All Questions
22,547 questions
6
votes
1
answer
307
views
Hochschild cohomology and differential operators
The Hochschild-Kostant-Rosenberg theorem says, that for a commutative algebra $R$ over a field $k$ with certain smoothness and finiteness, we have an identification $\mathrm{HH}^\bullet(R)\cong \...
- 985
1
vote
0
answers
85
views
Are there algorithms for lowering the degree of the polynomials which generate an ideal by strategically adding new variables?
Suppose I have an ideal $I$ in a polynomial ring $F[x_1,...,x_n]$ generated by a few polynomials of maximum degree $k$.
I want to embed the ideal $I$ into a larger ideal $J$ in a larger ring with ...
- 11
4
votes
1
answer
510
views
Help with understanding a rigid geometry proof
I am trying to read Coleman's paper "$p$-adic Banach Spaces and Families of Modular Forms". In Proposition A5.5, he considers a quasi-finite morphism $f:Z\to Y=\mathbb{B}^1_K$ where $Z$ is a ...
- 141
1
vote
0
answers
125
views
When is a vector bundle on a Shimura variety an automorphic vector bundle?
Let $(G, X)$ be a Shimura datum, let $K \subset G(\mathbb{A}_f)$ be an open compact subgroup, and denote by $\text{Sh}_K(G,X)$ the Shimura variety whose complex points are given by $G(\mathbb{Q})\...
- 159
0
votes
0
answers
163
views
Free action of finite group on a scheme
Let $X$ be an affine scheme over $S$ and let $G$ be a finite group acting freely on $X$.
I saw two definitions in the literature regarding "free action", the first that the map $G\times_S X\...
- 119
6
votes
2
answers
794
views
Tensor algebra and universal enveloping algebra
Let $\mathfrak g$ be a Lie algebra which is not reductive. Let $T(\mathfrak g)$ and $U(\mathfrak g)$ be the tensor algebra and universal enveloping algebra of $\mathfrak g$ respectively. We have a ...
- 673
0
votes
0
answers
98
views
$h^0(X, 4H-5E)$ on weak Fano threefold
Let $X$ be a smooth weak fano threesfold arising as the blowup of a smooth curve $C$ of degree and genus $(d,g)=(10,2)$ in a rank 1 smooth fano threefold $Y$, $-K_Y^3 = 22$. Let $H$ be a hyperplane in ...
- 71
2
votes
0
answers
163
views
Equivariant Künneth formula for partial flag variety
Let $G$ be a simply connected simple algebraic group over $\mathbb{C}$. Let $P$ be a parabolic subgroup of $G$, $\mathscr{F}:=G/P$ the partial flag variety associated to $P$. For a $G$-variety $X$, ...
- 653
2
votes
0
answers
91
views
Adelic description of moduli of stable vector bundle of rank n (over finite fields)?
Let $Bun_G$ be the moduli stack of $G$-bundles on a (geometrically irreducible smooth projective) curve $C$ over a finite field $k$, where $G$ is a split reductive group over $k$. Since Weil, we know ...
- 6,622
1
vote
0
answers
168
views
Hypergeometric sheaves on $\mathbb{A}^{1}_{E}$
Let $m, n$ be non-negative integers. Assume that $\boldsymbol{\chi} = \left( \chi_i \right)_{1 \leq i \leq m}$ and $\boldsymbol{\eta} = \left( \eta_j \right)_{1 \leq j \leq n}$ are two collections of ...
5
votes
1
answer
265
views
Non-existence of power divided structure on a maximal ideal of truncated polynomial rings (example from Koblitz)
In 3.3 of Berthelot-Ogus's book Notes on Crystalline Cohomology, an example from Koblitz is exhibited without proof.
Let $k$ be a field (or a commutative ring) with characteristic $p>0$, $$A:=k[x_1,...
- 441
3
votes
2
answers
284
views
Definition of $M_{1,0}$
Is there an explicit construction of the moduli space $M_{1,0}/\mathbb{Q}$ of genus $1$ curves whose set of $R$-points, for a $\mathbb{Q}$-algebra $R$, is the set of isomorphism classes of genus $1$-...
- 2,907
4
votes
1
answer
272
views
Is there a non-semistable simple sheaf?
Let $C$ be a smooth projective (irreducible) curve over an algebraically closed field $k$.
A sheaf is said to be simple if its endomorphism algebra is isomorphic to $k$.
It is known that a stable ...
- 405
6
votes
1
answer
822
views
Chromatic homotopy + algebraic geometry =?
In Homotopy Theory there is a famous theorem which shows that every cohomology theory satisfying a certain list of axioms is characterized by a formal group law, and that the spectrum associated to ...
- 2,907
3
votes
2
answers
271
views
Orbits under the automorphism group of projective space
Let $\mathbb{P}^d_K$ be projective space of dimension $d\geq 1$ over an infinite field $K$. Let $x\in\mathbb{P}^d_K$ with $\dim\overline{\lbrace x\rbrace}=n\leq d-1$.
My question: is the set $\lbrace ...
- 133
5
votes
0
answers
226
views
Cohomology of representation varieties and the Hochschild cohomology
Let $k$ be a field, $A$ a $k$-algebra, and $V$ a $k$-vector space. Then we can consider the representation varieties of $A$ on $V$: $\mathrm{Hom}_{k\textrm{-alg}}(A, \mathfrak{gl}(V))$ and $\mathrm{...
- 985
4
votes
2
answers
305
views
Is the property of being a torsor for a smooth affine group scheme detectable on the small étale site?
Let $S$ be a scheme, $G$ a smooth $S$-affine $S$-group scheme, and $X$ an $S$-scheme with a ($S$-linear) $G$-action $\alpha : G\times X\rightarrow X$.
Let $h_X$, $h_G$ be the representable sheaves on ...
- 7,527
3
votes
0
answers
166
views
Étale descent of étale motives for algebraic spaces
Let $X$ be a (sufficiently nice) algebraic space, one can define the category of étale motives $\mathbf{DA}(X,R)$ (with $R$ a ring) like the case of schemes (see for instance, La réalisation étale et ...
- 893
2
votes
1
answer
309
views
Serre functors and global dimensions
Let $k$ be a field.
Let $\mathcal{C}$ be an abelian category (over $k$).
We say that $\mathcal{C}$ has a finite global dimension if there exists integer $n > 0$ such that
$$
\operatorname{Ext}^i(M,...
- 889
3
votes
1
answer
413
views
Twists of elliptic curves
I have a few questions regarding twists of elliptic curves.
In the context of the Shafarevich group, I see people refer to the group of twists of an elliptic curve $E/\mathbb{Q}$ by $H^1(\mathbb{Q}, ...
- 2,907
22
votes
2
answers
2k
views
Coincidence between coefficients of tanh(tan(x/2)) and Chow ring computations?
In "Kodaira–Spencer Theory of Gravity and Exact Results for Quantum String Amplitudes" by Bershadsky, Cecotti, Ooguri, and Vafa (arxiv) on pg. 96 appear the two numbers $5760$ and $1451520$ ...
- 10.5k
4
votes
1
answer
321
views
Cohomological range of a perverse sheaf
I want to prove that, let $X$ be a smooth variety, then for a local system $L$ on $X$, $L[\dim X]$ has no quotient object in the abelian category of perverse sheaves supported on a proper closed ...
- 1,168
7
votes
1
answer
444
views
Road map and references for combinatorial Hodge theory
I'm a PhD student. I'm familiar with graduate level algebraic geometry and toric varieties.
I wanted to know a road map for getting into combinatorial Hodge theory and other prerequisites that I'll ...
- 839
5
votes
1
answer
340
views
Equations for dual cubic curves
Suppose I have a cubic curve $C$ (over $\mathbb C$) in Weierstrass form $$y^2=x^3+ax+b.$$
I would like to find the degree $6$ equation for protectively dual curve $C^*$. Do you know any place where ...
- 14.3k
4
votes
1
answer
221
views
Does every cubic threefold contain a genus 5 curve of degree 8?
Since a genus $5$ curve $C$ of degree $8$ is a complete intersection of $3$ quadrics $Q_1,Q_2,Q_3$ in $\mathbb{P}^4$, I would guess that $C$ is contained in a cubic threefold $X = \mathbb{V}(f)$ when ...
- 679
64
votes
6
answers
52k
views
Consequences of Kirti Joshi's new preprint about p-adic Teichmüller theory on the validity of IUT and on the ABC conjecture
Today, somebody posted on the nLab a link to Kirti Joshi's preprint on the arXiv from last month: https://arxiv.org/abs/2210.11635
In that preprint, Kirti Joshi claims that
he agrees with Scholze and ...
- 2,624
3
votes
0
answers
122
views
Weil restriction of a bunch of points or more general disjoint unions
$\DeclareMathOperator\Spec{Spec}$For a finite extension of fields $k'/k$, let $R_{k'/k}$ denote the Weil restriction functor from quasiprojective $k'$-schemes to quasiprojective $k$-schemes, defined ...
- 472
1
vote
0
answers
106
views
The proposition associated with a set
Given a set $U$ and a set $A \subseteq U$, is there an accepted symbol for the proposition $p$ over the universe $U$ such that for each $x \in U$, $p(x)$ is the assertion that $x \in A$? (The symbol $...
- 19.7k
7
votes
2
answers
617
views
Genus 0 curves on surfaces and the abc conjecture
One of the most obvious methods to prove that a given Diophantine equation $P(x_1, \dots, x_n)=0$ has infinitely many integer solutions is to find polynomials $P_1, \dots, P_n$ in one variable $u$, ...
- 7,182
1
vote
0
answers
114
views
Simultaneous elimination of variables in multiple polynomials
I have a system of $n=O(1)$ non-homogeneous polynomials of total degree $d=O(1)$ $p_1,\dots,p_r\in \mathbb Z[x_1,\dots,x_n]$. I would like to eliminate $n-1$ variables simultaneously from the $n$ ...
- 13.9k
-3
votes
2
answers
820
views
Is there a "weak" fundamental theorem of algebra for matrices?
Let $R$ be the ring of complex $n\times n$ matrices, where $n>1$.
Does every nonconstant polynomial in $R[X]$ have a root in $R$?
Note: The "strong" fundamental theorem of algebra for ...
- 360
6
votes
2
answers
1k
views
Question about the sum of odd powers equation
Quite surprisingly the following question appears while studying the billiard dynamics.
Assume we have $2n$ real numbers: $ x_1, x_2,..., x_{2n}$.
Assume also that $S_k=0$ for any odd positive integer ...
- 728
4
votes
2
answers
296
views
Boundedness of the preimage of sphere via homogeneous polynomials
I am stuck with the following question. Any help or reference would be greatly appreciated.
Assume $F:\mathbb R^n\to \mathbb R^m$ to be a homogeneous polynomial of degree $d$, and assume $F$ to be ...
- 311
21
votes
3
answers
808
views
Examples when quantum $q$ equals to arithmetic $q$
First, as a disclaimer, I should say that this post is not about any specific propositions, but is more of some philosophical flavor.
In the world of quantum mathematics, the letter $q$ is a standard ...
- 1,391
3
votes
1
answer
159
views
Reference request: generalized Jacobian variety for higher dimensional variety
Let $X\subset \mathbf{P}^n$ be a hypersurface such that the singular locus of $X$ consists of a single ordinary double point. I'm trying to find a reference to the "generalized" intermediate ...
- 389
2
votes
0
answers
60
views
Birational change the variety to the higher model if the nonKLT locus is connected?
I was reading the paper BCHM, there is an application of BCHM results to the proof of inversion of adjunction in this paper:
Corollary 1.4.5 (Inversion of adjunction). Let $(X, \Delta)$ be a log pair ...
- 225
2
votes
0
answers
196
views
Zariski Connectedness Theorem in Complex Geometry
Let $f: X \to Y$ be a proper surjective morphism of complex irreducible varieties such that general fibre of $f$ is connected and $Y$ integrally closed\normal. Say, we even assume wlog $Y=\text{Spec}(...
- 6,048
0
votes
2
answers
322
views
K3 surfaces and density of rational curves
A smooth, complex, projective surface, such that the canonical bundle is trivial and the irregularity is equal to zero is called a K3 surface. Recently I received feedback regarding work I had done. ...
- 912
2
votes
1
answer
159
views
Complexification of Néron models of Abelian varieties
Let $A$ be an abelian variety of dimension $g$ over the quotient field $K$ of a DVR $R$ which is a subfield of the complex field $\mathbb{C}$. Then by a result of Grothendieck, we know that there is a ...
- 85
1
vote
0
answers
64
views
Existence of a special uniformizer along a smooth section of a prestable curve
Let $R$ be a complete DVR with fraction field $K$, uniformizer $\pi$ and alg. closed residue field $k$.
Let $f : X\rightarrow \text{Spec }R$ be a prestable model of $\mathbb{P}^1_K$ with a $R$-section ...
- 7,527
7
votes
0
answers
203
views
Finite generation and finite presentation over a truncated valuation ring: is there an easier proof?
Let $K^+$ be a valuation ring which is $\pi$-adically complete for some pseudouniformizer $\pi$.
Nagata 053E proved that every finitely generated and flat (equivalently, torsion-free) $K^+$-algebra is ...
- 16.2k
6
votes
2
answers
442
views
Existence of functorial (K-)flat resolutions?
I am wondering about the following: Suppose $X$ is a reasonable scheme or stack with the resolution property. (So, all quasi-coherent sheaves admit a surjection from a flat sheaf.) Then I believe ...
- 91
2
votes
0
answers
137
views
Irreducible non-reductive subgroup in GL(n) over a characteristic 0 field
Let $V$ be an $n$-dimensional vector space over a characteristic $0$ field $k$ (or better, let $V=\mathbb{A}^n_k$). I wonder whether the following is true:
Absolutely irreducible subgroups $H$ of $\...
- 455
7
votes
3
answers
348
views
The rank of elliptic curves and related quadratic twists
Let $E/\mathbb{Q}$ be an elliptic curve, and let $k_1, k_2$ be square-free integers. Can anything be said about the related elliptic curves
$$\displaystyle E/\mathbb{Q}, E^{(k_1)}/\mathbb{Q}, E^{(k_2)}...
- 26.9k
0
votes
0
answers
97
views
Weight space decomposition of smooth representation of complex algebraic torus
Question: Let $T=(\mathbb{C}^{*})^{n}$ and $\pi:\mathcal{E}\to \mathbb{C}^{n}$ a smooth complex $T$-equivariant vector bundle (i.e. $\pi$ is $T$-equivariant and $T$ acts on the fibers linearly). The ...
- 101
4
votes
0
answers
177
views
What is the equivalent of Artin gluing for quasicoherent sheaves?
Given a topological space or locale $X$ and an open $j : U \hookrightarrow X$ with closed complement $i : K \hookrightarrow X$, the inverse image functor $\langle i^*, j^* \rangle : \textbf{Sh} (X) \...
- 15.9k
0
votes
0
answers
61
views
The generalized Laplace expansion for tensor
I'm reading this paper https://arxiv.org/abs/1308.3860.
In the Appendix (page 22), the author uses a generalized Laplace expansion for the determinant tensor, as shown in the picture1.
But I only ...
- 1
3
votes
0
answers
198
views
Concrete reasons to study derived categories of quasi-coherent sheaves on algebraic stacks?
Title says it all. There seems to be a lot of work done on derived categories of quasi-coherent sheaves on stacks, and yet I couldn't find many "external" applications. I'm mainly wondering ...
- 143
1
vote
1
answer
82
views
Vector bundle formed by tangent lines to a quadric curve in $\mathbb P^2$
Let $Q \cong \mathbb P^1$ be a quadric curve in $\mathbb P^2$. Consider the following rank two vector bundle $V$ on $Q$: the fiber of $V$ over a point $p$ of $Q$ is the two-dimensional subspace $V_p$ ...
- 2,974
8
votes
1
answer
525
views
How to go about finding polynomial from specified monodromy?
I want to find the polynomial $p(x,y)=0$ that corresponds to a four-sheeted Riemann surface with monodromy $(123),(132),(124),(142)$ at four branch points. Such a surface is genus 1, but I'm ...
- 81