Breaking a long section heading in a table of contents

You can manually set the title that appears in the TOC, for example:

\section[Lorem ipsum]{Lorem ipsum dolor sit amet}

      

        
        
        
      

    

Thus, the "long title" appears in the section itself, and the "short title" appears in the TOC. I haven't tried it, but the same number of words can be used in square brackets, but inserting manual line breaks with \\

.