Browsing by Author "Shafi, Qaisar"
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Item Higgs inflation, seesaw physics and fermion dark matter(Elsevier Science BV, 2015-06-03) Okada, Nobuchika; Shafi, Qaisar; NobuchikaOkada, QaisarShafi; Shafi, QaisarWe present an inflationary model in which the Standard Model Higgs doublet field with non-minimal coupling to gravity drives inflation, and the effective Higgs potential is stabilized by new physics which includes a dark matter particle and right-handed neutrinos for the seesaw mechanism. All of the new particles are fermions, so that the Higgs doublet is the unique inflaton candidate. With central values for the masses of the top quark and the Higgs boson, the renormalization group improved Higgs potential is employed to yield the scalar spectral index ns 0.968, the tensor-to-scalar ratio r 0.003, and the running of the spectral index α=dns/d lnk −5.2 ×10−4for the number of e-folds N0=60(ns 0.962, r 0.004, and α −7.5 ×10−4for N0=50). The fairly low value of r 0.003predicted in this class of models means that the ongoing space and land based experiments are not expected to observe gravity waves generated during inflation.Item Non-minimal quartic inflation in supersymmetric SO(10)(Elsevier Science, 2016-12-16) Leontaris, George K.; Okada, Nobuchika; Shafi, Qaisar; George K. Leontaris, Nobuchika Okada, Qaisar Shafi; Shafi, QaisarWe describe how quartic (λφ4) inflation with non-minimal coupling to gravity is realized in realistic supersymmetric SO(10)models. In a well-motivated example the 16 −16Higgs multiplets, which break SO(10)to SU(5)and yield masses for the right-handed neutrinos, provide the inflaton field φ. Thus, leptogenesis is a natural outcome in this class of SO(10)models. Moreover, the adjoint (45-plet) Higgs also acquires a GUT scale value during inflation so that the monopole problem is evaded. The scalar spectral index nsis in good agreement with the observations and r, the tensor to scalar ratio, is predicted for realistic values of GUT parameters to be of order 10−3–10−2.Item Primordial monopoles, proton decay, gravity waves and GUT inflation(Elsevier B.V., 2015-11-18) Seno˘guz, Vedat Nefer; Shafi, Qaisar; Vedat Nefer¸Seno˘guz, Qaisar Shafi; Shafi, QaisarWe consider non-supersymmetric GUT inflation models in which intermediate mass monopoles may survive inflation because of the restricted number of e-foldings experienced by the accompanying symmetry breaking. Thus, an observable flux of primordial magnetic monopoles, comparable to or a few orders below the Parker limitmay be present in the galaxy. The mass scale associated with the intermediate symmetry breaking is 1013GeVfor an observable flux level, with the corresponding monopoles an order of magnitude or so heavier. Examples based on SO(10)and E6yield such intermediate mass monopoles carrying respectively two and three units of Dirac magnetic charge. For GUT inflation driven by a gauge singlet scalar field with a Coleman–Weinberg or Higgs potential, compatibility with the Planck measurement of the scalar spectral index yields a Hubble constant (during horizon exit of cosmological scales) H∼7–9 ×1013GeV, with the tensor to scalar ratio rpredicted to be 0.02. Proton lifetime estimates for decays mediated by the superheavy gauge bosons are also provided.Item SU(5) × U(1)x axion model with observable proton decay(Physical Review D, 2021-09-27) Okada, Nobuchika; Raut, Digesh; Shafi, QaisarWe propose a SU(5) x U(1)x X U(1)PQ model, where U(1)x is the generalization of the B − L (baryon minus lepton number) gauge symmetry and U(1)PQ is the global Peccei-Quinn (PQ) symmetry. There are four fermions families in 5 + 10 representations of SU(5), a mirror family in 5 + 10 representations, and three SU(5) singlet Majorana fermions. The U(1)x related anomalies all cancel in the presence of the Majorana neutrinos. The SU(5) symmetry is broken at MGUT ≃ (6–9) x 10^15 GeV and the proton lifetime τp is estimated to be well within the expected sensitivity of the future hyper-Kamiokande experiment, τp ≲ 1.3 × 10^35 years. The SU(5) breaking also triggers the breaking of the PQ symmetry, resulting in axion dark matter (DM), with the axion decay constant fa of order MGUT or somewhat larger. The CASPEr experiment can search for such an axion DM candidate. The Hubble parameter during inflation must be low, Hinf ≲ 10^9 GeV, in order to successfully resolve the axion domain wall, axion DM isocurvature and SU(5) monopole problems. With the identification of the U(1)x breaking Higgs field with the inflaton field, we implement inflection-point inflation, which is capable of realizing the desired value for Hinf. The vectorlike fermions in the model are essential for achieving successful unification of the SM gauge couplings as well as the phenomenological viability of both axion DM and inflation scenario.