Electric dipole moments from Yukawa phases in supersymmetric theories

We study quark and electron EDMs generated by Yukawa couplings in supersymmetric models with different gauge groups, using the EDM properties under flavour transformations. In the MSSM (or if soft terms are mediated below the unification scale) the one loop contributions to the neutron EDM are smaller than in previous computations based on numerical methods, although increasing as tan^3\beta. A neutron EDM close to the experimental limits can be generated in SU(5), if tan\beta is large, through the u-quark EDM d_u, proportional to tan^4\beta. This effect has to be taken into account also in SO(10) with large tan\beta, where d_u is comparable to the d-quark EDM, proportional to tan\beta.Comment: 14 pages, figures included, PS-file also available at http://www.ft.uam.es/~strumia/14Art/14Art.htm

Split Supersymmetry

The naturalness criterion applied to the cosmological constant implies a new-physics threshold at 10^-3 eV. Either the naturalness criterion fails, or this threshold does not influence particle dynamics at higher energies. It has been suggested that the Higgs naturalness problem may follow the same fate. We investigate this possibility and, abandoning the hierarchy problem, we use unification and dark matter as the only guiding principles. The model recently proposed by Arkani-Hamed and Dimopoulos emerges as a very interesting option. We study it in detail, analysing its structure, and the conditions for obtaining unification and dark matter.Comment: 29 pages, comments, corrections and references adde

Flavour violation in supersymmetric SO(10) unification with a type II seesaw mechanism

We study flavour violation in a supersymmetric SO(10) implementation of the type II seesaw mechanism, which provides a predictive realization of triplet leptogenesis. The experimental upper bounds on lepton flavour violating processes have a significant impact on the leptogenesis dynamics, in particular they exclude the strong washout regime. Requiring successful leptogenesis then constrains the otherwise largely unknown overall size of flavour-violating observables, thus yielding testable predictions. In particular, the branching ratio for mu -> e gamma lies within the reach of the MEG experiment if the superpartner spectrum is accessible at the LHC, and the supersymmetric contribution to epsilon_K can account for a significant part of the experimental value. We show that this scenario can be realized in a consistent SO(10) model achieving gauge symmetry breaking and doublet-triplet splitting in agreement with the proton decay bounds, improving on the MSSM prediction for alpha_3(m_Z), and reproducing the measured quark and lepton masses.Comment: 40 pages, 10 figures. Accepted for publication in JHE

Naturalness After LHC run I

Thanks to the discovery of the Higgs boson, the 8 TeV run of the LHC was a tremendous success. At the same time, the lack of signals of physics beyond the Standard Model was unexpected. Waiting for the first results of the 13 TeV run, as assessment of the implications of such a puzzling situation is appropriate. After a critical appraisal of the naturalness argument, we will discuss i) the status of models addressing the naturalness problem (supersymmetry and composite Higgs as prototypical examples) and ii) possible alternative models evading the naturalness argument. Copyright © 2016 by INFN

Electric dipole moments in supersymmetric theories

Intrinsic EDMs in microscopic systems at a level of sensitivity achievable in experiments under way or foreseen are predicted in supersymmetric unified theories. I describe this and other sources of measurable EDMs and I show how these sources can be distinguished through experiments in different systems.Comment: 5 pages, LaTex2e using amstex.sty, amssymb.sty, apalike.sty, no figs., to appear in Proceedings of the XXIV ITEP Winter School of Physic

Neutrino Masses and Mixing in Brane-World Theories

We present a comprehensive study of five-dimensional brane-world models for neutrino physics based on flat compactifications. Particular emphasis is put on the inclusion of bulk mass terms. We derive a number of general results for such brane-world models with bulk mass terms. In particular, in the limit of small brane-bulk couplings, the electroweak eigenstates are predominantly given as a superposition of three light states with non-trivial small admixtures of bulk states. As a consequence, neutrinos can undergo standard oscillations as well as oscillation into bulk Kaluza-Klein states. We use this structure to construct a specific model based on Z_2 orbifolding and bulk Majorana masses which is compatible with all observed oscillation phenomena. The solar neutrino deficit is explained by oscillations into sterile bulk states while the atmospheric neutrino deficit is due to mu - tau oscillations with naturally maximal mixing. In addition, the model can accommodate the LSND result and a significant neutrino dark matter component. We also analyze the constraints from supernova energy loss on neutrino brane-world theories and show that our specific model is consistent with these constraints.Comment: 45 pages, Latex, 1 eps-figur

General considerations on lepton mass matrices

We classify the flavour groups and representations providing, in the symmetric limit, an approximate description of lepton masses and mixings. We assume that the light neutrinos are of Majorana type and that the flavour symmetry directly constrains their mass matrix. The representations can be characterised by the dimension, type (real, pseudoreal, complex), and equivalence of its irreducible components, and in terms of such a classification we find only six viable cases. It turns out that the neutrinos are always either anarchical or have an inverted hierarchical spectrum. Therefore, if the hint of a normal hierarchical spectrum were confirmed, we would conclude (under the above assumption) that symmetry breaking effects must play a primary role in the understanding of neutrino flavour observables. \ua9 Copyright owned by the author(s) under the terms of the Creative Commons

Unbroken flavour symmetries vs lepton masses and mixings

Assuming that light neutrino masses are described by the Weinberg operator and constrained by a flavour symmetry, we identify all flavour groups and representations providing an approximate description of lepton masses and mixings in the symmetric limit. It turns out that the neutrinos are always either anarchical or have an inverted hierarchical spectrum. We then investigate whether the flavour theory predictions obtained within the Weinberg operator description are equivalent to those obtained within the full UV theory, using type I seesaw as a prototypical example. That is not always the case, and the conditions for the equivalence are found. If the hint of a normal hierarchical neutrino spectrum were confirmed, we would then conclude that either the symmetry breaking effects play a primary role in the understanding of neutrino flavour observables, or the UV flavour theory does not provide the same predictions as the effective one

Can an unbroken flavour symmetry provide an approximate description of lepton masses and mixing?

We provide a complete answer to the following question: what are the flavour groups and representations providing, in the symmetric limit, an approximate description of lepton masses and mixings? We assume that neutrino masses are described by the Wein- berg operator. We show that the pattern of lepton masses and mixings only depends on the dimension, type (real, pseudoreal, complex), and equivalence of the irreducible components of the flavour representation, and we find only six viable cases. In all cases the neutrinos are either anarchical or have an inverted hierarchical spectrum. In the context of SU(5) unification, only the anarchical option is allowed. Therefore, if the hint of a normal hier- archical spectrum were confirmed, we would conclude (under the above assumption) that symmetry breaking effects must play a leading order role in the understanding of neutrino flavour observables. In order to obtain the above results, we develop a simple algorithm to determine the form of the lepton masses and mixings directly from the structure of the decomposition of the flavour representation in irreducible components, without the need to specify the form of the lepton mass matrices