B-factory signals for a warped extra dimension

We study predictions for B physics in a class of warped extra dimension models recently introduced, where few ( approximately 3) TeV Kaluza-Klein masses are consistent with electroweak data due to custodial symmetry. As in the standard model (SM), flavor violations arise due to the heavy top quark leading to striking signals: (i) New physics contributions to DeltaF=2 transitions are comparable to the SM, so the success of the SM unitarity triangle fit is a "coincidence." Thus, clean extractions of unitarity angles are likely to be affected, in addition to O(1) deviation from the SM prediction in B(s) mixing. (ii) O(1) deviation from various SM predictions for B-->X(s)l(+)l(-). (iii) Large mixing-induced CP asymmetry in radiative B decays. Also, the neutron electric dipole moment is roughly 20 times larger than the current bound so that this framework has a "CP problem."     

Sneutrino dark matter in gauged inverse seesaw models for neutrinos

Extending the minimal supersymmetric standard model to explain small neutrino masses via the inverse seesaw mechanism can lead to a new light supersymmetric scalar partner which can play the role of inelastic dark matter (IDM). It is a linear combination of the superpartners of the neutral fermions in the theory (the light left-handed neutrino and two heavy standard model singlet neutrinos) which can be very light with mass in ~5-20 GeV range, as suggested by some current direct detection experiments. The IDM in this class of models has keV-scale mass splitting, which is intimately connected to the small Majorana masses of neutrinos. We predict the differential scattering rate and annual modulation of the IDM signal which can be testable at future germanium- and xenon-based detectors.     

Higgs decay into two photons in a warped extra dimension

A detailed five-dimensional calculation of the Higgs-boson decay into two photons is performed in both the minimal and the custodially protected Randall–Sundrum (RS) model, where the Standard Model (SM) fields propagate in the bulk and the scalar sector lives on or near the IR brane. It is explicitly shown that the $R_\xi $ gauge invariance of the sum of diagrams involving bosonic fields in the SM also applies to the case of these RS scenarios. An exact expression for the $h\rightarrow \gamma \gamma $ amplitude in terms of the five-dimensional (5D) gauge-boson and fermion propagators is presented, which includes the full dependence on the Higgs-boson mass. Closed expressions for the 5D $W$ -boson propagators in the minimal and the custodial RS model are derived, which are valid to all orders in $v^2/M_{\text {KK}}^2$ . In contrast to the fermion case, the result for the bosonic contributions to the $h\rightarrow \gamma \gamma $ amplitude is insensitive to the details of the localization of the Higgs profile on or near the IR brane. The various RS predictions for the rate of the $pp\rightarrow h\rightarrow \gamma \gamma $ process are compared with the latest LHC data, and exclusion regions for the RS model parameters are derived.     

Light neutrinos from a mini-seesaw mechanism in warped space

The seesaw mechanism provides a simple explanation for the lightness of the known neutrinos. Under the standard assumption of a weak scale Dirac mass and a heavy sterile Majorana scale the neutrino mass is naturally suppressed below the weak scale. However, Nature may employ Dirac and Majorana scales that are much less than typically assumed, possibly even far below the weak scale. In this case the seesaw mechanism alone would not completely explain the lightness of the neutrinos. In this work we consider a warped framework that realizes this possibility by combining naturally suppressed Dirac and Majorana scales together in a mini-seesaw mechanism to generate light neutrino masses. Via the AdS/CFT correspondence the model is dual to a 4D theory with a hidden strongly coupled sector containing light composite right-handed neutrinos.     

Low-scale gravity mediation in warped extra dimension and collider phenomenology on hidden sector

We propose a new scenario of gravity-mediated supersymmetry breaking (gravity mediation) in a supersymmetric Randall-Sundrum model, where the gravity mediation takes place at a low scale due to the warped metric. We investigate collider phenomenology involving the hidden sector field, and find a possibility that the hidden sector field can be produced at the LHC and the ILC. The hidden sector may no longer be hidden. Talk presented by N Okada. The talk is based on the work of H Itoh, N Okada and T Yamashita, hep-ph/0606156.     

Majorana neutrinos in rare meson decays

The rare meson decays K ⁺ → π ^??⁺?′⁺ and D ⁺ → K ^??⁺?′⁺ (?, ?′ = e, μ), which are induced by Majorana neutrino exchange and which are accompanied by lepton-number nonconservation, are considered. The effects of the meson structure are taken into account on the basis of the Gaussian model for the respective Bethe-Salpeter amplitudes. It is shown that existing direct experimental constraints on the decay branching ratios are overly lenient and therefore give no way to set realistic limits on effective Majorana masses. On the basis of the constraints on the lepton-mixing parameters and neutrino masses from precision measurements of electroweak processes, neutrino-oscillation experiments, searches for neutrinoless double-beta decay of nuclei, and cosmological data, indirect constraints on the branching ratios for the decays in question are obtained and found to be much more stringent than the above direct constraints.     

Dirac and Majorana neutrinos in matter

We consider the matter effects on neutrinos moving in background on the basis of the corresponding quantum wave equations. Both Dirac and Majorana neutrino cases are discussed. The effects for Dirac neutrino reflection and trapping as well as neutrino—antineutrino annihilation and ν pair creation in matter at the interface between two media with different densities are considered. The spin light of neutrinos in matter is also discussed. The text was submitted by the authors in English.     

Radiative seesaw mechanism and degenerate neutrinos

The radiative seesaw mechanism of Witten generates the right-handed neutrino masses in SO(10) with the spinorial 16(H) Higgs field. We study here analytically the 2nd and 3rd generations for the minimal Yukawa structure containing and Higgs representations. In the approximation of small 2nd generation masses and gauge loop domination we find the following results: (1) beta-tau unification, (2) natural coexistence between large theta(l) and small theta(q), and (3) degenerate neutrinos.     

Double beta decays and Majorana neutrinos

Neutrino-less double beta decays (0νββ) are sensitive and realistic probes for studying the Majorana nature of neutrinos (ν), the ν-mass spectrum, the absolute ν-mass scale, the Majorana CP phases and other fundamental properties of neutrinos and weak interactions. Current 0νββ experiments, which use detectors with the mass sensitivity of the order of 300 meV, study the ν-mass in that mass region. Future experiments with higher sensitivities of the orders of 100meV and 30 meV, using different nuclei and methods (calorimetric, spectroscopic), are indispensable for establishing 0νββ in the quasi degenerate and the inverted hierarchy mass regions. R&D for ultra-high sensitivity detectors are encouraged for studying the normal hierarchy mass region. Theoretical and experimental studies for evaluating nuclear matrix elements are important for extracting the sensible ν-mass from the 0νββ rate. Charge exchange reactions by means of nuclear, electromagnetic and ν probes provide valuable data which are used to evaluate the nuclear matrix elenments. International collaborations for 0νββ experiments and for the matrix elements are crucial for next generation 0νββ studies.     

Multisupergravity from latticized extra dimension

The construction of the linearized four-dimensional multisupergravity from five-dimensional linearized supergravity with discretized fifth dimension is presented. The one-loop vacuum energy is evaluated when (anti)periodic boundary conditions are chosen for (bosons) fermions, respectively, or vice versa. It is proposed that the relation between discretized M-theory and strings may be found in the same fashion.     

The effects of Majorana phases in three-generation neutrinos

Neutrino-oscillation solutions for the atmospheric neutrino anomaly and the solar neutrino deficit can determine the texture of the neutrino mass matrix according to three types of neutrino mass hierarchy: Type A: , Type B: , and Type C: , where is the absolute mass of the ith generation neutrino. The relative sign assignments of the neutrino masses in each type of mass hierarchy play crucial roles in the stability against quantum corrections. Actually, two physical Majorana phases in the lepton flavor mixing matrix connect the relative sign assignments of the neutrino masses. Therefore, in this paper we analyze the stability of the mixing angles against quantum corrections according to three types of neutrino mass hierarchy (Type A, B, C) and two Majorana phases. The two phases play crucial roles in the stability of the mixing angles against quantum corrections. Received: 9 May 2000 / Revised version: 23 May 2000 / Published online: 8 September 2000     

Neutrino-less double beta decays and Majorana neutrinos

Neutrino-less double beta decays (0??? ??) are sensitive and realistic probes for studying the Majorana nature of neutrinos, the ?? mass spectrum and the absolute mass scale, the lepton sector CP and others beyond the standard electro-weak theory. This report reviews briefly 0??? ?? processes and Majorana neutrinos, the present and future 0??? ?? experiments and 0??? ?? nuclear matrix elements.