Browsing by Author "Shafi, Qaisar"
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Item 125 GeV Higgs, type III seesaw and gauge-Higgs unification(Elsevier, 2012-09-17) He, Bin; Okada, Nobuchika; Shafi, Qaisar; University of Delaware; University of Alabama TuscaloosaRecently, both the ATLAS and CMS experiments have observed an excess of events that could be the first evidence for a 125 GeV Higgs boson. This is a few GeV below the (absolute) vacuum stability bound on the Higgs mass in the Standard Model (SM), assuming a Planck mass ultraviolet (UV) cutoff. In this Letter, we study some implications of a 125 GeV Higgs boson for new physics in terms of the vacuum stability bound. We first consider the seesaw extension of the SM and find that in type III seesaw, the vacuum stability bound on the Higgs mass can be as low as 125 GeV for the seesaw scale around a TeV. Next we discuss some alternative new physics models which provide an effective ultraviolet cutoff lower than the Planck mass. An effective cutoff Lambda similar or equal to 10(11) GeV leads to a vacuum stability bound on the Higgs mass of 125 GeV. In a gauge-Higgs unification scenario with five-dimensional flat spacetime, the so-called gauge-Higgs condition can yield a Higgs mass of 125 GeV, with the compactification scale of the extra-dimension being identified as the cutoff scale Lambda similar or equal to 10(11) GeV. Identifying the compactification scale with the unification scale of the SM SU(2) gauge coupling and the top quark Yukawa coupling yields a Higgs mass of 121 +/- 2 GeV. (C) 2012 Elsevier B.V. All rights reserved.Item Color triplet diquarks at the LHC(Elsevier, 2010-03-29) Gogoladze, Ilia; Mimura, Yukihiro; Okada, Nobuchika; Shafi, Qaisar; University of Delaware; University of Alabama TuscaloosaWe consider a class of supersymmetric models containing baryon number violating processes such as observable n-(n) over bar oscillations that are mediated by color triplet diquark fields. For plausible values of the diquark-quark couplings, the scalar diquark with mass between a few hundred GeV and one TeV or so can be produced in the s-channel at the LHC and detected through its decay into a top quark and a hadronic jet. (C) 2010 Elsevier B.V. All rights reserved.Item Dark matter Z ' and XENON1T excess from U(1)(x) extended standard model(Elsevier, 2020) Okada, Nobuchika; Okada, Satomi; Raut, Digesh; Shafi, Qaisar; University of Alabama Tuscaloosa; University of DelawareA gauged \(U{\left(1\right)}_{X}\) symmetry appended to the Standard Model (SM) is particularly well motivated since it can account for the light neutrino masses by the seesaw mechanism, explain the origin of baryon asymmetry of the universe via leptogenesis, and help implement successful cosmological inflation with the \(U{\left(1\right)}_{X}\) breaking Higgs field as the inflaton. In this framework, we propose a light dark matter (DM) scenario in which the \(U{\left(1\right)}_{X}\) gauge boson \({Z}^{\prime }\) behaves as a DM particle in the universe. We discuss how this scenario with \({Z}^{\prime }\) mass of a few keV and a \(U{\left(1\right)}_{X}\) gauge coupling \({g}_{X}\simeq {10}^{-16}\) can nicely fit the excess in the electronic recoil energy spectrum recently reported by the XENON1T collaboration. In order to reproduce the observed DM relic density in the presence of such a tiny gauge coupling, we propose an extension of the model to a two-component DM scenario. The \({Z}^{\prime }\) DM density can be comparable to the observed DM density by the freeze-in mechanism through the coupling of \({Z}^{\prime }\) boson to a partner Higgs-portal scalar DM with a large \(U{\left(1\right)}_{X}\) charge.Item Gravity waves and gravitino dark matter in mu-hybrid inflation(Elsevier, 2018) Okada, Nobuchika; Shafi, Qaisar; University of Alabama Tuscaloosa; University of DelawareWe propose a novel reformulation of supersymmetric (more precisely μ-) hybrid inflation based on a local U(1) or any suitable extension of the minimal supersymmetric standard model (MSSM) which also resolves the μ problem. We employ a suitable Kahler potential which effectively yields quartic inflation with non-minimal coupling to gravity. Imposing the gravitino Big Bang Nucleosynthesis (BBN) constraint on the reheat temperature (\({T}_{r}\lesssim {10}^{6}\) GeV) and requiring a neutralino LSP, the tensor to scalar ratio (r) has a lower bound \(r\gtrsim 0.004\). The U(1) symmetry breaking scale lies between 10\(^{8}\) and 10\(^{12}\) GeV. We also discuss a scenario with gravitino dark matter whose mass is a few GeV.Item Higgs boson mass bounds in seesaw extended standard model with non-minimal gravitational coupling(Elsevier, 2011-01-10) He, Bin; Okada, Nobuchika; Shafi, Qaisar; University of Delaware; University of Alabama TuscaloosaIn the presence of non-minimal gravitational coupling xi H dagger HR. between the standard model (SM) Higgs doublet H and the curvature scalar R, the effective ultraviolet cutoff scale is given by Lambda approximate to mP/xi, where m(P) is the reduced Planck mass, and xi greater than or similar to 1 is a dimensionless coupling constant. In type I and type III seesaw extended SM, which can naturally explain the observed solar and atmospheric neutrino oscillations, we investigate the implications of this non-minimal gravitational coupling for the SM Higgs boson mass bounds based on vacuum stability and perturbativity arguments. A lower bound on the Higgs boson mass close to 120 GeV is realized with type III seesaw and xi similar to 10-10(3). (C) 2010 Elsevier B.V. All rights reserved.Item Higgs boson mass bounds in the Standard Model with type III and type I seesaw(Elsevier, 2008-10-02) Gogoladze, Ilia; Okada, Nobuchika; Shafi, Qaisar; University of Delaware; High Energy Accelerator Research Organization (KEK); University of Alabama TuscaloosaIn type III seesaw utilized to explain the observed solar and atmospheric neutrino oscillations the Standard Model (SM) particle spectrum is extended by introducing three SU(2)(L) triplet fermion fields. This can have important implications for the SM Higgs boson Mass (M-H) bounds based on vacuum stability and perturbativity arguments. We compute the appropriate renormalization group equations for type III seesaw, and then proceed to identify regions of the parameter space such that the SM Higgs boson mass window is enlarged to 125 GeV less than or similar to M-H less than or similar to 174 GeV, with the type III seesaw scale close to TeV. We also display regions of the parameter space for which the vacuum stability and perturbativity bounds merge together for large neutrino Yukawa couplings. Comparison with type I seesaw is also presented. (C) 2008 Elsevier B.V. All rights reserved.Item Higgs boson mass from gauge-Higgs unification(Elsevier, 2007-11-08) Gogoladze, Ilia; Okada, Nobuchika; Shafi, Qaisar; University of Delaware; University System of Maryland; University of Maryland College Park; High Energy Accelerator Research Organization (KEK); University of Alabama TuscaloosaIn certain five-dimensional gauge theories the Standard Model Higgs doublet is identified, after compactification on the orbifold S-1/Z(2), with the zero mode of the fifth component of the gauge field. An effective potential for the Higgs field is generated via quantum corrections, triggered by the breaking of the underlying gauge symmetry through boundary conditions. The quartic Higgs coupling can be estimated at low energies by employing the boundary condition that it vanishes at the compactification scale A, as required by five-dimensional gauge invariance. For Lambda greater than or similar to 10(13)-10(14) GeV, the Standard Model Higgs boson mass is found to be m(H) = 125 +/- 4 GeV, corresponding to a top quark pole mass M-t = 170.9 +/- 1.8 GeV. A more complete (gauge-Higgs-Yukawa) unification can be realized for Lambda similar to 10(8) GeV, which happens to be the scale at which the SU(2) weak coupling and the top quark Yukawa coupling have the same value. For this case, mH = 117 +/- 4 GeV. (C) 2007 Elsevier B.V. All rights reserved.Item Higgs inflation, seesaw physics and fermion dark matter(Elsevier, 2015-07-30) Okada, Nobuchika; Shafi, Qaisar; University of Alabama Tuscaloosa; University of DelawareWe 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 n(s) similar or equal to 0.968, the tensor-to-scalar ratio r similar or equal to 0.003, and the running of the spectral index alpha = dn(s)/d In k similar or equal to -5.2 x 10(-4) for the number of e-folds N-0 = 60 (n(s) similar or equal to 0.962, r similar or equal to 0.004, and alpha similar or equal to -7.5 x 10(-4) for N-0 = 50). The fairly low value of r similar or equal to 0.003 predicted in this class of models means that the ongoing space and land based experiments are not expected to observe gravity waves generated during inflation. (C) 2015 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license.Item Inflation, proton decay, and Higgs-portal dark matter in SO(10) x U(1)(psi)(Springer, 2019) Okada, Nobuchika; Raut, Digesh; Shafi, Qaisar; University of Alabama Tuscaloosa; University of DelawareWe propose a simple non-supersymmetric grand unified theory (GUT) based on the gauge group \(SO\left(10\right)×U{\left(1\right)}_{\psi }\). The model includes 3 generations of fermions in \(16\) ( \(+1\) ), \(10\) ( \(-2\) ) and \(1\) ( \(+4\) ) representations. The \(16\) -plets contain Standard Model (SM) fermions plus right-handed neutrinos, and the \(10\) -plet and the singlet fermions are introduced to make the model anomaly-free. Gauge coupling unification at \({M}_{\mathrm{GUT}}\simeq 5×{10}^{15}-{10}^{16}\) GeV is achieved by including an intermediate Pati–Salam breaking at \({M}_{I}\simeq {10}^{12}-{10}^{11}\) GeV, which is a natural scale for the seesaw mechanism. For \({M}_{I}\simeq {10}^{12}-{10}^{11}\), proton decay will be tested by the Hyper-Kamiokande experiment. The extra fermions acquire their masses from \(U{\left(1\right)}_{\psi }\) symmetry breaking, and a \(U{\left(1\right)}_{\psi }\) Higgs field drives a successful inflection-point inflation with a low Hubble parameter during inflation, \({H}_{\mathrm{inf}}\ll {M}_{I}\). Hence, cosmologically dangerous monopoles produced from SO(10) and PS breakings are diluted away. This is the first SO(10) model we are aware of in which relatively light intermediate mass ( \(\sim {10}^{10}-{10}^{12}\) GeV) primordial monopoles can be adequately suppressed. The reheating temperature after inflation can be high enough for successful leptogenesis. With the Higgs field contents of our model, a \({Z}_{2}\) symmetry remains unbroken after GUT symmetry breaking, and the lightest mass eigenstate among linear combinations of the \(10\) -plet and the singlet fermions serves as a Higgs-portal dark matter (DM). We identify the parameter regions to reproduce the observed DM relic density while satisfying the current constraint from the direct DM detection experiments. The present allowed region will be fully covered by the future direct detection experiments such as LUX-ZEPLIN DM experiment. In the presence of the extra fermions, the SM Higgs potential is stabilized up to \({M}_{I}\).Item Inflection-point inflation with axion dark matter in light of Trans-Planckian Censorship Conjecture(Elsevier, 2020) Okada, Nobuchika; Raut, Digesh; Shafi, Qaisar; University of Alabama Tuscaloosa; University of DelawareMotivated by the recently proposed Trans-Planckian Censorship Conjecture (TCC), we propose a gauged \(B-L\) model of inflection-point inflation with axion dark matter. The Hubble scale during inflation (\({H}_{\mathrm{inf}}\)) satisfies the TCC bound of \({H}_{\mathrm{inf}}\lesssim 1\) GeV, the axion dark matter scenario is free from the axion domain wall and isocurvature problems. The seesaw mechanism is automatically incorporated in the model and the observed baryon asymmetry of the universe can be reproduced via resonant leptogenesis.Item Leptonic CP violation and leptogenesis in minimal supersymmetric SU(4)(c) x SU(2)(L) x SU(2)(R)(American Physical Society, 2018) Okada, Nobuchika; Shafi, Qaisar; University of Alabama Tuscaloosa; University of DelawareWe consider a supersymmetric \({\mathrm{SU}\left(4\right)}_{c}×{\mathrm{SU}\left(2\right)}_{L}×\mathrm{SU}\left(2{\right)}_{R}\) model with a minimal number of Higgs multiplets and Dirac and Majorana \(CP\)-violating phases in the neutrino flavor mixing matrix. The model incorporates the charged fermion masses and quark mixings, and uses type I seesaw to explain the solar and atmospheric neutrino oscillations. With the neutrino oscillation data of two mass squared differences and three flavor mixing angles, we employ thermal leptogenesis and the observed baryon asymmetry to find the allowed regions for the Dirac and Majorana phases. For a normal neutrino mass hierarchy, we find that the observed baryon asymmetry can be reproduced by a Dirac phase of around \({\delta }_{CP}=3\pi /2\), which is strongly indicated by the recent T2K and \(\mathrm{NO}\nu A\) data. For the case of inverted neutrino mass hierarchy, the predicted baryon asymmetry is not compatible with the observed value.Item Light Z ' and dark matter from U(1)(x) gauge symmetry(Elsevier, 2020) Okada, Nobuchika; Okada, Satomi; Shafi, Qaisar; University of Alabama Tuscaloosa; University of DelawareWe consider a U(1)\(_{X}\) gauge symmetry extension of the Standard Model (SM) with a \({Z}^{\prime }\)-portal Majorana fermion dark matter that allows for a relatively light gauge boson \({Z}^{\prime }\) with mass of 10 MeV− a few GeV and a much heavier dark matter through the freeze-in mechanism. In a second scenario the roles are reversed, and the dark matter mass, in the keV range or so, lies well below the \({Z}^{\prime }\) mass, say, ∼1 GeV. We outline the parameter space that can be explored for these two scenarios at the future Lifetime Frontier experiments including Belle-II, FASER, LDMX and SHiP.Item mu-term hybrid inflation and split supersymmetry(Elsevier, 2017-12-10) Okada, Nobuchika; Shafi, Qaisar; University of Delaware; University of Alabama TuscaloosaWe consider mu-term hybrid inflation which, in its minimal format with gravity mediated supersymmetry breaking, leads to split supersymmetry. The MSSM eta-term in this framework is larger than the gravitino mass mG, and successful inflation requires mG(and hence also |mu|) greater than or similar to 5 x 10(7) GeV, such that the gravitino decays before the LSP neutralino freezes out. Assuming universal scalar masses of the same order as mG, this leads to split supersymmetry. The LSP wino with mass similar or equal to 2 TeV is a plausible dark matter candidate, the gluino may be accessible at the LHC, and the MSSM parameter tan beta similar or equal to 1.7 in order to be compatible with the measured Higgs boson mass. The tensor-to-scalar ratio r, a canonical measure of gravity waves, can be as high as 0.001. (C) 2017 The Authors. Published by Elsevier B.V.Item NMSSM and seesaw physics at LHC(Elsevier, 2009-02-23) Gogoladze, Ilia; Okada, Nobuchika; Shafi, Qaisar; University of Delaware; University System of Maryland; University of Maryland College Park; High Energy Accelerator Research Organization (KEK); University of Alabama TuscaloosaWe consider extensions of the next-to-minimal supersymmetric model (NMSSM) in which the observed neutrino masses are described in terms of effective dimension six (or seven) rather than dimension five operators. All such operators respect the discrete symmetries of the model. The new particles associated with the double (or triple) seesaw mechanism can have sizable couplings to the known leptons, even with a TeV seesaw scale. In the latter case some of these new short-lived particles could be produced and detected at the LHC. (C) 2009 Elsevier B.V. All rights reserved.Item Non-minimal quartic inflation in supersymmetric S O (10)(Elsevier, 2016) Leontaris, George K.; Okada, Nobuchika; Shafi, Qaisar; European Organization for Nuclear Research (CERN); University of Ioannina; University of Alabama Tuscaloosa; University of DelawareWe describe how quartic (\(λϕ^4\)) inflation with non-minimal coupling to gravity is realized in realistic supersymmetric SO(10) models. In a well-motivated example the 16−\({\overline{16}}\) Higgs 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 \(n_s\) is 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 Pseudo-Goldstone dark matter in a gauged B - L extended standard model(American Physical Society, 2021) Okada, Nobuchika; Raut, Digesh; Shafi, Qaisar; University of Alabama Tuscaloosa; University of DelawareGauging the global \(B-L\) (Baryon number minus Lepton number) symmetry in the standard model (SM) is well motivated since anomaly cancellations require the introduction of three right-handed neutrinos which play an essential role in naturally generating tiny SM neutrino masses through the seesaw mechanism. In the context of the \(B-L\) extended SM, we propose a pseudo-Goldstone boson dark matter (DM) scenario in which the imaginary component of a complex \(B-L\) Higgs field serves as the DM in the universe. The DM relic density is determined by the SM Higgs boson mediated process, but its elastic scattering with nucleons through the exchange of Higgs bosons is highly suppressed due to its pseudo-Goldstone boson nature. The model is therefore free from the constraints arising from direct DM detection experiments. We identify regions of the model parameter space for reproducing the observed DM density compatible with the constraints from the Large Hadron Collider and the indirect DM searches by Fermi Large Area Telescope and Major Atmospheric Gamma Imaging Cherenkov.Item Scalar dark matter, typeII seesaw and the DAMPE cosmic ray e(+)+ e(-) excess(Elsevier, 2018-04-10) Li, Tong; Okada, Nobuchika; Shafi, Qaisar; Nankai University; Monash University; University of Alabama Tuscaloosa; University of DelawareThe DArk Matter Particle Explorer (DAMPE) has reported a measurement of the flux of high energy cosmic ray electrons plus positrons (CREs) in the energy range between 25 GeV and 4.6 TeV. With unprecedented high energy resolution, the DAMPE data exhibit an excess of the CREs flux at an energy of around 1.4 TeV. In this letter, we discuss how the observed excess can be understood in a minimal framework where the Standard Model (SM) is supplemented by a stable SM singlet scalar as dark matter (DM) and typeII seesaw for generating the neutrino mass matrix. In our framework, a pair of DM particles annihilates into a pair of the SM SU(2) triplet scalars (Delta s) in type II seesaw, and the subsequent Delta decays create the primary source of the excessive CREs around 1.4 TeV. The lepton flavor structure of the primary source of CREs has a direct relation with the neutrino oscillation data. We find that the DM interpretation of the DAMPE excess determines the pattern of neutrino mass spectrum to be the inverted hierarchy type, taking into account the constraints from the Fermi-LAT observations of dwarf spheroidal galaxies. (c) 2018 The Author(s). Published by Elsevier B.V.Item SMART U(1)X: standard model with axion, right handed neutrinos, two Higgs doublets and U(1)X gauge symmetry(Springer, 2020) Okada, Nobuchika; Raut, Digesh; Shafi, Qaisar; University of Alabama Tuscaloosa; University of DelawareTo address five fundamental shortcomings of the Standard Model (SM) of particle physics and cosmology, we propose a phenomenologically viable framework based on a \(U{\left(1\right)}_{X}×U{\left(1\right)}_{\mathrm{PQ}}\) extension of the SM, that we call “SMART U(1) \({}_{X}\) ”. The \(U{\left(1\right)}_{X}\) gauge symmetry is a well-known generalization of the \(U{\left(1\right)}_{B-L}\) symmetry and \(U{\left(1\right)}_{\mathrm{PQ}}\) is the global Peccei–Quinn (PQ) symmetry. Three right handed neutrinos are added to cancel \(U{\left(1\right)}_{X}\) related anomalies, and they play a crucial role in understanding the observed neutrino oscillations and explaining the observed baryon asymmetry in the universe via leptogenesis. Implementation of PQ symmetry helps resolve the strong CP problem and also provides axion as a compelling dark matter (DM) candidate. The \(U{\left(1\right)}_{X}\) gauge symmetry enables us to implement the inflection-point inflation scenario with \({H}_{\mathrm{inf}}\lesssim 2×{10}^{7}\) GeV, where \({H}_{\mathrm{inf}}\) is the value of Hubble parameter during inflation. This is crucial to overcome a potential axion domain wall problem as well as the axion isocurvature problem. The SMART U(1) \({}_{X}\) framework can be successfully implemented in the presence of SU(5) grand unification, as we briefly show.Item Type II seesaw and the PAMELA/ATIC signals(Elsevier, 2009-08-24) Gogoladze, Ilia; Okada, Nobuchika; Shafi, Qaisar; University of Delaware; High Energy Accelerator Research Organization (KEK); University of Alabama TuscaloosaWe discuss how the cosmic ray signals reported by the PAMELA and ATIC/PPB-BETS experiments may be understood in a Standard Model (SM) framework supplemented by type II seesaw and a stable SM singlet scalar boson as dark matter. A particle physics explanation of the 'boost' factor can be provided by including an additional SM singlet scalar field. (C) 2009 Elsevier B.V. All rights reserved.Item Unparticle physics and gauge coupling unification(Elsevier, 2008-01-17) Gogoladze, Ilia; Okada, Nobuchika; Shafi, Qaisar; University of Delaware; University System of Maryland; University of Maryland College Park; High Energy Accelerator Research Organization (KEK); University of Alabama TuscaloosaUnparticle physics from a hidden conformal sector can alter the evolution of the Standard Model (SM) gauge couplings via TeV scale threshold corrections. We discuss how this may lead to gauge coupling unification at M-GUT approximate to 2 x 10(15)-5 x 10(17) GeV without introducing new particles in the SM sector. (C) 2007 Elsevier B.V. All rights reserved.