arXiv subjects

Kiwoon Choi

Publications and source records attributed to Kiwoon Choi.

At least 91 records · Page 5Linked to original sources

arXiv2003

Supersymmetry Breaking in Warped Geometry

We examine the soft supersymmetry breaking parameters in supersymmetric theories on a slice of AdS_5 which generate the hierarchical Yukawa couplings by dynamically localizing the bulk matter fields in extra dimension. Such models can be regarded as the AdS dual of the recently studied 4-dimensional models which contain a supersymmetric CFT to generate the hierarchical Yukawa couplings. In such models, if supersymmetry breaking is mediated by the bulk radion superfield and/or some brane chiral superfields, potentially dangerous flavor-violating soft parameters can be naturally suppressed, thereby avoiding the SUSY flavor problem. We present some models of radion-dominated supersymmetry breaking which yield a highly predictive form of soft parameters in this framework.

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arXiv2003

SUSY Flavor Problem and Warped Geometry

We point out that supersymmetric warped geometry can provide a solution to the SUSY flavor problem, while generating hierarchical Yukawa couplings. In supersymmetric theories in a slice of AdS_5 with the Kaluza-Klein scale M_KK much higher than the weak scale, if all visible fields originate from 5D bulk fields and supersymmetry breaking is mediated by the bulk radion superfield and/or some brane chiral superfields, potentially dangerous soft scalar masses and trilinear $A$ parameters at M_KK can be naturally suppressed compared to the gaugino masses by small warp factor. We present simple models yielding phenomenologically interesting patterns of soft parameters in this framework.

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arXiv2002

Radius-dependent gauge unification in AdS5

We examine the relation of the 4-dimensional low energy coupling of bulk gauge boson in a slice of AdS5 to the 5-dimensional fundamental couplings as a function of the orbifold radius R. This allows us to address the gauge coupling unification in AdS5 by means of the radius running as well as the conventional momentum running. We then compute the radius dependence of 1-loop low energy couplings in generic AdS5 theory with 4-dimensional supersymmetry, and discuss the low energy predictions when the 5-dimensional couplings are assumed to be unified.

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arXiv2002

Gauge coupling renormalization in orbifold field theories

We investigate the gauge coupling renormalization in orbifold field theories preserving 4-dimensional N=1 supersymmetry in the framework of 4-dimensional effective supergravity. As a concrete example, we consider the 5-dimensional Super-Yang-Mills theory on a slice of AdS_5. In our approach, one-loop gauge couplings can be determined by the loop-induced axion couplings and the tree level properties of 4-dimensional effective supergravity which are much easier to be computed.

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arXiv2002

Operator Analysis of Neutrinoless Double Beta Decay

We study the effective operators of the standard model fields which would yield an observable rate of neutrinoless double beta decay. We particularly focus on the possibility that neutrinoless double beta decay is dominantly induced by lepton-number-violating higher dimensional operators other than the Majorana neutrino mass. Our analysis can be applied to models in which neutrinoless double beta decay is induced either by a strong dynamics or by quantum gravity effects at a fundamental scale near the TeV scale as well as the conventional models in which neutrinoless double beta decay is induced by perturbative renormalizable interactions.

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arXiv2001

Sneutrino-Antisneutrino Mixing and Neutrino Mass in Anomaly--mediated Supersymmetry Breaking Scenario

In supersymmetric models with nonzero Majorana neutrino mass, the sneutrino and antisneutrino mix, which may lead to same sign dilepton signals in future collider experiments. We point out that the anomaly-mediated supersymmetry breaking scenario has a good potential to provide an observable rate of such signals for the neutrino masses suggested by the atmospheric and solar neutrino oscillations. The sneutrino mixing rate is naturally enhanced by m_{3/2}/m_{\tildeν}={\cal O}(4π/α) while the sneutrino decay rate is small enough on a sizable portion of the parameter space. We point out also that the sneutrino-antisneutrino mixing can provide much stronger information on some combinations of the neutrino masses and mixing angles than neutrino experiments.

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arXiv2001

Bi-maximal neutrino mixing and small U_{e3} from Abelian flavor symmetry

Atmospheric neutrino data strongly suggests a near-maximal ν_μ-ν_τ mixing and also solar neutrino data can be nicely explained by another near-maximal ν_e-ν_μ or ν_e-ν_τ mixing. We examine the possibility that this bi-maximal mixing of atmospheric and solar neutrinos arises naturally, while keeping U_{e3} and Δm^2_{sol}/Δm^2_{atm} small enough, as a consequence of Abelian flavor symmetry. Two simple scenarios of Abelian flavor symmetry within supersymmetric framework are considered to obtain the desired form of the neutrino mass matrix and the charged lepton mass matrix parameterized by the Cabibbo angle λ\approx 0.2. Future experiments at a neutrino factory measuring the size of U_{e3} and the sign of Δm^2_{32} could discriminate those scenarios as they predict distinctive values of U_{e3} in connection with Δm^2_{sol}/Δm^2_{atm} and also with the order of the neutrino mass eigenvalues.

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arXiv2001

Axino as a sterile neutrino

We present a supersymmetric axion model in which the fermionic superpartner of axion, i.e. the axino, corresponds to a sterile neutrino which would accommodate the LSND data with atmospheric and solar neutrino oscillations.

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arXiv2001

Probing the messenger of supersymmetry breaking by the muon anomalous magnetic moment

Motivated by the recently measured muon's anomalous magnetic moment $a_μ$, we examine the supersymmetry contribution to $a_μ$ in various mediation models of supersymmetry breaking which lead to predictive flavor conserving soft parameters at high energy scale. The studied models include dilaton/modulus-mediated models in heterotic string/$M$ theory, gauge-mediated model, no-scale or gaugino-mediated model, and also the minimal and deflected anomaly-mediated models. For each model, the range of $a^{SUSY}_μ$ allowed by other experimental constraints, e.g. b --> sγand the collider bounds on superparticle masses, is obtained together with the corresponding parameter region of the model. Gauge-mediated models with low messenger scale can give any $a^{SUSY}_μ$ within the $2σ$ bound. In many other models, b --> sγfavors $a^{SUSY}_μ$ smaller than either the $-1σ$ value ($26\times 10^{-10}$) or the central value ($42\times 10^{-10}$).

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arXiv2001

Atmospheric and Solar Neutrino Masses and Abelian Flavor Symmetry

Recent atmospheric and solar neutrino experiments suggest that neutrinos have small but nonzero masses. They further suggest that mass eigenvalues have certain degree of hierarchical structures, and also some mixing angles are near-maximal while the others are small. We first survey possible explanations for the smallness of neutrino masses. We then discuss some models in which the hierarchical pattern of neutrino masses and mixing angles arises as a consequence of U(1) flavor symmetries which would explain also the hierarchical quark and charged lepton masses.

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arXiv2001

Axino as a sterile neutrino and R parity violation

We point out that axino can be a natural candidate for sterile neutrino which would accommodate the LSND data with atmospheric and solar neutrino oscillations. It is shown that the so called 3+1 scheme can be easily realized when supersymmetry breaking is mediated by gauge interactions and also R-parity is properly broken. Among the currently possible solutions to the solar neutrino problem, only the large angle MSW oscillation is allowed in this scheme. The weak scale value of the Higgs $μ$ parameter and the required size of R-parity violation can be understood by means of spontaneously broken Peccei-Quinn symmetry.

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arXiv2000

String or M theory axion as a quintessence

A slow-rolling scalar field ($Q\equiv$ Quintessence) with potential energy $V_Q\sim (3\times 10^{-3} {\rm eV})^4$ has been proposed as the origin of accelerating universe at present. We investigate the effective potential of $Q$ in the framework of supergravity model including the quantum corrections induced by generic (nonrenormalizable) couplings of $Q$ to the gauge and charged matter multiplets. It is argued that the Kähler potential, superpotential and gauge kinetic functions of the underlying supergravity model are required to be invariant under the variation of $Q$ with an extremely fine accuracy in order to provide a working quintessence potential. Applying these results for string or $M$-theory, we point out that the heterotic $M$-theory or Type I string axion can be a plausible candidate for quintessence if (i) it does not couple to the instanton number of gauge interactions not weaker than those of the standard model and (ii) the modulus partner ${\rm Re}(Z)$ of the periodic quintessence axion ${\rm Im}(Z)\equiv {\rm Im}(Z)+1$ has a large VEV: ${\rm Re}(Z)\sim \frac{1}{2π}\ln(m_{3/2}^2 M_{Planck}^2/V_Q)$. It is stressed that such a large ${\rm Re}(Z)$ gives the gauge unification scale at around the phenomenologically favored value $3\times 10^{16}$ GeV. To provide an accelerating universe, the quintessence axion should be at near the top of its effective potential at present, which requires a severe fine tuning of the initial condition of $Q$ and $\dot{Q}$ in the early universe. We discuss a late time inflation scenario based on the modular and CP invariance of the moduli effective potential, yielding the required initial condition in a natural manner if the Kähler metric of the quintessence axion superfield receives a sizable nonperturbative contribution.

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arXiv2000

Lepton Flavor Violation and Bilinear R-parity Violation

We examine some flavor changing processes such as rare leptonic decays of the long-lived neutral kaon, muon-electron conversion in nuclei and radiative muon decay which are induced by the combined effects of bilinear and trilinear R-parity violations. These processes are used to put strong constraints on certain products of the bilinear and trilinear couplings. We also discuss the constraints on R-parity violation from neutrino masses and compare them with the constraints from flavor changing decay processes. Large range of parameter space satisfying the constraints from neutrino masses can be excluded by the flavor changing processes considered in this paper, and also vice versa.

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arXiv2000

Fermion Electric Dipole Moments in Supersymmetric Models with R-parity Violation

We analyze the electron and neutron electric dipole moments induced by R-parity violating interactions in supersymmetric models. It is pointed out that dominant contributions can come from one-loop diagrams involving both the bilinear and trilinear R-parity odd couplings, leading to somewhat severe constraints on the products of those couplings.

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arXiv1999

Quintessence, Flat Potential and String/M Theory Axion

A slow-rolling scalar field (Quintessence) has been proposed as the origin of accelerating universe at present. We discuss some features of quintessence, particularly those related with the {\it flatness} of its potential. We distinguish two types of quintessences, a metrical quintessence which couples to the particle physics sector {\it only} through the mixing with the spacetime metric and a non-metrical one without such property. It is stressed that these two types of quintessences have quite different features in regard to the fine tuning of parameters required for the flat potential, as well as different implications for the quintessence-mediated long range force. The fine tuning argument strongly suggests that non-metrical quintessence should correspond to the Goldstone boson of an almost exact nonlinear global symmetry whose explicit breaking by quantum gravity effects is highly suppressed. It is briefly discussed whether the radion field in higher dimensional theories can be a candidate for metrical quintessence. We finally discuss the possibility that string/$M$ theory axion corresponds to a Goldstone-type quintessence, and argue that a certain combination of the heterotic $M$ theory or Type I string theory axions can be a good candidate for quintessence if some conditions on the moduli dynamics are satisfied.

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arXiv1999

String theoretic axion coupling and the evolution of cosmic structures

We examine the effects of the axion coupling to $R\tilde{R}$ on the evolution of cosmic structures. It is shown that the evolutions of the scalar- and vector-type perturbations are not affected by this axion coupling. However the axion coupling causes an asymmetric evolution of the two polarization states of the tensor-type perturbation, which may lead to a sizable polarization asymmetry in the cosmological gravitational wave if inflation involves a period in which the axion coupling is important. The polarization asymmetry produced during inflation are conserved over the subsequent evolution as long as the scales remain in the large-scale limit, and thus this may lead to an observable trace in the cosmic microwave background radiation.

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arXiv1999

Dynamical solution to the $μ$ problem at TeV scale

We introduce a new confining force (μ-color) at TeV scale to dynamically generate a supersymmetry preserving mass scale which would replace the μparameter in the minimal supersymmetric standard model (MSSM). We discuss the Higgs phenomenology and also the pattern of soft supersymmetry breaking parameters allowing the correct electroweak symmetry breaking within the μ-color model, which have quite distinctive features from the MSSM and also from other generalizations of the MSSM.

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arXiv1999

Cosmological Gravitino Production in Gauge Mediated Supersymmetry Breaking Models

We study the cosmological gravitino production in gauge mediated supersymmetry breaking models, while properly taking into account the existence of the messenger mass scale. It is found that for sizable parameter range of the model the messenger sector contribution leads to more stringent upper bound on the reheat temperature obtained from the condition that the universe should not be overclosed by relic gravitinos. However it turns out that in the limit of relatively low messenger scale and large gravitino mass, the relic gravitino mass density can be smaller than the critical density independently of the reheat temperature, suggesting the possibility in this limit to have a high reheat temperature without the dilution of gravitinos at late time.

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