The monotone conjecture for arbitrary Schubert problems on flag manifolds

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Let α={α1<⋯<αk}\alpha=\{\alpha_1<\dotsb<\alpha_k\} with αk<n\alpha_k<n, and let (w1,…,wm)(w_1,\dotsc,w_m) be a Schubert problem for Fℓ(α;n)\mathbb{F}\ell(\alpha;n). For each permutation wiw_i, let δ(wi)\delta(w_i) be its set of descents. A list (t1,…,tm)∈(RP1)m(t_1,\dotsc,t_m)\in(\mathbb{R}\mathbb{P}^1)^m is monotone with respect to (w1,…,wm)(w_1,\dotsc,w_m) when the map ti↦δ(wi)t_i\mapsto\delta(w_i) is monotone for an ordering compatible with some orientation of RP1\mathbb{R}\mathbb{P}^1. General monotone conjecture. The intersection

Xw1(t1)∩Xw2(t2)∩⋯∩Xwm(tm)X_{w_1}(t_1)\cap X_{w_2}(t_2)\cap\dotsb\cap X_{w_m}(t_m)

is transverse and all its points of intersection are real whenever the points are monotone with respect to (w1,…,wm)(w_1,\dotsc,w_m). The conjecture extends the Grassmannian formulation to arbitrary Schubert problems; the source notes examples with no monotone points and reports computational evidence, but the general assertion remains open.

References

Primary source

James Ruffo, Yuval Sivan, Evgenia Soprunova and Frank Sottile, “Experimentation and conjectures in the real Schubert calculus for flag manifolds”, arXiv:math/0507377 (2005).

Additional references

2 papers in this index state this conjecture (2005). The statement above is taken from the most recent of them; the others are arXiv:math/0502040.

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