16,827 research outputs found
Spontaneous CP Violation in the Next-to-Minimal Supersymmetric Standard Model Revisited
We re-examine spontaneous CP violation at the tree level in the context of
the next-to-minimal supersymmetric standard model (NMSSM) with two Higgs
doublets and a gauge singlet field. We analyse the most general Higgs potential
without a discrete Z_3 symmetry, and derive an upper bound on the mass of the
lightest neutral Higgs boson consistent with present experimental data. We
investigate, in particular, its dependence on the admixture and CP-violating
phase of the gauge singlet field, as well as on tan(beta). To assess the
viability of the spontaneous CP violation scenario, we estimate epsilon_K by
applying the mass insertion approximation. We find that a non-trivial flavour
structure in the soft-breaking A terms is required to account for the observed
CP violation in the neutral kaon sector. Furthermore, combining the
minimisation conditions for spontaneous CP violation with the constraints
coming from K0-K0bar mixing, we find that the upper bound on the lightest
Higgs-boson mass becomes stronger. We also point out that the electric dipole
moments of electron and neutron are a serious challenge for SUSY models with
spontaneous CP violation.Comment: 19 pages, LaTeX2e, 5 figures; matches the published versio
Phenomenology of LFV at low-energies and at the LHC: strategies to probe the SUSY seesaw
We study the impact of a type-I SUSY seesaw concerning lepton flavour
violation (LFV) at low-energies and at the LHC. At the LHC, decays, in combination with other
observables, render feasible the reconstruction of the masses of the
intermediate sleptons, and hence the study of mass
differences. If interpreted as being due to the violation of lepton flavour,
high-energy observables, such as large slepton mass splittings and flavour
violating neutralino and slepton decays, are expected to be accompanied by
low-energy manifestations of LFV such as radiative and three-body lepton
decays. We discuss how to devise strategies based in the interplay of slepton
mass splittings as might be observed at the LHC and low-energy LFV observables
to derive important information on the underlying mechanism of LFV.Comment: 6 pages, 4 figures. To appear in the proceedings of the 11th
International Workshop on Tau Lepton Physics (TAU2010), Manchester, UK, 13-17
September 201
Lepton flavour violation: physics potential of a Linear Collider
We revisit the potential of a Linear Collider concerning the study of lepton
flavour violation, in view of new LHC bounds and of the (very) recent
developments in lepton physics. Working in the framework of a type I
supersymmetric seesaw, we evaluate the prospects of observing seesaw-induced
lepton flavour violating final states of the type e \mu + missing energy,
arising from e+ e- and e- e- collisions. In both cases we address the potential
background from standard model and supersymmetric charged currents. We also
explore the possibility of electron and positron beam polarisation. The
statistical significance of the signal, even in the absence of kinematical
and/or detector cuts, renders the observation of such flavour violating events
feasible over large regions of the parameter space. We further consider the
\mu-\mu- + E^T_miss final state in the e- e- beam option finding that, due to a
very suppressed background, this process turns out to be a truly clear probe of
a supersymmetric seesaw, assuming the latter to be the unique source of lepton
flavour violation.Comment: 30 pages, 48 figure
Potential of a Linear Collider for Lepton Flavour Violation studies in the SUSY seesaw
We study the potential of an e+- e- Linear Collider for charged lepton
flavour violation studies in a supersymmetric framework where neutrino masses
and mixings are explained by a type-I seesaw. Focusing on e-mu flavour
transitions, we evaluate the background from standard model and supersymmetric
charged currents to the e mu + missing E_T signal. We study the energy
dependence of both signal and background, and the effect of beam polarisation
in increasing the signal over background significance. Finally, we consider the
mu- mu- + missing E_T final state in e- e- collisions that, despite being
signal suppressed by requiring two e-mu flavour transitions, is found to be a
clear signature of charged lepton flavour violation due to a very reduced
standard model background.Comment: 8 pages, 5 figures. To appear in the proceedings of "DISCRETE 2012 -
3rd Symposium on Prospects in the Physics of Discrete Symmetries", Lisbon,
Portugal, 3-7 December 201
Future dynamics in f(R) theories
The gravity theories provide an alternative way to explain the current
cosmic acceleration without invoking dark energy matter component. However, the
freedom in the choice of the functional forms of gives rise to the
problem of how to constrain and break the degeneracy among these gravity
theories on theoretical and/or observational grounds. In this paper to proceed
further with the investigation on the potentialities, difficulties and
limitations of gravity, we examine the question as to whether the future
dynamics can be used to break the degeneracy between gravity theories by
investigating the future dynamics of spatially homogeneous and isotropic dust
flat models in two gravity theories, namely the well known gravity and another by A. Aviles et al., whose motivation comes
from the cosmographic approach to gravity. To this end we perform a
detailed numerical study of the future dynamic of these flat model in these
theories taking into account the recent constraints on the cosmological
parameters made by the Planck team. We show that besides being powerful for
discriminating between gravity theories, the future dynamics technique
can also be used to determine the fate of the Universe in the framework of
these gravity theories. Moreover, there emerges from our numerical
analysis that if we do not invoke a dark energy component with
equation-of-state parameter one still has dust flat FLRW solution
with a big rip, if gravity deviates from general relativity via . We also show that FLRW dust solutions with do not
necessarily lead to singularity.Comment: 12 pages, 8 figures. V2: Generality and implications of the results
are emphasized, connection with the recent literature improved, typos
corrected, references adde
The ionizing sources of luminous compact HII regions in the RCW106 and RCW122 clouds
Given the rarity of young O star candidates, compact HII regions embedded in
dense molecular cores continue to serve as potential sites to peer into the
details of high-mass star formation. To uncover the ionizing sources of the
most luminous and compact HII regions embedded in the RCW106 and RCW122 giant
molecular clouds, known to be relatively nearby (2-4 kpc) and isolated, thus
providing an opportunity to examine spatial scales of a few hundred to a
thousand AU in size. High spatial resolution (0.3"), mid-infrared spectra
(R=350), including the fine structure lines [ArIII] and [NeII], were obtained
for four luminous compact HII regions, embedded inside the dense cores within
the RCW106 and RCW122 molecular cloud complexes. At this resolution, these
targets reveal point-like sources surrounded by nebulosity of different
morphologies, uncovering details at spatial dimensions of <1000AU. The
point-like sources display [ArIII] and [NeII] lines - the ratios of which are
used to estimate the temperature of the embedded sources. The derived
temperatures are indicative of mid-late O type objects for all the sources with
[ArIII] emission. Previously known characteristics of these targets from the
literature, including evidence of disk or accretion suggest that the identified
sources may grow more to become early-type O stars by the end of the star
formation process
FCNCs in supersymmetric multi-Higgs doublet models
We conduct a general discussion of supersymmetric models with three families
in the Higgs sector. We analyse the scalar potential, and investigate the
minima conditions, deriving the mass matrices for the scalar, pseudoscalar and
charged states. Depending on the Yukawa couplings and the Higgs spectrum, the
model might allow the occurrence of potentially dangerous flavour changing
neutral currents at the tree-level. We compute model-independent contributions
for several observables, and as an example we apply this general analysis to a
specific model of quark-Higgs interactions, discussing how compatibility with
current experimental data constrains the Higgs sector.Comment: 30 pages, 9 figures. Comments and references added. Final version
published in Physical Review
Disc Clearing of Young Stellar Objects: Evidence for Fast Inside-out Dispersal
The time-scale over which and the modality by which young stellar objects
(YSOs) disperse their circumstellar discs dramatically influences the eventual
formation and evolution of planetary systems. By means of extensive radiative
transfer (RT) modelling, we have developed a new set of diagnostic diagrams in
the infrared colour-colour plane (K-[24] vs. K-[8]), to aid with the
classification of the evolutionary stage of YSOs from photometric observations.
Our diagrams allow the differentiation of sources with unevolved (primordial)
discs from those evolving according to different clearing scenarios (e.g.
homologous depletion vs. inside-out dispersal), as well as from sources that
have already lost their disc. Classification of over 1500 sources in 15 nearby
star-forming regions reveals that approximately 39 % of the sources lie in the
primordial disc region, whereas between 31 % and 32 % disperse from the
inside-out and up to 22 % of the sources have already lost their disc. Less
than 2 % of the objects in our sample lie in the homogeneous draining regime.
Time-scales for the transition phase are estimated to be typically a few 10^5
years independent of stellar mass. Therefore, regardless of spectral type, we
conclude that currently available infrared photometric surveys point to fast
(of order 10 % of the global disc lifetime) inside-out clearing as the
preferred mode of disc dispersal.Comment: 31 pages, 21 figures, 6 tables, accepted for publication in MNRA
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