Constraining the cosmic strings gravitational wave spectra in no-scale inflation with viable gravitino dark matter and nonthermal leptogenesis

Motivated by the NANOGrav 15 year data and other recent investigations of stochastic gravitational background radiation based on pulsar timing arrays, we show how superheavy strings survive inflation but the slightly heavier monopoles do not in a non-supersymmetric hybrid inflation model based on flipped SU(5). With the dimensionless string tension parameter Gμ ∼ 10-6, the gravitational wave spectrum emitted by the strings, which are metastable due to breaking caused by monopole-antimonopole quantum mechanical tunneling, is compatible with the latest NANOGrav measurement as well as the advanced LIGO-VIRGO third run data. The string network undergoes about 30 e-foldings of inflation which suppresses the spectrum in the LIGO-VIRGO frequency range. With the symmetry breaking chain SU(5)×U(1) X → SU(3) c ×SU(2) L ×U(1) Z ×U(1) X → SU(3) c ×SU(2) L ×U(1) Y , the estimated proton lifetime is of order 1036-1037 yrs.

Section: Jcap03(2024)006mentioning

confidence: 99%

Inflation, superheavy metastable strings and gravitational waves in non-supersymmetric flipped SU(5)

Lazarides,

Maji,

Moursy

et al. 2024

“…One way to evade the above constraint on Gµ relies on a metastable cosmic string network, which allows one to manipulate the gravitational wave spectrum and make it compatible with the observations despite the larger symmetry breaking scales [13][14][15][16][17][18][19][20]. The string metastability arises from the fact that it can break through the formation of monopoleantimonopole pairs.…”

Section: Introductionmentioning

confidence: 99%

Gravitational waves from quasi-stable strings

Lazarides

Maji

Shafi

2022

We estimate the stochastic gravitational wave spectrum emitted from a network of cosmic strings in which the latter are effectively stable against breaking by monopole pair creation. The monopoles are produced at a higher scale from an earlier symmetry breaking and experience significant inflation before reentering the horizon. This gives rise to monopole-antimonopole pairs connected by string segments and the string loop formation essentially ceases. As a consequence, the lower frequency portion of the gravitational wave spectrum is suppressed relative to the no-inflation case with stable strings, which evades the stringent PPTA bound on the dimensionless string tension Gμ. We display the modified spectrum, accessible in the ongoing and future experiments, for Gμ values in the range 10-10–10-15. We show how this 'quasi-stable' string network is realized in realistic grand unified theories.

“…In this paper, we implement shifted hybrid inflation scenario in the SU(5) × U(1) χ GUT model [20] where the SU (5) symmetry is broken during inflation and the U(1) χ symmetry radiatevely breaks to its Z 2 subgroup at some intermediate scale. The scalar spectral index n s lies in the observed range of Planck's results [26] provided the inflationary potential incorporates either the soft supersymmetry (SUSY) breaking terms [27][28][29][30][31][32][32][33][34], or higher-order terms in the Kählar potential [17,35]. Without these terms, the scalar spectral index n s lies close to 0.98 which is acceptable only if the effective number of light neutrino species are slightly greater than 3 [36].…”

Section: Jcap01(2023)019mentioning

confidence: 87%

Radiative symmetry breaking, cosmic strings and observable gravity waves in 𝖴(1)_𝖱 symmetric 𝖲𝖴(5) × 𝖴(1)_χ

Ahmed

Zubair

2023

Self Cite

We implement shifted hybrid inflation in the framework of supersymmetric SU(5) × U(1)χ GUT model which provides a natural solution to the monopole problem appearing in the spontaneous symmetry breaking of SU(5). The U(1)χ 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 GNμs are easily satisfied with the U(1)χ symmetry breaking scale which depends on the initial boundary conditions at the GUT scale. The dimension-5 proton lifetime for the decay p → K + ν̅, mediated by color-triplet Higgsinos is found to satisfy current Super-Kamiokande bounds for SUSY breaking scale M SUSY ≳ 12.5 TeV. We show that with minimal Kähler 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 ≲ 2.5 × 10-6 and SU(5) gauge symmetry breaking scale in the range (2 × 1015≲ Mα ≲ 2 × 1016) GeV. By employing non-minimal terms in the Kähler potential, the tensor-to-scalar ratio approaches observable values (r ≲ 10-3) with the SU(5) symmetry breaking scale Mα ≃ 2 × 1016 GeV.