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Yi-Yen Wu

Publications and source records attributed to Yi-Yen Wu.

13 recordsLinked to original sources
arXiv1999

Gaugino Masses in Modular Invariant Supergravity

We calculate gaugino masses in string-derived models with hidden-sector gaugino condensation. The linear multiplet formulation for the dilaton superfield is used to implement perturbative modular invariance. The contribution arising from quantum effects in the observable sector includes the term recently found in generic supergravity models. A much larger contribution is present if matter fields with Standard Model gauge couplings also couple to the Green-Schwarz counter term. We comment on the relation of our Kähler U(1) superspace formalism to other calculations.

hep-th↗
arXiv1999

Gaugino Condensation in N=1 Supergravity Models with Multiple Dilaton-Like Fields

We study supersymmetry breaking by hidden-sector gaugino condensation in N=1 D=4 supergravity models with multiple dilaton-like moduli fields. Our work is motivated by Type I string theory, in which the low-energy effective Lagrangian can have different dilaton-like fields coupling to different sectors of the theory. We construct the effective Lagrangian for gaugino condensation and use it to compute the visible-sector gaugino masses. We find that the gaugino masses can be of order the gravitino mass, in stark contrast to heterotic string models with a single dilaton field.

hep-th↗
arXiv1998

D-Instanton in AdS_5 and Instanton in SYM_4

Following the observation of Banks and Green that the D-instantons in AdS_5 correspond to the instantons in 4-dimensional supersymmetric Yang-Mills theory, we study in more detail this correspondence for individual instantons. The supergravity solution for a D-instanton in AdS_5 is found using the ansatz used previously for D-instantons in flat space. We check that the actions and supersymmetries match between the D-instanton solution and the Yang-Mills instanton. Generalizing this result, we propose that any supergravity solution satisfying the ansatz corresponds to a (anti-)self-dual Yang-Mills configuration. Using this ansatz a family of identities for correlation functions in the supersymmetric Yang-Mills theory are derived.

hep-th↗
arXiv1998

Towards a Noncommutative Geometric Approach to Matrix Compactification

In this paper we study generic M(atrix) theory compactifications that are specified by a set of quotient conditions. A procedure is proposed, which both associates an algebra to each compactification and leads deductively to general solutions for the matrix variables. The notion of noncommutative geometry on the dual space is central to this construction. As examples we apply this procedure to various orbifolds and orientifolds, including ALE spaces and quotients of tori. While the old solutions are derived in a uniform way, new solutions are obtained in several cases. Our study also leads to a new formulation of gauge theory on quantum spaces.

hep-th↗
arXiv1997

Recent Progress in Weakly-Coupled Heterotic String Phenomenology

Some recent developments in the weakly-coupled heterotic string phenomenology are reviewed. We discuss several important issues such as dilaton/moduli stabilization, supersymmetry breaking (by hidden-sector gaugino condensation), gauge coupling unification (or the Newton's constant), the QCD axion, as well as cosmological problems involving the dilaton/moduli and the axion.

hep-ph↗
arXiv1997

Supersymmetry Breaking in Superstring Theory by Gaugino Condensation and its Phenomenology

The weakly-coupled heterotic string is known to have problems of dilaton/moduli stabilization, supersymmetry breaking (by hidden-sector gaugino condensation), gauge coupling unification (or the Newton's constant), QCD axion, as well as cosmological problems. We study these problems by adopting the viewpoint that they arise mostly due to our limited calculational power, little knowledge of the vacuum structure, and an inappropriate treatment of gaugino condensation. It turns out that these problems can be solved or are much less severe after a more consistent and complete treatment. There are two kinds of non-perturbative effects in the construction of effective field theory: the field-theoretical non-perturbative effects of gaugino condensation (with a constraint ignored in the past) and the stringy non-perturbative effects conjectured by Shenker, which are best described using the linear multiplet formalism. Stringy non-perturbative corrections to the Kähler potential are invoked to stabilize the dilaton at a value compatible with a weak coupling regime. Modular invariance is ensured through the Green-Schwarz counterterm and string threshold corrections which, together with hidden matter condensation, lead to moduli stabilization at the self-dual point where the vev's of moduli's F-components vanish. In the vacuum, supersymmetry is broken at a realistic scale with vanishing cosmological constant. As for soft supersymmetry breaking, our model always leads to a dilaton-dominated scenario. For the strong CP problem, the model-independent axion has the right properties to be the QCD axion. Furthermore, there is a natural mass hierarchy between the dilaton/moduli and the gravitino, which could solve the cosmological moduli problem and the cosmological problem of the model-independent axion.

hep-th↗
arXiv1997

Supersymmetry breaking and weakly vs. strongly coupled string theory

In the context of the field theory limit of superstrings, we consider an almost realistic model of supersymmetry breaking by gaugino condensation which includes, through nonperturbative corrections to the Kähler potential, dilaton stabilization at a value compatible with a weak coupling regime. Invariance under modular transformations is ensured through a Green-Schwarz term and string threshold corrections, which lead to moduli stabilization at the self-dual point. We are thus in a position to discuss several issues of physical relevance: gravitino, dilaton and moduli masses, axion, soft supersymmetry breaking parameters and gauge coupling unification.

hep-th↗
arXiv1996

Dilaton Stabilization and Supersymmetry Breaking by Dynamical Gaugino Condensation in the Linear Multiplet Formalism of String Effective Theory

We study dynamical gaugino condensation in superstring effective theories using the linear multiplet representation for the dilaton superfield. An interesting necessary condition for the dilaton to be stabilized, which was first derived in generic models of static gaugino condensation, is shown to hold for generic models of dynamical gaugino condensation. We also point out that it is stringy non-perturbative effects that stabilize the dilaton and allow dynamical supersymmetry breaking via the field-theoretical non-perturbative effect of gaugino condensation. As a typical example, a toy S-dual model of a dynamical E_8 condensate is constructed and the dilaton is explicitly shown to be stabilized with broken supersymmetry and (fine-tuned) vanishing cosmological constant.

hep-th↗
arXiv1996

Modular Invariant Formulation of Multi-Gaugino and Matter Condensation

Using the linear multiplet formulation for the dilaton superfield, we construct an effective lagrangian for hidden-sector gaugino condensation in string effective field theories with arbitrary gauge groups and matter. Nonperturbative string corrections to the Kähler potential are invoked to stabilize the dilaton at a supersymmetry breaking minimum of the potential. When the cosmological constant is tuned to zero the moduli are stabilized at their self-dual points, and the vev's of their F-component superpartners vanish. Numerical analyses of one- and two-condensate examples with massless chiral matter show considerable enhancement of the gauge hierarchy with respect to the E_8 case. The nonperturbative string effects required for dilaton stabilization may have implications for gauge coupling unification. As a comparison, we also consider a parallel approach based on the commonly used chiral formulation.

hep-th↗
arXiv1996

Dilaton Stabilization in the Context of Dynamical Supersymmetry Breaking through Gaugino Condensation

We study gaugino condensation in the context of superstring effective theories using the linear multiplet formulation for the dilaton superfield. Including nonperturbative corrections to the Kähler potential for the dilaton may naturally achieve dilaton stabilization, with supersymmetry breaking and gaugino condensation; these three issues are interrelated in a very simple way. In a toy model with a single static condensate, a dilaton $vev$ is found within a phenomenologically interesting range. The effective theory differs significantly from condensate models studied previously in the chiral formulation.

hep-th↗
arXiv1995

The Minimal Supersymmetric Model of Higgs-Higgs Condensation

This paper is motivated by three issues associated with the supersymmetric extension of the standard model: the $μ$ problem, the possibility of raising the upper bound on the lightest-Higgs mass, and the triviality problem associated with the Higgs sector. A new scheme based on the Higgs-Higgs condensation is proposed, and it is shown that these three issues are well solved by this scheme. As the first realization of this new scheme, the Minimal Supersymmetric Model of Higgs-Higgs Condensation (MSMHHC) is constructed and studied in detail. The MSMHHC is identical with the MSSM (Minimal Supersymmetric Standard Model) in the fundamental particle content, and their lagrangians differ only in the Higgs sector. The Higgs sector of the MSMHHC is based on the softly-broken supersymmetric Nambu$-$Jona-Lasinio model with the four-field interaction of the Higgs doublets. At low energy, these two Higgs doublets condense into two neutral Higgs gauge singlets, and the low-energy effective lagrangian of the MSMHHC has the form of the non-minimal supersymmetric standard model which contains two more Higgs singlets than the MSSM. Another unique feature of the MSMHHC is that heavy top quark always implies strongly-interacting low-energy Higgs sector, i.e., a large mass for the lightest Higgs boson. A systematic study of the parameter space is also made in order to reveal the qualitative features of the MSMHHC. Finally, we comment on the question "How large can the lightest-Higgs mass be?" with the conclusion that the supersymmetric model of Higgs-Higgs condensation will be the most promising candidate if the lightest-Higgs mass of the MSSM is excluded by the future experiments.

hep-ph↗
arXiv1995

Triviality Bounds in the Next to Minimal Supersymmetric Standard Model

We study the implications of the triviality problem for the Higgs masses and other relevant parameters in the Next to Minimal Supersymmetric Standard Model (NMSSM). By means of triviality, a new way to constrain parameters is proposed, and therefore we are able to derive triviality bounds on the heaviest-Higgs mass, the lightest-Higgs mass, the soft SUSY- breaking parameters, and the vacuum expectation value of the Higgs gauge singlet through a thorough examination of the parameter space. The triviality upper bound on the lightest-Higgs mass predicted by NMSSM is indeed larger than the upper bound predicted by MSSM.

hep-ph↗