Reduction of one-loop n-point integrals

In this paper, we focus on both analytical expressions of three and four point integrals for the case of small Gram determinant and numerical improvement of $n$-point integrals for $n\ge5$. Explicit expressions of three and four-point integrals in the small Gram determinant region are provided by the new method. Furthermore, $n$-point one-loop integral with $n\ge5$ is always reduced to five number of $(n-1)$-point integrals regardless of how many points are on a loop, which improves dramatically the CPU time consuming. Besides, the theoretical and numerical error riginating from computing higher dimensional Cayley matrix could be reduced by the dimension of the matrix being always fixed to five. We suggest a general reduction formulae for five and more point scalar, vector, and tensor integrals at one-loop level.