Double-Spinor Superstrings on Coset Superspaces

The double-spinor formalism, proposed by Aisaka and Kazama, provides a basis for the pure-spinor formalism, which allows manifestly super-Poincare covariant quantization of superstrings. We extend it to the case of backgrounds realized by coset superspaces. A general method constructing reparametrization invariant action is given using two concrete examples, the flat space-time and AdS(5)xS(5). We find that it is natural to double not only the spinor coordinates but the whole superspace for describing double-spinor superstrings on such backgrounds. The reparametrization invariant action has local symmetries compensating those extra degrees of freedom, which guarantee the equivalence to the Green-Schwarz formalism.Comment: 14pages, no figure, PTPTeX; v2, references added; v3, english is improved, version appeared in PTP; v4, a reference adde

Hybrid Superstrings in NS-NS Plane Waves

By using the hybrid formalism, superstrings in four-dimensional NS-NS plane waves are studied in a manifest supersymmetric manner. This description of the superstring is obtained by a field redefinition of the RNS worldsheet fields and defined as a topological N=4 string theory. The Hilbert space consists of two types of representations describing short and long strings. We study the physical spectrum to find boson-fermion asymmetry in the massless spectrum of the short string. Some massive spectrum of the short string and the massless spectrum of the long string are also studied.Comment: 24 pages, no figure, PTPTeX, discussion on the massless spectrum of RNS superstring is modified, to appear in Prog. Theor. Phy

"Improving Small Sample Properties of the Empirical Likelihood Estimation"

We propose to use a simple modification of the maximum empirical likelihood (MEL) method for estimating structural equation in econometrics. The modified estimator improves both the asymptotic bias and the mean squared error of the MEL estimator in the orders of O(n -1) and O(n -2), respectively, at the same time. It also improves the asymptotic bias of the generalized method of moments (GMM) estimation (or the estimating equation (EE) method) significantly when there are many instruments in the econometric literatures.

Lower-dimensional superstrings in the double-spinor formalism

We study lower-dimensional superstrings in the double-spinor formalism introduced by Aisaka and Kazama. These superstrings can be consistently quantized and are equivalent to the lower-dimensional pure-spinor superstrings proposed by Grassi and Wyllard. The unexpected physical spectrum of the pure-spinor superstrings may thus be regarded as a manifestation of noncriticality. We also discuss how to couple these covariant superstrings to the compactified degrees of freedom described by the N=2 superconformal field theory.Comment: 32 pages, version published in Prog. Theor. Phy

"An Optimal Modification of the LIML Estimation for Many Instruments and Persistent Heteroscedasticity"

We consider the estimation of coefficients of a structural equation with many instrumental variables in a simultaneous equation system. It is mathematically equivalent to an estimating equation estimation or a reduced rank regression in the statistical linear models when the number of restrictions or the dimension increases with the sample size. As a semi- parametric method, we propose a class of modifications of the limited information maximum likelihood (LIML) estimator to improve its asymptotic properties as well as the small sample properties for many instruments and persistent heteroscedasticity. We show that an asymptotically optimal modification of the LIML estimator, which is called AOM-LIML, improves the LIML estimator and other estimation methods. We give a set of sufficient conditions for an asymptotic optimality when the number of instruments or the dimension is large with persistent heteroscedasticity including a case of many weak instruments.

On the Nonlinear Realization of the Superconformal Symmetry

The nonlinear realization of the superconformal symmetry in two dimensions is considered. The superconformal symmetry is realized by means of dimension $-1/2$\ Nambu-Goldstone fermion $\xi$\ and its dimension 3/2 conjugate $\eta$. A matter coupling of these Nambu- Goldstone fermions reproduce the realization found by Berkovits and Vafa to show the equivalence between the bosonic string and a $N=1$\ superstring. This indicates that this equivalence is a result of the super Higgs mechanism as a two dimensional field theory, in which the NG fermions become unphysical.Comment: 5 pages, phyzzx, OU-HET 19

Construction of action for heterotic string field theory including the Ramond sector

Extending the formulation for open superstring field theory given in arXiv:1508.00366, we attempt to construct a complete action for heterotic string field theory. The action is non-polynomial in the Ramond string field Psi, and we construct it order by order in Psi. Using a dual formulation in which the role of eta and Q is exchanged, the action is explicitly obtained at the quadratic and quartic order in Psi with the gauge transformations.Comment: 44pages; ver2: Modification for one of the author's address; ver3: appendix B is added (50 pages in total); ver4: typos are correcte