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I-Hsun Tsai

Publications and source records attributed to I-Hsun Tsai.

At least 19 recordsLinked to original sources
arXiv2026

Spectral bundles on Abelian varieties, complex projective spaces and Grassmannians

In this paper we study the spectral analysis of Bochner-Kodaira Laplacians on an Abelian variety, complex projective space $\mathbb{P}^{n}$ and a Grassmannian with a holomorphic line bundle. By imitating the method of creation and annihilation operators in physics, we convert those eigensections (of the \textquotedblleft higher energy" level) into holomorphic sections (of the \textquotedblleft lowest energy" level). This enables us to endow these spectral bundles, which are defined over the dual Abelian variety, with natural holomorphic structure. Using this conversion expressed in a concrete way, all the higher eigensections are explicitly expressible using holomorphic sections formed by theta functions. Moreover, we give an explicit formula for the dimension of the space of higher-level eigensections on $\mathbb{P}^{n}$ through vanishing theorems and the Hirzebruch-Riemann-Roch theorem. These give a theoretical study related to some problems newly discussed by string theorists using numerical analysis. Some partial results on Grassmannians are proved and some directions for future research are indicated.

math.DG↗
arXiv2026

Solution Module and Linear Closure

We introduce the notion of an ``initial condition'' for a module over a commutative Noetherian local ring, allowing for a recursive construction of its ``solution modules''. If the given module has zero-dimensional support, such as the residue field of the local ring and those encountered in residual complexes, we demonstrate that the solution module is an injective hull of the given module. The construction of the solution module for finitely generated given module is explicit and computable, devoid of the need for Zorn's lemma.

math.AC↗
arXiv2026

Characterization of fiberwise bimeromorphism and specialization of bimeromorphic types I: locally Moishezon case

Inspired by the recent works of M. Kontsevich--Y. Tschinkel and J. Nicaise--J. C. Ottem on specialization of birational types for smooth families (in the scheme category) and J. Koll{á}r's work on fiberwise bimeromorphism, we focus on characterizing the fiberwise bimeromorphism and utilizing the characterization to investigate the specialization of bimeromorphic types for non-smooth families in the complex analytic setting. We provide several criteria for a bimeromorphic map between two families over the same base to be fiberwise bimeromorphic. By combining these criteria with the relative Barlet cycle space theoretic argument motivated by D. Mumford--U. Persson, K. Timmerscheidt and T. de Fernex--D. Fusi, we establish the specialization of bimeromorphic types for locally Moishezon families with fibers having only canonical singularities and being of non-negative Kodaira dimension. These specialization results can easily lead to criteria for locally strongly bimeromorphic isotriviality. Throughout this paper, we unveil the connections among the four classical topics in bimeromorphic geometry: the deformation behavior of plurigenera (or even $1$-genus), fiberwise bimeromorphism, specialization of bimeromorphic types, and the bimeromorphic version of the deformation rigidity.

math.AG↗
arXiv2025

Heat kernel and local index theorem for open complex manifolds with $\mathbb{C}^{\ast }$-action

For a complex manifold $Σ$ with $\mathbb{C}^{\ast }$-action, we define the $m$-th $\mathbb{C}^{\ast }$ Fourier-Dolbeault cohomology group and consider the $m$-index on $Σ$. By applying the method of transversal heat kernel asymptotics, we obtain a local index formula for the $m$-index. We can reinterpret Kawasaki's Hirzebruch-Riemann-Roch formula for a compact complex orbifold with an orbifold holomorphic line bundle by our integral formulas over a (smooth) complex manifold and finitely many complex submanifolds arising from singular strata. We generalize $\mathbb{C}^{\ast }$-action to complex reductive Lie group $G$-action on a compact or noncompact complex manifold. Among others, we study the nonextendability of open group action and the space of all $G$-invariant holomorphic $p$-forms. Finally, in the case of two compatible holomorphic $\mathbb{C}^{\ast }$-actions, a mirror-type isomorphism is found between two linear spaces of holomorphic forms, and the Euler characteristic associated with these spaces can be computed by our $\mathbb{C}^{\ast }$ local index formula on the total space. In the perspective of the equivariant algebraic cobordism theory $Ω_{\ast }^{\mathbb{C}^{\ast }}(Σ),$ a speculative connection is remarked. Possible relevance to the recent development in physics and number theory is briefly mentioned.

math.DG↗
arXiv2024

Theta functions and adiabatic curvature on an Abelian variety

For an ample line bundle $L$ on an Abelian variety $M$, we study the theta functions associated with the family of line bundles $L\otimes T$ on $M$ indexed by $T\in \text{Pic}^{0}(M)$. Combined with an appropriate differential geometric setting, this leads to an explicit curvature computation of the direct image bundle $E$ on $\text{Pic}^{0}(M)$, whose fiber $E_{T}$ is the vector space spanned by the theta functions for the line bundle $L\otimes T$ on $M$. Some algebro-geometric properties of $E$ are also remarked.

math.AG↗
arXiv2022

Invariance of plurigenera and Chow-type lemma

This paper answers a question of Demailly whether a smooth family of nonsingular projective varieties admits the deformation invariance of plurigenera affirmatively, and proves this more generally for a flat family of varieties with only canonical singularities and uncountable ones therein being of general type and also two Chow-type lemmata on the structure of a family of projective complex analytic spaces.

math.AG↗
arXiv2020

Deformation limit and bimeromorphic embedding of Moishezon manifolds

Let $π: \mathcal{X}\rightarrow Δ$ be a holomorphic family of compact complex manifolds over an open disk in $\mathbb{C}$. If the fiber $π^{-1}(t)$ for each nonzero $t$ in an uncountable subset $B$ of $Δ$ is Moishezon and the reference fiber $X_0$ satisfies the local deformation invariance for Hodge number of type $(0,1)$ or admits a strongly Gauduchon metric introduced by D. Popovici, then $X_0$ is still Moishezon. We also obtain a bimeromorphic embedding $\mathcal{X}\dashrightarrow\mathbb{P}^N\timesΔ$. Our proof can be regarded as a new, algebraic proof of several results in this direction proposed and proved by Popovici in 2009, 2010 and 2013. However, our assumption with $0$ not necessarily being a limit point of $B$ and the bimeromorphic embedding are new. Our strategy of proof lies in constructing a global holomorphic line bundle over the total space of the holomorphic family and studying the bimeromorphic geometry of $π:\mathcal{X}\rightarrow Δ$. S.-T. Yau's solutions to certain degenerate Monge--Ampère equations are used.

math.AG↗
arXiv2020

A Local Index Theorem of Transversal Type on Manifolds with Locally Free $\mathbb{S}^1$-action

We study an index of a transversal Dirac operator on an odd-dimensional manifold $X$ with locally free $\mathbb{S}^1$-action. One difficulty of using heat kernel method lies in the understanding of the asymptotic expansion as $t\to 0^+$. By a probabilistic approach via the Feynman-Kac formula, the transversal heat kernel on $X$ can be linked to the ordinary heat kernel for functions on the orbifold $M=X/\mathbb{S}^1$ which is more tractable. After some technical results for a uniform bound estimate as $t\to 0^+$, we are reduced from the transversal, orbifold situation to the classical situation particularly at points of the principal stratum. One application asserts that for a certain class of spin orbifolds $M$, to the classical index problem of Kawasaki in the Riemannian setting the net contributions arising from the lower-dimensional strata beyond the principal one vanish identically.

math.DG↗
arXiv2020

Sheaf lines of Yang-Mills Instanton Sheaves

We calculate a sheaf line in CP^3 which is the real line supporting sheaf points on CP^3 of SL(2,C) Yang-Mills instanton (or SU(2) complex Yang-Mills instanton) sheaves for some given ADHM data we obtained previously. We found that this sheaf line is indeed a special jumping line over S^4 spacetime. In addition, we calculate the singularity structure of the connection A and the field strength F at the corresponding singular point on S^4 of this sheaf line. We found that the order of singularity at the singular point on S^4 associated with the sheaf line in CP^3 is higher than those of other singular points associated with normal jumping lines. We conjecture that this is a general feature for sheaf lines among jumping lines.

hep-th↗
arXiv2019

Theta Functions and Adiabatic Curvature on a Torus

Let $M$ be a complex torus, $L_{\hatμ}\to M$ be positive line bundles parametrized by $\hat μ\in {\rm Pic}^0(M)$, and $E\to {\rm Pic}^0(M)$ be a vector bundle with $E|_{\hatμ}\cong H^0(M, L_{\hat μ})$. We endow the total family $\{L_{\hatμ}\}_{\hatμ}$ with a Hermitian metric that induces the $L^2$-metric on $H^0(M, L_{\hat μ})$ hence on $E$. By using theta functions $\{θ_m\}_{m}$ on $M\times M$ as a family of functions on the first factor $M$ with parameters in the second factor $M$, our computation of the full curvature tensor $Θ_E$ of $E$ with respect to this $L^2$-metric shows that $Θ_E$ is essentially an identity matrix multiplied by a constant $2$-form, which yields in particular the adiabatic curvature $c_1(E)$. After a natural base change $M\to \hat M$ so that $E\times_{\hat M} M:=E'$, we also obtain that $E'$ splits holomorphically into a direct sum of line bundles each of which is isomorphic to $L_{\hatμ=0}^*$. Physically, the spaces $H^0(M, L_{\hat μ})$ correspond to the lowest eigenvalue with respect to certain family of Hamiltonian operators on $M$ parametrized by $\hatμ$ or in physical notation, by wave vectors $\bf k$.

math.AG↗
arXiv2018

Extended Complex Yang-Mills Instanton Sheaves

In the search of YM instanton sheaves with topological charge two, the rank of beta matrix in the monad construction can be dropped from the bundle case with rank(beta)= 2 to either rank(beta) = 1 [4] or 0 on some points of CP^3 of the sheaf cases. In this paper, we first show that the sheaf case with rank(beta)= 0 does not exist for the previous construction of SU(2) complex YM instantons [3]. We then show that in the new "extended complex YM instantons" discovered in this paper, rank(beta) can be either 2 on the whole CP^3 (bundle) with some given ADHM data or 1, 0 on some points of CP^3 with other ADHM data (sheaves). These extended SU(2) complex YM instantons have no real instanton counterparts.

hep-th↗
arXiv2018

Yang-Mills Instanton Sheaves

The SL(2,C) Yang-Mills instanton solutions constructed recently by the biquaternion method were shown to satisfy the complex version of the ADHM equations and the Monad construction. Moreover, we discover that, in addition to the holomorphic vector bundles on CP^3 similar to the case of SU(2) ADHM construction, the SL(2,C) instanton solutions can be used to explicitly construct instanton sheaves on CP^3. Presumably, the existence of these instanton sheaves is related to the singularities of the SL(2,C) instantons on S^4 which do not exist for SU(2) instantons.

hep-th↗
arXiv2017

Heat kernel asymptotics, local index theorem and trace integrals for CR manifolds with $S^1$ action

Among those transversally elliptic operators initiated by Atiyah and Singer, Kohn's $\Box_b$ operator on CR manifolds with $S^1$ action is a natural one of geometric significance for complex analysts. Our first main result establishes an asymptotic expansion for the heat kernel of such an operator with values in its Fourier components, which involves an unprecedented contribution in terms of a distance function from lower dimensional strata of the $S^1$-action. Our second main result computes a local index density, in terms of \emph{tangential} characteristic forms, on such manifolds including \emph{Sasakian manifolds} of interest in String Theory, by showing that certain non-trivial contributions from strata in the heat kernel expansion will eventually cancel out by applying Getzler's rescaling technique to off-diagonal estimates. This leads to a local result which can be thought of as a type of local index theorem on these CR manifolds. As applications of our CR index theorem we can prove a CR version of Grauert-Riemenschneider criterion, and produce many CR functions on a weakly pseudoconvex CR manifold with transversal $S^1$ action and many CR sections on some class of CR manifolds, answering (on this class of manifolds) some long-standing questions in several complex variables and CR geometry. We give examples of these CR manifolds, some of which arise from Brieskorn manifolds. Moreover in some cases, without use of equivariant cohomology method nor keeping contributions arising from lower dimensional strata as done in previous works, we can reinterpret Kawasaki's Hirzebruch-Riemann-Roch formula for a complex orbifold with an orbifold holomorphic line bundle, as an index theorem obtained by a single integral over a smooth CR manifold which is essentially the circle bundle of this line bundle.

math.DG↗
arXiv2015

Biquaternions and ADHM Construction of Non-Compact SL(2,C) Yang-Mills Instantons

We extend quaternion calculation in the ADHM construction of Sp(1) (=SU(2)) self-dual Yang-Mills (SDYM) instantons to the case of biquaternion. We use the biconjugate operation of biquaternion first introduced by Hamilton to construct the non-compact SL(2,C) k-instantons. The number of moduli for SL(2,C) k-instantons is found to be twice of that of Sp(1), 16k-6. These new SL(2,C) instanton solutions contain the SL(2,C) (M,N) instanton solutions constructed previously as a subset. The structures of singularities or jumping lines of the complete SL(2,C) k=1,2,3 instantons with 10,26,42 moduli parameters are particularly investigated. The existence of singular structures of the SL(2,C) k-instantons is mathematically consistent with recent results of solutions of complex ADHM equations. It may also help to clearify the long standing global singularity problems associated with Backlund transformations of SU(2) instantons.

hep-th↗
arXiv2004

Hochschild Cohomology and Twisted Complexes on Complex Manifolds

We use the theory of twisted resolutions and twisted complexes to give a proof of Kontsevich's claim that Yoneda product corresponds to cup product in a canonical isomorphism from the Ext groups of the product space with coefficients in the diagonal sheaf to the cohomology with coefficients in exterior powers of the tangent sheaf.

math.AG↗
arXiv2003

Hitchin's connection and differential operators with values in the determinant bundle

Let $C/M$ be a local universal family of smooth curves and $S/M$ be the family of moduli spaces of stable bundles with a fixed determinant on curves. In this paper, we find locally free sheaves $\Cal G_E$, $S(\Cal G_E)$ on $X=C\times_M S$ such that their first direct images are isomorphic to sheaves $\Cal D^{\le 1}_{S/M}(Θ)$, $\Cal D^{\le 1}_S(Θ)$ of 1-st order differential operators on the theta line bundle over $S$. As an application, we give a new construction of Hitchin's projective connection (or KZ-connection). Our main results have clearly an extension to some stable singular curves. Then we construct a logarithmic projective connection (in fact, a logarithmic projective heat operator on the theta line bundle) that extends Hitchin's connection to a coherent sheaf over an open set (with at least codimension two) of the moduli space of stable curves. Such an extension seems not reachable by other methods (as far as we know).

math.AG↗
arXiv2000

Deformation of spherical CR structures and the universal Picard variety

We study deformation of spherical $CR$ circle bundles over Riemann surfaces of genus > 1. There is a one to one correspondence between such deformation space and the so-called universal Picard variety. Our differential-geometric proof of the structure and dimension of the unramified universal Picard variety has its own interest, and our theory has its counterpart in the Teichmuller theory.

math.DG↗