a TeV scale. Compactification of the extra dimension on an orbifold $S^1/(Z_2\times Z'_2)$ allows fixed points where $SU(2)_L\times U(1)_Y$ representations can be assigned. We explain the long proton lifetime and the top-bottom mass hierarchy and etc. geometrically. We also show that local gauge anomalies on the orbifold can be exactly cancelled by a 5D Chern-Simons term with a jumping coefficient.

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arXiv2002

More self-tuning solutions with $H_{MNPQ}$

We find more self-tuning solutions by introducing a general form for Lagrangian of a 3-index antisymmetric tensor field $A_{MNP}$ in the RS II model. In particular, for the logarithmic Lagrangian, $\propto\log(-H^2)$, we obtained a closed form weak self-tuning solution.

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arXiv2002

Localized nonabelian anomalies at orbifold fixed points

Orbifold compactifications of 10D heterotic strings do allow different sets of chiral fermions at different fixed points. Even if the effective 4D theory is anomaly free by including the bulk fermions, there arise abelian and nonabelian fixed point anomalies from these chiral fermions. As the underlying string theory is well defined these localized fixed point anomalies of the chiral fermions are to be cancelled by a variant of the Green-Schwarz mechanism.

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arXiv2002

TeV scale 5D $SU(3)_W$ unification and the fixed point anomaly cancellation with chiral split multiplets

A possibility of 5D gauge unification of $SU(2)_L \times U(1)_Y$ in $SU(3)_W$ is examined. The orbifold compactification allows fixed points where $SU(2)_L\times U(1)_Y$ representations can be assigned. We present a few possibilities which give long proton lifetime, top-bottom mass hierarchy from geometry, and reasonable neutrino masses. In general, these {\it chiral models} can lead to fixed point anomalies. We can show easily, due to the simplicity of the model, that these anomalies are cancelled by the relevant Chern-Simons terms for all the models we consider. It is also shown that the fixed point U(1)--graviton--graviton anomaly cancels without the help from the Chern-Simons term. Hence, we conjecture that the fixed point anomalies can be cancelled if the effective 4D theory is made anomaly free by locating chiral fermions at the fixed points.

hep-th↗
arXiv2002

Top-bottom mass hierarchy, $s-μ$ puzzle and gauge coupling unification with split multiplets

A supersymmetric 5D SU(5) grand unification is considered. The SU(5) is broken down to $G_{SM}=SU(3)\times SU(2)\times U(1)$ by the $Z_2\times Z_2'$ assignment of the bulk field(s). The matter fields are located at the fixed point(s). In the bulk, a Higgs multiplet $\bar 5_H$(containing the bottom doublet $H_1$) and the SU(5) gauge multiplet are located. At one fixed point, $H_2$(the top doublet) and the standard model matter multiplets are presented. Because of the difference of the locations of $H_1$ and $H_2$, one can obtain a hierarchy between top and bottom Yukawa couplings. We also present a possibility to understand the $s-μ$ mass puzzle in this framework of the split multiplet.

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arXiv2002

Dual Description of Brane World Cosmological Constant with $H_{MNPQ}$

We present a short review of the recent 5D self-tuning solution of the cosmological constant problem with $1/H^2$ term, and present the dual description of the solution. In the dual description, we show that the presence of the coupling of the dual field($σ$) to the brane(which is a bit different from the original theory) maintains the self-tuning property.

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arXiv2001

Wave function of the radion in the brane background with a massless scalar field and a self-tuning problem

We consider flat solutions in the brane background with a massless scalar field appearing in 5D $H^2_{MNPQ}$. Since there exist bulk singularities or arises the divergent 4D Planck mass, we should introduce a compact extra dimension, the size of which is then fixed by brane tension(s) and a bulk cosmological constant. Inspecting scalar perturbations around the flat solutions, we find that the flat solutions are stable vacua from the positive mass spectrum of radion. We show that the massless radion mode is projected out by the boundary condition arising in cutting off the extra dimension. Thus, the fixed extra dimension is not alterable, which is not useful toward a self-tuning of the cosmological constant.

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arXiv2001

$Z_N$ orbifold compactifications in $AdS_6$ with Gauss-Bonnet term

We present a general setup for junctions of semi-infinite 4-branes in $AdS_6$ with the Gauss-Bonnet term. The 3-brane tension at the junction of 4-branes can be nonzero. Using the brane junctions as the origin of the $Z_N$ discrete rotation symmetry, we identify 3-brane tensions at three fixed points of the orbifold $T^2/Z_3$ in terms of the 4-brane tensions. As a result, the three 3-brane tensions can be simultaneously positive, which enables us to explain the mass hierarchy by taking one of two branes apart from the hidden brane as the visible brane, and hence does not introduce a severe cosmological problem.

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