Radiative symmetry breaking, cosmic strings and observable gravity waves in U(1)R symmetric SU(5) x U(1)χ

We implement shifted hybrid inflation in the framework of supersymmetric SU(5) x U(1)(chi) GUT model which provides a natural solution to the monopole problem appearing in the spontaneous symmetry breaking of SU(5). The U(1)(chi) symmetry is radiatevely broken after the end of inflation at an intermediate scale, yielding topologically stable cosmic strings. The Planck's bound on the gravitational interaction strength of these strings, characterized by G(N)mu(s) are easily satisfied with the U(1)(chi) symmetry breaking scale which depends on the initial boundary conditions at the GUT scale. The dimension-5 proton lifetime for the decay p -> K + (nu) over bar, mediated by color-triplet Higgsinos is found to satisfy current Super-Kamiokande bounds for SUSY breaking scale M-SUSY greater than or similar to 12.5TeV. We show that with minimal Kahler potential, the soft supersymmetry breaking terms play a vital role in bringing the scalar spectral index n(s) within the Planck's latest bounds, although with small tensor modes r less than or similar to 2.5 x 10(-6) and SU(5) gauge symmetry breaking scale in the range (2 x 10(15) less than or similar to M-alpha less than or similar to 2 x 10(16)) GeV. By employing non-minimal terms in the Kahler potential, the tensor-to-scalar ratio approaches observable values (r less than or similar to 10(-3)) with the SU(5) symmetry breaking scale M-alpha similar or equal to 2 x 10(16) GeV.

Automated summary

We implement shifted hybrid inflation in the framework of supersymmetric SU(5) x U(1)(chi) GUT model and provide a solution to the monopole problem in SU(5). We find that the U(1)(chi) symmetry is radiatevely broken after inflation, resulting in topologically stable cosmic strings. By introducing non-minimal terms in the Kahler potential, the tensor-to-scalar ratio approaches observable values.