## Advances in Differential Equations

- Adv. Differential Equations
- Volume 15, Number 11/12 (2010), 1033-1082.

### A new dynamical approach of Emden-Fowler equations and systems

Marie Françoise Bidaut-Veron and Hector Giacomini

#### Abstract

We give a new approach to general Emden-Fowler equations and systems of the form \begin{equation*} (E_{\varepsilon })-\Delta _{p}u=-{\rm div}(\left\vert \nabla u\right\vert ^{p-2}\nabla u)=\varepsilon \left\vert x\right\vert ^{a}u^{Q}, \end{equation*} \begin{equation*} (G)\left\{ \begin{array}{c} -\Delta _{p}u=-{\rm div}(\left\vert \nabla u\right\vert ^{p-2}\nabla u)=\varepsilon _{1}\left\vert x\right\vert ^{a}u^{s}v^{\delta }, \\ -\Delta _{q}v=-{\rm div}(\left\vert \nabla v\right\vert ^{q-2}\nabla u)=\varepsilon _{2}\left\vert x\right\vert ^{b}u^{\mu }v^{m},% \end{array}% \right. \end{equation*}% where $p,q,Q,\delta, \mu, s,m,$ $a,b$ are real parameters, $p,q\neq 1,$ and $% \varepsilon, \varepsilon _{1},\varepsilon _{2}=\pm 1.$ In the radial case we reduce the problem $(G)$ to a quadratic system of four coupled first-order autonomous equations of Kolmogorov type. In the scalar case the two equations $(E_{\varepsilon })$ with source ($\varepsilon =1)$ or absorption (% $\varepsilon =-1)$ are reduced to a unique system of order 2. The reduction of system $(G)$ allows us to obtain new local and global existence or nonexistence results. We consider in particular the case $\varepsilon _{1}=\varepsilon _{2}=1.$ We describe the behaviour of the ground states when the system is variational. We give a result of existence of ground states for a nonvariational system with $p=q=2$ and $s=m>0,$ that improves the former ones. It is obtained by introducing a new type of energy function. In the nonradial case we solve a conjecture of nonexistence of ground states for the system with $p=q=2$, $\delta =m+1$ and $\mu =s+1.$

#### Article information

**Source**

Adv. Differential Equations Volume 15, Number 11/12 (2010), 1033-1082.

**Dates**

First available in Project Euclid: 18 December 2012

**Permanent link to this document**

https://projecteuclid.org/euclid.ade/1355854434

**Mathematical Reviews number (MathSciNet)**

MR2743494

**Zentralblatt MATH identifier**

1230.34021

**Subjects**

Primary: 34B15: Nonlinear boundary value problems 34C20: Transformation and reduction of equations and systems, normal forms 34C37: Homoclinic and heteroclinic solutions 35J20: Variational methods for second-order elliptic equations 35J55 35J65: Nonlinear boundary value problems for linear elliptic equations 35J70: Degenerate elliptic equations 37J45: Periodic, homoclinic and heteroclinic orbits; variational methods, degree-theoretic methods

#### Citation

Bidaut-Veron, Marie Françoise; Giacomini, Hector. A new dynamical approach of Emden-Fowler equations and systems. Adv. Differential Equations 15 (2010), no. 11/12, 1033--1082.https://projecteuclid.org/euclid.ade/1355854434