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Indranil Biswas

Publications and source records attributed to Indranil Biswas.

At least 433 records · Page 24Linked to original sources
arXiv2011

Parabolic k-ample bundles

We construct projectivization of a parabolic vector bundle and a tautological line bundle over it. It is shown that a parabolic vector bundle is ample if and only if the tautological line bundle is ample. This allows us to generalize the notion of a k-ample bundle, introduced by Sommese, to the context of parabolic bundles. A parabolic vector bundle $E_*$ is defined to be k-ample if the tautological line bundle ${\mathcal O}_{{\mathbb P}(E_*)}(1)$ is $k$--ample. We establish some properties of parabolic k-ample bundles.

math.AG↗
arXiv2011

Rank one connections on abelian varieties

Let A be a complex abelian variety. The moduli space ${\mathcal M}_C$ of rank one algebraic connections on $A$ is a principal bundle over the dual abelian variety $A^\vee=\text{Pic}^0(A)$ for the group $H^0(A, Ω^1_A)$. Take any line bundle $L$ on $A^\vee$; let ${\mathcal C}(L)$ be the algebraic principal $H^0(A^\vee, Ω^1_{A^\vee})$-bundle over $A^\vee$ given by the sheaf of connections on $L$. The line bundle $L$ produces a homomorphism $H^0(A, Ω^1_A) \rightarrow H^0(A^\vee,\, Ω^1_{A^\vee})$. We prove that ${\mathcal C}(L)$ is isomorphic to the principal $H^0(A^\vee, Ω^1_{A^\vee})$-bundle obtained by extending the structure group of the principal $H^0(A,\, Ω^1_A)$-bundle ${\mathcal M}_C$ using this homomorphism given by $L$. We compute the ring of algebraic functions on ${\mathcal C}(L)$.

math.AG↗
arXiv2011

A remark on "Connections and Higgs fields on a principal bundle"

We show that a unipotent vector bundle on a non-Kaehler compact complex manifold does not admit a flat holomorphic connection in general. We also construct examples of topologically trivial stable vector bundle on compact Gauduchon manifold that does not admit any unitary flat connection.

math.DG↗
arXiv2011

A Torelli theorem for moduli spaces of principal bundles over a curve

Let X and X' be compact Riemann surfaces of genus at least 3, and let G and G' be nonabelian reductive complex groups. If one component M_G^d(X) of the moduli space for semistable principal G-bundles over X is isomorphic to another component M_{G'}^{d'}(X'), then X is isomorphic to X'.

math.AG↗
arXiv2011

Holomorphic Cartan geometry on manifolds with numerically effective tangent bundle

Let X be a compact connected Kaehler manifold such that the holomorphic tangent bundle TX is numerically effective. A theorem of Demailly, Peternell and Schenider says that there is a finite unramified Galois covering M --> X, a complex torus T, and a holomorphic surjective submersion f: M --> T, such that the fibers of f are Fano manifolds with numerically effective tangent bundle. A conjecture of Campana and Peternell says that the fibers of f are rational and homogeneous. Assume that X admits a holomorphic Cartan geometry. We prove that the fibers of f are rational homogeneous varieties. We also prove that the holomorphic principal G-bundle over T given by f, where G is the group of all holomorphic automorphisms of a fiber, admits a flat holomorphic connection.

math.CV↗
arXiv2011

Automorphisms of moduli spaces of symplectic bundle

Let X be an irreducible smooth complex projective curve of genus at least 3. Fix a line bundle L on X. Let M_{Sp}(L) be the moduli space of symplectic bundles (E, ExE ---> L) on X, with the symplectic form taking values in L. We show that the automorphism group of M_{Sp}(L) is generated by automorphisms sending E to ExM, where M is a 2-torsion line bundle, and automorphisms induced by automorphisms of X.

math.AG↗
arXiv2010

Brauer group of a moduli space of parabolic vector bundles over a curve

Let ${\mathcal P}{\mathcal M}^α_s$ be a moduli space of stable parabolic vector bundles of rank $n \geq 2$ and fixed determinant of degree $d$ over a compact connected Riemann surface $X$ of genus $g(X) \geq 2$. If $g(X) = 2$, then we assume that $n > 2$. Let $m$ denote the greatest common divisor of $d$, $n$ and the dimensions of all the successive quotients of the quasi-parabolic filtrations. We prove that the cohomological Brauer group ${\rm Br}({\mathcal P}{\mathcal M}^α_s)$ is isomorphic to the cyclic group ${\mathbb Z}/ m{\mathbb Z}$. We also show that ${\rm Br}({\mathcal P}{\mathcal M}^α_s)$ is generated by the Brauer class of the projective bundle over ${\mathcal P}{\mathcal M}^α_s$ obtained by restricting the universal projective bundle over $X\times {\mathcal P}{\mathcal M}^α_s$. We also prove that there is a universal vector bundle over $X\times {\mathcal P}{\mathcal M}^α_s$ if and only if $m=1$.

math.AG↗
arXiv2010

Determinant line bundle on moduli space of parabolic bundles

In \cite{BR1}, \cite{BR2}, a parabolic determinant line bundle on a moduli space of stable parabolic bundles was constructed, along with a Hermitian structure on it. The construction of the Hermitian structure was indirect: The parabolic determinant line bundle was identified with the pullback of the determinant line bundle on a moduli space of usual vector bundles over a covering curve. The Hermitian structure on the parabolic determinant bundle was taken to be the pullback of the Quillen metric on the determinant line bundle on the moduli space of usual vector bundles. Here a direct construction of the Hermitian structure is given. For that we need to establish a version of the correspondence between the stable parabolic bundles and the Hermitian--Einstein connections in the context of conical metrics. Also, a recently obtained parabolic analog of Faltings' criterion of semistability plays a crucial role.

math.DG↗
arXiv2010

Stable Higgs bundles on compact Gauduchon manifolds

Let $M$ be a compact complex manifold equipped with a Gauduchon metric. If $TM$ is holomorphically trivial, and (V, θ) is a stable SL(r,{\mathbb C})-Higgs bundle on $M$, then we show that $θ= 0$. We show that the correspondence between Higgs bundles and representations of the fundamental group for a compact Kaehler manifold does not extend to compact Gauduchon manifolds. This is done by applying the above result to G/Γ, where $Γ$ is a discrete torsionfree cocompact subgroup of a complex semisimple group $G$.

math.AG↗
arXiv2010

On the algebraic holonomy of stable principal bundles

Apart from math.AG/0608569, it contains the following applications of it. Let M be a simply connected, irreducible smooth complex projective variety of dimension $n$ such that the Picard number of $M$ is one. If the canonical line bundle $K_M$ is ample, then the algebraic holonomy of $TM$ is $\text{GL}(n, {\mathbb C})$. If $K^{-1}_M$ is ample, $\text{rank}(\text{NS}(M)) = 1$, the biholomorphic automorphism group of $M$ is finite, and $M$ admits a Kähler--Einstein metric, then the algebraic holonomy of $TM$ is ${\rm GL}(n, {\mathbb C})$.

math.AG↗
arXiv2010

Holomorphic Cartan geometries, Calabi--Yau manifolds and rational curves

We prove that if a Calabi--Yau manifold $M$ admits a holomorphic Cartan geometry, then $M$ is covered by a complex torus. This is done by establishing the Bogomolov inequality for semistable sheaves on compact Kähler manifolds. We also classify all holomorphic Cartan geometries on rationally connected complex projective manifolds.

math.AG↗
arXiv2010

Chen-Ruan cohomology of some moduli spaces, II

Let X be a compact connected Riemann surface of genus at least two. Let r be a prime number and ξa holomorphic line bundle on it such that r is not a divisor of degree(ξ). Let {\mathcal M}_ξ(r) denote the moduli space of stable vector bundles over X of rank r and determinant ξ. By Γwe will denote the group of line bundles L over X such that $L^{\otimes r}$ is trivial. This group Γacts on {\mathcal M}_ξ(r). We compute the Chen-Ruan cohomology of the corresponding orbifold.

math.AG↗
arXiv2010

Einstein-Hermitian connection on twisted Higgs bundles

Let $X$ be a smooth projective variety over $\mathbb C$. We prove that a twisted Higgs vector bundle $(\calE\, ,θ)$ on $X$ admits an Einstein--Hermitian connection if and only if $(\calE\, ,θ)$ is polystable. A similar result for twisted vector bundles (no Higgs fields) was proved by S. Wang in \cite{Wa}. Our approach is simpler.

math.AG↗
arXiv2010

Poincaré families of G-bundles on a curve

Let G be a reductive group over an algebraically closed field k. Consider the moduli space of stable principal G-bundles on a smooth projective curve C over k. We give necessary and sufficient conditions for the existence of Poincaré bundles over open subsets of this moduli space, and compute the orders of the corresponding obstruction classes. This generalizes the previous results of Newstead, Ramanan and Balaji-Biswas-Nagaraj-Newstead to all reductive groups, to all topological types of bundles, and also to all characteristics.

math.AG↗