GLOBAL HOPF BRANCHES IN A DELAYED MODEL FOR IMMUNE RESPONSE TO HTLV-1 INFECTIONS: COEXISTENCE OF MULTIPLE LIMIT CYCLES.

For an HTLV-I infection model, Li and Shu has shown in [6] that delayed CTL response can lead to com-plex bifurcations, and in particular, coexistence of multiple sta-ble periodic solutions. In this paper, we extend results of Li and Shu in [6] and investigate the case when there exist three sequences of Hopf bifurcation points. Through numerical sim-ulations, we show that two of the sequences lead to bounded global Hopf bifurcation branches as observed in [6], and a third sequence gives rise to unbounded Hopf branches that can pro-duce secondary period-doubling bifurcations. Our results show that multiple stable periodic solutions can co-exist in certain parameter regions. [ABSTRACT FROM AUTHOR]