@article {Bambusi20113379,
	title = {Degenerate KAM theory for partial differential equations},
	journal = {Journal of Differential Equations},
	volume = {250},
	number = {8},
	year = {2011},
	note = {cited By (since 1996)3},
	pages = {3379-3397},
	abstract = {This paper deals with degenerate KAM theory for lower dimensional elliptic tori of infinite dimensional Hamiltonian systems, depending on one parameter only. We assume that the linear frequencies are analytic functions of the parameter, satisfy a weak non-degeneracy condition of R{\"u}ssmann type and an asymptotic behavior. An application to nonlinear wave equations is given. {\textcopyright} 2010 Elsevier Inc.},
	issn = {00220396},
	doi = {10.1016/j.jde.2010.11.002},
	author = {Dario Bambusi and Massimiliano Berti and Elena Magistrelli}
}
@article {2006,
	title = {A Birkhoff-Lewis-Type Theorem for Some Hamiltonian PDEs},
	journal = {SIAM J. Math. Anal. 37 (2006) 83-102},
	number = {arXiv.org;math/0310182v1},
	year = {2006},
	abstract = {In this paper we give an extension of the Birkhoff--Lewis theorem to some semilinear PDEs. Accordingly we prove existence of infinitely many periodic orbits with large period accumulating at the origin. Such periodic orbits bifurcate from resonant finite dimensional invariant tori of the fourth order normal form of the system. Besides standard nonresonance and nondegeneracy assumptions, our main result is obtained assuming a regularizing property of the nonlinearity. We apply our main theorem to a semilinear beam equation and to a nonlinear Schr\\\\\\\"odinger equation with smoothing nonlinearity.},
	doi = {10.1137/S0036141003436107},
	url = {http://hdl.handle.net/1963/2159},
	author = {Dario Bambusi and Massimiliano Berti}
}
