Fixed point theorems for the sum of three classes of mixed monotone operators and applications.

In this paper we develop various new fixed point theorems for a class of operator equations with three general mixed monotone operators,namely $A(x,x)+B(x,x) +C(x,x)=x$ on ordered Banach spaces, where A, B, C are the mixed monotone operators. A is such that for any $t\in(0,1)$, there exists $\varphi(t)\in(t,1]$ such that for all $x,y\in P$, $A(tx,t^{-1}y)\geq\varphi(t)A(x,y)$; B is hypo-homogeneous, i.e. B satisfies that for any $t\in(0,1)$, $x,y\in P$, $B(tx,t^{-1}y)\geq tB(x,y)$; C is concave-convex, i.e. C satisfies that for fixed y, $C(\cdot,y):P\rightarrow P$ is concave; for fixed x, $C(x,\cdot)$: $P\rightarrow P$ is convex. Also we study the solution of the nonlinear eigenvalue equation $A(x,x)+B(x,x)+C(x,x)=\lambda x$ and discuss its dependency to the parameter. Our work extends many existing results in the field of study. As an application, we utilize the results obtained in this paper for the operator equation to study the existence and uniqueness of positive solutions for a class of nonlinear fractional differential equations with integral boundary conditions. [ABSTRACT FROM AUTHOR]