It is well known that baryon (lepton) number is not conserved in the standard electroweak theory due to the anomaly. As a consequence, the electroweak phase transition provides plausible ground for producing the baryon number asymmetry of the universe, besides erasing any prexisting asymmetry. This occurs via processes which surmount the instanton potential barrier. The barrier is given by the static saddle point solution of the electroweak theory, called the sphaleron, which we shall briefly expose. This is followed by a pedagogical account of how the asymmetry can be created during the electroweak phase transition including the pitfalls that await the innocent practitioner.

The astroparticle physics working group witnessed intense discussion and activity covering a broad range of topics ranging from supergravity and baryogenesis to compact stars and the large scale structure of the Universe. A summary of some of the subject areas in which collaborations were initiated during WHEPP-5 is presented below.

We consider the modification of a single-particle Schrödinger equation by the inclusion of an additional gravitational self-potential term which follows from the prescription that the ‘massdensity’ that enters this term is given by m|ψ($$\overrightarrow r $$,t)|², where ψ($$\overrightarrow r $$,t) is the wave function and m is the mass of the particle. This leads to a nonlinear equation, the ‘Newton-Schrödinger’ equation, which has been found to possess stationary self-bound solutions, whose energy can be determined using an asymptotic method. We find that such a particle strongly violates the superposition principle and becomes a black hole as its mass approaches the Planck mass.