Depth and Stanley depth of powers of the path ideal of a path graph

Abstract

Let $I_{n,m}:=(x_1x_2\cdots x_m,\; x_2x_3\cdots x_{m+1},\; \ldots,\; x_{n-m+1}\cdots x_n)$ be the $m$-path ideal of the path graph of length $n$, in the ring $S=K[x_1,\ldots,x_n]$. We prove that: $$\mathtt{depth}(S/I_{n,m}^t)=\begin{cases} n-t+2 - \left\lfloor \frac{n-t+2}{m+1} \right\rfloor - \left\lceil \frac{n-t+2}{m+1} \right\rceil, & t \leq n+1-m \\ m-1,& t > n+1-m \end{cases},\text{ for all }t\geq 1.$$ Also, we prove that $\mathtt{depth}(S/I_{n,m}) \geq \mathtt{sdepth}(S/I_{n,m}^t) \geq \mathtt{depth}(S/I_{n,m}^t)$ and $\mathtt{sdepth}(I_{n,m}^t)\geq \mathtt{depth}(I_{n,m}^t)$, for all $t\geq 1$.