References
The seminal paper on population momentum is Keyfitz (1971). Most of the published material on population momentum is quite technical. One of the demography textbooks covering population momentum is Preston, Heuveline and Guillot (2000). An non-technical introduction to the concept of population momentum can be found in a 1999 publication of the Population Reference Bureau (http://www.prb.org/pdf/PT_mar99.pdf 
)
Cerone P (1983). The long-term effects of time-dependent maternity behavior. Demography, 20(1), 79-86.
Bongaarts J (2007). Population growth and policy options in the developing world. Paper
presented at the Beijing Forum, Beijing. New York: The Population Council.
Espenshade T, Olgiati A, Levin S (2011). On nonstable and stable population momentum. Demography. 48(4): 1581-1599.
Frauenthal J (1975). Birth trajectory under changing fertility conditions. Demography, 12(3): 447-54.
Goldstein J (2002). Population momentum for gradual demographic transitions: an alternative approach. Demography, 39(1): 65-73.
Keyfitz N (1971). On the momentum of population growth. Demography, 8(1): 71-80.
Keyfitz N (1985). Applied mathematical demography. New York: Wiley.
Kim Y and Schoen R (1997). Population momentum expresses population aging. Demography, 34(3): 421-7.
Preston S (1986). The relation between actual and intrinsic growth rates. Population Studies, 40(3): 343-351
Preston S, Heuveline P, & Guillot M (2000). Demography: Measuring and modeling population processes. Wiley-Blackwell.
Schoen R and Kim Y (1991). Movement toward stability as a fundamental principle of population dynamics. Demography 28(3): 455-466.
Vincent P (1945). Potentiel d'accroissement d'une population. Journal de la Société de Statistique de Paris, 86(1–2): 16–39.