arXiv subjects
Publications and source records attributed to Gerhart Seidl.
A simple implementation of Noether's theorem for discrete symmetries in relativistic continuum field theories is presented. The associated conserved current is exemplified by charge conjugation and a cyclic symmetry. In addition, the quantum version of current conservation for discrete symmetries is briefly discussed.
We demonstrate, by giving a specific example, that supersymmetry can be left unbroken without running into conflict with observation. The key idea is to employ a discrete form of supersymmetry. Amongst other interesting features, this construction goes roughly half the way in removing the hierarchy between the observed cosmological constant and the vacuum energies expected from field theory.
We survey the lepton flavor violation branching ratios Br(mu->e,gamma), Br(tau->mu,gamma), and Br(tau->e,gamma) in mSUGRA for a broad class of lepton mass matrix textures that give nearly tribimaximal lepton mixing. Small neutrino masses are generated by the type-I seesaw mechanism with non-degenerate right-handed neutrino masses. The textures exhibit a hierarchical mass pattern and can be understood from flavor models giving rise to large leptonic mixing. We study the branching ratios for the most general CP-violating forms of the textures. It is demonstrated that the branching ratios can be enhanced by 2-3 orders of magnitude as compared to the CP-conserving case. The branching ratios exhibit, however, a strong dependence on the choice of the phases in the Lagrangian which affects the significance of flavor models. In particular, for general CP-phases, the lepton flavor violating rates appear to be essentially uncorrelated with the possible high- and low-energy lepton mixing parameters, such as the reactor angle.
We present a supersymmetric SU(5) GUT model with a discrete non-Abelian flavor symmetry that is broken by Wilson lines. The model is formulated in 4+3 dimensions compactified on a manifold S^3/Z_n. Symmetry breaking by Wilson lines is topological and allows to realize the necessary flavor symmetry breaking without a vacuum alignment mechanism. The model predicts the hierarchical pattern of charged fermion masses and quark mixing angles. Small normal hierarchical neutrino masses are generated by the type-I seesaw mechanism. The non-Abelian flavor symmetry predicts to leading order exact maximal atmospheric mixing while the solar angle emerges from a variant of quark-lepton complementarity. As a consequence, the resulting leptonic mixing matrix is in excellent agreement with current data and could be tested in future neutrino oscillation experiments.
We consider resonant Dirac leptogenesis in a geometry with three five-dimensional throats in the flat limit. The baryon asymmetry in the universe is generated by resonant decays of heavy Kaluza-Klein scalars that are copies of the standard model Higgs. Discrete exchange symmetries between the throats are responsible for establishing two key features of the model. First, they ensure a near degeneracy of the scalar masses and thus a resonant decay of the scalars. This allows for Dirac leptogenesis at low energies close to the TeV scale. Second, the discrete symmetries connect the observed baryon asymmetry with the Yukawa couplings of the low-energy theory. As a consequence, we obtain correlations between the low-energy leptonic mixing parameters and the Dirac CP phase that can be tested at future neutrino oscillation experiments such as neutrino factories.
We consider discretized gravity in 4+2 dimensions compactified on a disk of constant negative curvature. The curvature of the disk avoids the presence of dangerous ultra-light scalar modes but comes also along with a high multiplicity of states potentially jeopardizing a good strong-coupling behavior of the discretized theory. We demonstrate that for Standard Model matter propagating on the five-dimensional boundary submanifold of the disk, the strong coupling scale, as seen by an observer, can be parametrically larger than the local Planck scale. As a consequence, we obtain a description of weakly coupled discretized gravity on the boundary that can be compared with the continuum theory all the way up to the effective five-dimensional Planck scale.
We construct a class of supersymmetric SU(5) GUT models that produce nearly tribimaximal lepton mixing, the observed quark mixing matrix, and the quark and lepton masses, from discrete non-Abelian flavor symmetries. The SU(5) GUTs are formulated on two five-dimensional throats in the flat limit and the neutrino masses become small due to the type-I seesaw mechanism. The discrete non-Abelian flavor symmetries are given by semi-direct products of cyclic groups that are broken at the infrared branes at the tip of the throats. As a result, we obtain SU(5) GUTs that provide a combined description of non-Abelian flavor symmetries and quark-lepton complementarity.
We present a systematic group space scan of discrete Abelian flavor symmetries for lepton mass models that produce nearly tribimaximal lepton mixing. In our models, small neutrino masses are generated by the type-I seesaw mechanism. The lepton mass matrices emerge from higher-dimension operators via the Froggatt-Nielsen mechanism and are predicted as powers of a single expansion parameter εthat is of the order of the Cabibbo angle θ_C\simeq 0.2. We focus on solutions that can give close to tribimaximal lepton mixing with a very small reactor angle θ_{13}\approx 0 and find several thousand explicit such models that provide an excellent fit to current neutrino data. The models are rather general in the sense that large leptonic mixings can come from the charged leptons and/or neutrinos. Moreover, in the neutrino sector, both left- and right-handed neutrinos can mix maximally. We also find a new relation θ_{13}\lesssimε^3 for the reactor angle and a new sum rule θ_{23}\approxπ/4+ε/\sqrt{2} for the atmospheric angle, allowing the models to be tested in future neutrino oscillation experiments.
We systematically construct realistic mass matrices for the type-I seesaw mechanism out of more than 20 trillion possibilities. We use only very generic assumptions from extended quark-lepton complementarity, i.e., the leptonic mixing angles between flavor and mass eigenstates are either maximal, or parameterized by a single small quantity epsilon that is of the order of the Cabibbo angle epsilon theta_C. The small quantity epsilon also describes all fermion mass hierarchies. We show that special cases often considered in the literature, such as having a symmetric Dirac mass matrix or small mixing among charged leptons, constitute only a tiny fraction of our possibilities. Moreover, we find that in most cases the spectrum of right-handed neutrino masses is only mildly hierarchical. As a result, we provide for the charged leptons and neutrinos a selected list of 1981 qualitatively different Yukawa coupling matrices (or textures) that are parameterized by the Cabibbo angle and allow for a perfect fit to current data. In addition, we also briefly show how the textures could be generated in explicit models from flavor symmetries.
We systematically investigate the parameter space of neutrino and charged lepton mass matrices for textures motivated by an extended quark-lepton complementarity. As the basic hypothesis, we postulate that all mixing angles in U_l and U_nu be either maximal or described by powers of a single small quantity epsilon ~ theta_C. All mass hierarchies are described by this epsilon as well. In this study, we do not assume specific forms for U_l and U_nu, such as large mixing coming from the neutrino sector only. We perform a systematic scan of the 262,144 generated mixing matrices for being compatible with current experimental data, and find a sample of 2,468 possibilities. We then analyze and classify the effective charged lepton and neutrino mass textures, where we especially focus on a subset of models getting under pressure for small theta_13. In addition, we predict the mixing angle distributions from our sample of all valid textures, and study the robustness of this prediction. We also demonstrate how our procedure can be extended to predictions of the Dirac and Majorana phases in U_PMNS. For instance, we find that CP conservation in neutrino oscillations is preferred, and we can impose a lower bound on the mixing matrix element for neutrinoless double beta decay.
We present a model for neutrino oscillations in the presence of a deconstructed non-gravitational large extra dimension compactified on the boundary of a two-dimensional disk. In the deconstructed phase, sub-mm lattice spacings are generated from the hierarchy of energy scales between 1 TeV and the usual B-L breaking scale 10^{15} GeV. Here, short distance cutoffs down to 1 eV can be motivated by the strong coupling behavior of gravity in local discrete extra dimensions. This could make it possible to probe the discretization of extra dimensions and non-trivial field configurations in theory spaces which have only a few sites, i.e., for coarse latticizations. Thus, the model has relevance to present and future precision neutrino oscillation experiments.
We consider discretized gravity in six dimensions, where the two extra dimensions have been compactified on a hyperbolic disk of constant curvature. We analyze different realizations of lattice gravity on the disk at the level of an effective field theory for massive gravitons. It is shown that the observed strong coupling scale of lattice gravity in discretized five-dimensional flat or warped space can be increased when the latticized fifth dimension is wrapped around a hyperbolic disk that has a non-trivial warp factor. As an application, we also discuss the generation of naturally small Dirac neutrino masses via a discrete volume suppression mechanism and discuss briefly collider implications of our model.
We consider a description of lattice gravity in six dimensions, where the two extra dimensions have been compactified on a warped hyperbolic disk of constant curvature. We analyze a fine-grained latticization of the hyperbolic disk in the context of an effective theory for massive gravitons. We find that in six-dimensional warped hyperbolic space, lattice gravity appears near the boundary of the disk more weakly coupled than in discretized five-dimensional flat or warped space. Specifically, near the IR branes, the local strong coupling scale can become as large as the local Planck scale.
We propose a lower limit on the size of a single discrete gravitational extra dimension in the context of an effective field theory for massive gravitons. The limit arises in this setup from the requirement that the Casimir energy density of quantum fields is in agreement with the observed dark energy density of the universe. The Casimir energy densities can be exponentially suppressed to an almost arbitrarily small value by the masses of heavy bulk fields, thereby allowing a tiny size of the extra dimension. This suppression is only restricted by the strong coupling scale of the theory, which is known to be related to the compactification scale via an UV/IR connection for local gravitational theory spaces. We thus obtain an upper limit on the compactification scale of the discrete gravitational extra dimension in the range 10^7 GeV...10^12 GeV, while the strong coupling scale is by a factor 10^2 larger than the compactification scale. We also comment on a possible cancelation of the gravitational contribution to the quantum effective potential.
We present a Higgsless Standard Model in six dimensions, based on the Standard Model gauge group SU(2)xU(1), with two flat extra dimensions compactified on a rectangle. The electroweak symmetry is broken by boundary conditions and realistic gauge boson masses can be accomodated by proper choice of the compactification scales and brane kinetic terms. With respect to oblique corrections, the agreement with electroweak precision tests is somewhat improved compared to the simplest five-dimensional Higgsless models.
We construct a family of simple gauge models in which three sterile neutrinos become naturally light by virtue of a generalized seesaw mechanism involving a chiral gauge symmetry. Examples where the chiral gauge group is SU(5)', SU(7)', SU(3)' and/or their descendants are presented. A unified model based on SO(10) x SO(10)' which embeds many of these models is constructed wherein three light sterile neutrinos are just as natural as the three ordinary neutrinos. These gauge models have relevance to current neutrino oscillation data, including the LSND anomaly.
We formulate a set of naturalness criteria for sterile neutrinos (ν') to be light, needed for reconciling the LSND neutrino anomaly with the other neutrino data. A light sterile neutrino becomes as natural as the light active neutrinos if it carries quantum numbers of a chiral gauge symmetry broken at the TeV scale. The simplest such theory is shown to be an SU(2) gauge theory with the ν' transforming as a spin 3/2 multiplet. We develop this model and show that it leads naturally to the phenomenologically viable (3+2) neutrino oscillation scheme. We also present next-to-minimal models for light sterile neutrinos based on a chiral U(1) gauge symmetry.
We demonstrate a dynamical origin for the dimension-five seesaw operator in dimensional deconstruction models. Light neutrino masses arise from the seesaw scale which corresponds to the inverse lattice spacing. It is shown that the deconstructing limit naturally prefers maximal leptonic mixing. Higher-order corrections which are allowed by gauge invariance can transform the bi-maximal into a bi-large mixing. These terms may appear to be non-renormalizable at scales smaller than the deconstruction scale.