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Kiwoon Choi

Publications and source records attributed to Kiwoon Choi.

At least 109 records · Page 6Linked to original sources
arXiv1998

Atmospheric and Solar Neutrino Masses from Horizontal U(1) Symmetry

We study the neutrino mass matrix in supersymmetric models in which the quark and charged lepton mass hierarchies and also the suppression of baryon or lepton number violating couplings are all explained by horizontal $U(1)_X$ symmetry. It is found that the neutrino masses and mixing angles suggested by recent atmospheric and solar neutrino experiments arise naturally in this framework which fits in best with gauge-mediated supersymmetry breaking with large $\tanβ$. This framework highly favors the small angle MSW oscillation of solar neutrinos, and determine the order of magnitudes of all the neutrino mixing angles and mass hierarchies.

hep-ph↗
arXiv1998

Small Instanton Contribution to the Axion Potential in Supersymmetric Models

Small size QCD instantons may spoil the axion solution to the strong CP problem if QCD is not asymptotically free at high energy scales. We examine this issue in supersymmetric models using a manifestly supersymmetric scheme to compute the axion potential induced by small size instantons. Applying this scheme for a class of illustrative models, it is found that the resulting high energy axion potential is highly model-dependent, but suppressed by more powers of the soft supersymmetry breaking parameters and/or of the other small mass scales than what is expected based on a naive instanton graph analysis. Our analysis suggests that the axion solution is stable against the small QCD instanton effects in a wide class of supersymmetric models even when QCD is not asymtotically free at high energy scales.

hep-ph↗
arXiv1998

Moduli Stabilization in Heterotic $M$-theory

We examine the stabilization of the two typical moduli, the length $ρ$ of the eleventh segment and the volume $V$ of the internal six manifold, in compactified heterotic $M$-theory. It is shown that, under certain conditions, the phenomenologically favored vacuum expectation values of $ρ$ and $V$ can be obtained by the combined effects of multi-gaugino condensations on the hidden wall and the membrane instantons wrapping the three cycle of the internal six manifold.

hep-th↗
arXiv1998

Cosmology of Light Moduli

In string/M-theory with a large compactification radius, some axion-like moduli can be much lighter than the gravitino. Generic moduli in gauge-mediated supersymmetry breaking models also have a mass far below the weak scale. Motivated by these, we examine the cosmological implications of light moduli for the mass range from the weak scale to an extremely small scale of order 10^{-26} eV, and obtain an upper bound on the initial moduli misalignment for both cases with and without a late entropy production.

hep-ph↗
arXiv1997

Four-Dimensional Effective Supergravity and Soft Terms in M-Theory

We provide a simple macroscopic analysis of the four-dimensional effective supergravity of the Hořava-Witten M-theory which is expanded in powers of $κ^{2/3}/ρV^{1/3}$ and $κ^{2/3}ρ/V^{2/3}$ where $κ^2$, $V$ and $ρ$ denote the eleven-dimensional gravitational coupling, the Calabi-Yau volume and the eleventh length respectively. Possible higher order terms in the Kähler potential are identified and matched with the heterotic string corrections. In the context of this M-theory expansion, we analyze the soft supersymmetry-breaking terms under the assumption that supersymmetry is spontaneously broken by the auxiliary components of the bulk moduli superfields. It is examined how the pattern of soft terms changes when one moves from the weakly coupled heterotic string limit to the M-theory limit.

hep-th↗
arXiv1997

Supergravity Radiative Effects on Soft Terms and the $μ$ Term

We compute quadratically divergent supergravity one-loop effects on soft supersymmetry-breaking parameters and the $μ$ term in generic hidden sector supergravity models. These effects can significantly modify the matching condition for soft parameters at the Planck scale and also provide several new sources of the $μ$ term which are naturally of order the weak scale. We also discuss some phenomenological implications of these effects, particularly the violation of the scalar mass universality which may lead to dangerous FCNC phenomena, and apply the results to superstring effective supergravity models.

hep-ph↗
arXiv1997

Axions and the Strong CP Problem in M-theory

We examine the possibility that the strong CP problem is solved by string-theoretic axions in strong-coupling limit of the E_8 x E_8 heterotic string theory (M-theory). We first discuss some generic features of gauge kinetic functions in compactified M-theory, and examine in detail the axion potential induced by the explicit breakings other than the QCD anomaly of the non-linear U(1)_{PQ} symmetries of string-theoretic axions. It is argued based on supersymmetry and discrete gauge symmetries that if the compactification radius is large enough, there can be a U(1)_{PQ}-symmetry whose breaking other than the QCD anomaly, whatever its microscopic origin is, is suppressed enough for the axion mechanism to work. Phenomenological viability of such a large radius crucially depends upon the quantized coefficients in gauge kinetic functions. We note that the large radius required for the axion mechanism is viable only in a limited class of models. For instance, for compactifications on a smooth Calabi-Yau manifold with a vanishing second E_8 field strength, it is viable only when the quantized flux of the antisymmetric tensor field in M-theory has a minimal nonzero value. It is also stressed that this large compactification radius allows the QCD axion in M-theory to be cosmologically viable in the presence of a late time entropy production.

hep-th↗
arXiv1997

Cosmology of Radiatively Generated Axion Scale

We discuss some cosmological aspects of supersymmetric axion models in which the axion scale is radiatively generated in terms of the weak scale and the Planck scale. They include thermal inflation, axions produced by the decay of oscillating Peccei-Quinn flatons, late time baryogenesis, and finally the possibility to raise up the cosmological upper bound on the axion scale in thermal inflation scenario.

hep-ph↗
arXiv1996

Supersymmetry Hierarchy Problems and Anomalous Horizontal U(1) Symmetry

It is suggested that various hierarchy problems in supersymmetric standard model, i.e. the Yukawa hierarchies, the μproblem, and the suppression of dangerous baryon and/or lepton number (B/L) violating couplings, are resolved altogether in the framework of horizontal U(1) symmetry whose spontaneous breaking results in the appearance of one expansion parameter (the Cabibbo angle). Within a reasonable range of U(1) charges, there exist a few models compatible with experiments. The specific sizes of B/L violating couplings of these models are calculated and several phenomenological consequences are discussed.

hep-ph↗
arXiv1996

Proton Decay with a Light Gravitino or Axino

We consider the proton decay in supersymmetric models with a gravitino or axino lighter than the proton. This consideration leads to a stringent limit on the R parity and B violating Yukawa coupling of the superpotential operator U^c_i D^c_j D^c_k as $λ"_{112} < 10^{-15} (m_{3/2}/eV)$ for a light gravitino, and $λ"_{112} < 10^{-15} (F_a/ 10^{10} GeV)$ for a light DFSZ axino. For hadronic axino, the constraint is weakened by the factor of 10^{3}.

hep-ph↗
arXiv1996

The $μ$ problem, and B and L Conservation with a Discrete Gauge R Symmetry

We examine in a generic context how the $μ$ problem can be resolved by means of a spontaneously broken gauge symmetry. We then focus on the new scheme based on a discrete gauge R symmetry which is spontaneously broken by nonperturbative hidden sector dynamics triggering supersymmetry breaking also. The possibility to suppress the dangerous baryon and/or lepton number violating interactions by means of this discrete R symmetry is examined also together with some phenomenological consequences.

hep-ph↗
arXiv1996

Axion Cosmology with a Stronger QCD in the Early Universe

We examine in the context of supersymmetric models whether the usual cosmological upper bound on the axion decay constant can be relaxed by assuming a period of stronger QCD in the early universe. By evaluating the axion potential in the early universe and also taking into account the dilaton potential energy, it is argued that a stronger QCD is not useful for raising up the bound.

hep-ph↗
arXiv1995

Goldstone Supermultiplet as the Messenger of Supersymmetry Breaking

We consider supersymmetric models in which a (pseudo) Goldstone supermultiplet plays the role of the messenger of supersymmetry breaking. Such models lead to a highly predictive form of flavor and CP conserving soft terms, particularly the soft scalar masses and trilinear couplings vanish at the scale where the (approximate) global symmetry is spontaneously broken. We discuss also the possibility for realizing this scheme in supergravity models derived from string theories.

hep-ph↗
arXiv1995

Phenomenology of Soft Terms in the Presence of Nonvanishing Hidden Sector Potential Energy

We argue that the hidden sector potential energy is generically of order the intermediate scale although the true cosmological constant does vanish. This would significantly change the predicted values of soft parameters for a variety of supergravity models including those derived from string theory. We stress that this point is particularly relevant for supergravity models in which the soft masses of observable fields vanish at tree level. Implications of a nonzero hidden sector potential energy for low energy phenomenology are also studied.

hep-ph↗
arXiv1994

An Automatic Invisible Axion In The SUSY Preon Model

It is shown that the recently proposed preon model which provides a unified origin of the diverse mass scale and an explanation of family replication as well as of inter-family mass-hierarchy, possesses a Peccei-Quinn symmetry whose spontaneous breaking leads to an automatic invisible axion. Existence of the PQ-symmetry is simply a consequence of supersymmetry and requirement of minimality in the field-content and interactions, which propose that the lagrangian should possess only those terms which are dictated by the gauge principle and no others. In addition to the axion, the model also generates two superlight Goldstone bosons and their superpartners which are cosmologically safe.

hep-ph↗
arXiv1994

Cosmological Constant and Soft Terms in Supergravity

Some of the soft SUSY breaking parameters in hidden sector supergravity model depend on the expectation value of the hidden sector scalar potential, $ $, whose tree level value is equal to the tree level cosmological constant. The current practice of calculating soft parameters assumes that $ =0$. Quantum correction to the cosmological constant can differ from the correction to $ $ by an amount of order $m^2_{3/2}M_{Pl}^2/8π$. This implies that, for the vanishing cosmological constant, the $ $--dependent parts of soft terms can be sizable, and hence the supergravity phenomenology should be accordingly modified.

hep-ph↗
arXiv1994

Small Flavor Conserving CP Violation in Superstring Models

It is well known that supersymmetric models allow new sources for CP violation that arise from soft supersymmetry breaking terms. If unsuppressed, these new CP-violating phases would give too large a neutron electric dipole moment. We discuss a mechanism for suppressing SUSY phases in string-inspired supergravity models in which supersymmetry is assumed to be broken by the auxiliary components of the dilaton and moduli superfields. (To appear in the Proceeding of the Third KEK Topical Conference on CP Violation, its Implication to Particle Physics and Cosmology)

hep-ph↗