5,597 research outputs found
Scheming in the SMEFT
We discuss the constraints on the Standard Model Effective Field Theory
inferred from global fits to electroweak data. Special attention is paid to two
unconstrained combinations of Wilson coefficients that are present when the
analysis is restricted to measurements of
scatterings. We illustrate how these unconstrained directions arise due to a
reparameterization invariance that characterizes
processes but is not respected in
scatterings. This invariance is independent of the operator basis adopted and
of the choice of the input parameters. This is verified comparing the results
obtained in the {} input scheme with
those of a {} scheme.Comment: 5 + 1 pages, 2 figures. Contribution to the proceedings of EPS-HEP
2017, European Physical Society conference on High Energy Physics, 5-12 July
2017, Venice, Ital
Higgs physics beyond the SM: the non-linear EFT approach
Depending on whether electroweak physics beyond the Standard Model is based
on a linear or on a non-linear implementation of the electroweak symmetry
breaking, a linear or a chiral Effective Lagrangian is more appropriate. In
this talk, the main low-energy signals that allow to recognize whether the
observed Higgs scalar is a dynamical (composite) particle or rather an
elementary one are presented, in a model-independent way. The patterns of
effective couplings produced upon the assumption of specific composite Higgs
models are also discussed.Comment: 8 pages, 1 figure. Proceedings of the talk given at the XXIXth
Rencontres de Physique de la Vall\'ee d'Aoste, La Thuile (Italy), March 201
Signatures of dynamical scalars
Effective Lagrangians represent an important, model independent tool for
studying physics beyond the Standard Model, via its impact on electroweak scale
observables. In particular, two different effective descriptions may be
appropriate, depending on how the electroweak symmetry breaking is realized at
high energies: a linear effective Lagrangian is best suited in presence of
linear dynamics, while a non-linear -chiral- one is more pertinent for
scenarios featuring a non-linear realization. In this talk I will present a few
examples of low-energy signals that differentiate the phenomenology of the two
descriptions, thus providing a powerful insight into the nature of the Higgs
boson.Comment: 4 pages; contribution to the Proceedings of the 50th Rencontres de
Moriond, Electroweak Session. arXiv admin note: substantial text overlap with
arXiv:1505.0063
Scheming in the SMEFT... and a reparameterization invariance!
We explain a reparameterization invariance in the Standard Model Effective
Field Theory present when considering scatterings (with a fermion) and how this leads to unconstrained
combinations of Wilson coefficients in global data analyses restricted to these
measurements. We develop a input parameter
scheme and compare results to the case when an input parameter set
is used to constrain this effective
theory from the global data set, confirming the input parameter independence of
the unconstrained combinations of Wilson coefficients, and supporting the
reparameterization invariance explanation. We discuss some conceptual issues
related to these degeneracies that are relevant for LHC data reporting and
analysis.Comment: 41 pages, 8 tables, 8 figures. addendum in appendix - results
obtained allowing two independent flavor contractions for the operator Q_ll
in the U(3)^5 flavor symmetric limi
The Neutrino Option
The minimal seesaw scenario can radiatively generate the Higgs potential to
induce electroweak symmetry breaking while supplying an origin of the Higgs
vacuum expectation value from an underlying Majorana scale. If the Higgs
potential and (derived) electroweak scale have this origin, the heavy singlet states are expected to reside at for couplings
between the Majorana sector and the Standard Model. In this framework, the
challenge of the electroweak scale hierarchy problem is replaced with a need to
generate or accommodate PeV Majorana mass scales in ultraviolet models; the
usual hierarchy problem is absent as the electroweak scale is not a fundamental
scale.Comment: 5 pages, 5 figures, one radiative potential. Updated version
consistent with the one accepted for publication in PRL (title changed in the
journal
Examining the neutrino option
The neutrino option is a scenario where the electroweak scale, and thereby
the Higgs mass, is generated simultaneously with neutrino masses in the seesaw
model. This occurs via the leading one loop and tree level diagrams matching
the seesaw model onto the Standard Model Effective Field Theory. We advance the
study of this scenario by determining one loop corrections to the leading order
matching results systematically, performing a detailed numerical analysis of
the consistency of this approach with Neutrino data and the Standard Model
particle masses, and by examining the embedding of this scenario into a more
ultraviolet complete model. We find that the neutrino option remains a viable
and intriguing scenario to explain the origin of observed particle masses.Comment: 26 pages, 6 figures v2, typo corrections and refs adde
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