Duane A. Dicus

Residual Symmetries for Neutrino Mixing with a Large θ 13 and Nearly Maximal δ D

The residual Z(2)(s)(k) and Z(2)(s)(k) symmetries induce a direct and unique phenomenological relation with θx (≡ θ13) expressed in terms of the other two mixing angles θs(≡ θ12) and θa(≡ θ23) and the Dirac CP phase δD. Z(2)(s)(k) predicts a θx probability distribution centered around 3°-6° with an uncertainty of 2°-4°, while those from Z(2)(s)(k) are approximately a factor of 2 larger. Either result fits the T2K, MINOS, and Double Chooz measurements. Alternately, a prediction for the Dirac CP phase δD results in a peak at ± 74° (± 106°) for Z(2)(s)(k) or ± 123° (± 57°) for Z(2)(s)(k) which is consistent with the latest global fit. We also give a distribution for the leptonic Jarlskog invariant Jν which can provide further tests from measurements at T2K and NOνA.

Unitarity of compactified five-dimensional Yang-Mills theory

Abstract Compactified five-dimensional Yang–Mills theory results in an effective four-dimensional theory with a Kaluza–Klein (KK) tower of massive vector bosons. We explicitly demonstrate that the scattering of the massive vector bosons is unitary at tree-level for low energies, and analyze the relationship between the unitarity violation scale in the KK theory and the nonrenormalizability scale in the five-dimensional gauge theory. In the compactified theory, low-energy unitarity is ensured through an interlacing cancellation among contributions from the relevant KK levels. Such cancellations can be understood using a Kaluza–Klein equivalence theorem which results from the geometric “Higgs” mechanism of compactification. In these theories, the unitarity violation is delayed to energy scales higher than the customary limit through the introduction of additional vector bosons rather than Higgs scalars.

Z2 symmetry prediction for the leptonic Dirac CP phase

Abstract Model-independent consequences of applying a generalized hidden horizontal Z 2 symmetry to the neutrino mass matrix are explored. The Dirac CP phase δ D can be expressed in terms of the three mixing angles as 4 c a s a c s s s s x cos δ D = ( s s 2 − c s 2 s x 2 ) ( c a 2 − s a 2 ) where the s i , c i are sines and cosines of the atmospheric, solar, and reactor angles. This relation is independent of neutrino masses and whether neutrinos are Dirac- or Majorana-type. Given the present constraints on the angles, δ D is constrained to be almost maximal, a result which can be explored in experiments such as NOνA and T2K. The Majorana CP phases do not receive any constraint and are thus model-dependent. Also a distribution of θ x with a lower limit is obtained without specifying δ D .

Cosmological implications of massive, unstable neutrinos

We consider the cosmological consequences of the existence of massive, neutral, weakly interacting leptons (v/sub H/). Bounds are calculated on the v/sub H/ mass, lifetime, and allowed interaction strength by assuming minimal modification of the standard big-bang model. Our chief conclusions are :(1) The v/sub H/ may be stable if its mass is greater than a few GeV. (2) For intermediate masses, for which the v/sub H/ must be unstable, if its principal decay mode creates photons, masses less than 10/sup -/2 MeV are ruled out and its lifetime must be less than 1 year. (3) If the v/sub H/ decays exclusively into neutrinos, it may have a considerably longer lifetime and give rise to a present-day enerfy density sufficiently high to make the universe radiation-dominated and closed.

Higgs-Boson Production in Association with Bottom Quarks at Next-to-Leading Order

We argue that the leading-order subprocess for Higgs-boson production in association with bottom quarks is b{bar b}{r_arrow}H. This process is an important source of Higgs bosons with enhanced Yukawa coupling to bottom quarks. We calculate the corrections to this cross section at next-to-leading-order in 1/ln(m{sub H}/m{sub b}) and {alpha}{sub s} and at next-to-next-to-leading order in 1/ln(m{sub H}/m{sub b}). {copyright} {ital 1999} {ital The American Physical Society}

Model-Independent Prediction of a Large Reactor Angle theta_13

The residual Z(2)(s)(k) and Z(2)(s)(k) symmetries induce a direct and unique phenomenological relation with θx (≡ θ13) expressed in terms of the other two mixing angles θs(≡ θ12) and θa(≡ θ23) and the Dirac CP phase δD. Z(2)(s)(k) predicts a θx probability distribution centered around 3°-6° with an uncertainty of 2°-4°, while those from Z(2)(s)(k) are approximately a factor of 2 larger. Either result fits the T2K, MINOS, and Double Chooz measurements. Alternately, a prediction for the Dirac CP phase δD results in a peak at ± 74° (± 106°) for Z(2)(s)(k) or ± 123° (± 57°) for Z(2)(s)(k) which is consistent with the latest global fit. We also give a distribution for the leptonic Jarlskog invariant Jν which can provide further tests from measurements at T2K and NOνA.

Higgs decay to top quarks at hadron colliders

Abstract Higgs bosons which decay principally to top quarks, such as in the minimal supersymmetric model, produce a peak-dip structure in the gg→t t invariant-mass spectrum. This structure is potentially observable at the CERN Large Hadron Collider.

Higgs boson pair production from gluon fusion

Abstract We calculate Higgs-boson pair production from gluon fusion at future hadron colliders. We find that the box diagram is appreciably larger then the triangle diagram for Higgs-boson masses which are experimentally accessible. This obscures the observation of the three-Higgs-boson vertex, which is present in the latter diagram.

Minimal schemes for large neutrino mixings with inverted hierarchy

Existing oscillation data point to non-zero neutrino masses with large mixings. We analyze the generic features of the neutrino Majorana mass matrix with inverted hierarchy and construct realistic minimal schemes for the neutrino mass matrix that can explain the large (but not maximal) νe–νμ mixing of MSW-LAM as well as the nearly maximal νμ–ντ mixing and the small (or negligible) νe→ντ transition. These minimal schemes are quite unique and turn out to be extremely predictive. Implications for neutrinoless double beta decay, tritium beta decay and cosmology are analyzed.

Structure of cosmological CP violation via neutrino seesaw

Abstract The cosmological matter–antimatter asymmetry can originate from CP-violating interactions of seesaw Majorana neutrinos via leptogenesis in the thermal phase of the early universe. Having the cosmological CP-phase for leptogenesis requires at least two right-handed Majorana neutrinos. Using only the low energy neutrino observables, we quantitatively reconstruct a minimal neutrino seesaw. We establish a general criterion for minimal seesaw schemes in which the cosmological CP-phase is completely reconstructed from the low energy CP-phases measured by neutrino oscillation and neutrinoless double-beta decay experiments. We reveal and analyze two distinct classes of such minimal schemes that are shown to be highly predictive. Extension of our reconstruction formalism to a three-heavy-neutrino seesaw is discussed.