Single-photon stimulated radiative interactions are universally symmetric relative to emission and absorption. We point out that certain multiphoton stimulated processes, whose completion is dependent on the spontaneous emission of at least one photon, do not behave analogously. The broken symmetry found in such cases invalidates simple correlations between population inversion and laser gain. ...

— Non-linear sigma models that arise from the supersymmetric approach to disordered electron systems contain a non-compact bosonic sector. We study the model with target space H2, the two-hyperboloid with isometry group SU(1,1), and prove that in three dimensions moments of the fields are finite in the thermodynamic limit. Thus the non-compact symmetry SU(1,1) is spontaneously broken. The bound...

The theory of symmetry breaking in presence of gauge fields is presented, following the historical track. Particular emphasis is placed upon the underlying concepts. Invited talks presented at the 2001 Corfu Summer Institute on Elementary Particle Physics 2 E-mail : [email protected]

CONTENTS I. Introduction: Short and long range interactions 843 II. Spontaneous Symmetry Breaking 844 A. Spontaneous symmetry breaking in phase transitions 844 B. Spontaneous symmetry breaking in field theory 845 III. The BEH Mechanism 846 A. The fate of the Nambu-Goldstone boson and vector boson masses 846 B. The fate of the massive scalar boson 847 C. Fermion masses 848 D. Why is the mechanis...

In this work spontaneous (non-dynamical) breaking (effective hiding) of the unitary quantum mechanical dynamical symmetry (superposition) is considered. It represents an especial but very interesting case of the general formalism of the spontaneous symmetry breaking (effective hiding). Conceptual analogies with spontaneous breaking of the gauge symmetry in Weinberg-Sallam’s electro-weak interac...

For spontaneous breaking of global or gauge symmetry, it is superfluous to assume that the vacuum expectation value of the scalar field manifesting the symmetry is nonvanishing. The vacuum with spontaneous symmetry breaking simply corresponds to the nonzero number of particles of one or more components of the real scalar field.