Inflation and Unification

Two distinct classes of realistic inflationary models consistent with present observations are reviewed. The first example relies on the Coleman-Weinberg potential and is readily realized within the framework of spontaneously broken global symmetries (for instance, global U(1)B−L). Depending on the parameters either new or large field inflation is possible. The second example exploits supersymmetry which makes implementation of inflation within local gauge theories much more accessible. An example based on spontaneously broken local U(1)B−L is discussed. Leptogenesis is naturally realized in both cases. PACS. 98.80.Cq Particle-theory and field-theory models of the early Universe 1 From new to large field inflation An inflationary scenario [1,2] may be termed successful if it satisfies the following criteria: 1) The total number of e-folds N during inflation is large enough to resolve the horizon and flatness problems. Thus,N &50–60, but it can be somewhat smaller for low scale inflation. 2) The predictions are consistent with observations of the microwave background and large scale structure formation. In particular, the predictions for ns, r and α should be consistent with the most recent WMAP results [3] (see also [4] for a brief survey of models). 3) Satisfactory resolution of the monopole problem in grand unified theories (GUTs) is achieved. 4) Explanation of the origin of the observed baryon asymmetry is provided. In this section we review a class of inflation models which appeared in the early eighties in the framework of non-supersymmetric GUTs and employed a GUT singlet scalar field φ [6,7,8]. These (Shafi-Vilenkin) models satisfy, as we will see, the above criteria and are based on a Coleman-Weinberg (CW) potential [9]