arXiv subjects

K. S. Babu

Publications and source records attributed to K. S. Babu.

204 records · Page 12Linked to original sources

arXiv1992

Family Symmetry, Gravity, and the Strong CP Problem

We show how in a class of models Peccei--Quinn symmetry can be realized as an automatic consequence of a gauged $U(1)$ family symmetry. These models provide a solution to the strong CP problem either via a massless $u$--quark or via the DFSZ invisible axion. The local family symmetry protects against potentially large corrections to $\overlineθ $ induced by quantum gravitational effects. In a supersymmetric extension, the `$μ$--problem' is shown to have a natural solution in the context of gravitationally induced operators. We also present a plausible mechanism which can explain the inter--generational mass hierarchy in such a context.

hep-ph↗

arXiv1992

The fermion mass problem

In this talk I review the `puzzles' associated with the fermion mass matrices and describe some recent attempts to resolve them, at least partially. Models which attempt to explain the observed mass hierarchy as arising from radiative corrections are discussed. I then scrutinize possible inter--relations among quark and lepton masses and the mixing angles in the context of grand unified theories. It is argued that the absence of CP violation in the strong interaction sector (the strong CP problem) may also have its origin in the structure of the quark mass matrices; such a resolution does not invoke approximate global $U(1)$ symmetries resulting in the axion. Arguments in favor of tiny neutrino masses are summarized (the solar neutrino puzzle, atmospheric neutrino problem) and ways to accommodate them naturally are described.

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

Predictive Neutrino Spectrum in Minimal $SO(10)$ Grand Unification

We show that minimal SO(10) Grand Unification models where the fermions have Yukawa couplings to only one (complex) {\bf 10} and one {\bf 126} of Higgs scalars lead to a very predictive neutrino spectrum. This comes about since the standard model doublet contained in the {\bf 126} of Higgs (needed for the see--saw mechanism) receives an induced vacuum expectation value at tree--level, which, in addition to correcting the bad asymptotic mass relations $m_d=m_e$ and $m_s=m_μ$, also relates the Majorana neutrino mass matrix to observables in the charged fermion sectors. We find that (i) the $ν_e-ν_μ$ mixing angle relevant for the solar neutrinos can be considerably smaller than the Cabibbo angle and lies in the range ${\rm sin}θ_{e μ}= 0-0.3$, (ii) $ν_e-ν_τ$ mixing is sin$θ_{e τ} \simeq 3|V_{td}| \simeq 0.05$, (iii) the $ν_μ-ν_τ$ mixing angle is large, ${\rm sin}θ_{μτ} \simeq 3|V_{cb}|=0.12-0.16$, and (iv) $m_{ν_τ}/m_{ν_μ} \ge 10^3$, implying that $ν_μ-ν_τ$ oscillations should be accessible to forthcoming experiments.

hep-ph↗

arXiv1992

Bounds on mini-charged neutrinos in the minimal standard model

In the minimal Standard Model (MSM) with three generations of quarks and leptons, neutrinos can have tiny charges consistent with electromagnetic gauge invariance. There are three types of non-standard electric charge, given by $Q_{st} + ε(L_i - L_j)$, where $i, j = e, μ, τ$ $(i \neq j)$, $Q_{st}$ is standard electric charge, $L_i$ is a family-lepton--number, and $ε$ is an arbitrary parameter which is put equal to zero in the usual incarnation of the MSM. These three non-standard electric charges are of considerable theoretical interest because they are compatible with the MSM Lagrangian and $SU(3)_c \otimes SU(2)_L \otimes U(1)_Y$ gauge anomaly cancellation. The two most conspicuous implications of such non-standard electric charges are the presence of two generations of massless charged neutrinos and a breakdown in electromagnetic universality for $e$, $μ$ and $τ$. We use results from (i) charge conservation in $β$-decay, (ii) physical consequences of charged atoms in various contexts, (iii) the anomalous magnetic moments of charged leptons, (iv) neutrino-electron scattering, (v) energy loss in red giant and white dwarf stars, and (vi) limits on a cosmologically induced thermal photon mass, to place bounds on $ε$. While the constraints derived for $ε$ 10^{-21}$), the $L_μ-L_τ$ case allows $ε$ to be as large as $10^{-14}$.

hep-ph↗