arXiv subjects
Publications and source records attributed to Hiroshi Oda.
We give the inversion formula and the Plancherel formula for the hypergeometric Fourier transform associated with a root system of type $BC$, when the multiplicity parameters are not necessarily nonnegative.
We give an explicit formula for the Harish-Chandra $c$-function for a small $K$-type on a split real Lie group of type $G_2$. As an application we give an explicit formula for spherical inversion for this small $K$-type.
For a connected semisimple real Lie group $G$ of non-compact type, Wallach introduced a class of $K$-types called small. We classify all small $K$-types for all simple Lie groups and prove except just one case that each elementary spherical function for each small $K$-type $(π,V)$ can be expressed as a product of hyperbolic cosines and a Heckman-Opdam hypergeometric function. As an application, the inversion formula for the spherical transform on $G\times_K V$ is obtained from Opdam's theory on hypergeometric Fourier transforms.
The classical radial part formula for the invariant differential operators and the K-invariant functions on a Riemannian symmetric space G/K is generalized to some non-invariant cases by use of Cherednik operators and a graded Hecke algebra H naturally attached to G/K. We introduce a category C_{rad} whose object is a pair of a (g_C,K)-module and an H-module satisfying some axioms which are formally the same as the generalized Chevalley restriction theorem and the generalized radial part formula. Various pairs of analogous notions in the representation theories for G and H, such as the Helgason-Fourier transform and the Opdam-Cherednik transform, are unified in terms of C_{rad}. We construct natural functors which send an H-module to a (g_C,K)-module and have some universal properties intimately related to C_{rad}.
We present global solutions of optically thin, two-temperature black hole accretion disks incorporating magnetic fields. We assume that the πϕ-component of the Maxwell stress is proportional to the total pressure, and prescribe the radial dependence of the magnetic flux advection rate in order to complete the set of basic equations. We obtained magnetically supported (low-β) disk solutions, whose luminosity exceeds the maximum luminosity for an advection-dominated accretion flow (ADAF), L > 0.4 α^2 L_Edd, where L_Edd is the Eddington luminosity. The accretion flow is composed of the outer ADAF, a luminous hot accretion flow (LHAF) inside the transition layer from the outer ADAF to the low-β disk, the low-β disk, and the inner ADAF. The low-β disk region becomes wider as the mass-accretion rate increases further. In the low-β disk, the magnetic heating balances the radiative cooling, and the electron temperature decreases from ~ 10^9.5 K to ~ 10^8 K as the luminosity increases. These results are consistent with the anti-correlation between the energy cutoff in X-ray spectra (hence the electron temperature) and the luminosity when L > 0.1 L_Edd, observed in the bright/hard state during the bright hard-to-soft transitions of transient outbursts in galactic black hole candidates.
We obtained thermal equilibrium solutions for optically thin, two-temperature black hole accretion disks incorporating magnetic fields. The main objective of this study is to explain the bright/hard state observed during the bright/slow transition of galactic black hole candidates. We assume that the energy transfer from ions to electrons occurs via Coulomb collisions. Bremsstrahlung, synchrotron, and inverse Compton scattering are considered as the radiative cooling processes. In order to complete the set of basic equations, we specify the magnetic flux advection rate. We find magnetically supported (low-beta), thermally stable solutions. In these solutions, the total amount of the heating via the dissipation of turbulent magnetic fields goes into electrons and balances the radiative cooling. The low-$β$ solutions extend to high mass accretion rates and the electron temperature is moderately cool. High luminosities and moderately high energy cutoffs in the X-ray spectrum observed in the bright/hard state can be explained by the low-beta solutions.
Let g be a complex reductive Lie algebra and U(g) the universal enveloping algebra of g. Associated to a faithful irreducible finite dimensional representation of g, a square matrix F with entries in U(g) naturally arises and if we consider the entries of F are elements in End(M) of a given U(g)-module M, the minimal polynomial of F is defined as the usual one for an associative algebra over the complex field. Suppose M is a generalized Verma module induced from a character of a parabolic subalgebra of g. In this paper a polynomial q(x) with the parameter of the character is constructed, which equals the minimal polynomial for the generic parameter. Then the two-sided ideal of U(g) generated by the entries of q(F) is studied. We give a sufficient condition for the parameter such that the ideal describes the difference of two left ideals related to M and the corresponding Verma module. The result has many applications. For example we can explicitly give a generator system of the annihilator of M for the generic parameter. This paper also deals with many concrete examples.
A basic exact sequence by Harish-Chandra related to the invariant differential operators on a Riemannian symmetric space G/K is generalized for each K-type in a certain class which we call `single-petaled'. The argument also includes a further generalization of Broer's generalization of the Chevalley restriction theorem.