159 research outputs found
Strategies to link tiny neutrino masses with huge missing mass of the Universe
With the start of the LHC, interest in electroweak scale models for the
neutrino mass has grown. In this letter, we review two specific models that
simultaneously explain neutrino masses and provide a suitable DM candidate. We
discuss the implications of these models for various observations and
experiments including the LHC, Lepton Flavor Violating (LFV) rare decays,
direct and indirect dark matter searches and Kaon decay.Comment: 17 pages, one diagram, talk given at International Conference on
Flavor Physics in the LHC era in Singapor
A novel ultrafast-low-dose computed tomography protocol allows concomitant coronary artery evaluation and lung cancer screening
BACKGROUND:Cardiac computed tomography (CT) is often performed in patients who are at high risk for lung cancer in whom screening is currently recommended. We tested diagnostic ability and radiation exposure of a novel ultra-low-dose CT protocol that allows concomitant coronary artery evaluation and lung screening.
METHODS: We studied 30 current or former heavy smoker subjects with suspected or known coronary artery disease who underwent CT assessment of both coronary arteries and thoracic area (Revolution CT, General Electric). A new ultrafast-low-dose single protocol was used for ECG-gated helical acquisition of the heart and the whole chest. A single IV iodine bolus (70-90 ml) was used. All patients with CT evidence of coronary stenosis underwent also invasive coronary angiography.
RESULTS: All the coronary segments were assessable in 28/30 (93%) patients. Only 8 coronary segments were not assessable in 2 patients due to motion artefacts (assessability: 98%; 477/485 segments). In the assessable segments, 20/21 significant stenoses (> 70% reduction of vessel diameter) were correctly diagnosed. Pulmonary nodules were detected in 5 patients, thus requiring to schedule follow-up surveillance CT thorax. Effective dose was 1.3 ± 0.9 mSv (range: 0.8-3.2 mSv). Noteworthy, no contrast or radiation dose increment was required with the new protocol as compared to conventional coronary CT protocol.
CONCLUSIONS:The novel ultrafast-low-dose CT protocol allows lung cancer screening at time of coronary artery evaluation. The new approach might enhance the cost-effectiveness of coronary CT in heavy smokers with suspected or known coronary artery disease
Finite Gluon Fusion Amplitude in the Gauge-Higgs Unification
We show that the gluon fusion amplitude in the gauge-Higgs unification
scenario is finite in any dimension regardless of its nonrenormalizability.
This result is supported by the fact that the local operator describing the
gluon fusion process is forbidden by the higher dimensional gauge invariance.
We explicitly calculate the gluon fusion amplitude in an arbitrary dimensional
gauge-Higgs unification model and indeed obtain the finite result.Comment: 15 pages, final version to appear in MPL
Precision Measurements and Fermion Geography in the Randall-Sundrum Model Revisited
We re-examine the implications of allowing fermion fields to propagate in the
five-dimensional bulk of the Randall-Sundrum (RS) localized gravity model. We
find that mixing between the Standard Model top quark and its Kaluza Klein
excitations generates large contributions to the rho parameter and consequently
restricts the fundamental RS scale to lie above 100 TeV. To circumvent this
bound we propose a `mixed' scenario which localizes the third generation
fermions on the TeV brane and allows the lighter generations to propagate in
the full five-dimensional bulk. We show that this construction naturally
reproduces the observed m_c / m_t and m_s / m_b hierarchies. We explore the
signatures of this scenario in precision measurements and future high energy
collider experiments. We find that the region of parameter space that addresses
the hierarchies of fermion Yukawa couplings permits a Higgs boson with a mass
of 500 GeV and remains otherwise invisible at the LHC. However, the entire
parameter region consistent with electroweak precision data is testable at
future linear colliders. We briefly discuss possible constraints on this
scenario arising from flavor changing neutral currents.Comment: 44 pages, 20 ps files; VII, typos fixed and refs adde
A Simple Explanation for DAMA with Moderate Channeling
We consider the possibility that the DAMA signal arises from channeled events
in simple models where the dark matter interaction with nuclei is suppressed at
small momenta. As with the standard WIMP, these models have two parameters (the
dark matter mass and the size of the cross-section), without the need to
introduce an additional energy threshold type of parameter. We find that they
can be consistent with channeling fractions as low as about ~ 15%, so long as
at least ~70% of the nuclear recoil energy for channeled events is deposited
electronically. Given that there are reasons not to expect very large
channeling fractions, these scenarios make the channeling explanation of DAMA
much more compelling.Comment: 6 pages, 2 figure
The W boson production cross section at the LHC through O(alpha_s^2)
We compute the O(alpha_s^2) QCD corrections to the fully differential
cross-section pp \to W X \to l \nu X, retaining all effects from spin
correlations. The knowledge of these corrections makes it possible to calculate
with high precision the W boson production rate and acceptance at the LHC,
subject to realistic cuts on the lepton and missing energy distributions. For
certain choices of cuts we find large corrections when going from
next-to-leading order (NLO) to next-to-next-to-leading order (NNLO) in
perturbation theory. These corrections are significantly larger than those
obtained by parton-shower event generators merged with NLO calculations. Our
calculation may be used to assess and significantly reduce the QCD
uncertainties in the many studies of boson production planned at the LHC.Comment: 4 pages, revte
The electroweak form factor \hat{\kappa}(q^2) and the running of \sin^2 \hat{\theta}_W
Gauge independent form factors \rho^(e; e) and \hat{\kappa}^(e; e)(q^2) for
Moller scattering at s << m_W^2 are derived. It is pointed out that
\hat{\kappa}^(e; e) is very different from its counterparts in other processes.
The relation between the effective parameter \hat{\kappa}^(e; e)(q^2,\mu)
\sin^2 \hat{\theta}_W(\mu) and \sin^2 \theta_eff is derived in a
scale-independent manner. A gauge and process-independent running parameter
\sin^2 \hat{\theta}_W (q^2), based on the pinch-technique self-energy a_{\gamma
Z} (q^2), is discussed for all q^2 values. At q^2=0 it absorbs very accurately
the Czarnecki-Marciano calculation of the Moller scattering asymmetry at low s
values, and at q^2 = m^2_Z it is rather close to \sin^2 \theta_eff. The q^2
dependence of \sin^2 \hat{\theta}_W (q^2) is displayed in the space and
time-like domains.Comment: A new paragraph has been inserted at the beginning of the discussion
in Section
Contrasting Supersymmetry and Universal Extra Dimensions at the CLIC Multi-TeV e+e- Collider
Universal extra dimensions and supersymmetry have rather similar experimental
signatures at hadron colliders. The proper interpretation of an LHC discovery
in either case may therefore require further data from a lepton collider. In
this paper we identify methods for discriminating between the two scenarios at
the linear collider. We study the processes of Kaluza-Klein muon pair
production in universal extra dimensions in parallel to smuon pair production
in supersymmetry, accounting for the effects of detector resolution, beam-beam
interactions and accelerator induced backgrounds. We find that the angular
distributions of the final state muons, the energy spectrum of the radiative
return photon and the total cross-section measurement are powerful
discriminators between the two models. Accurate determination of the particle
masses can be obtained both by a study of the momentum spectrum of the final
state leptons and by a scan of the particle pair production thresholds. We also
calculate the production rates of various Kaluza-Klein particles and discuss
the associated signatures.Comment: 20 pages, 13 figures, typeset in JHEP style, uses axodraw. Added new
section 5. Version to appear in JHE
Combining Monte Carlo generators with next-to-next-to-leading order calculations: event reweighting for Higgs boson production at the LHC
We study a phenomenological ansatz for merging next-to-next-to-leading order
(NNLO) calculations with Monte Carlo event generators. We reweight them to
match bin-integrated NNLO differential distributions. To test this procedure,
we study the Higgs boson production cross-section at the LHC, for which a fully
differential partonic NNLO calculation is available. We normalize PYTHIA and
MC@NLO Monte Carlo events for Higgs production in the gluon fusion channel to
reproduce the bin integrated NNLO double differential distribution in the
transverse momentum and rapidity of the Higgs boson. These events are used to
compute differential distributions for the photons in the pp \to H \to \gamma
\gamma decay channel, and are compared to predictions from fixed-order
perturbation theory at NNLO. We find agreement between the reweighted
generators and the NNLO result in kinematic regions where we expect a good
description using fixed-order perturbation theory. Kinematic boundaries where
resummation is required are also modeled correctly using this procedure. We
then use these events to compute distributions in the pp \to H \to W^+W^- \to
l^+l^- \nu\bar{\nu} channel, for which an accurate description is needed for
measurements at the LHC. We find that the final state lepton distributions
obtained from PYTHIA are not significantly changed by the reweighting
procedure.Comment: 18 pages, 14 fig
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