271 research outputs found
Multi-Photon Signals from Composite Models at LHC
We analyze the collider signals of composite scalars that emerge in certain
little Higgs models and models of vectorlike confinement. Similar to the decay
of the pion into photon pairs, these scalars mainly decay through
anomaly-induced interactions into electroweak gauge bosons, leading to a
distinct signal with three or more photons in the final state. We study the
standard model backgrounds for these signals, and find that the LHC can
discover these models over a large range of parameter space with 30 fb
at 14 TeV. An early discovery at the current 7 TeV run is possible in some
regions of parameter space. We also discuss possibilities to measure the spin
of the particles in the and decay channels.Comment: 18 pages, LaTe
UV friendly T-parity in the SU(6)/Sp(6) little Higgs model
Electroweak precision tests put stringent constraints on the parameter space
of little Higgs models. Tree-level exchange of TeV scale particles in a generic
little Higgs model produce higher dimensional operators that make contributions
to electroweak observables that are typically too large. To avoid this problem
a discrete symmetry dubbed T-parity can be introduced to forbid the dangerous
couplings. However, it was realized that in simple group models such as the
littlest Higgs model, the implementation of T-parity in a UV completion could
present some challenges. The situation is analogous to the one in QCD where the
pion can easily be defined as being odd under a new symmetry in the
chiral Lagrangian, but this is not a symmetry of the quark Lagrangian. In
this paper we examine the possibility of implementing a T-parity in the low
energy model that might be easier to realize in the UV. In our
model, the T-parity acts on the low energy non-linear sigma model field in way
which is different to what was originally proposed for the Littlest Higgs, and
lead to a different low energy theory. In particular, the Higgs sector of this
model is a inert two Higgs doublets model with an approximate custodial
symmetry. We examine the contributions of the various sectors of the model to
electroweak precision data, and to the dark matter abundance.Comment: 21 pages,4 figures. Clarifications added, typos corrected and
references added. Published in JHE
Strong interface-induced spin-orbit coupling in graphene on WS2
Interfacial interactions allow the electronic properties of graphene to be
modified, as recently demonstrated by the appearance of satellite Dirac cones
in the band structure of graphene on hexagonal boron nitride (hBN) substrates.
Ongoing research strives to explore interfacial interactions in a broader class
of materials in order to engineer targeted electronic properties. Here we show
that at an interface with a tungsten disulfide (WS2) substrate, the strength of
the spin-orbit interaction (SOI) in graphene is very strongly enhanced. The
induced SOI leads to a pronounced low-temperature weak anti-localization (WAL)
effect, from which we determine the spin-relaxation time. We find that
spin-relaxation time in graphene is two-to-three orders of magnitude smaller on
WS2 than on SiO2 or hBN, and that it is comparable to the intervalley
scattering time. To interpret our findings we have performed first-principle
electronic structure calculations, which both confirm that carriers in
graphene-on-WS2 experience a strong SOI and allow us to extract a
spin-dependent low-energy effective Hamiltonian. Our analysis further shows
that the use of WS2 substrates opens a possible new route to access topological
states of matter in graphene-based systems.Comment: Originally submitted version in compliance with editorial guidelines.
Final version with expanded discussion of the relation between theory and
experiments to be published in Nature Communication
Composite Octet Searches with Jet Substructure
Many new physics models with strongly interacting sectors predict a mass
hierarchy between the lightest vector meson and the lightest pseudoscalar
mesons. We examine the power of jet substructure tools to extend the 7 TeV LHC
sensitivity to these new states for the case of QCD octet mesons, considering
both two gluon and two b-jet decay modes for the pseudoscalar mesons. We
develop both a simple dijet search using only the jet mass and a more
sophisticated jet substructure analysis, both of which can discover the
composite octets in a dijet-like signature. The reach depends on the mass
hierarchy between the vector and pseudoscalar mesons. We find that for the
pseudoscalar-to-vector meson mass ratio below approximately 0.2 the simple jet
mass analysis provides the best discovery limit; for a ratio between 0.2 and
the QCD-like value of 0.3, the sophisticated jet substructure analysis has the
best discovery potential; for a ratio above approximately 0.3, the standard
four-jet analysis is more suitable.Comment: 21 pages, 8 figure
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