Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We study the D-term contribution for anomalous U(1) symmetries in type I string models and derive a general formula for the D-term contribution, assuming that the dominant source of supersymmetry breaking is given by the F terms of the dilaton, (overall) moduli, or twisted moduli fields. On the basis of the formula, we also point out that there are several features different from the case of heterotic string models. The differences originate from the different forms of the Kahler potential between twisted moduli fields in type I string models and the dilaton field in heterotic string models.

DOI： 10.1103/PhysRevD.69.086004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We study the dilaton stabilization in models with anomalous U(l) symmetry by adding specific string-motivated, non-perturbative corrections to the tree-level dilaton Kahler potential. We find that the non-perturbative effects can stabilize the dilaton at a desirably large value. We also observe that the size of Fayet-Iliopoulos term is reduced at the stabilized point. (C) 2004 Published by Elsevier B.V.

DOI： 10.1016/j.physleb.2003.12.044

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE  

In this paper, we study flavor violation in supersymmetric models with gauged flavor symmetries. There are several sources of flavor violation in these theories. The dominant flavor violation is the tree-level D-term contribution to scalar masses generated by flavor symmetry breaking. We present a new approach for suppressing these phenomenologically dangerous effects by separating the flavor-breaking sector from the supersymmetry-breaking sector. This separation can be achieved either in geometrical setups or in a dynamical way. We also point out that radiative corrections from the gauginos of gauged flavor symmetries can yield sizable generation-dependent masses of scalars. Generically the gaugino mass effects are not suppressed, even if the dominant D-term contribution is suppressed. We also analyze the constraints on the flavor symmetry sector resulting from these flavor-violating corrections.

DOI： 10.1088/1126-6708/2003/02/022

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We discuss issues in a scenario where hierarchical Yukawa couplings are generated through the strong dynamics of superconformal field theories (SCFTs). Independently of the mediation mechanism of supersymmetry breaking, the infrared convergence property of SCFTs can provide an interesting solution to the supersymmetric flavor problem; sfermion masses are suppressed around the decoupling scale of SCFTs and eventually become degenerate to some degree, thanks to family-independent radiative corrections governed by the gaugino masses of the minimal supersymmetric standard model (MSSM). We discuss under what conditions the degeneracy of the sfermion mass can be estimated in a simple manner. We also discuss the constraints from lepton flavor violations. We then explicitly study sfermion mass degeneracy within the framework of grand unified theories coupled to SCFTs. It is found that the degeneracy for right-handed sleptons becomes worse in the conventional SU(5) model than in the MSSM. On the other hand, in the flipped SU(5)xU(1) model, each right-handed lepton is still an SU(5) singlet, whereas the B-ino mass M-1 is determined by two independent gaugino masses of SU(5)xU(1). These two properties enable us to have an improved degeneracy for the right-handed sleptons. We also speculate on how further improvement can be obtained in the SCFT approach.

DOI： 10.1103/PhysRevD.66.095011

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1143/PTPS.123.387

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevD.62.084025

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Yukawa Institute for Theoretical Physics  

We discuss the embedding of anomalous U(1) supersymmetry breaking into supergravity, working in the effective theory after integrating out a strongly interacting non-Abelian gauge sector. By explicitly performing the fine-tuning of the cosmological constant, we calculate the gravitino mass and the supergravity correction to the expectation value of the auxiliary field D, the latter of which was previously argued to give rise to a dominant source of soft scalar masses. Unlike the conventional scheme of the hidden-sector gaugino condensation, we generically find a rather large gravitino mass m3/2 of order Λ̂3 / ξMpl, expressed in terms of the scale Λ̂ of the gaugino condensation and the scale ξ of the Fayet-Iliopoulos term. The explicit solution is given for the constant added to the superpotential in order to cancel the vacuum energy. In particular, we identify the parameter region in which no solution is found, as well as the parameter region in which the vacuum energy vanishes without adding the constant term. We also show how the allowed parameter region is reduced by requiring the positivity of the D-term soft mass-squared. Finally, we briefly discuss the constraint on the dilaton Kähler potential when the dynamical effect of the dilaton is included.

DOI： 10.1143/PTP.101.439

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

''Anomalous'' U(1) gauge symmetry with a Green-Schwarz anomaly cancellation mechanism is discussed in the orbifold construction of four-dimensional heterotic string models. Some conditions are given as criteria to have ''anomalous'' U(1) in orbifold string models. In particular, ''anomalous'' U(1) is absent if the massless twisted matter has no mixing between visible and hidden sectors or if a certain type of discrete symmetries are found. We then give a general procedure for classifying orbifold models with ''anomalous'' U(1) and for identifying the ''anomalous'' U(1) basis. We illustrate our procedure in Z(3) and Z(4) orbifold models. According to our procedure, the classification of ''anomalous'' U(1) can be reduced to classification in the absence of a Wilson line. We also discuss discrete symmetries left unbroken after the ''anomalous'' U(1) breaking. This includes a possible relation between ''anomalous'' U(1) and discrete R symmetries. (C) 1997 Elsevier Science B.V.

DOI： 10.1016/S0550-3213(97)00210-1

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1143/ptp/92.6.1161

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

We Present a new Procedure for improving the effective potential by using the renormalization group equation (RGE) in the presence of several mass scales. We propose a modification of the mass-dependent (MD) renormalization scheme (MDBAR) scheme) so that the scalar mass parameter runs at most logarithmically on the one hand and the decoupling of heavy particles is naturally incorporated in the RGE's on the other. Thanks to these properties, the procedure in the MDBAR scheme turns out to be very simple compared with the regionwise procedure in the modified minimal subtraction scheme proposed previously. The relation with other schemes is also discussed both analytically and numerically.

DOI： 10.1103/PhysRevD.49.5393

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

We examine a simple approximation to the one-loop Higgs potential in the supersymmetric standard model. We study the conditions under which our approximation can well simulate the full one-loop results. The results by our method are compared with those by the full one-loop potential as well as the tree one in several examples. It turns out that our method works quite well in many cases and thus provides a useful calculating method, instead of a complicated evaluation of one-loop potential.

DOI： 10.1142/S0217732393003111

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：KYOTO UNIV  

Previously proposed procedure for improving the effective potential by using renormalization group equation (RGE) is generalized so as to be applicable to any system containing several different mass scales. If one knows L-loop effective potential and (L + 1)-loop RGE coefficient functions, this procedure gives an improved potential which satisfies the RGE and contains all of the leading, next-to-leading, ..., and L-th-to-leading log terms. Our procedure here also clarifies how naturally the so-called effective field theory can be incorporated in the RGE in MSBAR scheme.

DOI： 10.1143/PTP.90.405

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

A general procedure is presented how to improve the effective potential by using the renormalization group equation (RGE) in the MSBAR scheme. If one knows the L-loop effective potential and the RGE coefficient functions up to the (L+1)-loop level, this procedure gives an improved potential which satisfies the RGE and contains all of the leading, nest-to-leading, ..., and Lth-to-leading log terms.

DOI： 10.1016/0370-2693(93)90725-W

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD  

We examine whether the unification constraints on the Yukawa couplings and on the Higgs masses in the minimal supersymmetric Standard Model can be consistent with the observed mass pattern of the third generation fermions. The effects of the QCD interaction and the SU(2)R breaking owing to the U(1)Y gauge interaction and the absence of nu(tau)R are crucial. We observe that the parameter choice of "no-scale" supergravity is favored and the SUSY breaking scale has a lower bound, in order for the top quark to be much heavier than the bottom quark.

DOI： 10.1142/S0217732392002779

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1103/PhysRevD.44.R2957

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