TY - JOUR

T1 - Embedded solitons in Lagrangian and semi-Lagrangian systems

AU - Kaup, D. J.

AU - Malomed, Boris A.

N1 - Funding Information:
BAM appreciates hospitality of the Department of Mathematics at the University of Central Florida. This research has been supported in part by NSF grant #DMS0129714.

PY - 2003/10/1

Y1 - 2003/10/1

N2 - We develop the technique of the variational approximation (VA) for solitons in two directions. First, one may have a physical model which does not admit the usual Lagrangian representation, as some terms were discarded for various reasons. For instance, the second-harmonic-generation (SHG) model considered here, which includes the Kerr nonlinearity, lacks the usual Lagrangian representation if one ignores the Kerr nonlinearity of the second-harmonic, as compared to that of the fundamental. However, we show that, with a natural modification, one may still apply the VA to those seemingly flawed systems as efficiently as it applies to their fully Lagrangian counterparts. We call such models, that do not admit the usual Lagrangian representation, semi-Lagrangian systems. Second, we show that, upon adding an infinitesimal tail that does not vanish at infinity, to a usual soliton ansatz, one can obtain an analytical criterion which (within the framework of VA) gives a condition for finding embedded solitons (ESs), i.e., isolated truly localized solutions existing inside the continuous spectrum of the radiation modes. The criterion takes a form of orthogonality of the radiation mode in the infinite tail to the soliton core. To test the criterion, we have applied it to both the semi-Lagrangian truncated version of the SHG model and to the same model in its full form. In the former case, the criterion (combined with VA for the soliton proper) yields an exact solution for the ES. In the latter case, the criterion selects the ES with a relative error ≈1%.

AB - We develop the technique of the variational approximation (VA) for solitons in two directions. First, one may have a physical model which does not admit the usual Lagrangian representation, as some terms were discarded for various reasons. For instance, the second-harmonic-generation (SHG) model considered here, which includes the Kerr nonlinearity, lacks the usual Lagrangian representation if one ignores the Kerr nonlinearity of the second-harmonic, as compared to that of the fundamental. However, we show that, with a natural modification, one may still apply the VA to those seemingly flawed systems as efficiently as it applies to their fully Lagrangian counterparts. We call such models, that do not admit the usual Lagrangian representation, semi-Lagrangian systems. Second, we show that, upon adding an infinitesimal tail that does not vanish at infinity, to a usual soliton ansatz, one can obtain an analytical criterion which (within the framework of VA) gives a condition for finding embedded solitons (ESs), i.e., isolated truly localized solutions existing inside the continuous spectrum of the radiation modes. The criterion takes a form of orthogonality of the radiation mode in the infinite tail to the soliton core. To test the criterion, we have applied it to both the semi-Lagrangian truncated version of the SHG model and to the same model in its full form. In the former case, the criterion (combined with VA for the soliton proper) yields an exact solution for the ES. In the latter case, the criterion selects the ES with a relative error ≈1%.

KW - Lagrangian

KW - Second-harmonic-generation

KW - Solitons

KW - Variational approximation

UR - http://www.scopus.com/inward/record.url?scp=0141754167&partnerID=8YFLogxK

U2 - 10.1016/S0167-2789(03)00219-7

DO - 10.1016/S0167-2789(03)00219-7

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AN - SCOPUS:0141754167

SN - 0167-2789

VL - 184

SP - 153

EP - 161

JO - Physica D: Nonlinear Phenomena

JF - Physica D: Nonlinear Phenomena

IS - 1-4

ER -