arXiv subjects
Publications and source records attributed to Ernest Ma.
In this talk I address the theoretical issue of what new physics is required to make $m_ν\neq 0$. I then discuss what other things may happen besides neutrino oscillations. In particular I consider a possible new scenario of leptogenesis in R parity nonconserving supersymmetry.
There are two basic theoretical approaches to obtaining neutrino mass and mixing. In the minimalist approach, one adds just enough new stuff to the Minimal Standard Model to get $m_ν\neq 0$ and $U_{αi} \neq 1$. In the holistic approach, one uses a general framework or principle to enlarge the Minimal Standard Model such that, among other things, $m_ν\neq 0$ and $U_{αi} \neq 1$. In both cases, there are important side effects besides neutrino oscillations. I discuss a number of examples, including the possibility of leptogenesis from R parity nonconservation in supersymmetry.
It is known that realistic neutrino masses for neutrino oscillations may be obtained from R parity nonconserving supersymmetry. It is also known that such interactions would erase any preexisting lepton or baryon asymmetry of the Universe because of the inevitable intervention of the electroweak sphalerons. We now show how a crucial subset of these R parity nonconserving terms may in fact create its own successful leptogenesis.
The 1999 precision electroweak data from LEP and SLC persist in showing some slight discrepancies from the assumed standard model, mostly regarding $b$ and $c$ quarks. We show how their mixing with exotic heavy quarks could result in a more consistent fit of all the data, including two unconventional interpretations of the top quark.
The permutation symmetry $S_3$ is appplied to obtain two equal Majorana neutrino masses, while maintaining three different charged-lepton masses and suppressing neutrinoless double beta decay. The resulting radiative splitting of the two neutrinos is shown to be suitable for solar neutrino vacuum oscillations.
We present a new and novel synthesis of all existing neutrino data regarding the disappearance and appearance of $ν_e$ and $ν_μ$. We assume four neutrinos: $ν_e, ν_μ, ν_τ$, as well as a heavier singlet neutrino $ν_s$ of a few eV. The latter may decay into a massless Goldstone boson (the singlet Majoron) and a linear combination of the doublet antineutrinos. We comment on how this scenario may be verified or falsified in future experiments.
Extending the minimal standard model of particle interactions (without right-handed singlet neutrinos) to include a heavy scalar triplet $ξ$ to obtain nonzero Majorana neutrino masses, I derive the following simple realistic connection between atmospheric and solar neutrino vacuum oscillations: $(Δm^2)_{sol} (Δm^2)_{atm} / m_ν^4 ~(\sin^2 2 θ)_{atm} = 2 I^2$, where $m_ν$ is the assumed common approximate mass of each neutrino (which may be suitable for hot dark matter) and $I = (3/16 π^2)(G_F/\sqrt 2) m_τ^2 \ln (m_ξ^2/m_W^2)$ comes from the radiative splitting of the degeneracy due to the charged leptons.
Assuming equal tree-level Majorana masses for the standard-model neutrinos, either from the canonical seesaw mechanism or from a heavy scalar triplet, I discuss how their radiative splitting may be relevant to neutrinoless double beta decay and neutrino oscillations.
Two neutrinos of Majorana masses $m_{1,2}$ with mixing angle $θ$ are unstable against radiative corrections in the limit $m_1 = m_2$, but are stable for $m_1 = -m_2$ (i.e. opposite CP eigenstates) with $θ= 45^\circ$ which corresponds to an additional symmetry.
Assuming the Majorana masses of $ν_e$ and the linear combination $c ν_τ- s ν_μ$ to be equal from their couplings to a heavy scalar triplet $ξ$, I show that their radiative splitting is given by $Δm^2/m_ν^2 = (3 c^2/4 π^2) (G_F/\sqrt 2) m_τ^2 \ln (m_ξ^2/m_W^2)$. This is applicable to the small-angle matter-enhanced oscillation solution of the solar neutrino deficit and restricts $m_ν$ to be between 0.20 and 0.36 eV if $c^2 = 0.7$ and $m_ξ= 10^{14}$ GeV.
Assuming the canonical seesaw mechanism together with an SO(3) family symmetry for leptons, broken only by the charged-lepton masses, I show that the three neutrinos of Majorana mass $m_0$ are split radiatively in two loops by a maximum finite calculable amount of order $10^{-9} m_0$. This is very suitable for dark matter and vacuum solar neutrino oscillations. I also discuss how atmospheric neutrino oscillations can be incorporated.
If a global continuous symmetry of a supersymmetric field theory is spontaneously broken while preserving the supersymmetry, the resulting theory has a massless superfield. One of its two bosonic degrees of freedom is the familiar phase rotation of the usual massless Nambu-Goldstone boson, but the other is a scale transformation. An indeterminate mass scale is thus generated. In the fermion sector, a seesaw texture appears which may be suitable for a possible light sterile neutrino. This feature persists even after the gauging of the continuous symmetry or the breaking of the supersymmetry to resolve the aforementioned mass-scale ambiguity.
Models of leptogenesis often invoke the out-of-equilibrium decays of heavy right-handed neutrinos in order to create a baryon asymmetry of the universe through the electroweak phase transition. Their presumed existence argues strongly for the presence of an $SU(2)_R$ gauge symmetry. We study the equilibrating effects of the resulting additional right-handed interactions and find that successful leptogenesis requires that $m_N \gtrsim 10^{16}$ GeV if $m_N > m_{W_R}$, and $m_{W_R} \gtrsim 3 \times 10^6 GeV (m_N /10^2 GeV)^{2/3}$ if $m_{N} m_{W_R}$ option is excluded in a supersymmetric theory with gravitinos.
If a family symmetry exists so that all three neutrinos have equal Majorana masses (via the seesaw mechanism), then the breaking of this symmetry from charged-lepton masses (via two-loop double $W$ exchange) implies $Δm$ less than about $10^{-9}m_0$. With the common mass $m_0 \sim$ eV for hot dark matter, $Δm^2 \sim 10^{-10}$ eV$^2$ is natural for vacuum solar neutrino oscillations.
Neutrino masses are zero in the minimal supersymmetric standard model. I discuss how they may become nonzero with new interactions which may or may not violate R-parity conservation.
In the supersymmetric standard model of particle interactions, R-parity nonconservation is often invoked to obtain nonzero neutrino masses. We point out here that such interactions of the supersymmetric particles would erase any pre-existing lepton or baryon asymmetry of the universe before the electroweak phase transition through the $B + L$ violating sphaleron processes. We then show how neutrino masses may be obtained in supersymmetry (assuming R-parity conservation) together with successful leptogenesis and predict the possible existence of new observable particles.
We have constructed an explicit see-saw model containing two singlet neutrinos, one carrying a $(B-3L_e)$ gauge charge with an intermediate mass scale of $\sim O(10^{10})$ GeV along with a sterile one near the GUT (grand unification theory) scale of $\sim O(10^{16})$ GeV. With these mass scales and a reasonable range of Yukawa couplings, the model can naturally account for the near-maximal mixing of atmospheric neutrino oscillations and the small mixing matter-enhanced oscillation solution to the solar neutrino deficit.
We present a minimal see-saw model based on an extension of the standard model (SM) which includes an additional U(1), with gauge charge $B - \frac{3}{2} (L_μ+ L_τ)$. Requirement of anomaly cancellation implies the existence of two right-handed singlet neutrinos, carrying this gauge charge, which have normal Dirac couplings to $ν_μ$ and $ν_τ$ but suppressed ones to $ν_e$. Assuming the U(1) symmetry breaking scale to be 10$^{12-16}$~GeV, this model can naturally account for the large (small) mixing solutions to the atmospheric (solar) neutrino oscillations.