Semi-shifted hybrid inflation with B-L cosmic strings
Abstract
We discuss a new inflationary scenario which is realized within the extended supersymmetric Pati-Salam model which yields an acceptable b-quark mass for universal boundary conditions and mu>0 by modestly violating Yukawa unification and leads to new shifted, new smooth, or standard-smooth hybrid inflation. Inflation takes place along a "semi-shifted" classically flat direction on which the U(1)B-L gauge group remains unbroken. After the end of inflation, U(1)B-L breaks spontaneously and a network of local cosmic strings, which contribute a small amount to the curvature perturbation, is produced. We show that, in minimal supergravity, this "semi-shifted" inflationary scenario is compatible with a recent fit to data which uses field-theory simulations of a local string network. Taking into account the requirement of gauge unification, we find that, for spectral index ns=1, the predicted fractional contribution f10 of strings to the temperature power spectrum at multipole l=10 is about 0.039. Also, for f10=0.10, which is the best-fit value, we obtain that ns is about 1.0254. Spectral indices lower than about 0.98 are excluded and blue spectra are slightly favored. Magnetic monopoles are not formed at the end of semi-shifted hybrid inflation.