39 research outputs found
Divergences and Symmetries in Higgs-Gauge Unification Theories
In theories with extra dimensions the Standard Model Higgs field can be
identified with the internal components of higher-dimensional gauge fields
(Higgs-gauge unification). The higher-dimensional gauge symmetry prevents the
Higgs mass from quadratic divergences, but at the fixed points of the orbifold
this symmetry is broken and divergences can arise if U(1) subgroups are
conserved. We show that another symmetry, remnant of the internal rotation
group after orbifold projection, can avoid the generation of such divergences.Comment: 6 pages, 1 figure. Talk given at the "XL Rencontres de Moriond on
Electroweak Interactions and Unified Theories", La Thuile, Italy, 5-12 Mar
200
Is the 125 GeV Higgs the superpartner of a neutrino?
Recent LHC searches have provided strong evidence for the Higgs, a boson
whose gauge quantum numbers coincide with those of a SM fermion, the neutrino.
This raises the mandatory question of whether Higgs and neutrino can be related
by supersymmetry. We study this possibility in a model in which an approximate
R-symmetry acts as a lepton number. We show that Higgs physics resembles that
of the SM-Higgs with the exception of a novel invisible decay into Goldstino
and neutrino with a branching fraction that can be as large as ~10%. Based on
naturalness criteria, only stops and sbottoms are required to be lighter than
the TeV with a phenomenology dictated by the R-symmetry. They have novel decays
into quarks+leptons that could be seen at the LHC, allowing to distinguish
these scenarios from the ordinary MSSM.Comment: 19 pages, 8 figure
Minimal muon anomalous magnetic moment
We classify all possible one-particle (scalar and fermion) extensions of the
Standard Model that can contribute to the anomalous magnetic moment of leptons.
We review the cases already discussed in the literature and complete the
picture by performing the calculation for a fermionic doublet with hypercharge
-3/2. We conclude that, out of the listed possibilities, only two scalar
leptoquarks and the pseudoscalar of a peculiar two-Higgs-doublet model could be
the responsibles for the muon anomalous magnetic moment discrepancy. Were this
the case, this particles could be seen in the next LHC run. To this aim,
especially to test the leptoquark hypothesis, we suggest to look for final
states with tops and muons.Comment: 15 pages, uses axodra
Massive vectors and loop observables: the case
We discuss the use of massive vectors for the interpretation of some recent
experimental anomalies, with special attention to the muon . We restrict
our discussion to the case where the massive vector is embedded into a
spontaneously broken gauge symmetry, so that the predictions are not affected
by the choice of an arbitrary energy cut-off. Extended gauge symmetries,
however, typically impose strong constraints on the mass of the new vector
boson and for the muon they basically rule out, barring the case of
abelian gauge extensions, the explanation of the discrepancy in terms of a
single vector extension of the standard model. We finally comment on the use of
massive vectors for -meson decay and di-photon anomalies.Comment: 25 pages, 1 figure. References added, to appear in JHE
Probing a slepton Higgs on all frontiers
We study several aspects of supersymmetric models with a symmetry
where the Higgs doublet is identified with the superpartner of a lepton. We
derive new, stronger bounds on the gaugino masses based on current
measurements, and also propose ways to probe the model up to scales of
at future colliders. Since the
symmetry cannot be exact, we analyze the effects of -symmetry
breaking on neutrino masses and proton decay. In particular, we find that
getting the neutrino mixing angles to agree with experiments in a minimal model
requires a UV cutoff for the theory at around .Comment: 33 pages, 5 figures; v2: added reference. Matches version published
in JHE
Type-II Majoron Dark Matter
We discuss in detail the possibility that the ``type-II majoron'' -- that is,
the pseudo Nambu-Goldstone boson that arises in the context of the type-II
seesaw mechanism if the lepton number is spontaneously broken by an additional
singlet scalar -- account for the dark matter (DM) observed in the universe. We
study the requirements the model's parameters have to fulfill in order to
reproduce the measured DM relic abundance through two possible production
mechanisms in the early universe, freeze-in and misalignment, both during a
standard radiation-dominated era and early matter domination. We then study
possible signals of type-II majoron DM and the present and expected constraints
on the parameter space that can be obtained from cosmological observations,
direct detection experiments, and present and future searches for decaying DM
at neutrino telescopes and cosmic-ray experiments. We find that -- depending on
the majoron mass, the production mechanism, and the vacuum expectation value of
the type-II triplet -- all of the three decay modes (photons, electrons,
neutrinos) of majoron DM particles can yield observable signals at future
indirect searches for DM. Furthermore, in a corner of the parameter space,
detection of majoron DM is possible through electron recoil at running and
future direct detection experiments.Comment: 23 pages + appendices and bibliography, 6 figures; v2: typos
corrected, references and comments added, conclusions unchanged, version
accepted for publication in PR
General bounds on non-standard neutrino interactions
We derive model-independent bounds on production and detection non-standard
neutrino interactions (NSI). We find that the constraints for NSI parameters
are around O(10^{-2}) to O(10^{-1}). Furthermore, we review and update the
constraints on matter NSI. We conclude that the bounds on production and
detection NSI are generally one order of magnitude stronger than their matter
counterparts.Comment: 18 pages, revtex4, 1 axodraw figure. Minor changes, matches published
versio
Global bounds on the Type-III Seesaw
We derive general bounds on the Type-III Seesaw parameters from a global fit to flavor and electroweak precision data. We explore and compare three Type-III Seesaw realizations: a general scenario, where an arbitrary number of heavy triplets is integrated out without any further assumption, and the more constrained cases in which only 3 or 2 (minimal scenario) additional heavy states are included. The latter assumption implies rather non-trivial correlations in the Yukawa flavor structure of the model so as to reproduce the neutrino masses and mixings as measured in neutrino oscillations experiments and thus qualitative differences can be found with the more general scenario. In particular, we find that, while the bounds on most elements of the dimension 6 operator coefficients are of order 10â4 for the general and 3-triplet cases, the 2-triplet scenario is more strongly constrained with bounds between 10â5 and 10â7 for the different flavours. We also discuss how these correlations affect the present CMS constraints on the Type-III Seesaw in the minimal 2-triplet scenario
Equivalent effective Lagrangians for Scherk-Schwarz compactifications
We discuss the general form of the mass terms that can appear in the
effective field theories of coordinate-dependent compactifications a la
Scherk-Schwarz. As an illustrative example, we consider an interacting
five-dimensional theory compactified on the orbifold S^1/Z_2, with a fermion
subject to twisted periodicity conditions. We show how the same physics can be
described by equivalent effective Lagrangians for periodic fields, related by
field redefinitions and differing only in the form of the five-dimensional mass
terms. In a suitable limit, these mass terms can be localized at the orbifold
fixed points. We also show how to reconstruct the twist parameter from any
given mass terms of the allowed form. Finally, after mentioning some possible
generalizations of our results, we re-discuss the example of brane-induced
supersymmetry breaking in five-dimensional Poincare' supergravity, and comment
on its relation with gaugino condensation in M-theory.Comment: 17 pages, 3 figures. Published versio