3,535 research outputs found
Search strategies for top partners in composite Higgs models
We consider how best to search for top partners in generic composite Higgs
models. We begin by classifying the possible group representations carried by
top partners in models with and without a custodial symmetry protecting the rate for
decays. We identify a number of minimal models whose top partners only have
electric charges of or and thus decay
to top or bottom quarks via a single Higgs or electroweak gauge boson. We
develop an inclusive search for these based on a top veto, which we find to be
more effective than existing searches. Less minimal models feature light states
that can be sought in final states with like-sign leptons and so we find that 2
straightforward LHC searches give a reasonable coverage of the gamut of
composite Higgs models.BG acknowledges the support of the Science and Technology Facilities Council, the In-
stitute for Particle Physics Phenomenology, and King’s College, Cambridge and thanks
R. Contino and R. Rattazzi for discussions. DS acknowledges the support of the Science
and Technology Facilities Council, as well as Emmanuel College, Cambridge, and thanks
O.Matsedonskyi for FeynRules help. TM thanks C. Lester for discussions on mass variables.This is the final version. It was first published by Springer at http://link.springer.com/article/10.1007%2FJHEP08%282014%29171
Phenomenology of a light scalar: the dilaton
We make use of the language of non-linear realizations to analyze
electro-weak symmetry breaking scenarios in which a light dilaton emerges from
the breaking of a nearly conformal strong dynamics, and compare the
phenomenology of the dilaton to that of the well motivated light composite
Higgs scenario. We argue that -- in addition to departures in the
decay/production rates into massless gauge bosons mediated by the conformal
anomaly -- characterizing features of the light dilaton scenario (as well as
other scenarios admitting a light CP-even scalar not directly related to the
breaking of the electro-weak symmetry) are off-shell events at high invariant
mass involving two longitudinally polarized vector bosons and a dilaton, and
tree-level flavor violating processes. Accommodating both electro-weak
precision measurements and flavor constraints appears especially challenging in
the ambiguous scenario in which the Higgs and the dilaton fields strongly mix.
We show that warped higgsless models of electro-weak symmetry breaking are
explicit and tractable realizations of this limiting case.
The relation between the naive radion profile often adopted in the study of
holographic realizations of the light dilaton scenario and the actual dynamical
dilaton field is clarified in the Appendix.Comment: 21 page
Mass spectrometry of B. subtilis CopZ: Cu(I)-binding and interactions with bacillithiol
CopZ from Bacillus subtilis is a well-studied member of the highly conserved family of Atx1-like copper chaperones. It was previously shown via solution and crystallographic studies to undergo Cu(I)-mediated dimerisation, where the CopZ dimer can bind between one and four Cu(I) ions. However, these studies could not provide information about the changing distribution of species at increasing Cu(I) levels. To address this, electrospray ionisation mass spectrometry using soft ionisation was applied to CopZ under native conditions. Data revealed folded, monomeric CopZ in apo- and Cu(I)-bound forms, along with Cu(I)-bound dimeric forms of CopZ at higher Cu(I) loading. Cu4(CopZ)2 was the major dimeric species at loadings >1 Cu(I)/CopZ, indicating the cooperative formation of the tetranuclear Cu(I)-bound species. As the principal low molecular weight thiol in B. subtilis, bacillithiol (BSH) may play a role in copper homeostasis. Mass spectrometry showed that increasing BSH led to a reduction in Cu(I)-bound dimeric forms, and the formation of S-bacillithiolated apo-CopZ and BSH adducts of Cu(I)-bound forms of CopZ, where BSH likely acts as a Cu(I) ligand. These data, along with the high affinity of BSH for Cu(I), determined here to be β2(BSH) = ∼4 × 1017 M−2, are consistent with a role for BSH alongside CopZ in buffering cellular Cu(I) levels. Here, mass spectrometry provides a high resolution overview of CopZ–Cu(I) speciation that cannot be obtained from less discriminating solution-phase methods, thus illustrating the potential for the wider application of this technique to studies of metal–protein interactions
Cold Fermi-gas with long range interaction in a harmonic trap
We study equilibrium density and spin density profiles for a model of cold
one-dimensional spin 1/2 fermions interacting via inverse square interaction
and exchange in an external harmonic trap. This model is the well-known
spin-Calogero model (sCM) and its fully nonlinear collective field theory
description is known. We extend the field theory description to the presence of
an external harmonic trap and obtain analytic results for statics and dynamics
of the system. For instance, we find how the equilibrium density profile
changes upon tuning the interaction strength. The results we obtain for
equilibrium configurations are very similar to the ones obtained recently by Ma
and Yang [1] for a model of fermions with short ranged interactions. Our main
approximation is the neglect of the terms of higher order in spatial
derivatives in equations of motion - gradientless approximation [2]. Within
this approximation the hydrodynamic equations of motion can be written as a set
of decoupled forced Riemann-Hopf equations for the dressed Fermi momenta of the
model. This enables us to write analytical solutions for the dynamics of spin
and charge. We describe the time evolution of the charge density when an
initial non-equilibrium profile is created by cooling the gas with an
additional potential in place and then suddenly removing the potential. We
present our results as a simple "single-particle" evolution in the phase-space
reminiscing a similar description of the dynamics of non-interacting
one-dimensional fermions.Comment: 11 pages, 5 figures (figure typo corrected and references added
Resistive Random Access Memories (RRAMs) Based on Metal Nanoparticles
It is demonstrated that planar structures based on silver nanoparticleshosted in a polymer matrix show reliable and reproducible switching properties attractive for non-volatile memory applications. These systems can be programmed between a low conductance (off-state) and high conductance (on-state) with an on/off ratio of 3 orders of magnitude, large retention times and good cycle endurance. The planar structure design offers a series of advantages discussed in this contribution, which make it an ideal tool to elucidate the resistive switching phenomena
DMRG studies of critical SU(N) spin chains
The DMRG method is applied to integrable models of antiferromagnetic spin
chains for fundamental and higher representations of SU(2), SU(3), and SU(4).
From the low energy spectrum and the entanglement entropy, we compute the
central charge and the primary field scaling dimensions. These parameters allow
us to identify uniquely the Wess-Zumino-Witten models capturing the low energy
sectors of the models we consider.Comment: 14 pages, 8 figures; final version, to appear in Ann. Phy
Mapping the shoreface of coastal sediment compartments to improve shoreline change forecasts in New South Wales, Australia
The potential response of shoreface depositional environments to sea level rise over the present century and beyond remains poorly understood. The shoreface is shaped by wave action across a sedimentary seabed and may aggrade or deflate depending on the balance between time-averaged wave energy and the availability and character of sediment, within the context of the inherited geological control. For embayed and accommodation-dominated coastal settings, where shoreline change is particularly sensitive to cross-shore sediment transport, whether the shoreface is a source or sink for coastal sediment during rising sea level may be a crucial determinant of future shoreline change. While simple equilibrium-based models (e.g. the Bruun Rule) are widely used in coastal risk planning practice to predict shoreline change due to sea level rise, the relevance of fundamental model assumptions to the shoreface depositional setting is often overlooked due to limited knowledge about the geomorphology of the nearshore seabed. We present high-resolution mapping of the shoreface-inner shelf in southeastern Australia from airborne lidar and vessel-based multibeam echosounder surveys, which reveals a more complex seabed than was previously known. The mapping data are used to interpret the extent, depositional character and morphodynamic state of the shoreface, by comparing the observed geomorphology to theoretical predictions from wave-driven sediment transport theory. The benefits of high-resolution seabed mapping for improving shoreline change predictions in practice are explored by comparing idealised shoreline change modelling based on our understanding of shoreface geomorphology and morphodynamics before and after the mapping exercise
Identifying the science and technology dimensions of emerging public policy issues through horizon scanning
Public policy requires public support, which in turn implies a need to enable the public not just to understand policy but also to be engaged in its development. Where complex science and technology issues are involved in policy making, this takes time, so it is important to identify emerging issues of this type and prepare engagement plans. In our horizon scanning exercise, we used a modified Delphi technique [1]. A wide group of people with interests in the science and policy interface (drawn from policy makers, policy adviser, practitioners, the private sector and academics) elicited a long list of emergent policy issues in which science and technology would feature strongly and which would also necessitate public engagement as policies are developed. This was then refined to a short list of top priorities for policy makers. Thirty issues were identified within broad areas of business and technology; energy and environment; government, politics and education; health, healthcare, population and aging; information, communication, infrastructure and transport; and public safety and national security.Public policy requires public support, which in turn implies a need to enable the public not just to understand policy but also to be engaged in its development. Where complex science and technology issues are involved in policy making, this takes time, so it is important to identify emerging issues of this type and prepare engagement plans. In our horizon scanning exercise, we used a modified Delphi technique [1]. A wide group of people with interests in the science and policy interface (drawn from policy makers, policy adviser, practitioners, the private sector and academics) elicited a long list of emergent policy issues in which science and technology would feature strongly and which would also necessitate public engagement as policies are developed. This was then refined to a short list of top priorities for policy makers. Thirty issues were identified within broad areas of business and technology; energy and environment; government, politics and education; health, healthcare, population and aging; information, communication, infrastructure and transport; and public safety and national security
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