Existence of hypercylinder expanders of the inverse mean curvature flow

Abstract: We will give a new proof of the existence of hypercylinder expander of the inverse mean curvature flow which is a radially symmetric homothetic soliton of the inverse mean curvature flow in $\mathbb{R}^n\times \mathbb{R}$, $n\ge 2$, of the form $(r,y(r))$ or $(r(y),y)$ where $r=|x|$, $x\in\mathbb{R}^n$, is the radially symmetric coordinate and $y\in \mathbb{R}$. More precisely for any $\lambda>\frac{1}{n-1}$ and $\mu>0$, we will give a new proof of the existence of a unique even solution $r(y)$ of the equation $\frac{r''(y)}{1+r'(y)^2}=\frac{n-1}{r(y)}-\frac{1+r'(y)^2}{\lambda(r(y)-yr'(y))}$ in $\mathbb{R}$ which satisfies $r(0)=\mu$, $r'(0)=0$ and $r(y)>yr'(y)>0$ for any $y\in\mathbb{R}$. We will prove that $\lim_{y\to\infty}r(y)=\infty$ and $a_1:=\lim_{y\to\infty}r'(y)$ exists with $0\le a_1<\infty$. We will also give a new proof of the existence of a constant $y_1>0$ such that $r''(y_1)=0$, $r''(y)>0$ for any $0<y<y_1$ and $r''(y)\<0$ for any $y>y_1$.