A Multiplication Technique for the Factorization of Bivariate Quaternionic Polynomials

We consider bivariate polynomials over the skew field of quaternions, where the indeterminates commute with all coefficients and with each other. We analyze existence of univariate factorizations, that is, factorizations with univariate linear factors. A necessary condition for existence of univariate factorizations is factorization of the norm polynomial into a product of univariate polynomials. This condition is, however, not sufficient. Our central result states that univariate factorizations exist after multiplication with a suitable univariate real polynomial as long as the necessary factorization condition is fulfilled. We present an algorithm for computing this real polynomial and a corresponding univariate factorization. If a univariate factorization of the original polynomial exists, a suitable input of the algorithm produces a constant multiplication factor, thus giving an a posteriori condition for existence of univariate factorizations. Some factorizations obtained in this way are of interest in mechanism science. We present an example of a curious closed-loop mechanism with eight revolute joints.

Nonidentifiability in the presence of factorization for truncated data

Summary A time to event, $X$, is left-truncated by $T$ if $X$ can be observed only if $T<X$. This often results in oversampling of large values of $X$, and necessitates adjustment of estimation procedures to avoid bias. Simple risk-set adjustments can be made to standard risk-set-based estimators to accommodate left truncation when $T$ and $X$ are quasi-independent. We derive a weaker factorization condition for the conditional distribution of $T$ given $X$ in the observable region that permits risk-set adjustment for estimation of the distribution of $X$, but not of the distribution of $T$. Quasi-independence results when the analogous factorization condition for $X$ given $T$ holds also, in which case the distributions of $X$ and $T$ are easily estimated. While we can test for factorization, if the test does not reject, we cannot identify which factorization condition holds, or whether quasi-independence holds. Hence we require an unverifiable assumption in order to estimate the distribution of $X$ or $T$ based on truncated data. This contrasts with the common understanding that truncation is different from censoring in requiring no unverifiable assumptions for estimation. We illustrate these concepts through a simulation of left-truncated and right-censored data.

ORNSTEIN–UHLENBECK PROCESSES IN BANACH SPACES AND THEIR SPECTRAL REPRESENTATIONS

For Q the variance of some centred Gaussian random vector in a separable Banach space it is shown that, necessarily, Q factors through $\ell^2$ as a product of 2-summing operators. This factorization condition is sufficient when the Banach space is of Gaussian type 2. The stochastic integral of a deterministic family of operators with respect to a Q-Wiener process is shown to exist under a continuity condition involving the 2-summing norm. A Langevin equation$$ \rd\bm{Z}_t+\sLa\bm{Z}_t\,\rd t=\rd\bm{B}_t, $$with values in a separable Banach space, is studied. The operator $\sLa$ is closed and densely defined. A weak solution $(\bm{Z}_t,\bm{B}_t)$, where $\bm{Z}_t$ is centred, Gaussian and stationary, while $\bm{B}_t$ is a Q-Wiener process, is given when $\ri\sLa$ and $\ri\sLa^*$ generate $C_0$ groups and the resolvent of $\sLa$ is uniformly bounded on the imaginary axis. Both $\bm{Z}_t$ and $\bm{B}_t$ are stochastic integrals with respect to a spectral Q-Wiener process.AMS 2000 Mathematics subject classification: Primary 60G15. Secondary 46E40; 47B10; 47D03; 60H10

SUPER YANG-MILLS THEORIES COUPLED TO SUPERGRAVTTY: TANGENT BUNDLE TO A SUPERGROUP MANIFOLD APPROACH

Supersymmetric Yang-Mills theories coupled to supergravity are analyzed by using the tangent bundle to a supergroup manifold as geometrical framework. The factorization condition imposed on these theories is considered from this point of view. The so-called H-gauge transformation for both, the super Yang-Mills and supergravity one-forms gauge fields are obtained as a consequence of a change of trivialization in the corresponding coset manifold. Also, we briefly point out the existence of factorized solutions not diffeomorphically equivalent for the set of pseudo-connections one-forms or gauge fields.