1,270 research outputs found
Effects of Top-quark Compositeness on Higgs Boson Production at the LHC
Motivated by the possibility that the right-handed top-quark (t_R) is
composite, we discuss the effects of dimension-six operators on the Higgs boson
production at the LHC. When t_R is the only composite particle among the
Standard Model (SM) particles, the (V+A)\otimes (V+A) type four-top-quark
contact interaction is expected to have the largest coefficient among the
dimension-six operators, according to the Naive Dimensional Analysis (NDA). We
find that, to lowest order in QCD and other SM interactions, the cross section
of the SM Higgs boson production via gluon fusion does not receive corrections
from one insertion of the new contact interaction vertex. We also discuss the
effects of other dimension-six operators whose coefficients are expected to be
the second and the third largest from NDA. We find that the operator which
consists of two t_R's and two SM Higgs boson doublets can recognizably change
the Higgs boson production cross section from the SM prediction if the cut-off
scale is \sim 1TeV.Comment: 12 pages, 7 figures. v2: explanations improved in Section 3, other
minor changes. Version published in JHE
The radiative lepton flavor violating decays in the split fermion scenario in the two Higgs doublet model
We study the branching ratios of the lepton flavor violating processes \mu ->
e \gamma, \tau -> e \gamma and \tau -> \mu\gamma in the split fermion scenario,
in the framework of the two Higgs doublet model. We observe that the branching
ratios are relatively more sensitive to the compactification scale and the
Gaussian widths of the leptons in the extra dimensions, for two extra
dimensions and especially for the \tau -> \mu \gamma decay.Comment: 19 pages, 7 Figure
Spatial mapping of band bending in semiconductor devices using in-situ quantum sensors
Band bending is a central concept in solid-state physics that arises from
local variations in charge distribution especially near semiconductor
interfaces and surfaces. Its precision measurement is vital in a variety of
contexts from the optimisation of field effect transistors to the engineering
of qubit devices with enhanced stability and coherence. Existing methods are
surface sensitive and are unable to probe band bending at depth from surface or
bulk charges related to crystal defects. Here we propose an in-situ method for
probing band bending in a semiconductor device by imaging an array of
atomic-sized quantum sensing defects to report on the local electric field. We
implement the concept using the nitrogen-vacancy centre in diamond, and map the
electric field at different depths under various surface terminations. We then
fabricate a two-terminal device based on the conductive two-dimensional hole
gas formed at a hydrogen-terminated diamond surface, and observe an unexpected
spatial modulation of the electric field attributed to a complex interplay
between charge injection and photo-ionisation effects. Our method opens the way
to three-dimensional mapping of band bending in diamond and other
semiconductors hosting suitable quantum sensors, combined with simultaneous
imaging of charge transport in complex operating devices.Comment: This is a pre-print of an article published in Nature Electronics.
The final authenticated version is available online at
https://dx.doi.org/10.1038/s41928-018-0130-
Heavy-light decay topologies as a new strategy to discover a heavy gluon
We study the collider phenomenology of the lightest Kaluza-Klein excitation
of the gluon, G*, in theories with a warped extra dimension. We do so by means
of a two-site effective lagrangian which includes only the lowest-lying spin-1
and spin-1/2 resonances. We point out the importance of the decays of G* to one
SM plus one heavy fermion, that were overlooked in the previous literature. It
turns out that, when kinematically allowed, such heavy-light decays are
powerful channels for discovering the G*. In particular, we present a
parton-level Montecarlo analysis of the final state Wtb that follows from the
decay of G* to one SM top or bottom quark plus its heavy partner. We find that
at \sqrt{s} = 7 TeV and with 10 fb^{-1} of integrated luminosity, the LHC can
discover a KK gluon with mass in the range M_{G*} = (1.8 - 2.2) TeV if its
coupling to a pair of light quarks is g_{G*qqbar} = (0.2-0.5) g_3. The same
process is also competitive for the discovery of the top and bottom partners as
well. We find, for example, that the LHC at \sqrt{s} = 7 TeV can discover a 1
TeV KK bottom quark with an integrated luminosity of (5.3 - 0.61) fb^{-1} for
g_{G*qqbar} = (0.2-0.5) g_3.Comment: 36 pages, 13 figures. v2: a few typos corrected, comments added,
version published in JHE
Colored Resonant Signals at the LHC: Largest Rate and Simplest Topology
We study the colored resonance production at the LHC in a most general
approach. We classify the possible colored resonances based on group theory
decomposition, and construct their effective interactions with light partons.
The production cross section from annihilation of valence quarks or gluons may
be on the order of 400 - 1000 pb at LHC energies for a mass of 1 TeV with
nominal couplings, leading to the largest production rates for new physics at
the TeV scale, and simplest event topology with dijet final states. We apply
the new dijet data from the LHC experiments to put bounds on various possible
colored resonant states. The current bounds range from 0.9 to 2.7 TeV. The
formulation is readily applicable for future searches including other decay
modes.Comment: 29 pages, 9 figures. References updated and additional K-factors
include
Searches for W' and Z' in models with large extra dimensions
Characteristic features of processes mediated by gauge bosons are discussed
in the framework of theories with large extra dimensions. It is shown that if
gauge bosons propagate in the bulk, then there arises a destructive
interference not only between W and W' (or Z and Z'), but also between W' and
Z' and the Kaluza-Klein towers of higher excitations of W and Z bosons
respectively. Specific calculations are made and plotted for the LHC with the
center of mass energy 14 TeV.Comment: 7 pages, 4 figures, added reference, corrected misprints. Talk given
at 16th International Seminar on High Energy Physics "QUARKS-2010", Kolomna,
Russia, 6-12 June, 2010. To appear in Theor. Math. Phy
KK Parity in Warped Extra Dimension
We construct models with a Kaluza-Klein (KK) parity in a five- dimensional
warped geometry, in an attempt to address the little hierarchy problem present
in setups with bulk Standard Model fields. The lightest KK particle (LKP) is
stable and can play the role of dark matter. We consider the possibilities of
gluing two identical slices of 5D AdS in either the UV (IR-UV-IR model) or the
IR region (UV-IR-UV model) and discuss the model-building issues as well as
phenomenological properties in both cases. In particular, we find that the
UV-IR-UV model is not gravitationally stable and that additional mechanisms
might be required in the IR-UV-IR model in order to address flavor issues.
Collider signals of the warped KK parity are different from either the
conventional warped extra dimension without KK parity, in which the new
particles are not necessarily pair-produced, or the KK parity in flat universal
extra dimensions, where each KK level is nearly degenerate in mass. Dark matter
and collider properties of a TeV mass KK Z gauge boson as the LKP are
discussed.Comment: 35 pages, 11 figure
TeV Mini Black Hole Decay at Future Colliders
It is generally believed that mini black holes decay by emitting elementary
particles with a black body energy spectrum. The original calculation lead to
the conclusion that about the 90% of the black hole mass is radiated away in
the form of photons, neutrinos and light leptons, mainly electrons and muons.
With the advent of String Theory, such a scenario must be updated by including
new effects coming from the stringy nature of particles and interactions.By
taking for granted that black holes can be produced in hadronic collisions,
then their decay must take into account that: (i) we live in a D3-Brane
embedded into an higher dimensional bulk spacetime; (ii) fundamental
interactions, including gravity, are unified at TeV energy scale. Thus, the
formal description of the Hawking radiation mechanism has to be extended to the
case of more than four spacetime dimensions and include the presence of
D-branes. Furthermore, unification of fundamental interactions at an energy
scale many order of magnitude lower than the Planck energy implies that any
kind of fundamental particle, not only leptons, is expected to be emitted. A
detailed understanding of the new scenario is instrumental for optimal tuning
of detectors at future colliders, where, hopefully, this exciting new physics
will be tested. In this article we review higher dimensional black hole decay,
considering not only the emission of particles according to Hawking mechanism,
but also their near horizon QED/QCD interactions. The ultimate motivation is to
build up a phenomenologically reliable scenario, allowing a clear experimental
signature of the event.Comment: 22 pages, 9 figures, 4 tables; ``quick review'' for Class. and
Quantum Gra
Contributions on the development of the reproductive system in Sternotherus odoratus (latreille)
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47667/1/441_2004_Article_BF00572100.pd
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