Smoothness of Picard scheme of an abelian variety as in Mumford's book











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In Mumford's book, he shows $Pic^0$ of an abelian scheme is smooth by considering obstruction class:
enter image description hereenter image description here



why is the homomorphism $mu^*-p_1^*-p_2^*$ is injective on the second chomology? Mumford said in the last paragraph that we shall use structure of cohomology of abelian varieties (it's a wedge product of first cohomology) and Kunneth formula, but I don't know how to deduce the injectivity from those facts.










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    up vote
    2
    down vote

    favorite












    In Mumford's book, he shows $Pic^0$ of an abelian scheme is smooth by considering obstruction class:
    enter image description hereenter image description here



    why is the homomorphism $mu^*-p_1^*-p_2^*$ is injective on the second chomology? Mumford said in the last paragraph that we shall use structure of cohomology of abelian varieties (it's a wedge product of first cohomology) and Kunneth formula, but I don't know how to deduce the injectivity from those facts.










    share|cite|improve this question
























      up vote
      2
      down vote

      favorite









      up vote
      2
      down vote

      favorite











      In Mumford's book, he shows $Pic^0$ of an abelian scheme is smooth by considering obstruction class:
      enter image description hereenter image description here



      why is the homomorphism $mu^*-p_1^*-p_2^*$ is injective on the second chomology? Mumford said in the last paragraph that we shall use structure of cohomology of abelian varieties (it's a wedge product of first cohomology) and Kunneth formula, but I don't know how to deduce the injectivity from those facts.










      share|cite|improve this question













      In Mumford's book, he shows $Pic^0$ of an abelian scheme is smooth by considering obstruction class:
      enter image description hereenter image description here



      why is the homomorphism $mu^*-p_1^*-p_2^*$ is injective on the second chomology? Mumford said in the last paragraph that we shall use structure of cohomology of abelian varieties (it's a wedge product of first cohomology) and Kunneth formula, but I don't know how to deduce the injectivity from those facts.







      algebraic-geometry abelian-varieties






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      asked Nov 23 at 2:14









      zzy

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