# All Questions

**0**

votes

**1**answer

40 views

### Radical and Centric not Essential P-group

I'm looking that in the Fusion System categories, the p-subgroups that are essential, are centric (by definition) and radical (by implication of the definition), but I want to know if there is an ...

**5**

votes

**0**answers

74 views

+50

### K theory for pre $C^*$-algebras

In noncommutative geometry when one want to go to the differentiable level, one is forced to work with algebras which are no longer $C^*$. It is nice if we don't loose much information by the ...

**9**

votes

**2**answers

155 views

### Triangulation with simplices of same volume

Let $M$ be a Riemannian smooth compact manifold.
It is known that $M$ has a triangulation, for any dimension. But do we know if there exists a triangulation such that all simplices have same volume ?
...

**6**

votes

**0**answers

92 views

### Constructing the largest finite group with a fixed number of conjugacy classes

It is known that there are finitely many finite groups with a given number of conjugacy classes. How can one construct (or get a character table for) the groups $G$ that realize the maximum possible ...

**3**

votes

**1**answer

58 views

### Extremal Lipschitz convex functions

Let $B_d$ the unit ball in $\mathbb{R}^d$, and let $F_d$ be the set of convex functions with Lipschitz constant at most 1 from $B_d$ to $\mathbb{R}$.
When $d=1$ (so the domain is the just the ...

**0**

votes

**0**answers

40 views

### Lower bounds on the measure of balls in attractor sets

I'm looking for a source for the following result.
Let $f: \mathbb{R}^d \rightarrow \mathbb{R}$ be a smooth function and consider the $d$-manifold $M = \{(x, f(x)): x \in \mathbb{R}^d\} \subset ...

**7**

votes

**0**answers

207 views

### Morphisms for good reduction are maps respecting filtration

Please see edits below!
So, let $A,A'/K$ be abelian varieties where $K$ is a $p$-adic local field with residue field $k$. Suppose further that they have good reduction with models ...

**2**

votes

**0**answers

60 views

### Eigenvalues of the imaginary part of the Symplectic action on Siegel upper half plane

Let $A,B\in M_n(\mathbb{R})$ and $U=A+iB$ unitary. $R=diag(r_1,r_2,…,r_n)$ is a diagonal matrix with $r_i>0, \forall i $. I need to calculate $\det(Ae^{-R}A^T+Be^{R}B^T)$. This matrix ...

**2**

votes

**2**answers

222 views

### CW 4 manifolds with single 4 cell

Let $M$ be a connected compact closed 4 manifold. Then $H_4(M)=\mathbb{Z}$. If we assume it is smooth, from Morse theory we know that $M$ has a CW structure. But can we find a CW structure of $M$ with ...

**0**

votes

**0**answers

141 views

### Johnson's Theorem - Proof (Runde) Clarification

I am reading Runde's Lectures on Amenability. In the proof of Johnson's theorem where he proves "$L^{1}(G)$ is amenable Banach algebra implies $G$ is amenable" : he defines a $L^1(G)$ bimodule action ...

**2**

votes

**0**answers

58 views

### Hausdorff dimension = entropy/Lyapunov exponent for the baker's map?

Let $\Sigma=\{0,1\}^{\mathbb Z}$ and let $\sigma:\Sigma\to\Sigma$ be the left shift. Then it is well known that $(\Sigma, \sigma)$ is conjugate to the baker's map $B$ of the unit square:
$$
B(x,y) = ...

**1**

vote

**0**answers

34 views

### convergence of ODE [closed]

I have 2 coupled linear ODEs. I used Mathematica to solve for analytical solution. But the analytical solution looks too complicated. I only need to derive some monotonicity property of the solution. ...

**2**

votes

**1**answer

115 views

### Appropriate morphisms and 2-morphisms in Ind(C)

As I was trying to understand the category $Ind(C)$ of diagrams of the form $I \to C$, where $I$ is a small filtered $(0,1)$-category, I wondered whether it is possible to define morphisms directly, ...

**2**

votes

**0**answers

38 views

### Fracturing $t$-structures

$\def\tee{\mathfrak{t}}$ Let $\tee_1,\tee_2$ be two $t$-structures on a triangulated category $\cal T$; call them fracturing if the two fiber sequences $\tau^\le_1X\to X\to \tau^\ge_1X$ and ...

**1**

vote

**2**answers

261 views

### Is it true that $\Phi_n(2)$ has a divisor of the form $kn+1$ for all $n\neq 6$?

Let $\Phi_n(x)$ be the $n$ th cyclotomic polynomial. I've checked the values of $\Phi_n(2)$ for some small $n\geq 2$ and noticed that there is always a divisor of $\Phi_n(2)$ of the form $kn+1$ ...

**2**

votes

**0**answers

46 views

### Are there nilpotent Manin Triples?

Let $\mathfrak{g}$ be a Lie bialgebra and denote by $\mathfrak{d}$ the double of $\mathfrak{g}$, i.e. $\mathfrak{d}$ is a Manin triple. Are there known examples or conditions on $\mathfrak{g}$ for ...

**3**

votes

**1**answer

73 views

### t-structure induced on the Verdier quotient ${\cal T}/\cal S$

Let $\mathfrak t$ be a $t$-structure on a triangulated category $\cal T$. Let $\cal S$ be a thick (or even non-thick) triangulated subcategory, and ${\cal T}/\cal S$ the Verdier quotient.
Is there a ...

**15**

votes

**2**answers

295 views

### Table of (integral) cohomology groups of K(Z,n)

Can I find somewhere a table of the (first few) cohomology groups of $K(\mathbb{Z},n)$ with integer coefficients?
It seems like a natural counterpart to the table of the homotopy groups of spheres, ...

**2**

votes

**3**answers

215 views

### Nonzero solutions of an infinite product

Let $-\frac{1}{2}\le a \le\frac{1}{2}$ and $b\in[0,\infty)$.
Definitions: $$f_k(a;b):=\frac{(2k+\frac{1}{2}+a)^2+b}{(2k+\frac{1}{2}-a)^2+b}(\frac{k}{k+1})^{2a},$$
$$f(a;b):=\prod\limits_{k=1}^\infty ...

**2**

votes

**2**answers

135 views

### Converse to Lichnerowicz Vanishing Theorem?

The Lichnerowicz vanishing theorem says that if on a compact 4-dimensional spin manifold there exists a metric whose scalar curvature $R>0$, then there are no harmonic spinors; $$D\psi=0 \implies ...

**3**

votes

**1**answer

178 views

### Self-containing trees

Suppose that $r^2-r-1=0$ and that $T$ is the tree with root $1$ such that the children of each node $x$ are $rx$ and $x+1$. Remove all duplicates as they occur, and let $T(r)$ denote the remaining ...

**1**

vote

**1**answer

37 views

### range of singular values of sub-matrices

Assume we have a $m \times n$ matrix $A$ with real entries representing an operator $T$ on $n$ dimensional real vector space $V$. Then we select a $n-1$ dimensional subspace of $E$ of $V$ and ...

**0**

votes

**0**answers

62 views

### Is $n+\frac {1}{2}$ in Kendall-Mann numbers and quantum harmonic oscillator related?

It is known that quantum harmonic oscillator is connected to the symmetric group of infinite order which is isomorphic to the permutation group. According to Cayley's theorem any finite group is ...

**1**

vote

**0**answers

34 views

### explicit conformal map of sinus-shaped region

I wonder weather an explicit conformal map of a sinus-shaped region given by $\Re(z) \in [0, 1+\delta \sin(\Im(z)) ]$ onto say a strip or a ball is known (of course $0<\delta < 1$). Thank you.

**1**

vote

**0**answers

23 views

### Does the support of a regular holonomic D-module always have finitely many orbits?

I am learning about $D$-module theory and came across a theorem that says that coherent equivariant $D$-modules whose support has finitely many orbits are automatically regular holonomic. Are there ...

**3**

votes

**0**answers

81 views

### Can the matrix exponential be equal to the elementwise exponential [closed]

Just out of curiosity: does there exist a matrix $A=(a_{i,j}) \in \mathbb{C}^{n\times n}, n>1$ such that $(e^{a_{i,j}})\in \mathbb{C}^{n\times n}$ is equal to the matrix exponential ...

**0**

votes

**0**answers

39 views

### Invariance of spin coefficients

I have a question about how spin coefficients (Newman Penrose formalism) transform.
I know that if we perform a tetrad rotation, say of Class III:
$(l,n,m,\overline{m})\mapsto \left(\frac{1}{A}l, ...

**3**

votes

**0**answers

94 views

### When a ring is a polynomial ring?

In the paper (2.11) the authors show that if $k^*$ is a separable algebraic extension of $k$ and $x_1,x_2, \ldots, x_n$ are indeterminates over $k^*$ and a normal one dimensional ring $A$ with $k ...

**-3**

votes

**2**answers

150 views

### What is the number of self-inverse permutations on a set of cardinality $N$?

Given a function (aka 'permutation') $f:A \rightarrow A$, where $A$ is a finite set such that $|A| = N$, we call it a self-inverse if $f(f(x)) = x$. The sequence of how many such functions exist for ...

**2**

votes

**0**answers

24 views

### Ordered cross ratios for the uniform matroid

At the moment I am studying a proof by Gel'fand, Rybnikov and Stone (Theorem 4 in the paper "Projective Orientations of Matroids"). To be more precise, I am try ing to describe a new presentation by ...

**5**

votes

**3**answers

283 views

### Character Values for Alternating Groups of degree $\geq 7$

Is it true that in each row and column of the character table of alternating groups with degree $\geq 7$ there are at most two complex values? Any reference will be highly appreciated.

**1**

vote

**0**answers

54 views

### Multimodal property of polynomial logistic distribution

Let $P(x)$ be a polynomial (of an odd degree $n$) strictly increasing on $(-\infty, +\infty).$
Then $F(x)=\displaystyle \frac{1}{1+\exp\{-P(x)\}}$ is a distribution function of a polynomial logistic ...

**2**

votes

**0**answers

64 views

### Split multiplicative galois representation and specialization

My questions stems from my attempt to understand the paper of Greenberg and Stevens about the Mazur-tate-Teitelbaum conjecture (you can find the paper here). To understand this question you probably ...

**1**

vote

**0**answers

59 views

### $C^{1,2}$ regularity of (weak) solutions to the heat equation

Let $\Omega$ be a bounded Lipschitz domain (smoother if needed), and consider the heat equation
$$u_t - \Delta u = 0$$
$$\frac{\partial u(t,x)}{\partial \nu(x)} = a(t,x) - b(t,x)u(t,x)$$
$$u(0) = ...

**1**

vote

**0**answers

112 views

### Isomorphism vs. projective equivalence: the $10$-dimensional spinor variety

Let $S$ be the $10$-dimensional Spinor variety parametrizing one of the two families of $4$-dimensional linear subspaces of the non-singular quadric in $\mathbb{P}^{9}$. I have read that there exist ...

**-4**

votes

**0**answers

31 views

### basic proof in maths needed [closed]

Let there are n distinct numbers like 1,5,9,12 etc. Now to derive the diversity, I want to find out:sum of square/square of sum of these numbers.
What is the proof or logic behind it? Can someone ...

**3**

votes

**1**answer

70 views

### Comodules of Cosemisimple Hopf Algebras

A cosemisimple Hopf algebra is one which is the sum of its cosimple sub-cobalgebras. Is it clear that a comodule of a cosemisimple Hopf algebra always decomposes into irreducible parts? Moreover, will ...

**1**

vote

**1**answer

250 views

### Automorphisms of rings fixing all prime ideals

Let $f,g:A \to B$ be two ring homomorphisms of noetherian rings satisfying that for any prime ideal $\mathfrak{q} \subset B$, $f^{-1}(\mathfrak{q})=g^{-1}(\mathfrak{q})=:\mathfrak{p}$ and the induced ...

**0**

votes

**0**answers

87 views

### Writing an abstract [closed]

In my paper I give a new characterization of $A$. And $A$ already
has a famous equivalence condition. Also with a similar argument
I give a characterization for $C$. I state the abstract as follow.
...

**1**

vote

**0**answers

59 views

### Need a reference/proof for computing the regularity of ideal of points in $\mathbb P^d$?

In a lecture notes on 'Cohomology modules' i read the following remark:
Given a set $X$ of points in $\mathbb P^d$,using the Local Cohomology modules one can easily compute the reg$(S_X)$ where ...

**0**

votes

**0**answers

68 views

### Question regarding Geometric meaning of Noether normalization theorem for projective varieties [migrated]

In Ernst Kunz's ''commutative algebra and algebraic geometry'' book, ch.2, proposition 4.5 the author states:
The Noether Normalization Theorem admits the following application in projective ...

**0**

votes

**0**answers

49 views

### Try to understand the relation between Poisson Lie groups and Lie bialgebras

I am trying to understand the relation between Poisson Lie groups and Lie bialgebras. In the book Lectures on quantum groups, Page 20, Theorem 22 says that given a Poisson Lie group, we can construct ...

**1**

vote

**1**answer

71 views

### Reference for a local density theorem for binary vectors

I have the following theorem written on my whiteboard, but have misplaced the reference. I believe the probabilistic method may be involved in the proof. Any pointers appreciated.
Theorem Let ...

**5**

votes

**0**answers

133 views

### Hemi-Semi Direct Product

In the category of racks (similarly quandles), instead of well-known semi direct product, we have hemi-semi direct product construction as seen on Wagemann & Crans.
As far as I know, semi direct ...

**-5**

votes

**0**answers

52 views

### Can we show numerically? [closed]

Ee have a decomposition of a unitary matrix $U$ by $WAW^*$ where $A$ is diagonal matrix, the symbol $^*$ means transconjugate. An infinitesimal shift $dU$ changes the matrices by $dA$ and $dW$. Can ...

**1**

vote

**0**answers

99 views

### Referencing your own research paper on a conference board? [closed]

Is it considered poor etiquette to refer a viewer to a research paper while looking at a conference poster? The paper could be placed on the same table so it is readily accessible.

**2**

votes

**0**answers

70 views

### Maximum number of $4$-cycles

Suppose we have a balanced bipartite planar maximum degree $k$ graph.
How many such graphs on $2n$ vertices have at most $f(n)$ maximum number of $4$ cycles for a given function $f:\Bbb ...

**-3**

votes

**0**answers

31 views

### Nilpotent Lie algebra [closed]

Lemma: Let $T$ be a maximal torus on $\mathfrak{g}$, $\{x_1,\ldots,x_l\}$ a $T$-msg (minimal system generator), $\lambda_i$ the weight of $x_i$ . The dimension of $T$ is equal to the rank of ...

**1**

vote

**0**answers

67 views

### Is there an efficient algorithm to find all the maximum matching in any tree?

A matching in a graph (G) is a set of mutually non-adjacent edges of (G). A maximum matching is a matching of maximal cardinality. A tree is an acyclic connected graph.
Is there an efficient ...

**0**

votes

**1**answer

70 views

### Predictable quadratic Variation <.> has same intervals of constancy as the process

From
Revuz and Yor - Continuous Martingales and Brownian Motion 1999
Chapter IV Proposition 1.13
it is proven, that for a continuous local martingale $M_t$ the intervals of ...