Noriaki Kitazawa

On climbing scalars in String Theory

Abstract In string models with “brane supersymmetry breaking” exponential potentials emerge at (closed-string) tree level but are not accompanied by tachyons. Potentials of this type have long been a source of embarrassment in flat space, but can have interesting implications for Cosmology. For instance, in ten dimensions the logarithmic slope | V ′ / V | lies precisely at a “critical” value where the Lucchin–Matarrese attractor disappears while the scalar field is forced to climb up the potential when it emerges from the Big Bang. This type of behavior is in principle perturbative in the string coupling, persists after compactification, could have trapped scalar fields inside potential wells as a result of the cosmological evolution and could have also injected the inflationary phase of our Universe.

Flavor structure and coupling selection rule from intersecting D-branes

We study flavor structure and the coupling selection rule in intersecting D-brane configurations on T{sup 2}xT{sup 2}xT{sup 2} as well as its orbifold/orientifold compactifications. We formulate the selection rule for Yukawa couplings and its extensions to generic n-point couplings. We investigate the possible flavor structure, which can appear from intersecting D-brane configuration. Then, we show there is a certain rule among intersecting numbers for states corresponding to allowed Yukawa couplings, and also it is found that their couplings are determined by discrete Abelian symmetries. Our studies on the flavor structure and the coupling selection rule in this class of models show that there is no solution to derive realistic Yukawa matrices only from stringy 3-point couplings at the tree-level within the framework of the minimal matter content of the supersymmetric standard model.

Model-independent analysis of B-B-bar mixing and CP violation in B decays.

We present a framework to analyze the effects of new physics beyond the standard model on {ital B}-{bar {ital B}} mixing and {ital CP} violation in {ital B} decays in a model-independent manner. Assuming that the tree level decay amplitudes are dominated by the standard model ones, new physics contributions to {ital B}-{bar {ital B}} mixing can be extracted from several measurements at {ital B} factories. Using this framework, we show the present constraint on new physics contributions to {ital B}-{bar {ital B}} mixing and illustrate the constraints expected to be given by future experiments at {ital B} factories. We also point out the possibility that {ital CP} asymmetries in {ital B}{r_arrow}{psi}{ital K}{sub {ital S}}, {ital B}{r_arrow}{pi}{pi}, and {ital B}{r_arrow}{ital DK} modes look consistent with the standard model, even if a large new physics contribution is present in {ital B}-{bar {ital B}} mixing. {copyright} {ital 1996 The American Physical Society.}

A new dynamics of electroweak symmetry breaking with classically scale invariance

We propose a new dynamics of the electroweak symmetry breaking in a classically scale invariant version of the standard model. The scale invariance is broken by the condensations of additional fermions under a strong coupling dynamics. The electroweak symmetry breaking is triggered by negative mass squared of the elementary Higgs doublet, which is dynamically generated through the bosonic seesaw mechanism. We introduce a real pseudo-scalar singlet field interacting with additional fermions and Higgs doublet in order to avoid massless Nambu–Goldstone bosons from the chiral symmetry breaking in a strong coupling sector. We investigate the mass spectra and decay rates of these pseudo-Nambu–Goldstone bosons, and show they can decay fast enough without cosmological problems. We further show that our model can make the electroweak vacuum stable.

Tadpole resummations in string theory

Abstract While R–R tadpoles should be canceled for consistency, string models with broken supersymmetry generally have uncanceled NS–NS tadpoles. Their presence signals that the background does not solve the field equations, so that these models are in “wrong” vacua. In this Letter we investigate, with reference to some prototype examples, whether the true values of physical quantities can be recovered resumming the NS–NS tadpoles, hence by an approach that is related to the analysis based on String Field Theory by open–closed duality. We show that, indeed, the positive classical vacuum energy of a D p -brane of the bosonic string is exactly canceled by the negative contribution arising from tree-level tadpole resummation, in complete agreement with Sens conjecture on open-string tachyon condensation and with the consequent analysis based on String Field Theory. We also show that the vanishing classical vacuum energy of the SO(8192) unoriented bosonic open-string theory does not receive any tree-level corrections from the tadpole resummation. This result is consistent with the fact that this (unstable) configuration is free from tadpoles of massless closed-string modes, although there is a tadpole of the closed string tachyon. The application of this method to superstring models with broken supersymmetry is also discussed.

Yukawa coupling structure in intersecting D-brane models

Abstract.The structure of Yukawa coupling matrices is investigated in type IIA T6/(Z2 x Z2) orientifold models with intersecting D-branes. Yukawa coupling matrices are difficult to be made realistic in conventional models in which the generation structure emerges by the multiple intersection of D-branes in the factorized T6 = T2 x T2 x T2. We study the new type of flavor structure, where Yukawa couplings are dynamically generated, and show this type of models lead to non-trivial structures of Yukawa coupling matrices, which can be realistic.

R mediation of dynamical supersymmetry breaking

We propose a simple scenario of the dynamical supersymmetry breaking in four dimensional supergravity theories. The supersymmetry breaking sector is assumed to be completely separated as a sequestered sector from the visible sector, except for the communication by the gravity and U(1)_R gauge interactions, and the supersymmetry breaking is mediated by the superconformal anomaly and U(1)_R gauge interaction. Supersymmetry is dynamically broken by the interplay between the non-perturbative effect of the gauge interaction and Fayet-Iliopoulos D-term of U(1)_R which necessarily exists in supergravity theories with gauged U(1)_R symmetry. We construct an explicit model which gives phenomenologically acceptable mass spectrum of superpartners with vanishing (or very small) cosmological constant.

Heavy meson effective theory with 1MQ correction

We construct an effective Lagrangian of heavy and light mesons with

Dynamical supersymmetry breaking with gauged U(1)(R) symmetry

1/M_Q

Models of dynamical supersymmetry breaking with gauged U(1)R symmetry

correction. The Lagrangian is constructed model independent way by using only the information of the symmetry of QCD. Reparameterisation invariance at the meson level is taken into account for the consistency of the theory. The partial decay width of the process