标题： 弦云作为$2+1$维$f( R) = R^n$引力中的源 显示英文标题

标题： Cloud of strings as source in $2+1$-dimensional $f( R) = R^n$ gravity

摘要： 我们给出了在$% 2+1-$维度的$f\left( R\right) =R^{n}$改进引力中可能存在的黑洞的三个参数精确解，该引力与一束弦最小耦合。 这三个参数是$n,$弦云耦合常数$\xi $和一个积分常数$C$。 尽管通常需要分别考虑每组参数；但对于$n$一个大于一的偶数，我们提供了一个统一的图像，提供了黑洞。 对于$n\geq 1$我们在粒子约束的背景下分析了零/类时测地线。 显示英文摘要

摘要： We present three parameters exact solutions with possible black holes in $% 2+1-$dimensional $f\left( R\right) =R^{n}$ modified gravity coupled minimally to a cloud of strings. These three parameters are $n,$ the cloud of string coupling constant $\xi $ and an integration constant $C$. Although in general one has to consider each set of parameters separately; for $n$ an even integer greater than one we give a unified picture providing black holes. For $n\geq 1$ we analyze null / timelike geodesic within the context of particle confinement.