Theoretical Uncertainties in Proton Lifetime Estimates

We recapitulate the primary sources of theoretical uncertainties in proton lifetime estimates in renormalizable, four-dimensional and non-supersymmetric grand unifications that represent the most conservative framework in which this question may be addressed at the perturbative level. We point out that many of these uncertainties are so severe that there are only very few scenarios in which an NLO approach, as crucial as it is for a real testability of any specific model, is actually sensible. Among these, the most promising seems to be the minimal renormalizable SO(10) GUT whose high-energy gauge symmetry is spontaneously broken by the adjoint and the five-index antisymmetric irreducible representations.Comment: 6 pages, 1 figure, prepared for the proceedings of the CETUP* 2015 program (Neutrinos and Beyond Standard Model Physics session: July 6 - July 17, 2015), Lead, South Dakot

Grain boundary stresses in elastic materials

A simple analytical model of intergranular normal stresses is proposed for a general elastic polycrystalline material with arbitrary shaped and randomly oriented grains under uniform loading. The model provides algebraic expressions for the local grain-boundary-normal stress and the corresponding uncertainties, as a function of the grain-boundary type, its inclination with respect to the direction of external loading and material-elasticity parameters. The knowledge of intergranular normal stresses is a necessary prerequisite in any local damage modeling approach, e.g., to predict the intergranular stress-corrosion cracking, grain-boundary sliding or fatigue-crack-initiation sites in structural materials. The model is derived in a perturbative manner, starting with the exact solution of a simple setup and later successively refining it to account for higher order complexities of realistic polycrystalline materials. In the simplest scenario, a bicrystal model is embedded in an isotropic elastic medium and solved for uniaxial loading conditions, assuming 1D Reuss and Voigt approximations on different length scales. In the final iteration, the grain boundary becomes a part of a 3D structure consisting of five 1D chains with arbitrary number of grains and surrounded by an anisotropic elastic medium. Constitutive equations can be solved for arbitrary uniform loading, for any grain-boundary type and choice of elastic polycrystalline material. At each iteration, the algebraic expressions for the local grain-boundary-normal stress, along with the corresponding statistical distributions, are derived and their accuracy systematically verified and validated against the finite element simulation results of different Voronoi microstructures.Comment: 28 pages, 20 figure

Supersymmetry breaking induced by radiative corrections

We show that simultaneous gauge and supersymmetry breaking can be induced by radiative corrections, a la Coleman-Weinberg. When a certain correlation among the superpotential parameters is present, a local supersymmetry-breaking minimum is found in the effective potential of a gauge non-singlet field, in a region where the tree-level potential is almost flat. Supersymmetry breaking is then transmitted to the MSSM through gauge and chiral messenger loops, thus avoiding the suppression of gaugino masses characteristic of direct gauge mediation models. The use of a single field ensures that no dangerous tachyonic scalar masses are generated at the one-loop level. We illustrate this mechanism with an explicit example based on an SU(5) model with a single adjoint. An interesting feature of the scenario is that the GUT scale is increased with respect to standard unification, thus allowing for a larger colour Higgs triplet mass, as preferred by the experimental lower bound on the proton lifetime.Comment: 22 pages, 3 figures. Two references added, small redactional changes, some discussion improved. Results unchange

Challenging the minimal supersymmetric SU(5) model

8 pages, 2 figures, plenary talk presented by B.B. at the VIIth International Conference on Interconnections between Particle Physics and Cosmology PPC13, Deadwood, South Dakota, July 8-13, 2013. To be published in the ProceedingsWe review the main constraints on the parameter space of the minimal renormalizable supersymmetric SU(5) grand unified theory. They consist of the Higgs mass, proton decay, electroweak symmetry breaking and fermion masses. Superpartner masses are constrained both from below and from above, giving hope for confirming or definitely ruling out the theory in the future. This contribution is based on Ref. [1]

Verbesina longipes Hemsl.

We explore the potential of a selected model of radiative neutrino masses to be implemented in a renormalizable SU(5) unification framework. The Zee-type model under consideration uncovers the SU(5) representations in which the new fields are embedded and which may contain also other light states leading to the unification of gauge couplings. We perform an exhaustive search which reveals specific patterns of new states and demonstrate that such patterns are consistent with a general choice of relevant scalar potential. It turns out that all of the specific scenarios which lead to successful unification include the colored scalars testable at the LHC

Resurrecting the minimal renormalizable supersymmetric SU(5) model

53 pages, 13 figuresInternational audienceIt is a well-known fact that the minimal renormalizable supersymmetric SU(5) model is ruled out assuming superpartner masses of the order of a few TeV. Giving up this constraint and assuming only SU(5) boundary conditions for the soft terms, we find that the model is still alive. The viable region of the parameter space typically features superpartner masses of order $10^2$ to $10^4$ TeV, with tan beta values between 2 and 5, but lighter spectra with single states around 10 TeV are also possible. The main constraints come from proton decay, the Higgs mass, the requirement of the SU(5) spectrum being reasonably below the Planck scale, and the lifetime of the universe. A generic feature of the model is metastability of the electroweak vacuum. In the absence of a suitable dark matter particle in the neutralino sector, a light (order GeV or smaller) gravitino is a natural candidate

A single grain boundary parameter to characterize normal stress fluctuations in materials with elastic cubic grains

International audienceA finite element analysis of intergranular normal stresses is performed in order to identify a possible statistical correlationbetween the intergranular normal stresses and the corresponding grain boundary type within a polycrystalline aggregate. Elasticcontinuum grains of cubic lattice symmetry are assumed in the analysis. Meaningful results are obtained by analyzing the first twostatistical moments of grain boundary normal stresses obtained on several grain boundary types.Among the five macroscopic parameters (5D) describing a grain boundary, the orientation of the grain boundary plane relativeto the two adjacent crystal lattices (4D) is found to be the most important property influencing the normal stresses. To accountfor it, a single new (1D) parameter E12 is introduced, which combines the geometrical aspect of grain boundary with its materialproperties and measures the average stiffness of grain boundary neighborhood along the grain boundary normal direction. It isdemonstrated that E12, in combination with Zener elastic anisotropy index A, is able to accurately predict normal stress fluctuationson any grain boundary type in a material with cubic lattice symmetry. It is argued that largest normal stresses most likely form ongrain boundaries whose normals are oriented along the stiffest direction in both adjacent grains ( for crystals with A > 1 or for crystals with A < 1). Moreover, it is shown that classification of grain boundaries according to their propensity to exhibitlarge normal stresses can be trivially reduced to the (analytical) calculation of the corresponding effective stiffness parameter E12.A few practical implications are discussed relevant to intergranular stress-corrosion cracking of Coincidence Site Lattice grainboundaries. For example, it is highlighted that in face-centered cubic materials the coherent sigma3 twin grain boundaries, which areknown for their very high cracking resistance, nevertheless exhibit largest intergranular normal stresses, indicating that crackingresistance is associated with high grain boundary strength