3,870 research outputs found
A Z' Model for the CDF Dijet Anomaly
We adopt a bottom-up approach to constructing a new physics model to explain
the CDF excess seen in dijets with an associated lepton and missing transverse
energy. We find that the 145 GeV broad feature seen by CDF in the dijet
invariant mass distribution can be explained by a Z' boson with a mass of 145
GeV that couples only to first generation quarks. After dijet resonance
constraints are considered, a sizeable region of the parameter space favored by
the CDF anomaly remains viable.Comment: 16 pages, 3 figures; v2, added references; v3, fixed reference
Collider constraints and new tests of color octet vectors
We analyze the collider sensitivity for new colored resonances in ,
, and final states. While searches in the single production
channel are model-dependent, the pair production rate is model independent and
the existing and searches impose strong constraints on the
relevant branching fractions, where or . We point out the missing,
complementary searches in the mixed decay modes, ,
, and . We propose analysis strategies for
the and decays and find their sensivity
surpasses that of existing searches when the decay widths to tops and light
jets are comparable. If no other decays are present, collective lower limits on
the resonance mass can be set at 1.5~TeV using 37~fb of 13~TeV data.Comment: 22 pages, 3 figures, 2 table
A Tale of Two Portals: Testing Light, Hidden New Physics at Future Colliders
We investigate the prospects for producing new, light, hidden states at a
future collider in a Higgsed dark model, which we call the
Double Dark Portal model. The simultaneous presence of both vector and scalar
portal couplings immediately modifies the Standard Model Higgsstrahlung
channel, , at leading order in each coupling. In addition, each
portal leads to complementary signals which can be probed at direct and
indirect detection dark matter experiments. After accounting for current
constraints from LEP and LHC, we demonstrate that a future Higgs
factory will have unique and leading sensitivity to the two portal couplings by
studying a host of new production, decay, and radiative return processes.
Besides the possibility of exotic Higgs decays, we highlight the importance of
direct dark vector and dark scalar production at machines, whose
invisible decays can be tagged from the recoil mass method.Comment: 47 pages, 9 figures, 1 table. v2: references added, version matched
to JHE
Hardening and Strain Localisation in Helium-Ion-Implanted Tungsten
Tungsten is the main candidate material for plasma-facing armour components
in future fusion reactors. In-service, fusion neutron irradiation creates
lattice defects through collision cascades. Helium, injected from plasma,
aggravates damage by increasing defect retention. Both can be mimicked using
helium-ion-implantation. In a recent study on 3000 appm helium-implanted
tungsten (W-3000He), we hypothesized helium-induced irradiation hardening,
followed by softening during deformation. The hypothesis was founded on
observations of large increase in hardness, substantial pile-up and slip-step
formation around nano-indents and Laue diffraction measurements of localised
deformation underlying indents. Here we test this hypothesis by implementing it
in a crystal plasticity finite element (CPFE) formulation, simulating
nano-indentation in W-3000He at 300 K. The model considers thermally-activated
dislocation glide through helium-defect obstacles, whose barrier strength is
derived as a function of defect concentration and morphology. Only one fitting
parameter is used for the simulated helium-implanted tungsten; defect removal
rate. The simulation captures the localised large pile-up remarkably well and
predicts confined fields of lattice distortions and geometrically necessary
dislocation underlying indents which agree quantitatively with previous Laue
measurements. Strain localisation is further confirmed through high resolution
electron backscatter diffraction and transmission electron microscopy
measurements on cross-section lift-outs from centre of nano-indents in
W-3000He
Orientation-dependent indentation response of helium-implanted tungsten
A literature review of studies investigating the topography of nano-indents
in ion-implanted materials reveals seemingly inconsistent observations, with
report of both pile-up and sink-in. This may be due to the crystallographic
orientation of the measured sample point, which is often not considered when
evaluating implantation-induced changes in the deformation response. Here we
explore the orientation dependence of spherical nano-indentation in pure and
helium-implanted tungsten, considering grains with , and
out-of-plane orientations. Atomic force microscopy (AFM) of indents in
unimplanted tungsten shows little orientation dependence. However, in the
implanted material a much larger, more localised pile-up is observed for
grains than for and orientations. Based on the observations for
grains, we hypothesise that a large initial hardening due to
helium-induced defects is followed by localised defect removal and subsequent
strain softening. A crystal plasticity finite element model of the indentation
process, formulated based on this hypothesis, accurately reproduces the
experimentally-observed orientation-dependence of indent morphology. The
results suggest that the mechanism governing the interaction of helium-induced
defects with glide dislocations is orientation independent. Rather, differences
in pile-up morphology are due to the relative orientations of the crystal slip
systems, sample surface and spherical indenter. This highlights the importance
of accounting for crystallographic orientation when probing the deformation
behaviour of ion-implanted materials using nano-indentation
A Viable Flavor Model for Quarks and Leptons in RS with T' Family Symmetry
We propose a Randall-Sundrum model with a bulk family symmetry based on the
double tetrahedral group, T', which generates the tri-bimaximal neutrino mixing
pattern and a realistic CKM matrix. The T' symmetry forbids tree-level
flavor-changing-neutral-currents in both the quark and lepton sectors, as
different generations of fermions are unified into multiplets of T'. This
results in a low first KK mass scale and thus the model can be tested at
collider experiments.Comment: 4 pages; based on talk presented at the 17th International Conference
on Supersymmetry and the Unification of Fundamental Interactions (SUSY09),
Boston, MA, June 5-10, 200
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