Let
G be an edge-colored graph. We use
e(G) and
c(G) to denote the
number of edges of
G and the number of colors appearing on
E(G),
respectively. For a vertex
v∈V(G), the \emph{color neighborhood} of
v is
defined as the set of colors assigned to the edges incident to
v. A subgraph
of
G is \emph{rainbow} if all of its edges are assigned with distinct colors.
The well-known Mantel's theorem states that a graph
G on
n vertices
contains a triangle if
e(G)≥⌊4n2⌋+1. Rademacher
(1941) showed that
G contains at least
⌊2n⌋ triangles
under the same condition. Li, Ning, Xu and Zhang (2014) proved a rainbow
version of Mantel's theorem: An edge-colored graph
G has a rainbow triangle
if
e(G)+c(G)≥n(n+1)/2. In this paper, we first characterize all graphs
G satisfying
e(G)+c(G)≥n(n+1)/2−1 but containing no rainbow triangles.
Motivated by Rademacher's theorem, we then characterize all graphs
G which
satisfy
e(G)+c(G)≥n(n+1)/2 but contain only one rainbow triangle. We
further obtain two results on color neighborhood conditions for the existence
of rainbow short cycles. Our results improve a previous theorem due to
Broersma, Li, Woeginger, and Zhang (2005). Moreover, we provide a sufficient
condition in terms of color neighborhood for the existence of a specified
number of vertex-disjoint rainbow cycles.