arXiv subjects

Madeleine Burkhart

Publications and source records attributed to Madeleine Burkhart.

6 recordsLinked to original sources

arXiv2021

Intrinsically spherical 3-linked graphs

We exhibit several families of planar graphs that are minor-minimal intrinsically spherical $3$-linked. A graph is intrinsically spherical 3-linked if it is planar graph that has, in every spherical embedding, a non-split 3-link consisting of two disjoint cycles ($S^1$s) and two disjoint vertices ($S^0$), or a cycle and two pairs of disjoint vertices. We conjecture that $K_4 \dot{\bigcup} K_4$, $K_{3,2} \dot{\bigcup} K_{3,2}$, and $K_4 \dot{\bigcup} K_{3,2}$ form the complete set of minor-minimal intrinsically type I spherical 3-linked graphs (that is, in every spherical embedding, have a nonsplit link of two cycles and one $S^0$).

math.CO↗

arXiv2019

Causal geodesic incompleteness of spacetimes arising from IMP gluing

In 2002, Isenberg-Mazzeo-Pollack (IMP) constructed a series of vacuum initial data sets via a gluing construction. In this paper, we investigate some local geometry of these initial data sets as well as implications regarding their spacetime developments. In particular, we state conditions for the existence of outer trapped surfaces near the center of the IMP gluing neck and thence use a generalization of the Penrose incompleteness theorem to deduce null incompleteness of the resulting spacetimes.

gr-qc↗

arXiv2019

Null geodesic incompleteness of spacetimes with no CMC Cauchy surfaces

Chruściel, Isenberg, and Pollack constructed a class of vacuum cosmological spacetimes that do not admit Cauchy surfaces with constant mean curvature. We prove that, for sufficiently large values of the gluing parameter, these examples are both future and past null geodesically incomplete. The authors are honored to dedicate this paper to Robert Bartnik on the occasion of his 60th birthday.

gr-qc↗

arXiv2017

Nilpotent Orbits for Borel Subgroups of $SO_{5}(k)$

Let $G$ be a quasi-simple algebraic group defined over an algebraically closed field $k$ and $B$ a Borel subgroup of $G$ acting on the nilradical $\mathfrak{n}$ of its Lie algebra $\mathfrak{b}$ via the Adjoint representation. It is known that $B$ has only finitely many orbits in only five cases: when $G$ is of type $A_{n}$ for $n \leq 4$, and when $G$ is type $B_{2}$. In this paper, we elaborate on this work in the case when $G =SO_{5}(k)$ (type $B_{2})$ by finding the polynomial defining equations of each orbit. We use these equations to determine the dimension of the orbits and the closure ordering on the set of orbits. The other four cases, when $G$ is type $A_{n}$, can be approached the same way and are treated in a separate paper.

math.GR↗

arXiv2017

Defining Equations of Nilpotent Orbits for Borel Subgroups of Modality Zero in Type $A_{n}$

Let $G$ be a quasi-simple algebraic group defined over an algebraically closed field $k$ and $B$ a Borel subgroup of $G$ acting on the nilradical $\mathfrak{n}$ of its Lie algebra $\mathfrak{b}$ via the Adjoint representation. It is known that $B$ has only finitely many orbits in only five cases: when $G$ is of type $A_{n}$ for $n \leq 4$, and when $G$ is type $B_{2}$. In this paper, we elaborate on this work in the case when $G =SL_{n +1}(k)$ (type $A_{n})$, for $n \leq 4$, by finding the polynomial defining equations of each orbit. Consequences of these equations include the dimension of the orbits and the closure ordering on the set of orbits, although these facts are already known. The other case, when $G$ is type $B_{2}$, can be approached the same way and is treated in a separate paper, where we believe the determination of the closure order is new.

math.RT↗

arXiv2014

Symplectic embeddings of 4-dimensional ellipsoids into polydiscs

McDuff and Schlenk have recently determined exactly when a four-dimensional symplectic ellipsoid symplectically embeds into a symplectic ball. Similarly, Frenkel and Müller have recently determined exactly when a symplectic ellipsoid symplectically embeds into a symplectic cube. Symplectic embeddings of more complicated structures, however, remain mostly unexplored. We study when a symplectic ellipsoid $E(a,b)$ symplectically embeds into a polydisc $P(c,d)$. We prove that there exists a constant $C$ depending only on $d/c$ (here, $d$ is assumed greater than $c$) such that if $b/a$ is greater than $C$, then the only obstruction to symplectically embedding $E(a,b)$ into $P(c,d)$ is the volume obstruction. We also conjecture exactly when an ellipsoid embeds into a scaling of $P(1,b)$ for $b$ greater than or equal to $6$, and conjecture about the set of $(a,b)$ such that the only obstruction to embedding $E(1,a)$ into a scaling of $P(1,b)$ is the classical volume. Finally, we verify our conjecture for $b = \frac{13}{2}$.

math.SG↗