3,190 research outputs found

### A radiatively improved fermiophobic Higgs boson scenario

The naive fermiophobic scenario is unstable under radiative corrections, due
to the chiral-symmetry breaking induced by fermion mass terms. In a recent
study, the problem of including the radiative corrections has been tackled via
an effective field theory approach. The renormalized Yukawa couplings are
assumed to vanish at a high energy scale $\Lambda$, and their values at the
electroweak scale are computed via modified Renormalization Group Equations. We
show that, in case a fermiophobic Higgs scenario shows up at the LHC, a linear
collider program will be needed to accurately measure the radiative Yukawa
structure, and consequently constrain the $\Lambda$ scale.Comment: 7 pages, 3 figures, Proceedings of the 2011 International Workshop on
Future Linear Colliders (LCWS11), Granada (Spain), 26-30 September 201

### Looking for anomalous gamma-gamma-H and Z-gamma-H couplings at future linear collider

We consider the possibility of studying anomalous contributions to the
gamma-gamma-H and Z-gamma-H vertices through the process e-gamma--> e-H at
future e-gamma linear colliders, with Sqrt(S)=500-1500 GeV. We make a model
independent analysis based on SU(2)xU(1) invariant effective operators of dim=6
added to the standard model lagrangian. We consider a light Higgs boson (mostly
decaying in bar(b)-b pairs), and include all the relevant backgrounds. Initial
e-beam polarization effects are also analyzed. We find that the process
e-gamma--> e-H provides an excellent opportunity to strongly constrain both the
CP-even and the CP-odd anomalous contributions to the gamma-gamma-H and
Z-gamma-H vertices.Comment: LaTeX, 33 pages, 16 eps figures, extended section

### Quantum Spin Hall Effect in Graphene

We study the effects of spin orbit interactions on the low energy electronic
structure of a single plane of graphene. We find that in an experimentally
accessible low temperature regime the symmetry allowed spin orbit potential
converts graphene from an ideal two dimensional semimetallic state to a quantum
spin Hall insulator. This novel electronic state of matter is gapped in the
bulk and supports the quantized transport of spin and charge in gapless edge
states that propagate at the sample boundaries. The edge states are non chiral,
but they are insensitive to disorder because their directionality is correlated
with spin. The spin and charge conductances in these edge states are calculated
and the effects of temperature, chemical potential, Rashba coupling, disorder
and symmetry breaking fields are discussed.Comment: 4 pages, published versio

### Searching for massless dark photons at the lhc via higgs production

Massless dark photons are predicted in hidden-sector models with an unbroken dark U(1) gauge symmetry. A particular class of these models, aiming to solve both the Yukawa-hierarchy and the dark-matter problems of the standard model, manifests natural Higgs nondecoupling properties for the dark photon. As a consequence, we show that the Higgs-boson production at colliders followed by the Higgs decay into a photon and a dark photon provides a very promising dark-photon production mechanism. This decay gives rise to an unconventional Higgs signature characterized by a resonating gamma-plus-missing-momentum system with a monochromatic photon. We discuss the sensitivity of the LHC to the corresponding signal for a Higgs boson produced in both gluon-fusion and vector-boson-fusion channels. Â© Copyright owned by the author(s).Peer reviewe

### Measuring the SUSY Breaking Scale at the LHC in the Slepton NLSP Scenario of GMSB Models

We report a study on the measurement of the SUSY breaking scale sqrt(F) in
the framework of gauge-mediated supersymmetry breaking (GMSB) models at the
LHC. The work is focused on the GMSB scenario where a stau is the
next-to-lightest SUSY particle (NLSP) and decays into a gravitino with lifetime
c*tau_NLSP in the range 0.5 m to 1 km. We study the identification of
long-lived sleptons using the momentum and time of flight measurements in the
muon chambers of the ATLAS experiment. A realistic evaluation of the
statistical and systematic uncertainties on the measurement of the slepton mass
and lifetime is performed, based on a detailed simulation of the detector
response. Accessible range and precision on sqrt(F) achievable with a counting
method are assessed. Many features of our analysis can be extended to the study
of different theoretical frameworks with similar signatures at the LHC.Comment: 28 pages, 12 figures (18 eps files). Revised version v2(published in
JHEP): Some important corrections and additions to v

### Effect of balconies on air quality in deep street canyons

This study discusses the effect of balconies on the dispersion of vehicular pollutants inside a deep street
canyon and on the mass transfer rate between the canyon and the above atmosphere. 3D computational
fluid dynamics (CFD) simulations were performed considering the presence of balconies of different
dimensions in a deep street canyon with aspect ratio H/W Â¼ 3. The effect of two geometrical parameters
has been investigated: the balcony depth and the horizontal distance between two balconies, the other
geometrical parameters remaining constant. CFD simulations have been carried out adopting the scale
adaptive simulation (SAS) model. Results show that the presence of balconies can determine a significant
modification in the flow field inside the street canyon with a less homogeneous dispersion of pollutants
emitted by vehicles circulating in the street and a less effective mass exchange with the above atmosphere.
At the present models developed to assess pollutant concentration levels in street canyons do not
consider the presence of balconies. As consequence, an underestimation of real concentration levels
could occur. Therefore, results obtained can give a contribution in the development of more feasible air
pollution models in urban areas at local scale, and useful information for design of building facades that
minimize the entrapping of vehicular pollutants at pedestrian level in street canyon

### A SUSY Inspired Simplified Model for the 750 GeV Diphoton Excess

The evidence for a new singlet scalar particle from the 750 GeV diphoton
excess, and the absence of any other signal of new physics at the LHC so far,
suggest the existence of new coloured scalars. To study this possibility, we
propose a supersymmetry inspired simplified model, extending the Standard Model
with a singlet scalar and with heavy scalar fields carrying both colour and
electric charges -- the `squarks'. To allow the latter to decay, and to
generate the dark matter of the Universe, we also add a neutral fermion to the
particle content. We show that this model provides a two-parameter fit to the
observed diphoton excess consistently with cosmology, while the allowed
parameter space is bounded by the consistency of the model. In the context of
our simplified model this implies the existence of other supersymmetric
particles accessible at the LHC, rendering this scenario falsifiable. If this
excess persists, it will imply a paradigm shift in assessing supersymmetry
breaking and the role of scalars in low scale physics.Comment: 7 pages, 2 figures, SUSY incarnat

### Ultrahigh energy neutrino scattering onto relic light neutrinos in galactic halo as a possible source of highest energy extragalactic cosmic rays

The diffuse relic neutrinos with light mass are transparent to Ultrahigh
energy (UHE) neutrinos at thousands EeV, born by photoproduction of pions by
UHE protons on relic 2.73 K BBR radiation and originated in AGNs at cosmic
distances. However these UHE $\nu$s may interact with those (mainly heaviest
$\nu_{\mu_r}$, $\nu_{\tau_r}$ and respective antineutrinos) clustered into HDM
galactic halos. UHE photons or protons, secondaries of $\nu\nu_r$ scattering,
might be the final observed signature of such high-energy chain reactions and
may be responsible of the highest extragalactic cosmic-ray (CR) events. The
chain-reactions conversion efficiency, ramifications and energetics are
considered for the October 1991 CR event at 320 EeV observed by the Fly's Eye
detector in Utah. These quantities seem compatible with the distance, direction
and power (observed at MeV gamma energies) of the Seyfert galaxy MCG 8-11-11.
The $\nu\nu_r$ interaction probability is favoured by at least three order of
magnitude with respect to a direct $\nu$ scattering onto the Earth atmosphere.
Therefore, it may better explain the extragalactic origin of the puzzling 320
EeV event, while offering indirect evidence of a hot dark galactic halo of
light (i.e., $m_\nu\sim$ tens eV) neutrinos, probably of tau flavour.Comment: 25 pages, 1 figure minor corrections, updated references. In press in
AP

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