25,381 research outputs found
Light charged Higgs boson production at the Large Hadron electron Collider
We study the production of a light charged Higgs boson at the future Large
Hadron electron Collider (LHeC), through the process
considering both decay channels and in the final state. We analyse these processes in the context of the
2-Higgs Doublet Model Type III (2HDM-III) and assess the LHeC sensitivity to
such signals against a variety of both reducible and irreducible
backgrounds. We confirm that prospects for detection in the 2HDM-III are
excellent assuming standard collider energy and luminosity conditions.Comment: 12 pages, 12 figures. Accepted in Physical Review
Axion Like Particles and the Inverse Seesaw Mechanism
Light pseudoscalars known as axion like particles (ALPs) may be behind
physical phenomena like the Universe transparency to ultra-energetic photons,
the soft -ray excess from the Coma cluster, and the 3.5 keV line. We
explore the connection of these particles with the inverse seesaw (ISS)
mechanism for neutrino mass generation. We propose a very restrictive setting
where the scalar field hosting the ALP is also responsible for generating the
ISS mass scales through its vacuum expectation value on gravity induced
nonrenormalizable operators. A discrete gauge symmetry protects the theory from
the appearance of overly strong gravitational effects and discrete anomaly
cancellation imposes strong constraints on the order of the group. The
anomalous U symmetry leading to the ALP is an extended lepton number and
the protective discrete symmetry can be always chosen as a subgroup of a
combination of the lepton number and the baryon number.Comment: 29pp. v4: published version with erratum. Conclusions unchange
Vacuum stability conditions of the economical 3-3-1 model from copositivity
By applying copositivity criterion to the scalar potential of the economical
model, we derive necessary and sufficient bounded-from-below conditions
at tree level. Although these are a large number of intricate inequalities for
the dimensionless parameters of the scalar potential, we present general
enlightening relations in this work. Additionally, we use constraints coming
from the minimization of the scalar potential by means of the orbit space
method, the positivity of the squared masses of the extra scalars, the Higgs
boson mass, the gauge boson mass and its mixing angle with the SM
boson in order to further restrict the parameter space of this model.Comment: 22 pages, 7 figures, added text and references. Matches published
versio
Dynamical Mass Generation and Confinement in Maxwell-Chern-Simons Planar Quantum Electrodynamics
We study the non-perturbative phenomena of Dynamical Mass Generation and
Confinement by truncating at the non-perturbative level the Schwinger-Dyson
equations in Maxwell-Chern-Simons planar quantum electrodynamics. We obtain
numerical solutions for the fermion propagator in Landau gauge within the
so-called rainbow approximation. A comparison with the ordinary theory without
the Chern-Simons term is presented.Comment: 9 pages, 9 figures; prepared for the XIV Mexican School of Particles
and Fields, 4-12 November 2010, Morelia, Michoacan, Mexic
Testing the Modern Merger Hypothesis via the Assembly of Massive Blue Elliptical Galaxies in the Local Universe
The modern merger hypothesis offers a method of forming a new elliptical
galaxy through merging two equal-mass, gas-rich disk galaxies fuelling a
nuclear starburst followed by efficient quenching and dynamical stabilization.
A key prediction of this scenario is a central concentration of young stars
during the brief phase of morphological transformation from highly-disturbed
remnant to new elliptical galaxy. To test this aspect of the merger hypothesis,
we use integral field spectroscopy to track the stellar Balmer absorption and
4000\AA\ break strength indices as a function of galactic radius for 12 massive
(), nearby (),
visually-selected plausible new ellipticals with blue-cloud optical colours and
varying degrees of morphological peculiarities. We find that these index values
and their radial dependence correlate with specific morphological features such
that the most disturbed galaxies have the smallest 4000\AA\ break strengths and
the largest Balmer absorption values. Overall, two-thirds of our sample are
inconsistent with the predictions of the modern merger hypothesis. Of these
eight, half exhibit signatures consistent with recent minor merger
interactions. The other half have star formation histories similar to local,
quiescent early-type galaxies. Of the remaining four galaxies, three have the
strong morphological disturbances and star-forming optical colours consistent
with being remnants of recent, gas-rich major mergers, but exhibit a weak,
central burst consistent with forming of their stars. The final
galaxy possesses spectroscopic signatures of a strong, centrally-concentrated
starburst and quiescent core optical colours indicative of recent quenching
(i.e., a post-starburst signature) as prescribed by the modern merger
hypothesis.Comment: 25 pages, 37 figures, accepted to MNRA
Probing phase coexistence and stabilization of the spin-ordered ferrimagnetic state by Calcium addition in the YBa_{1-x}Ca_{x}Co_{2}O_{5.5} layered cobaltites using neutron diffraction
In this article we study the effects of a partial substitution of Ba with the
smaller cation Ca in the layered cobaltites YBaCo_2O_{5+\delta} for \delta
\approx 0.5. Neutron thermodiffractograms are reported for the compounds
YBa_{0.95}Ca_{0.05}Co_2O_{5.5} (x_{Ca}=0.05) and YBa_{0.90}Ca_{0.10}Co_2O_{5.5}
(x_{Ca}=0.10) in the temperature range 20 K \leq T \leq 300 K, as well as high
resolution neutron diffraction experiments at selected temperatures for the
samples x_{Ca}=0.05, x_{Ca}=0.10 and the parent compound x_{Ca}=0. We have
found the magnetic properties to be strongly affected by the cationic
substitution. Although the "122" perovskite structure seems unaffected by Ca
addition, the magnetic arrangements of Co ions are drastically modified: the
antiferromagnetic (AFM) long-range order is destroyed, and a ferrimagnetic
phase with spin state order is stabilized below T \sim 290 K. For the sample
with x_{Ca}=0.05 a fraction of AFM phase coexists with the ferrimagnetic one
below T \sim 190 K, whereas for x_{Ca}=0.10 the AFM order is completely lost.
The systematic refinement of the whole series has allowed for a better
understanding of the observed low-temperature diffraction patterns of the
parent compound, YBaCo_2O_{5.5}, which had not yet been clarified. A two-phase
scenario is proposed for the x_{Ca}=0 compound which is compatible with the
phase coexistence observed in the x_{Ca}=0.05 sample
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