1,030 research outputs found
C−H Bond Activation by Iridium(III) and Iridium(IV) Oxo Complexes
Oxidation of an iridium(III) oxo precursor enabled the structural, spectroscopic, and quantum-chemical characterization of the first well-defined iridium(IV) oxo complex. Side-by-side examination of the proton-coupled electron transfer thermochemistry revealed similar driving forces for the isostructural oxo complexes in two redox states due to compensating contributions from H+ and e− transfer. However, C−H activation of dihydroanthracene revealed significant hydrogen tunneling for the distinctly more basic iridium(III) oxo complex. Our findings complement the growing body of data that relate tunneling to ground state properties as predictors for the selectivity of C−H bond activation.</p
An Optimal Execution Problem with Market Impact
We study an optimal execution problem in a continuous-time market model that
considers market impact. We formulate the problem as a stochastic control
problem and investigate properties of the corresponding value function. We find
that right-continuity at the time origin is associated with the strength of
market impact for large sales, otherwise the value function is continuous.
Moreover, we show the semi-group property (Bellman principle) and characterise
the value function as a viscosity solution of the corresponding
Hamilton-Jacobi-Bellman equation. We introduce some examples where the forms of
the optimal strategies change completely, depending on the amount of the
trader's security holdings and where optimal strategies in the Black-Scholes
type market with nonlinear market impact are not block liquidation but gradual
liquidation, even when the trader is risk-neutral.Comment: 36 pages, 8 figures, a modified version of the article "An optimal
execution problem with market impact" in Finance and Stochastics (2014
Examination of Protonation-Induced Dinitrogen Splitting by in Situ EXAFS Spectroscopy
The splitting of dinitrogen into nitride complexes emerged as a key reaction for nitrogen fixation strategies at ambient conditions. However, the impact of auxiliary ligands or accessible spin states on the thermodynamics and kinetics of N-N cleavage is yet to be examined in detail. We recently reported N-N bond splitting of a {Mo(μ2:η1:η1-N2)Mo}-complex upon protonation of the diphosphinoamide auxiliary ligands. The reactivity was associated with a low-spin to high-spin transition that was induced by the protonation reaction in the coordination periphery, mainly based on computational results. Here, this proposal is evaluated by an XAS study of a series of linearly N2 bridged Mo pincer complexes. Structural characterization of the transient protonation product by EXAFS spectroscopy confirms the proposed spin transition prior to N-N bond cleavage
Impact of massive neutrinos on the Higgs self-coupling and electroweak vacuum stability
The presence of right-handed neutrinos in the type I seesaw mechanism may
lead to significant corrections to the RG evolution of the Higgs self-coupling.
Compared to the Standard Model case, the Higgs mass window can become narrower,
and the cutoff scale become lower. Naively, these effects decrease with
decreasing right-handed neutrino mass. However, we point out that the unknown
Dirac Yukawa matrix may impact the vacuum stability constraints even in the low
scale seesaw case not far away from the electroweak scale, hence much below the
canonical seesaw scale of 10^15 GeV. This includes situations in which
production of right-handed neutrinos at colliders is possible. We illustrate
this within a particular parametrization of the Dirac Yukawas and with explicit
low scale seesaw models. We also note the effect of massive neutrinos on the
top quark Yukawa coupling, whose high energy value can be increased with
respect to the Standard Model case.Comment: 17 pages, 7 figures, minor revisions, version to appear in JHE
The 3-3-1 model with S_4 flavor symmetry
We construct a 3-3-1 model based on family symmetry S_4 responsible for the
neutrino and quark masses. The tribimaximal neutrino mixing and the diagonal
quark mixing have been obtained. The new lepton charge \mathcal{L} related to
the ordinary lepton charge L and a SU(3) charge by L=2/\sqrt{3} T_8+\mathcal{L}
and the lepton parity P_l=(-)^L known as a residual symmetry of L have been
introduced which provide insights in this kind of model. The expected vacuum
alignments resulting in potential minimization can origin from appropriate
violation terms of S_4 and \mathcal{L}. The smallness of seesaw contributions
can be explained from the existence of such terms too. If P_l is not broken by
the vacuum values of the scalar fields, there is no mixing between the exotic
and the ordinary quarks at the tree level.Comment: 20 pages, revised versio
Vacuum stability, neutrinos, and dark matter
Motivated by the discovery hint of the Standard Model (SM) Higgs mass around
125 GeV at the LHC, we study the vacuum stability and perturbativity bounds on
Higgs scalar of the SM extensions including neutrinos and dark matter (DM).
Guided by the SM gauge symmetry and the minimal changes in the SM Higgs
potential we consider two extensions of neutrino sector (Type-I and Type-III
seesaw mechanisms) and DM sector (a real scalar singlet (darkon) and minimal
dark matter (MDM)) respectively. The darkon contributes positively to the
function of the Higgs quartic coupling and can stabilize the
SM vacuum up to high scale. Similar to the top quark in the SM we find the
cause of instability is sensitive to the size of new Yukawa couplings between
heavy neutrinos and Higgs boson, namely, the scale of seesaw mechanism. MDM and
Type-III seesaw fermion triplet, two nontrivial representations of
group, will bring the additional positive contributions to the gauge coupling
renormalization group (RG) evolution and would also help to stabilize
the electroweak vacuum up to high scale.Comment: 18 pages, 15 figures; published versio
Proceedings of the 2nd Workshop on Flavor Symmetries and Consequences in Accelerators and Cosmology (FLASY12)
These are the proceedings of the 2nd Workshop on Flavor Symmetries and
Consequences in Accelerators and Cosmology, held 30 June 2012 - 4 July 2012,
Dortmund, Germany.Comment: Order 400 pages, several figures including the group picture v2:
corrected author list and contributio
Constraining Bosonic Supersymmetry from Higgs results and 8 TeV ATLAS multi-jets plus missing energy data
The collider phenomenology of models with Universal Extra Dimensions (UED) is
surprisingly similar to that of supersymmetric (SUSY) scenarios. For each
level-1 bosonic (fermionic) Kaluza-Klein (KK) state, there is a fermionic
(bosonic) analog in SUSY and thus UED scenarios are often known as bosonic
supersymmetry. The minimal version of UED (mUED) gives rise to a
quasi-degenerate particle spectrum at each KK-level and thus, can not explain
the enhanced Higgs to diphoton decay rate hinted by the ATLAS collaboration of
the Large Hadron Collider (LHC) experiment. However, in the non-minimal version
of the UED (nmUED) model, the enhanced Higgs to diphoton decay rate can be
easily explained via the suitable choice of boundary localized kinetic (BLK)
terms for higher dimensional fermions and gauge bosons. BLK terms remove the
degeneracy in the KK mass spectrum and thus, pair production of level-1 quarks
and gluons at the LHC gives rise to hard jets, leptons and large missing energy
in the final state. These final states are studied in details by the ATLAS and
CMS collaborations in the context of SUSY scenarios. We find that the absence
of any significant deviation of the data from the Standard Model (SM)
prediction puts a lower bound of about 2.1 TeV on equal mass excited quarks and
gluons.Comment: 19 page
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