## Differential and Integral Equations

- Differential Integral Equations
- Volume 16, Number 1 (2003), 51-76.

### On some sharp conditions for lower semicontinuity in $L^1$

Michele Gori, Francesco Maggi, and Paolo Marcellini

#### Abstract

Let $\Omega $ be an open set of $\mathbb{R}^{n}$ and let $f:\Omega \times
\mathbb{R}\times \mathbb{R}^{n}$ be a nonnegative continuous function, convex with respect
to $\xi \in \mathbb{R}^{n}$. Following the well known theory originated by Serrin
Serrin [14] in 1961, we deal with the lower semicontinuity of the integral $F\left(
u,\Omega \right) =\int_{\Omega }f\left( x,u(x),Du(x)\right) \,dx$ with respect to the
$L_{\text{loc} }^{1}\left( \Omega \right) $ strong convergence. Only recently it has been
discovered that dependence of $f\left( x,s,\xi \right) $ on the $x$ variable plays a
crucial role in the lower semicontinuity. In this paper we propose a mild assumption on
$x$ that allows us to consider discontinuous integrands too. More precisely, we assume
that $f\left( x,s,\xi \right) $ is a nonnegative *Carathéodory* function,
convex with respect to $\xi $ , continuous in $\left( s,\xi \right) $ and such that
$f(\cdot ,s,\xi )\in W_{\text{loc}}^{1,1}\left( \Omega \right) $ for every $s\in
\mathbb{R}$ and $\xi \in \mathbb{R}^{n}$, with the $L^{1}$ norm of $f_{x}(\cdot ,s,\xi )$
locally bounded. We also discuss some other conditions on $x$; in particular we prove that
Hölder continuity of $f$ with respect to $x$ is not sufficient for lower
semicontinuity, even in the one dimensional case, thus giving an answer to a problem posed
by the authors in [12]. Finally, we investigate the lower semicontinuity
of the integral $F\left( u,\Omega \right) $, with respect to the strong norm topology of
$L_{\text{ loc}}^{1}\left( \Omega \right) $, in the vector-valued case, i.e., when $
f:\Omega \times \mathbb{R}^{m}\times \mathbb{R}^{m\times n}\rightarrow \mathbb{R}$ for
some $n\geq 1$ and $m>1$.

#### Article information

**Source**

Differential Integral Equations, Volume 16, Number 1 (2003), 51-76.

**Dates**

First available in Project Euclid: 21 December 2012

**Permanent link to this document**

https://projecteuclid.org/euclid.die/1356060696

**Mathematical Reviews number (MathSciNet)**

MR1948872

**Zentralblatt MATH identifier**

1028.49012

**Subjects**

Primary: 49J45: Methods involving semicontinuity and convergence; relaxation

Secondary: 35J20: Variational methods for second-order elliptic equations

#### Citation

Gori, Michele; Maggi, Francesco; Marcellini, Paolo. On some sharp conditions for lower semicontinuity in $L^1$. Differential Integral Equations 16 (2003), no. 1, 51--76. https://projecteuclid.org/euclid.die/1356060696