We apply the statefinder hierarchy plus the fractional growth parameter to explore the extended Ricci dark energy ( ERDE ) model , in which there are two independent coefficients \alpha and \beta .
By adjusting them , we plot evolution trajectories of some typical parameters , including the Hubble expansion rate E , deceleration parameter q , the third- and fourth-order hierarchy S _ { 3 } ^ { ( 1 ) } and S _ { 4 } ^ { ( 1 ) } and fractional growth parameter \epsilon , respectively , as well as several combinations of them .
For the case of variable \alpha and constant \beta , in the low-redshift region the evolution trajectories of E are in high degeneracy and that of q separate somewhat .
However , the \Lambda CDM model is confounded with ERDE in both of these cases . S _ { 3 } ^ { ( 1 ) } and S _ { 4 } ^ { ( 1 ) } , especially the former , perform much better .
They can differentiate well only varieties of cases within ERDE except \Lambda CDM in the low-redshift region .
For the high-redshift region , combinations \ { S _ { n } ^ { ( 1 ) } , \epsilon \ } can break the degeneracy .
Both of \ { S _ { 3 } ^ { ( 1 ) } , \epsilon \ } and \ { S _ { 4 } ^ { ( 1 ) } , \epsilon \ } have the ability to discriminate ERDE with \alpha = 1 from \Lambda CDM , of which the degeneracy can not be broken by all the before-mentioned parameters .
For the case of variable \beta and constant \alpha , S _ { 3 } ^ { ( 1 ) } ( z ) and S _ { 4 } ^ { ( 1 ) } ( z ) can only discriminate ERDE from \Lambda CDM .
Nothing but pairs \ { S _ { 3 } ^ { ( 1 ) } , \epsilon \ } and \ { S _ { 4 } ^ { ( 1 ) } , \epsilon \ } can discriminate not only within ERDE but also ERDE from \Lambda CDM .
Finally , we find that S _ { 3 } ^ { ( 1 ) } is surprisingly a better choice to discriminate within ERDE itself , and ERDE from \Lambda CDM as well , rather than S _ { 4 } ^ { ( 1 ) } .