March  2016, 8(1): 13-34. doi: 10.3934/jgm.2016.8.13

Symplectic reduction at zero angular momentum

1. 

Department of Applied Mathematics and Statistics, Johns Hopkins University, 3400 N. Charles St, Baltimore, MD 21218, United States

2. 

Departamento de Matemática Aplicada, Av. Athos da Silveira Ramos 149, Centro de Tecnologia - Bloco C, CEP: 21941-909 - Rio de Janeiro, Brazil

3. 

Department of Mathematics and Computer Science, Rhodes College, 2000 N. Parkway, Memphis, TN 38112, United States

Received  April 2015 Revised  August 2015 Published  February 2016

We study the symplectic reduction of the phase space describing $k$ particles in $\mathbb{R}^n$ with total angular momentum zero. This corresponds to the singular symplectic quotient associated to the diagonal action of $O_n$ on $k$ copies of $T^\ast\mathbb{R}^n$ at the zero value of the homogeneous quadratic moment map. We give a description of the ideal of relations of the ring of regular functions of the symplectic quotient. Using this description, we demonstrate $\mathbb{Z}^+$-graded regular symplectomorphisms among the $O_n$- and $SO_n$-symplectic quotients and determine which of these quotients are graded regularly symplectomorphic to linear symplectic orbifolds. We demonstrate that when $n \leq k$, the zero fibre of the moment map has rational singularities and hence is normal and Cohen-Macaulay. We also demonstrate that for small values of $k$, the ring of regular functions on the symplectic quotient is graded Gorenstein.
Citation: Joshua Cape, Hans-Christian Herbig, Christopher Seaton. Symplectic reduction at zero angular momentum. Journal of Geometric Mechanics, 2016, 8 (1) : 13-34. doi: 10.3934/jgm.2016.8.13
References:
[1]

J. M. Arms, M. J. Gotay and G. Jennings, Geometric and algebraic reduction for singular momentum maps,, Adv. Math., 79 (1990), 43. doi: 10.1016/0001-8708(90)90058-U.

[2]

A. Beauville, Symplectic singularities,, Invent. Math., 139 (2000), 541. doi: 10.1007/s002229900043.

[3]

L. Bos and M. J. Gotay, Reduced canonical formalism for a particle with zero angular momentum,, in XIIIth International Colloquium on Group Theoretical Methods in Physics (College Park, (1984), 83.

[4]

J.-F. Boutot, Singularités rationnelles et quotients par les groupes réductifs,, Invent. Math., 88 (1987), 65. doi: 10.1007/BF01405091.

[5]

D. Cox, J. Little and D. O'Shea, Ideals, Varieties, and Algorithms. An Introduction to Computational Algebraic Geometry and Commutative Algebra,, 2nd edition, (1997).

[6]

H. Derksen and G. Kemper, Computational Invariant Theory,, Invariant Theory and Algebraic Transformation Groups, (2002). doi: 10.1007/978-3-662-04958-7.

[7]

C. Farsi, H.-C. Herbig and C. Seaton, On orbifold criteria for symplectic toric quotients,, SIGMA Symmetry Integrability Geom. Methods Appl., 9 (2013). doi: 10.3842/SIGMA.2013.032.

[8]

H. Flenner, Rationale quasihomogene Singularitäten,, Arch. Math. (Basel), 36 (1981), 35. doi: 10.1007/BF01223666.

[9]

M. J. Gotay, Reduction of homogeneous Yang-Mills fields,, J. Geom. Phys., 6 (1989), 349. doi: 10.1016/0393-0440(89)90009-0.

[10]

D. R. Grayson and M. E. Stillman, Macaulay2, a software system for research in algebraic geometry,, 2012. Available from: , ().

[11]

H.-C. Herbig, D. Herden and C. Seaton, On compositions with $x^2/(1-x)$,, Proc. Amer. Math. Soc., 143 (2015), 4583. doi: 10.1090/proc/12806.

[12]

H.-C. Herbig and G. W. Schwarz, The Koszul complex of a moment map,, J. Symplectic Geom., 11 (2013), 497. doi: 10.4310/JSG.2013.v11.n3.a9.

[13]

H.-C. Herbig, G. W. Schwarz and C. Seaton, When is a symplectic quotient an orbifold?,, Adv. Math., 280 (2015), 208. doi: 10.1016/j.aim.2015.04.016.

[14]

H.-C. Herbig and C. Seaton, An impossibility theorem for linear symplectic circle quotients,, Rep. Math. Phys., 75 (2015), 303. doi: 10.1016/S0034-4877(15)00019-1.

[15]

H.-C. Herbig and C. Seaton, The Hilbert series of a linear symplectic circle quotient,, Exp. Math., 23 (2014), 46. doi: 10.1080/10586458.2013.863745.

[16]

J. Huebschmann, Singularities and Poisson geometry of certain representation spaces,, in Quantization of Singular Symplectic Quotients, (2001), 119.

[17]

J. Huebschmann, Kähler spaces, nilpotent orbits, and singular reduction,, Mem. Amer. Math. Soc., 172 (2004). doi: 10.1090/memo/0814.

[18]

C. Huneke, Tight closure, parameter ideals, and geometry,, in Six Lectures on Commutative Algebra, (2010), 187. doi: 10.1007/978-3-0346-0329-4_3.

[19]

G. Kempf and L. Ness, The length of vectors in representation spaces,, in Algebraic Geometry (Proc. Summer Meeting, (1978), 233.

[20]

F. Kirwan, Convexity properties of the moment mapping. III,, Invent. Math., 77 (1984), 547. doi: 10.1007/BF01388838.

[21]

E. Lerman, R. Montgomery and R. Sjamaar, Examples of singular reduction,, in Symplectic Geometry, (1993), 127.

[22]

K. McGerty and T. Nevins, Derived equivalence for quantum symplectic resolutions,, Selecta Math. (N.S.), 20 (2014), 675. doi: 10.1007/s00029-013-0142-6.

[23]

C. Procesi and G. Schwarz, Inequalities defining orbit spaces,, Invent. Math., 81 (1985), 539. doi: 10.1007/BF01388587.

[24]

G. W. Schwarz, Lifting smooth homotopies of orbit spaces,, Inst. Hautes Études Sci. Publ. Math., 51 (1980), 37.

[25]

G. W. Schwarz, The topology of algebraic quotients,, in Topological Methods in Algebraic Transformation Groups (New Brunswick, (1988), 135.

[26]

G. W. Schwarz, Lifting differential operators from orbit spaces,, Ann. Sci. École Norm. Sup. (4), 28 (1995), 253.

[27]

R. Sjamaar, Holomorphic slices, symplectic reduction and multiplicities of representations,, Ann. of Math. (2), 141 (1995), 87. doi: 10.2307/2118628.

[28]

R. Sjamaar and E. Lerman, Stratified symplectic spaces and reduction,, Ann. of Math. (2), 134 (1991), 375. doi: 10.2307/2944350.

[29]

R. P. Stanley, Hilbert functions of graded algebras,, Advances in Math., 28 (1978), 57. doi: 10.1016/0001-8708(78)90045-2.

[30]

R. Terpereau, Schémas de Hilbert Invariants et Théorie Classique Des Invariants,, Thesis (Ph.D.)-Université de Grenoble, (2012).

[31]

È. B. Vinberg and V. L. Popov, Invariant Theory,, in Algebraic Geometry. IV, (1989), 123. doi: 10.1007/978-3-662-03073-8.

[32]

K. Watanabe, Certain invariant subrings are Gorenstein. I,, Osaka J. Math., 11 (1974), 1.

[33]

K. Watanabe, Certain invariant subrings are Gorenstein. II,, Osaka J. Math., 11 (1974), 379.

[34]

K. Watanabe, Rational singularities with $k^*$-action,, in Commutative Algebra (Trento, (1981), 339.

[35]

H. Weyl, The Classical Groups. Their Invariants and Representations,, Princeton University Press, (1939).

[36]

Wolfram Research, Mathematica edition: Version 7.0,, , ().

show all references

References:
[1]

J. M. Arms, M. J. Gotay and G. Jennings, Geometric and algebraic reduction for singular momentum maps,, Adv. Math., 79 (1990), 43. doi: 10.1016/0001-8708(90)90058-U.

[2]

A. Beauville, Symplectic singularities,, Invent. Math., 139 (2000), 541. doi: 10.1007/s002229900043.

[3]

L. Bos and M. J. Gotay, Reduced canonical formalism for a particle with zero angular momentum,, in XIIIth International Colloquium on Group Theoretical Methods in Physics (College Park, (1984), 83.

[4]

J.-F. Boutot, Singularités rationnelles et quotients par les groupes réductifs,, Invent. Math., 88 (1987), 65. doi: 10.1007/BF01405091.

[5]

D. Cox, J. Little and D. O'Shea, Ideals, Varieties, and Algorithms. An Introduction to Computational Algebraic Geometry and Commutative Algebra,, 2nd edition, (1997).

[6]

H. Derksen and G. Kemper, Computational Invariant Theory,, Invariant Theory and Algebraic Transformation Groups, (2002). doi: 10.1007/978-3-662-04958-7.

[7]

C. Farsi, H.-C. Herbig and C. Seaton, On orbifold criteria for symplectic toric quotients,, SIGMA Symmetry Integrability Geom. Methods Appl., 9 (2013). doi: 10.3842/SIGMA.2013.032.

[8]

H. Flenner, Rationale quasihomogene Singularitäten,, Arch. Math. (Basel), 36 (1981), 35. doi: 10.1007/BF01223666.

[9]

M. J. Gotay, Reduction of homogeneous Yang-Mills fields,, J. Geom. Phys., 6 (1989), 349. doi: 10.1016/0393-0440(89)90009-0.

[10]

D. R. Grayson and M. E. Stillman, Macaulay2, a software system for research in algebraic geometry,, 2012. Available from: , ().

[11]

H.-C. Herbig, D. Herden and C. Seaton, On compositions with $x^2/(1-x)$,, Proc. Amer. Math. Soc., 143 (2015), 4583. doi: 10.1090/proc/12806.

[12]

H.-C. Herbig and G. W. Schwarz, The Koszul complex of a moment map,, J. Symplectic Geom., 11 (2013), 497. doi: 10.4310/JSG.2013.v11.n3.a9.

[13]

H.-C. Herbig, G. W. Schwarz and C. Seaton, When is a symplectic quotient an orbifold?,, Adv. Math., 280 (2015), 208. doi: 10.1016/j.aim.2015.04.016.

[14]

H.-C. Herbig and C. Seaton, An impossibility theorem for linear symplectic circle quotients,, Rep. Math. Phys., 75 (2015), 303. doi: 10.1016/S0034-4877(15)00019-1.

[15]

H.-C. Herbig and C. Seaton, The Hilbert series of a linear symplectic circle quotient,, Exp. Math., 23 (2014), 46. doi: 10.1080/10586458.2013.863745.

[16]

J. Huebschmann, Singularities and Poisson geometry of certain representation spaces,, in Quantization of Singular Symplectic Quotients, (2001), 119.

[17]

J. Huebschmann, Kähler spaces, nilpotent orbits, and singular reduction,, Mem. Amer. Math. Soc., 172 (2004). doi: 10.1090/memo/0814.

[18]

C. Huneke, Tight closure, parameter ideals, and geometry,, in Six Lectures on Commutative Algebra, (2010), 187. doi: 10.1007/978-3-0346-0329-4_3.

[19]

G. Kempf and L. Ness, The length of vectors in representation spaces,, in Algebraic Geometry (Proc. Summer Meeting, (1978), 233.

[20]

F. Kirwan, Convexity properties of the moment mapping. III,, Invent. Math., 77 (1984), 547. doi: 10.1007/BF01388838.

[21]

E. Lerman, R. Montgomery and R. Sjamaar, Examples of singular reduction,, in Symplectic Geometry, (1993), 127.

[22]

K. McGerty and T. Nevins, Derived equivalence for quantum symplectic resolutions,, Selecta Math. (N.S.), 20 (2014), 675. doi: 10.1007/s00029-013-0142-6.

[23]

C. Procesi and G. Schwarz, Inequalities defining orbit spaces,, Invent. Math., 81 (1985), 539. doi: 10.1007/BF01388587.

[24]

G. W. Schwarz, Lifting smooth homotopies of orbit spaces,, Inst. Hautes Études Sci. Publ. Math., 51 (1980), 37.

[25]

G. W. Schwarz, The topology of algebraic quotients,, in Topological Methods in Algebraic Transformation Groups (New Brunswick, (1988), 135.

[26]

G. W. Schwarz, Lifting differential operators from orbit spaces,, Ann. Sci. École Norm. Sup. (4), 28 (1995), 253.

[27]

R. Sjamaar, Holomorphic slices, symplectic reduction and multiplicities of representations,, Ann. of Math. (2), 141 (1995), 87. doi: 10.2307/2118628.

[28]

R. Sjamaar and E. Lerman, Stratified symplectic spaces and reduction,, Ann. of Math. (2), 134 (1991), 375. doi: 10.2307/2944350.

[29]

R. P. Stanley, Hilbert functions of graded algebras,, Advances in Math., 28 (1978), 57. doi: 10.1016/0001-8708(78)90045-2.

[30]

R. Terpereau, Schémas de Hilbert Invariants et Théorie Classique Des Invariants,, Thesis (Ph.D.)-Université de Grenoble, (2012).

[31]

È. B. Vinberg and V. L. Popov, Invariant Theory,, in Algebraic Geometry. IV, (1989), 123. doi: 10.1007/978-3-662-03073-8.

[32]

K. Watanabe, Certain invariant subrings are Gorenstein. I,, Osaka J. Math., 11 (1974), 1.

[33]

K. Watanabe, Certain invariant subrings are Gorenstein. II,, Osaka J. Math., 11 (1974), 379.

[34]

K. Watanabe, Rational singularities with $k^*$-action,, in Commutative Algebra (Trento, (1981), 339.

[35]

H. Weyl, The Classical Groups. Their Invariants and Representations,, Princeton University Press, (1939).

[36]

Wolfram Research, Mathematica edition: Version 7.0,, , ().

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