arXiv subjects

Q. Shafi

Publications and source records attributed to Q. Shafi.

46 records · Page 3Linked to original sources

arXiv1994

Supersymmetric Models With Tan(beta) Close to Unity

Within the framework of supersymmetric grand unification, estimates of the $b$ quark mass based on the asymptotic relation $m_b \simeq m_τ$ single out the region with $\tanβ$ close to unity, particularly if $m_t(m_t) \stackrel{_<}{_\sim} 170\ GeV$. We explore the radiative breaking of the electroweak symmetry and the associated sparticle and higgs spectroscopy in models with $1 < \tanβ\stackrel{_<}{_\sim} 1.6$. The lightest scalar higgs is expected to have a mass below $100\ GeV$, while the remaining four higgs masses exceed $300\ GeV$. The lower bounds on some of the sparticle masses are within the range of LEP 200.

hep-ph↗

arXiv1994

Gauge Hierarchy in ${\bf SU(3)_c \times SU(3)_L \times SU(3)_R}$ and Low Energy Implication

We explore the gauge hierarchy problem within the framework of supersymmetric $SU(3)_c \times SU(3)_L \times SU(3)_R$ with a minimal set of higgs supermultiplets. Imposition of a suitable discrete (alternatively $R$) symmetry `prevents' the electroweak higgs doublets from becoming superheavy through renormalizable couplings. A full resolution of the problem requires consideration of the non-renormalizable couplings which play an essential role. Other key differences from the minimal supersymmetric $SU(5)$ model include the fact that the proton is stable and that an effective $5 + \bar{5}$ supermultiplet appears around the $TeV$ mass scale.

hep-ph↗

arXiv1993

Zeroing In On the Top Quark, LSP and Scalar Higgs Masses

We estimate the top quark, lightest sparticle (LSP) and scalar higgs masses within a supersymmetric grand unified framework in which $\tanβ\simeq m_t/m_b$ and the electroweak symmetry is radiatively broken. The requirement that the calculated $b$ quark mass lie close to its measured value, together with the cosmological constraint $Ω_{LSP} \approx 1$, fixes the top quark mass to be $m_t(m_t) \approx 170 \pm 15\ GeV$. The LSP (of bino purity $\stackrel{_>}{_\sim} 98\%)$ has mass $\sim 200 - 350\ GeV$. In the scalar higgs sector the CP-odd scalar mass $m_A \stackrel{_<}{_\sim} 220\ GeV$. With $m_A \stackrel{_>}{_\sim} M_Z$, as suggested by the decay $b \rightarrow sγ$, we find $M_Z \stackrel{_<}{_\sim} m_{h^0} (m_{H^0}) \stackrel{_<}{_\sim} 140 (220)\ GeV$ and $120\ GeV \stackrel{_<}{_\sim} m_{H^\pm} \stackrel{_<}{_\sim} 240\ GeV$.

hep-ph↗

arXiv1993

A Simple Model of Large Scale Structure Formation

We explore constraints on inflationary models employing data on large scale structure mainly from COBE temperature anisotropies and IRAS selected galaxy surveys, taking care not to apply linear perturbation theory to data in the non-linear regime. In models where the tensor contribution to the COBE signal is negligible, we find the spectral index of density fluctuations $n$ must exceed 0.7. Furthermore the COBE signal cannot be dominated by the tensor component, implying $n>0.85$ in such models. The data favors cold plus hot dark matter models with $n$ close to unity and $Ω_{HDM} \sim 0.20 - 0.35$. We present realistic grand unified theories, including supersymmetric versions, which produce inflation with these properties.

astro-ph↗

arXiv1993

Supersymmetric Unification without Proton Decay

We present a supersymmetric grand unification scheme based on the gauge group SU(3)_c X SU(3)_L X SU(3)_R in which the proton and the lightest supersymmetric particle are stable, neutrinos are necessarily massive, and the observed baryon asymmetry originates in the lepton sector. Such models are also consistent with the measured value of sin^2Θ_W as well as unification of the gauge couplings.

hep-ph↗

arXiv1993

A Predictive Inflationary Scenario Without The Gauge Singlet

We propose a new realization of the chaotic inflationary scenario in which the scalar field responsible for inflation also spontaneously breaks the underlying gauge symmetry at a superheavy scale $\sim 10^{15} - 10^{17}\; GeV$. A possible framework is provided by the superstring inspired gauge models, in which case several predictions are essentially model independent. The spectral index for the scalar perturbations $n \simeq 0.92 - 0.88$, while the ratio of the tensor to the scalar quadrupole anisotropy is $(ΔT/T)^2_T/(ΔT/T)^2_S \approx 0.4 - 0.7$. On smaller angular scales, $δT/T (1^\circ ) \approx (9 - 16) \times 10^{-6}$ and $δT/T (2.1^\circ ) \approx (6 - 10) \times 10^{-6}$. Implications for magnetic monopoles and cosmic strings as well as the gauge hierarchy problem are pointed out.

hep-ph↗

arXiv1993

Leptonic Fritzsch Matrices and Neutrino Oscillations

It was recently shown by the authors that the Fritzsch ansatz for the quark mass matrices prescribed at the supersymmetric grand unified scale is compatible with a moderately heavy top quark ($m_t \simeq 120-150~GeV$). Here we extend the ansatz to incorporate the charged leptons and the neutrinos. It is found that the $ν_e-ν_μ$ mixing angle is small and consistent with the MSW solution of the solar neutrino puzzle. Furthermore, the model predicts observable $ν_μ-ν_τ$ oscillations with sin$^22θ_{μτ} \simeq 0.1$ and $ν_τ$ mass in the $(1-3)~eV$ range.

hep-ph↗

arXiv1992

Heavy top quark from Fritzsch mass matrices

It is shown, contrary to common belief, that the Fritzsch ansatz for the quark mass matrices admits a heavy top quark. With the ansatz prescribed at the supersymmetric grand unified (GUT) scale, one finds that the top quark may be as heavy as 145 GeV, provided that tan$β$ (the ratio of the vacuum expectation values of the two higgs doublets) $\gg 1$. Within a non-supersymmetric GUT framework with two (one) light higgs doublets, the corresponding approximate upper bound on the top mass is $120~ (90)$ GeV. Our results are based on a general one--loop renormalization group analysis of the quark masses and mixing angles and are readily applied to alternative mass matrix ansätze.

hep-ph↗

arXiv1992

From Fermion Mass Matrices to Neutrino Oscillations

We present an ansatz for the quark and lepton mass matrices, derivable from SO(10) type GUTs, which accommodates a heavy $(> 92 GeV)$ top quark and permits large mixings in the $ν_μ\leftrightarrow ν_τ$ sector (as suggested by the recent Kamiokande and IMB data on the atmospheric neutrinos). The well known asymptotic relations $m_b = m_τ$, $m_s = \frac{1}{3} m_μ$ and $m_dm_s = m_e m_μ$ all hold to a good approximation. Depending on $ν_μ\leftrightarrow ν_τ$ mixing which can even be maximal, the mixing angle relevant for solar neutrino oscillation lies in the range $7.8 \times 10^{-3} \stackrel{_<}{_\sim} \sin^2 2θ_{eμ} \stackrel{_<}{_\sim} 2.1 \times 10^{-2}$. For the $^{71}$Ga experiment the event rate, normalized against the standard solar model prediction of 132 SNU, is estimated to be between 80 and 20 SNU.

hep-ph↗

arXiv1992

Inflation and Large Scale Structure Formation After COBE

The simplest realizations of the new inflationary scenario typically give rise to primordial density fluctuations which deviate logarithmically from the scale free Harrison - Zeldovich spectrum. We consider a number of such examples and, in each case we normalize the amplitude of the fluctuations with the recent COBE measurement of the microwave background anisotropy. The predictions for the bulk velocities as well as anisotropies on smaller (~1-2 degrees) angular scales are compared with the Harrison-Zeldovich case. Deviations from the latter range from a few to about 15 percent. We also estimate the redshift beyond which the quasars would not be expected to be seen. The inflationary quasar cutoff redshifts can vary by as much as 25\% from the Harrison-Zeldovich case. We find that the inflationary scenario provides a good starting point for a theory of large scale structure in the universe provided the dark matter is a combination of cold plus (~10-30 \%) hot components.

hep-ph↗