256 research outputs found
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
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