Contact processes on random graphs with power law degree distributions have critical value 0
Chatterjee, Shirshendu ; Durrett, Rick
Ann. Probab., Tome 37 (2009) no. 1, p. 2332-2356 / Harvested from Project Euclid
If we consider the contact process with infection rate λ on a random graph on n vertices with power law degree distributions, mean field calculations suggest that the critical value λc of the infection rate is positive if the power α>3. Physicists seem to regard this as an established fact, since the result has recently been generalized to bipartite graphs by Gómez-Gardeñes et al. [Proc. Natl. Acad. Sci. USA 105 (2008) 1399–1404]. Here, we show that the critical value λc is zero for any value of α>3, and the contact process starting from all vertices infected, with a probability tending to 1 as n→∞, maintains a positive density of infected sites for time at least exp(n1−δ) for any δ>0. Using the last result, together with the contact process duality, we can establish the existence of a quasi-stationary distribution in which a randomly chosen vertex is occupied with probability ρ(λ). It is expected that ρ(λ)∼Cλβ as λ→0. Here we show that α−1≤β≤2α−3, and so β>2 for α>3. Thus even though the graph is locally tree-like, β does not take the mean field critical value β=1.
Publié le : 2009-11-15
Classification:  Contact process,  power-law random graph,  epidemic threshold,  60K35,  05C80
@article{1258380791,
     author = {Chatterjee, Shirshendu and Durrett, Rick},
     title = {Contact processes on random graphs with power law degree distributions have critical value 0},
     journal = {Ann. Probab.},
     volume = {37},
     number = {1},
     year = {2009},
     pages = { 2332-2356},
     language = {en},
     url = {http://dml.mathdoc.fr/item/1258380791}
}
Chatterjee, Shirshendu; Durrett, Rick. Contact processes on random graphs with power law degree distributions have critical value 0. Ann. Probab., Tome 37 (2009) no. 1, pp.  2332-2356. http://gdmltest.u-ga.fr/item/1258380791/