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過去の記録
過去の記録 ～03/28｜本日 03/29 | 今後の予定 03/30～
2018年06月19日(火)
代数幾何学セミナー
15:30-17:00 数理科学研究科棟(駒場) 122号室
若林 泰央 氏 (東工大)
Dormant Miura opers and Tango structures (Japanese (writing in English))
若林 泰央 氏 (東工大)
Dormant Miura opers and Tango structures (Japanese (writing in English))
[ 講演概要 ]
Tango（丹後）構造とは, 正標数の代数曲線で定義された然るべき直線束であり, （小平消滅定理の反例となるなどの, いわゆる）「病理的な」正標数の代数多様体を構成するうえで基本的な概念です. 本発表では, このTango構造と, 一見すると無関係にも見える幾つかのトピック（dormant Miura oper, 3正則グラフのナンバリング, Gaudin模型の対角化etc.）との結びつきや関連する結果について説明させていただきたく予定です.（各トピックについて発表者はそれほど詳しくありませんので, この機会にぜひ皆さまの知見を伺えればと思っております.）
Tango（丹後）構造とは, 正標数の代数曲線で定義された然るべき直線束であり, （小平消滅定理の反例となるなどの, いわゆる）「病理的な」正標数の代数多様体を構成するうえで基本的な概念です. 本発表では, このTango構造と, 一見すると無関係にも見える幾つかのトピック（dormant Miura oper, 3正則グラフのナンバリング, Gaudin模型の対角化etc.）との結びつきや関連する結果について説明させていただきたく予定です.（各トピックについて発表者はそれほど詳しくありませんので, この機会にぜひ皆さまの知見を伺えればと思っております.）
解析学火曜セミナー
16:50-18:20 数理科学研究科棟(駒場) 128号室
Rowan Killip 氏 (UCLA)
KdV is wellposed in $H^{-1}$ (English)
Rowan Killip 氏 (UCLA)
KdV is wellposed in $H^{-1}$ (English)
数値解析セミナー
16:50-18:20 数理科学研究科棟(駒場) 002号室
吉川周二 氏 (大分大学理工学部)
Small data global existence for the semi-discrete scheme of a model system of hyperbolic balance laws (Japanese)
吉川周二 氏 (大分大学理工学部)
Small data global existence for the semi-discrete scheme of a model system of hyperbolic balance laws (Japanese)
[ 講演概要 ]
エネルギー法の差分解法への応用を意識し, 準線形の双曲型保存則系のあるモデルシステムを例に挙げて, この問題の時間に関して中点則で離散化した半離散解法の時間大域解の存在について議論したい. オリジナルの問題は, Racke(1992)や松村--西原(2004)のテキストで紹介されたエネルギー法によって, 初期値が小さいという仮定の下でアプリオリ評価が得られ, 時間大域解の存在を証明できる. 本発表では, 上記の半離散解法もオリジナルの連続問題と同様にして時間大域解の存在を示すことが可能であることについて紹介したい. また誤差評価もこのエネルギー構造を利用して示すことができることも時間があれば触れる. 本研究は川島秀一氏(早稲田大学)との共同研究に基づく.
エネルギー法の差分解法への応用を意識し, 準線形の双曲型保存則系のあるモデルシステムを例に挙げて, この問題の時間に関して中点則で離散化した半離散解法の時間大域解の存在について議論したい. オリジナルの問題は, Racke(1992)や松村--西原(2004)のテキストで紹介されたエネルギー法によって, 初期値が小さいという仮定の下でアプリオリ評価が得られ, 時間大域解の存在を証明できる. 本発表では, 上記の半離散解法もオリジナルの連続問題と同様にして時間大域解の存在を示すことが可能であることについて紹介したい. また誤差評価もこのエネルギー構造を利用して示すことができることも時間があれば触れる. 本研究は川島秀一氏(早稲田大学)との共同研究に基づく.
トポロジー火曜セミナー
17:00-18:30 数理科学研究科棟(駒場) 056号室
Tea: Common Room 16:30-17:00
今野 北斗 氏 (東京大学大学院数理科学研究科)
Characteristic classes via 4-dimensional gauge theory (JAPANESE)
Tea: Common Room 16:30-17:00
今野 北斗 氏 (東京大学大学院数理科学研究科)
Characteristic classes via 4-dimensional gauge theory (JAPANESE)
[ 講演概要 ]
Using gauge theory, more precisely SO(3)-Yang-Mills theory and Seiberg-Witten theory, I will construct characteristic classes of 4-manifold bundles. These characteristic classes are extensions of the SO(3)-Donaldson invariant and the Seiberg-Witten invariant to families of 4-manifolds, and can detect non-triviality of smooth 4-manifold bundles. The basic idea of the construction of these characteristic classes is to consider an infinite dimensional analogue of classical characteristic classes of manifold bundles, typified by the Mumford-Morita-Miller classes for surface bundles.
Using gauge theory, more precisely SO(3)-Yang-Mills theory and Seiberg-Witten theory, I will construct characteristic classes of 4-manifold bundles. These characteristic classes are extensions of the SO(3)-Donaldson invariant and the Seiberg-Witten invariant to families of 4-manifolds, and can detect non-triviality of smooth 4-manifold bundles. The basic idea of the construction of these characteristic classes is to consider an infinite dimensional analogue of classical characteristic classes of manifold bundles, typified by the Mumford-Morita-Miller classes for surface bundles.
トポロジー火曜セミナー
14:30-16:00 数理科学研究科棟(駒場) 056号室
RIKEN iTHEMS と共催
深谷 賢治 氏 (サイモンズセンター, SUNY)
相対かつ同変ラグランジアンフレアーホモロジーとアティヤ-フレアー予想 (JAPANESE)
RIKEN iTHEMS と共催
深谷 賢治 氏 (サイモンズセンター, SUNY)
相対かつ同変ラグランジアンフレアーホモロジーとアティヤ-フレアー予想 (JAPANESE)
[ 講演概要 ]
アティヤ-フレアー予想は，ゲージ理論におけるフレアーホモロジーとラグランジアンフレアーホモロジーの間の関係に関するものである．その一つの困難は，ラグランジアンフレアーホモロジーを考えるシンプレクティック多様体が特異点を持つことである．双対かつ同変ラグランジアンフレアーホモロジーを考えることで，この困難が解消し，少なくともアティヤ-フレアー予想を数学的に厳密な予想として定式化できることを説明する．
アティヤ-フレアー予想は，ゲージ理論におけるフレアーホモロジーとラグランジアンフレアーホモロジーの間の関係に関するものである．その一つの困難は，ラグランジアンフレアーホモロジーを考えるシンプレクティック多様体が特異点を持つことである．双対かつ同変ラグランジアンフレアーホモロジーを考えることで，この困難が解消し，少なくともアティヤ-フレアー予想を数学的に厳密な予想として定式化できることを説明する．
2018年06月18日(月)
東京確率論セミナー
16:00-17:30 数理科学研究科棟(駒場) 126号室
種村 秀紀 氏 (慶應義塾大学理工学部数理科学科)
相互作用をもつ無限個の剛体球の系 (JAPANESE)
種村 秀紀 氏 (慶應義塾大学理工学部数理科学科)
相互作用をもつ無限個の剛体球の系 (JAPANESE)
[ 講演概要 ]
粒子間にハードコア相互作用があるとき、その粒子系は剛体球の系と見なすことができ、さらに各々の粒子が独立なブラウン運動により駆動されている場合は、Skorohod 型方程式の解として表すことができる。本講演では、粒子数が無限個であり、剛体球間に長距離相互作用がある場合に、対応する無限次元Skorohod 型方程式を導入し、その解の存在と一意性について議論する。
粒子間にハードコア相互作用があるとき、その粒子系は剛体球の系と見なすことができ、さらに各々の粒子が独立なブラウン運動により駆動されている場合は、Skorohod 型方程式の解として表すことができる。本講演では、粒子数が無限個であり、剛体球間に長距離相互作用がある場合に、対応する無限次元Skorohod 型方程式を導入し、その解の存在と一意性について議論する。
作用素環セミナー
16:45-18:15 数理科学研究科棟(駒場) 122号室
Ryszard Nest 氏 (Copenhagen Univ.)
Equivariant index theorem (English)
Ryszard Nest 氏 (Copenhagen Univ.)
Equivariant index theorem (English)
2018年06月13日(水)
作用素環セミナー
16:45-18:15 数理科学研究科棟(駒場) 126号室
田中亮吉 氏 (東北大学)
Poisson boundary for the discrete affine group (English)
田中亮吉 氏 (東北大学)
Poisson boundary for the discrete affine group (English)
2018年06月12日(火)
代数幾何学セミナー
15:30-17:00 数理科学研究科棟(駒場) 122号室
柴田 崇広 氏 (京都大学)
Ample canonical heights for endomorphisms on projective varieties (English or Japanese)
柴田 崇広 氏 (京都大学)
Ample canonical heights for endomorphisms on projective varieties (English or Japanese)
[ 講演概要 ]
Given a smooth projective variety on a number field and an
endomorphism on it, we would like to know how the height of a point
grows by iteration of the action of the endomorphism. When the
endomorphism is polarized, Call and Silverman construct the canonical
height, which is an important tool for the calculation of growth of
heights. In this talk, we will give a generalization of the Call-
Silverman canonical heights for not necessarily polarized endomorphisms,
ample canonical heights, and propose an analogue of the Northcott
finiteness theorem as a conjecture. We will see that the conjecture
holds when the variety is an abelian variety or a surface.
Given a smooth projective variety on a number field and an
endomorphism on it, we would like to know how the height of a point
grows by iteration of the action of the endomorphism. When the
endomorphism is polarized, Call and Silverman construct the canonical
height, which is an important tool for the calculation of growth of
heights. In this talk, we will give a generalization of the Call-
Silverman canonical heights for not necessarily polarized endomorphisms,
ample canonical heights, and propose an analogue of the Northcott
finiteness theorem as a conjecture. We will see that the conjecture
holds when the variety is an abelian variety or a surface.
トポロジー火曜セミナー
17:00-18:30 数理科学研究科棟(駒場) 056号室
Tea: Common Room 16:30-17:00
三松 佳彦 氏 (中央大学)
Turbulization of 2-dimensional foliations on 4-manifolds (JAPANESE)
Tea: Common Room 16:30-17:00
三松 佳彦 氏 (中央大学)
Turbulization of 2-dimensional foliations on 4-manifolds (JAPANESE)
[ 講演概要 ]
This is a report on a joint work with Elmar VOGT(Freie Universität Berlin). For codimension 1 foliations, the process of turbulization, i.e., inserting a Reeb component along a closed transversal, is well-known, while for higher codimensional foliation, similar processes were not understood until around 2006.
In this talk, first we formulate the turbulization along a closed transversal. Then in our dimension setting, namely 2-dimensional foliations on 4-manifolds ((4,2)-foliations), a cohomological criterion is given for a given transversal to a foliation, which tells the turbulization is possible or not, relying on the Thurston's h-principle. Also we give cocrete geometric constructions of turbulizations.
The cohomological criterion for turbulization is deduced from a more general criterion for a given embedded surface to be a compact leaf or a closed transversal of some foliation, which is stated in terms of the euler classes of tangent and normal bndle of the foliation to look for. The anormalous cohomological solutions for certain cases suggested the geometric realization of turbulization, while the cohomological criterion is obtained by the h-principle.
Some other modifications are also formulated for (4,2)-foliations and their possibility are assured by the anormalous solutions mentioned above. For some of them, good geometric realizations are not yet known. So far the difficulty lies on the problem of the connected components of the space of representations of the surface groups to Diff S^1.
If the time permits, some special features on the h-principle for 2-dimensional foliations are also explained.
This is a report on a joint work with Elmar VOGT(Freie Universität Berlin). For codimension 1 foliations, the process of turbulization, i.e., inserting a Reeb component along a closed transversal, is well-known, while for higher codimensional foliation, similar processes were not understood until around 2006.
In this talk, first we formulate the turbulization along a closed transversal. Then in our dimension setting, namely 2-dimensional foliations on 4-manifolds ((4,2)-foliations), a cohomological criterion is given for a given transversal to a foliation, which tells the turbulization is possible or not, relying on the Thurston's h-principle. Also we give cocrete geometric constructions of turbulizations.
The cohomological criterion for turbulization is deduced from a more general criterion for a given embedded surface to be a compact leaf or a closed transversal of some foliation, which is stated in terms of the euler classes of tangent and normal bndle of the foliation to look for. The anormalous cohomological solutions for certain cases suggested the geometric realization of turbulization, while the cohomological criterion is obtained by the h-principle.
Some other modifications are also formulated for (4,2)-foliations and their possibility are assured by the anormalous solutions mentioned above. For some of them, good geometric realizations are not yet known. So far the difficulty lies on the problem of the connected components of the space of representations of the surface groups to Diff S^1.
If the time permits, some special features on the h-principle for 2-dimensional foliations are also explained.
講演会
15:00-16:00 数理科学研究科棟(駒場) 056号室
Alexander Kupers 氏 (Harvard University)
Cellular E_2-algebras and the unstable homology of mapping class groups
Alexander Kupers 氏 (Harvard University)
Cellular E_2-algebras and the unstable homology of mapping class groups
[ 講演概要 ]
We discuss joint work with Soren Galatius and Oscar Randal-Williams on the application of higher-algebraic techniques to classical questions about the homology of mapping class groups. This uses a new "multiplicative" approach to homological stability -- in contrast to the "additive" one due to Quillen -- which has the advantage of providing information outside of the stable range.
We discuss joint work with Soren Galatius and Oscar Randal-Williams on the application of higher-algebraic techniques to classical questions about the homology of mapping class groups. This uses a new "multiplicative" approach to homological stability -- in contrast to the "additive" one due to Quillen -- which has the advantage of providing information outside of the stable range.
2018年06月11日(月)
複素解析幾何セミナー
10:30-12:00 数理科学研究科棟(駒場) 128号室
千葉 優作 氏 (お茶の水女子大学)
Cohomology of non-pluriharmonic loci (JAPANESE)
千葉 優作 氏 (お茶の水女子大学)
Cohomology of non-pluriharmonic loci (JAPANESE)
[ 講演概要 ]
In this talk, we study a pseudoconvex counterpart of the Lefschetz hyperplane theorem.
We show a relation between the cohomology of a pseudoconvex domain and the cohomology of the non-pluriharmonic locus of an exhaustive plurisubharmonic function.
In this talk, we study a pseudoconvex counterpart of the Lefschetz hyperplane theorem.
We show a relation between the cohomology of a pseudoconvex domain and the cohomology of the non-pluriharmonic locus of an exhaustive plurisubharmonic function.
2018年06月06日(水)
代数学コロキウム
17:30-18:30 数理科学研究科棟(駒場) 056号室
Nicolas Templier 氏 (Cornell University)
On the Ramanujan conjecture for automorphic forms over function fields
Nicolas Templier 氏 (Cornell University)
On the Ramanujan conjecture for automorphic forms over function fields
[ 講演概要 ]
Let G be a reductive group over a function field of large enough characteristic. We prove the temperedness at unramified places of automorphic representations of G, subject to a local assumption at one place, stronger than supercuspidality. Such an assumption is necessary, as was first shown by Saito-Kurokawa and Howe-Piatetskii-Shapiro in the 70's. Our method relies on the l-adic geometry of Bun_G, and on trace formulas. Work with Will Sawin.
（本講演は「東京北京パリ数論幾何セミナー」として, インターネットによる東大数理, Morningside Center of Mathematics と IHES の双方向同時中継で行います．今回はパリからの中継です．）
Let G be a reductive group over a function field of large enough characteristic. We prove the temperedness at unramified places of automorphic representations of G, subject to a local assumption at one place, stronger than supercuspidality. Such an assumption is necessary, as was first shown by Saito-Kurokawa and Howe-Piatetskii-Shapiro in the 70's. Our method relies on the l-adic geometry of Bun_G, and on trace formulas. Work with Will Sawin.
（本講演は「東京北京パリ数論幾何セミナー」として, インターネットによる東大数理, Morningside Center of Mathematics と IHES の双方向同時中継で行います．今回はパリからの中継です．）
2018年06月05日(火)
トポロジー火曜セミナー
17:00-18:30 数理科学研究科棟(駒場) 056号室
Tea: Common Room 16:30-17:00
松井 宏樹 氏 (千葉大学)
Topological full groups and generalizations of the Higman-Thompson groups (JAPANESE)
Tea: Common Room 16:30-17:00
松井 宏樹 氏 (千葉大学)
Topological full groups and generalizations of the Higman-Thompson groups (JAPANESE)
[ 講演概要 ]
For a topological dynamical system on the Cantor set, one can introduce its topological full group, which is a countable subgroup of the homeomorphism group of the Cantor set. The Higman-Thompson group V_n is regarded as the topological full group of the one-sided full shift over n symbols. Replacing the one-sided full shift with other dynamical systems, we obtain variants of the Higman-Thompson group. It is then natural to ask whether those generalized Higman-Thompson groups possess similar (or different) features. I would like to discuss isomorphism classes of these groups, finiteness properties, abelianizations, connections to C*-algebras and their K-theory, and so on.
For a topological dynamical system on the Cantor set, one can introduce its topological full group, which is a countable subgroup of the homeomorphism group of the Cantor set. The Higman-Thompson group V_n is regarded as the topological full group of the one-sided full shift over n symbols. Replacing the one-sided full shift with other dynamical systems, we obtain variants of the Higman-Thompson group. It is then natural to ask whether those generalized Higman-Thompson groups possess similar (or different) features. I would like to discuss isomorphism classes of these groups, finiteness properties, abelianizations, connections to C*-algebras and their K-theory, and so on.
2018年06月04日(月)
東京確率論セミナー
16:00-17:30 数理科学研究科棟(駒場) 126号室
三竹 大寿 氏 (東京大学大学院数理科学研究科)
退化粘性ハミルトン・ヤコビ方程式の一意性集合 (JAPANESE)
三竹 大寿 氏 (東京大学大学院数理科学研究科)
退化粘性ハミルトン・ヤコビ方程式の一意性集合 (JAPANESE)
[ 講演概要 ]
Hamilton-Jacobi (HJ)方程式の初期値問題の解の長時間挙動を考えた時に現れる定常問題を，加法的固有値問題と呼ぶ．この加法的固有値問題の粘性解は，一意性が成り立たないことがよく知られている．力学系におけるAubry-Mather理論と粘性解理論との関係を整理することで発展した弱Kolmogorov-Arnold-Moser (KAM) 理論において，Mather集合またはAubry集合上で一致する粘性解は一意的であることが証明された．つまり，これらの集合は，加法的固有値問題の粘性解の一意性集合の役割を果たす．
最適確率制御問題を考えると自然に現れる退化粘性HJ方程式は，粘性解理論においてより自然な枠組みとして考えることができるが，従来の弱KAM理論では，決定論的な力学系しか扱えないため，取り扱いが困難であった．この点に注目をして，講演者は偏微分方程式論の立場から取り組むことで，弱KAM理論を発展させてきた．本講演では，特に退化粘性HJ方程式の加法的固有値問題の一意性集合について，最近得られた結果について紹介する．
解析のポイントは，対応する一般化されたMather測度を非線形随伴法で構成する点にある．この点での解析手段は，偏微分方程式論において閉じている話題ではあるが，背景に最適確率制御の問題を抱えているため，確率論において一つの新しい題材を提供できればと思っている．なお，本研究はH. V. Tran氏（U. Wisconsin-Madison)との共同研究である．
Hamilton-Jacobi (HJ)方程式の初期値問題の解の長時間挙動を考えた時に現れる定常問題を，加法的固有値問題と呼ぶ．この加法的固有値問題の粘性解は，一意性が成り立たないことがよく知られている．力学系におけるAubry-Mather理論と粘性解理論との関係を整理することで発展した弱Kolmogorov-Arnold-Moser (KAM) 理論において，Mather集合またはAubry集合上で一致する粘性解は一意的であることが証明された．つまり，これらの集合は，加法的固有値問題の粘性解の一意性集合の役割を果たす．
最適確率制御問題を考えると自然に現れる退化粘性HJ方程式は，粘性解理論においてより自然な枠組みとして考えることができるが，従来の弱KAM理論では，決定論的な力学系しか扱えないため，取り扱いが困難であった．この点に注目をして，講演者は偏微分方程式論の立場から取り組むことで，弱KAM理論を発展させてきた．本講演では，特に退化粘性HJ方程式の加法的固有値問題の一意性集合について，最近得られた結果について紹介する．
解析のポイントは，対応する一般化されたMather測度を非線形随伴法で構成する点にある．この点での解析手段は，偏微分方程式論において閉じている話題ではあるが，背景に最適確率制御の問題を抱えているため，確率論において一つの新しい題材を提供できればと思っている．なお，本研究はH. V. Tran氏（U. Wisconsin-Madison)との共同研究である．
複素解析幾何セミナー
10:30-12:00 数理科学研究科棟(駒場) 128号室
野口潤次郎 氏 (東京大学)
Picardの大定理とManin-Mumford予想(Raynaudの定理) (JAPANESE)
野口潤次郎 氏 (東京大学)
Picardの大定理とManin-Mumford予想(Raynaudの定理) (JAPANESE)
[ 講演概要 ]
Manin-Mumford予想とは，関数体上のMordell予想が解決された後の1960年代後半にManinとMumfordにより(独立に)提示されたもので1983年にM. Raynaudにより『代数体上定義されたアーベル多様体の代数的部分空間$X$内のトージョン点集合$X_{tor}$の$\mathbb{Z}$-閉包は部分群の平行移動の有限和である』という形で解決された．この結果は内容の深さからか多くの研究者の関心を呼び、その後，一般化や種々の別証明がM. Hindry ('88), E. Hrushovski ('96), Pila-Zannier ('08)等により与えられてきた．最後のPila-Zannierがここでの話に関係する．
本講演では，準アーベル多様体に対し拡張されたPicardの大定理(N. '81)を用いて上記Manin-Mumford予想(Raynaudの定理)を準アーベル多様体の場合に証明する．
Nevanlinna理論とDiophantus幾何については，これまで類似の観点からの議論・成果が多くあったが，今回の結果は証明レベルでの直接的な関係で，この様な関係を講演者は永く求めてきた(missing link)．その意味で今般の知見は新しいもものであると思う．両理論の間をモデル理論の"o-minimal sets 理論''が取り持つ点も興味深いところと思う．
Manin-Mumford予想とは，関数体上のMordell予想が解決された後の1960年代後半にManinとMumfordにより(独立に)提示されたもので1983年にM. Raynaudにより『代数体上定義されたアーベル多様体の代数的部分空間$X$内のトージョン点集合$X_{tor}$の$\mathbb{Z}$-閉包は部分群の平行移動の有限和である』という形で解決された．この結果は内容の深さからか多くの研究者の関心を呼び、その後，一般化や種々の別証明がM. Hindry ('88), E. Hrushovski ('96), Pila-Zannier ('08)等により与えられてきた．最後のPila-Zannierがここでの話に関係する．
本講演では，準アーベル多様体に対し拡張されたPicardの大定理(N. '81)を用いて上記Manin-Mumford予想(Raynaudの定理)を準アーベル多様体の場合に証明する．
Nevanlinna理論とDiophantus幾何については，これまで類似の観点からの議論・成果が多くあったが，今回の結果は証明レベルでの直接的な関係で，この様な関係を講演者は永く求めてきた(missing link)．その意味で今般の知見は新しいもものであると思う．両理論の間をモデル理論の"o-minimal sets 理論''が取り持つ点も興味深いところと思う．
2018年05月31日(木)
数値解析セミナー
16:30-18:00 数理科学研究科棟(駒場) 056号室
Olivier Pironneau 氏 (Sorbonne University and Academy of Sciences)
Parallel Computing Methods for Quantitative Finance: the Parareal Algorithm for American Options (English)
Olivier Pironneau 氏 (Sorbonne University and Academy of Sciences)
Parallel Computing Methods for Quantitative Finance: the Parareal Algorithm for American Options (English)
[ 講演概要 ]
With parallelism in mind we investigate the parareal method for American contracts both theoretically and numerically. Least-Square Monte-Carlo (LSMC) and parareal time decomposition with two or more levels are used, leading to an efficient parallel implementation which scales linearly with the number of processors and is appropriate to any multiprocessor-memory architecture in its multilevel version. We prove $L^2$ superlinear convergence for an LSMC backward in time computation of American contracts, when the conditional expectations are known, i.e. before Monte-Carlo discretization. In all cases the computing time is increased only by a constant factor, compared to the sequential algorithm on the finest grid, and speed-up is guaranteed when the number of processors is larger than that constant. A numerical implementation will be shown to confirm the theoretical error estimates.
With parallelism in mind we investigate the parareal method for American contracts both theoretically and numerically. Least-Square Monte-Carlo (LSMC) and parareal time decomposition with two or more levels are used, leading to an efficient parallel implementation which scales linearly with the number of processors and is appropriate to any multiprocessor-memory architecture in its multilevel version. We prove $L^2$ superlinear convergence for an LSMC backward in time computation of American contracts, when the conditional expectations are known, i.e. before Monte-Carlo discretization. In all cases the computing time is increased only by a constant factor, compared to the sequential algorithm on the finest grid, and speed-up is guaranteed when the number of processors is larger than that constant. A numerical implementation will be shown to confirm the theoretical error estimates.
2018年05月30日(水)
代数学コロキウム
17:00-18:00 数理科学研究科棟(駒場) 056号室
竹内大智 氏 (東京大学数理科学研究科)
Blow-ups and the class field theory for curves (JAPANESE)
竹内大智 氏 (東京大学数理科学研究科)
Blow-ups and the class field theory for curves (JAPANESE)
[ 講演概要 ]
幾何学的類体論とは、有限体上一変数代数関数体に対する類体論の、係数が一般の完全体の場合への拡張であり、M. Rosenlichtにより証明された定理である。一方1980年代、P. Deligneにより、順分岐の場合の別証明が見いだされた。それは曲線の対称積が、そのJacobi多様体上の射影（或いはアフィン）空間束になることを用いるものである。本講演では対称積のブローアップを考えることで、一般の分岐の場合でも類似の方法で証明できることを説明する。
幾何学的類体論とは、有限体上一変数代数関数体に対する類体論の、係数が一般の完全体の場合への拡張であり、M. Rosenlichtにより証明された定理である。一方1980年代、P. Deligneにより、順分岐の場合の別証明が見いだされた。それは曲線の対称積が、そのJacobi多様体上の射影（或いはアフィン）空間束になることを用いるものである。本講演では対称積のブローアップを考えることで、一般の分岐の場合でも類似の方法で証明できることを説明する。
2018年05月29日(火)
トポロジー火曜セミナー
17:00-18:30 数理科学研究科棟(駒場) 056号室
Tea: Common Room 16:30-17:00
佐藤 光樹 氏 (東京大学大学院数理科学研究科)
A partial order on nu+ equivalence classes (JAPANESE)
Tea: Common Room 16:30-17:00
佐藤 光樹 氏 (東京大学大学院数理科学研究科)
A partial order on nu+ equivalence classes (JAPANESE)
[ 講演概要 ]
The nu+ equivalence is an equivalence relation on the knot concordance group. Hom proves that many concordance invariants derived from Heegaard Floer homology are invariant under nu+ equivalence. In this work, we introduce a partial order on nu+ equivalence classes, and study its algebraic and geometrical properties. As an application, we prove that any genus one knot is nu+ equivalent to one of the unknot, the trefoil and its mirror.
The nu+ equivalence is an equivalence relation on the knot concordance group. Hom proves that many concordance invariants derived from Heegaard Floer homology are invariant under nu+ equivalence. In this work, we introduce a partial order on nu+ equivalence classes, and study its algebraic and geometrical properties. As an application, we prove that any genus one knot is nu+ equivalent to one of the unknot, the trefoil and its mirror.
代数幾何学セミナー
15:30-17:00 数理科学研究科棟(駒場) 122号室
Alessandra Sarti 氏 (Universit\'e de Poitiers)
Nikulin configurations on Kummer surfaces (English)
Alessandra Sarti 氏 (Universit\'e de Poitiers)
Nikulin configurations on Kummer surfaces (English)
[ 講演概要 ]
A Nikulin configuration is the data of
16 disjoint smooth rational curves on a K3 surface.
According to results of Nikulin this means that the K3 surface
is a Kummer surface and the abelian surface in the Kummer structure
is determined by the 16 curves. An old question of Shioda is about the
existence of non isomorphic Kummer structures on the same Kummer K3
surface.
The question was positively answered and studied by several authors, and
it was shown that the number of non-isomorphic Kummer structures is
finite,
but no explicit geometric construction of such structures was given.
In the talk I will show how to construct explicitely non isomorphic
Kummer structures on generic Kummer K3 surfaces.
This is a joint work with X. Roulleau.
A Nikulin configuration is the data of
16 disjoint smooth rational curves on a K3 surface.
According to results of Nikulin this means that the K3 surface
is a Kummer surface and the abelian surface in the Kummer structure
is determined by the 16 curves. An old question of Shioda is about the
existence of non isomorphic Kummer structures on the same Kummer K3
surface.
The question was positively answered and studied by several authors, and
it was shown that the number of non-isomorphic Kummer structures is
finite,
but no explicit geometric construction of such structures was given.
In the talk I will show how to construct explicitely non isomorphic
Kummer structures on generic Kummer K3 surfaces.
This is a joint work with X. Roulleau.
2018年05月28日(月)
複素解析幾何セミナー
10:30-12:00 数理科学研究科棟(駒場) 128号室
中村聡 氏 (東北大学)
A generalization of Kähler Einstein metrics for Fano manifolds with non-vanishing Futaki invariant (JAPANESE)
中村聡 氏 (東北大学)
A generalization of Kähler Einstein metrics for Fano manifolds with non-vanishing Futaki invariant (JAPANESE)
[ 講演概要 ]
The existence problem of Kähler Einstein metrics for Fano manifolds was one of the central problems in Kähler Geometry. The vanishing of the Futaki invariant is known as an obstruction to the existence of Kähler Einstein metrics. Generalized Kähler Einstein metrics (GKE for short), introduced by Mabuchi in 2000, is a generalization of Kähler Einstein metrics for Fano manifolds with non-vanishing Futaki invariant. In this talk, we give the followings:
(i) The positivity for the Hessian of the Ricci Calabi functional which characterizes GKE as its critical points, and its application.
(ii) A criterion for the existence of GKE on toric Fano manifolds from view points of an algebraic stability and an analytic stability.
The existence problem of Kähler Einstein metrics for Fano manifolds was one of the central problems in Kähler Geometry. The vanishing of the Futaki invariant is known as an obstruction to the existence of Kähler Einstein metrics. Generalized Kähler Einstein metrics (GKE for short), introduced by Mabuchi in 2000, is a generalization of Kähler Einstein metrics for Fano manifolds with non-vanishing Futaki invariant. In this talk, we give the followings:
(i) The positivity for the Hessian of the Ricci Calabi functional which characterizes GKE as its critical points, and its application.
(ii) A criterion for the existence of GKE on toric Fano manifolds from view points of an algebraic stability and an analytic stability.
数理人口学・数理生物学セミナー
15:30-16:30 数理科学研究科棟(駒場) 122号室
Sourav Kumar Sasmal 氏 (Department of Physics and Mathematics, Aoyama Gakuin University)
T-cell mediated adaptive immunity in primary dengue infections
https://www.sciencedirect.com/science/article/pii/S0022519317303211
Sourav Kumar Sasmal 氏 (Department of Physics and Mathematics, Aoyama Gakuin University)
T-cell mediated adaptive immunity in primary dengue infections
[ 講演概要 ]
Currently, dengue virus (DENV) is the most common mosquito-borne viral disease in the world, which is endemic across tropical Asia, Latin America, and Africa. The global DENV incidence is increasing day by day due to climate changing. According to a report, DENV cases increase almost five times since 1980, than the previous 30 years. Mathematical modeling is a common tool for understanding, studying and analyzing the mechanisms that govern the dynamics of infectious disease. In addition, models can be used to study different mitigation measures to control outbreaks. Here, we present a mathematical model of DENV dynamics in micro-environment (cellular level) consisting of healthy cells, infected cells, virus particles and T -cell mediated adaptive immunity. We have considered the explicit role of cytokines and antibody in our model. We find that the virus load goes down to zero within 6 days as it is common for DENV infection. We have shown that the cytokine mediated virus clearance plays a very important role in dengue dynamics. It can change the dynamical behavior of the system and causes essential extinction of the virus. Finally, we have incorporated the antiviral treatment effect for DENV in our model and shown that the basic reproduction number is directly proportional to the antiviral treatment effects.
[ 参考URL ]Currently, dengue virus (DENV) is the most common mosquito-borne viral disease in the world, which is endemic across tropical Asia, Latin America, and Africa. The global DENV incidence is increasing day by day due to climate changing. According to a report, DENV cases increase almost five times since 1980, than the previous 30 years. Mathematical modeling is a common tool for understanding, studying and analyzing the mechanisms that govern the dynamics of infectious disease. In addition, models can be used to study different mitigation measures to control outbreaks. Here, we present a mathematical model of DENV dynamics in micro-environment (cellular level) consisting of healthy cells, infected cells, virus particles and T -cell mediated adaptive immunity. We have considered the explicit role of cytokines and antibody in our model. We find that the virus load goes down to zero within 6 days as it is common for DENV infection. We have shown that the cytokine mediated virus clearance plays a very important role in dengue dynamics. It can change the dynamical behavior of the system and causes essential extinction of the virus. Finally, we have incorporated the antiviral treatment effect for DENV in our model and shown that the basic reproduction number is directly proportional to the antiviral treatment effects.
https://www.sciencedirect.com/science/article/pii/S0022519317303211
2018年05月25日(金)
談話会・数理科学講演会
15:30-16:30 数理科学研究科棟(駒場) 056号室
阿部紀行 氏 (東京大学大学院数理科学研究科)
p進簡約群の法p表現 (日本語)
阿部紀行 氏 (東京大学大学院数理科学研究科)
p進簡約群の法p表現 (日本語)
[ 講演概要 ]
近年p進Langlands対応や法p Langlands対応を動機として，p進簡約群の標数pの体の上の表現（法p表現）の研究が行われています．そのような表現論の現状，特に既約表現の分類についてお話しします．
近年p進Langlands対応や法p Langlands対応を動機として，p進簡約群の標数pの体の上の表現（法p表現）の研究が行われています．そのような表現論の現状，特に既約表現の分類についてお話しします．
代数幾何学セミナー
15:30-17:00 数理科学研究科棟(駒場) 122号室
普段と違う金曜日にセミナーを行います。The seminar will be held on Friday. This is a different day from usual.
De Qi Zhang 氏 (Singapore)
Endomorphisms of normal projective variety and equivariant-MMP (English)
普段と違う金曜日にセミナーを行います。The seminar will be held on Friday. This is a different day from usual.
De Qi Zhang 氏 (Singapore)
Endomorphisms of normal projective variety and equivariant-MMP (English)
[ 講演概要 ]
We report some recent joint works on polarized or int-amplified endomorphisms f on a normal projective variety X with mild singularities, and prove the pseudo-effectivity of the anti-canonical divisor of X, and the f-equivariance, after replacing f by its power, for every minimal model program starting from X. Fano varieties and Q-abelian varieties turn out to be building blocks having such symmetries. The ground field is closed and of characteristic 0 or at least 7.
We report some recent joint works on polarized or int-amplified endomorphisms f on a normal projective variety X with mild singularities, and prove the pseudo-effectivity of the anti-canonical divisor of X, and the f-equivariance, after replacing f by its power, for every minimal model program starting from X. Fano varieties and Q-abelian varieties turn out to be building blocks having such symmetries. The ground field is closed and of characteristic 0 or at least 7.
2018年05月24日(木)
応用解析セミナー
16:00-17:30 数理科学研究科棟(駒場) 128号室
柳田英二 氏 (東京工業大学)
Sign-changing solutions for a one-dimensional semilinear parabolic problem (Japanese)
柳田英二 氏 (東京工業大学)
Sign-changing solutions for a one-dimensional semilinear parabolic problem (Japanese)
[ 講演概要 ]
This talk is concerned with a nonlinear parabolic equation on a bounded interval with the homogeneous Dirichlet or Neumann boundary condition. Under rather general conditions on the nonlinearity, we consider the blow-up and global existence of sign-changing solutions. It is shown that there exists a nonnegative integer $k$ such that the solution blows up in finite time if the initial value changes its sign at most $k$ times, whereas there exists a stationary solution with more than $k$ zeros. The proof is based on an intersection number argument combined with a topological method.
This talk is concerned with a nonlinear parabolic equation on a bounded interval with the homogeneous Dirichlet or Neumann boundary condition. Under rather general conditions on the nonlinearity, we consider the blow-up and global existence of sign-changing solutions. It is shown that there exists a nonnegative integer $k$ such that the solution blows up in finite time if the initial value changes its sign at most $k$ times, whereas there exists a stationary solution with more than $k$ zeros. The proof is based on an intersection number argument combined with a topological method.
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