Quantum Product and Parabolic Orbits in Homogeneous Spaces

Chaput, Manivel, and Perrin proved in [3] a formula describing the quantum product by Schubert classes associated to cominuscule weights in a rational projective homogeneous space X. In the case where X has Picard rank one, we relate this formula to the stratification of X by P-orbits, where P is the parabolic subgroup associated to the cominuscule weight. We deduce a decomposition of the Hasse diagram of X, i.e., the diagram describing the cup-product with the hyperplane class. For all classical Grassmannians, we give a complete description of parabolic orbits associated to cominuscule weights, and we make the decomposition of the Hasse diagram explicit

On highly regular strongly regular graphs

In this paper we unify several existing regularity conditions for graphs, including strong regularity, $k$-isoregularity, and the $t$-vertex condition. We develop an algebraic composition/decomposition theory of regularity conditions. Using our theoretical results we show that a family of non rank 3 graphs known to satisfy the $7$-vertex condition fulfills an even stronger condition, $(3,7)$-regularity (the notion is defined in the text). Derived from this family we obtain a new infinite family of non rank $3$ strongly regular graphs satisfying the $6$-vertex condition. This strengthens and generalizes previous results by Reichard.Comment: 29 page

Adverse Selection with individual- and joint-life annuities

This paper includes couples on the demand side and analyses their implications on the problem of adverse selection in the annuity market. First, we examine the pooling equilibrium for individual-life annuities and show that in the presence of couples the rate of return on individuallife annuities is lower in case that couples do not have the advantage of joint consumption of "family public goods" as well as in case of a logarithmic utility function. Second, we examine the market for joint-life annuities. Due to their higher chance that only one partner survives to the retirement, couples with short-lived partners put more weight on the survivor benefit than couples with at least one longer-lived partner. This fact is used by annuity companies to separate couples according to their partners' life-expectancies. Hence, we find that only a separating equilibrium may exist. These results are obtained in a framework where couples are mandated to buy joint-life annuities and only single persons buy individual-life annuities. When relaxing this assumption by allowing couples to choose between individual- and joint-life annuities, we find that in equilibrium couples with long-lived partners buy individual-life annuities, while couples with short-lived partners buy joint-life annuities. However, couples with one long-lived and one short-lived partner may decide for either type of annuities, depending on the exogenous parameters. Accordingly, we identify two different types of equilibria.annuity market; uncertain lifetime; adverse selection; equilibrium

A comparison of Landau-Ginzburg models for odd-dimensional Quadrics

In [Rie08], the second author defined a Landau-Ginzburg model for homogeneous spaces G/P, as a regular function on an affine subvariety of the Langlands dual group. In this paper, we reformulate this LG model (X^, W_t) in the case of the odd-dimensional quadric, as a rational function on a Langlands dual projective space, in the spirit of work by R. Marsh and the second author for type A Grassmannians and by both authors for Lagrangian Grassmannians. We also compare this LG model with the one obtained independently by Gorbounov and Smirnov, and we use this comparison to deduce part of a conjecture of the second author for odd-dimensional quadrics