950 research outputs found
The Axion and the Goldstone Higgs
We consider the renormalizable -model, in which the
Higgs particle has a pseudo-Nambu-Goldstone boson character, and explore what
the minimal field extension required to implement the Peccei-Quinn symmetry
(PQ) is, within the partial compositeness scenario. It turns out that the
minimal model does not require the enlargement of the exotic fermionic sector,
but only the addition of a singlet scalar: it is sufficient that the exotic
fermions involved in partial compositeness and the singlet scalar become
charged under Peccei-Quinn transformations. We explore the phenomenological
predictions for photonic signals in axion searches for all models discussed.
Because of the constraints imposed on the exotic fermion sector by the Standard
Model fermion masses, the expected range of allowed axion-photon couplings
turns out to be generically narrowed with respect to that of standard invisible
axion models, impacting the experimental quest.Comment: 31 pages, 2 Figures. Description improved, results unchange
Determining the Neutrino Mass Hierarchy and CP Violation in NOvA with a Second Off-Axis Detector
We consider a Super-NOvA-like experimental configuration based on the use of
two detectors in a long-baseline experiment as NOvA. We take the far detector
as in the present NOvA proposal and add a second detector at a shorter
baseline. The location of the second off-axis detector is chosen such that the
ratio L/E is the same for both detectors, being L the baseline and E the
neutrino energy. We consider liquid argon and water-Cherenkov techniques for
the second off-axis detector and study, for different experimental setups, the
detector mass required for the determination of the neutrino mass hierarchy,
for different values of theta13. We also study the capabilities of such an
experimental setup for determining CP violation in the neutrino sector. Our
results show that by adding a second off-axis detector a remarkable enhancement
on the capabilities of the current NOvA experiment could be achieved.Comment: 20 p
Are small neutrino masses unveiling the missing mass problem of the Universe?
We present a scenario in which a remarkably simple relation linking dark
matter properties and neutrino masses naturally emerges. This framework points
towards a low energy theory where the neutrino mass originates from the
existence of a light scalar dark matter particle in the MeV mass range. A very
surprising aspect of this scenario is that the required MeV dark matter is one
of the favoured candidates to explain the mysterious emission of 511 keV
photons in the centre of our galaxy. A possible interpretation of these
findings is that dark matter is the stepping stone of a theory beyond the
standard model instead of being an embarrassing relic whose energy density must
be accounted for in any successful model building.Comment: 4pages, 2 figures. Two paragraphs have been added. One for the
complex case; the other one for the UV completio
How BAO measurements can fail to detect quintessence
We model the nonlinear growth of cosmic structure in different dark energy
models, using large volume N-body simulations. We consider a range of
quintessence models which feature both rapidly and slowly varying dark energy
equations of state, and compare the growth of structure to that in a universe
with a cosmological constant. The adoption of a quintessence model changes the
expansion history of the universe, the form of the linear theory power spectrum
and can alter key observables, such as the horizon scale and the distance to
last scattering. The difference in structure formation can be explained to
first order by the difference in growth factor at a given epoch; this scaling
also accounts for the nonlinear growth at the 15% level. We find that
quintessence models which feature late , rapid transitions towards
in the equation of state, can have identical baryonic acoustic
oscillation (BAO) peak positions to those in CDM, despite being very
different from CDM both today and at high redshifts .
We find that a second class of models which feature non-negligible amounts of
dark energy at early times cannot be distinguished from CDM using
measurements of the mass function or the BAO. These results highlight the need
to accurately model quintessence dark energy in N-body simulations when testing
cosmological probes of dynamical dark energy.Comment: 10 pages, 7 figures, to appear in the Invisible Univers International
Conference AIP proceedings serie
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