4,703 research outputs found
Invisible Z decay width bounds on active-sterile neutrino mixing in the (3+1) and (3+2) models
In this work we consider the standard model extended with singlet sterile
neutrinos with mass in the eV range and mixed with the active neutrinos. The
active-sterile neutrino mixing renders new contributions to the invisible Z
decay width which, in the case of light sterile neutrinos, depends on the
active-sterile mixing matrix elements only. We then use the current
experimental value of the invisible Z decay width to obtain bounds on these
mixing matrix elements for both (3+1) and (3+2) models.Comment: 10 pages, 5 figure
Explaining ATLAS and CMS Results Within the Reduced Minimal 3-3-1 model
Recently the ATLAS and CMS collaborations announced the discovery of a higgs
particle with a mass of GeV. The results are mildly consistent with
the Standard Model Higgs boson. However, the combined data from these
collaborations seem to point to an excess in the
channel. In this work we analyze under which conditions this excess may be
plausibly explained within the reduced minimal 3-3-1 model, while being
consistent with bb, WW, ZZ and channels. Moreover, we derive the
properties of the heavy neutral and the doubly charged scalars predicted by the
model. We then conclude that at a scale of a few TeV, this model provides a
good fit to the ATLAS and CMS signal strength measurements, and therefore
stands as an appealing alternative to the standard model.Comment: 23 pages, 9 figures. References adde
Combining type I and type II seesaw mechanisms in the minimal 3-3-1 model
The minimal 3-3-1 model is perturbative until energies around 4-5TeV, posing
a challenge to generate neutrino masses at eV scale, mainly if one aims to take
advantage of the seesaw mechanism. As a means to circumvent this problem we
propose a modification of the model such that it accommodates the type I and
type II seesaw mechanisms altogether. We show that the conjunction of both
mechanisms yield a neutrino mass expression suppressed by a high power of the
cutoff scale, , in its denominator. With such a suppression term we
naturally obtain neutrino masses at eV scale when is around few TeV. We
also investigate the size of lepton flavor violation through the process .Comment: about 15 pages, no figure
Lookback time bounds from energy conditions
In general relativity, the energy conditions are invoked to restrict general
energy-momentum tensors on physical grounds. We show that in the standard
Friedmann-Lemaitre-Robertson-Walker (FLRW) approach to cosmological modeling,
where the energy and matter components of the cosmic fluid are unknown, the
energy conditions provide model-independent bounds on the behavior of the
lookback time of cosmic sources as a function of the redshift for any value of
the spatial curvature. We also confront such bounds with a lookback time sample
which is built from the age estimates of 32 galaxies lying in the interval
and by assuming the total expanding age of the
Universe to be Gyr, as obtained from current cosmic microwave
background experiments. In agreement with previous results, we show that all
energy conditions seem to have been violated at some point of the recent past
of cosmic evolution.Comment: 7 pages, 3 figures. v2: Minor changes, published in Phys.Rev.D in the
present for
Energy Conditions and Cosmic Acceleration
In general relativity, the energy conditions are invoked to restrict general
energy-momentum tensors in different frameworks, and to derive
general results that hold in a variety of general contexts on physical grounds.
We show that in the standard Friedmann-Lemaitre-Robertson-Walker (FLRW)
approach, where the equation of state of the cosmological fluid is unknown, the
energy conditions provide model-independent bounds on the behavior of the
distance modulus of cosmic sources as a function of the redshift for any
spatial curvature. We use the most recent type Ia supernovae (SNe Ia)
observations, which include the new Hubble Space Telescope SNe Ia events, to
carry out a model-independent analysis of the energy conditions violation in
the context of the standard cosmology. We show that both the null (NEC), weak
(WEC) and dominant (DEC) conditions, which are associated with the existence of
the so-called phantom fields, seem to have been violated only recently (), whereas the condition for attractive gravity, i.e., the strong
energy condition (SEC) was firstly violated billions of years ago, at .Comment: 6 pages, 3 figures. v2: References added, misprints corrected,
published in Phys.Rev.D in the present for
- …