arXiv subjects
Publications and source records attributed to R. N. Mohapatra.
In a class of supersymmetric left-right models (SUSYLR) of weak interactions where R-parity is automatically conserved, we show that spontaneous breakdown of parity CANNOT occur without spontaneous breakdown of R-parity. This intriguing result connects two physically different scales in supersymmetric models.
There are strong indications for neutrino masses and mixings in the data on solar neutrinos as well as in the observed deficit of muon neutrinos from the atmosphere. The COBE data and other analysis of the large scale structure in the Universe also seems to require a hot component in the universe's dark matter, which can be interpreted as a massive neutrino with mass in the few eV range. Non-zero neutrino mass is a strong indication of a new local $B-L$ symmetry of electro-weak interactions . In particular, it is noted that the simplest picture based on the left-right symmetric unification with a high scale for the $B-L$ symmetry (as well as the scale of the right-handed gauge boson $W_R$) as required by the constraints of grandunification and present LEP data in a minimal $SO(10)$ model, can accomodate the solar neutrino data and a weak hot dark matter neutrino but not the atmospheric neutrino puzzle. A model with low scale $W_R$ ( in the TeV range) where the Dirac mass of the neutrino arises at the one loop level can also do the same job. The low $W_R$ picture can be tested in many rare decay experiments.
Definitions of the control sequences included, but no other changes.
Several misprints in the earlier version (hep-ph/9301286) have been corrected.
We analyse the impact of quantum gravity on the possible solutions to the strong CP problem which utilize the spontaneously broken discrete symmetries, such as parity and time reversal invariance. We find that the stability of the solution under Planck scale effects provides an upper limit on the scale $Λ$ of relevant symmetry breaking. This result is model dependent and the bound is most restrictive for the seesaw type models of fermion masses, with $Λ< 10^6$ GeV.
We point out that in a class of supersymmetric models where R-parity violation is induced by the spontaneous breaking of local $B-L$ symmetry, the R-parity violating $W$ decay $W\rightarrow\slepγ$ and $Z$ decay $Z\rightarrow\snuγ$, forbidden in the minimal supersymmetric standard model (MSSM), occur at an enhanced rate compared to other models with R-parity breaking. We find that the branching fractions for these modes can be of order $10^{-5}$ .
The hypothesis that non-perturbative gravitational effects lead to explicit breaking of global symmetries is considered in the context of Majoron models. We find that the nonvanishing Majoron mass generated by these effects can overclose the universe unless the massive Majoron is unstable. The cosmological mass density constraints can then be satisfied only if $V_{BL} < 10$ TeV, where $V_{BL}$ is the scale of $B-L$ symmetry breaking.
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.
We compute the threshold uncertainties due to unknown masses of the Higgs bosons on the predictions for the intermediate and unification scales, $M_I$ and $M_U$ respectively in SO(10) models.We focus on models with separate breaking scales for Parity and $SU(2)_R$ symmetries since they provide a natural realization of the see-saw mechanism for neutrino masses. For the two step symmetry breaking chains ,where left-right symmetric gauge groups appear at the intermediate scale, we find that parity invariance of the theory at the unification scale drastically reduces the GUT threshold effects in some cases. Including the effects of the intermediate scale thresholds ,we compute the uncertainty in the above mass scales and study their implications for proton lifetime and neutrino masses. An important outcome of our analysis is that if the currently favored nonadiabatic MSW solution to the solar neutrino puzzle is accepted , it will rule out the $SU(2)_LXSU(2)_RXU(1)_{B-L}X SU(3)_c$ as an intermediate symmetry for SO(10) breaking whereas the intermediate symmetry $SU(2)_LXSU(2)_RXSU(4)_c$, is quite consistent with it.