1,608 research outputs found
Direct determination of neutrino mass parameters at future colliders
If the observed light neutrino masses are induced by their Yukawa couplings
to singlet right-handed neutrinos, natural smallness of those renders direct
collider tests of the electroweak scale neutrino mass mechanisms almost
impossible both in the case of Dirac and Majorana (seesaw of type I) neutrinos.
However, in the triplet Higgs seesaw scenario the smallness of light neutrino
masses may come from the smallness of B-L breaking parameters, allowing sizable
Yukawa couplings even for a TeV scale triplet. We show that, in this scenario,
measuring the branching fractions of doubly charged Higgs to different
same-charged lepton flavours at LHC and/or ILC experiments will allow one to
measure the neutrino mass parameters which neutrino oscillation experiments are
insensitive to, including the neutrino mass hierarchy, lightest neutrino mass
and Majorana phases.Comment: A mistake corrected, experimental errors revised, new references
added, conclusions unchange
Excitonic Dynamical Franz-Keldysh Effect
The Dynamical Franz-Keldysh Effect is exposed by exploring near-bandgap
absorption in the presence of intense THz electric fields. It bridges the gap
between the DC Franz- Keldysh effect and multi-photon absorption and competes
with the THz AC Stark Effect in shifting the energy of the excitonic resonance.
A theoretical model which includes the strong THz field non-perturbatively via
a non-equilibrium Green Functions technique is able to describe the Dynamical
Franz-Keldysh Effect in the presence of excitonic absorption.Comment: 4 pages in revtex with 5 figures included using epsf. Submitted to
Physical Review Letter
Stability, folding dynamics, and long-range conformational transition of the synaptic t-SNARE complex
Synaptic soluble N-ethylmaleimide-sensitive factor attachment
protein receptors (SNAREs) couple their stepwise folding to fusion
of synaptic vesicles with plasma membranes. In this process, three
SNAREs assemble into a stable four-helix bundle. Arguably, the
first and rate-limiting step of SNARE assembly is the formation of
an activated binary t-SNARE complex on the plasma membrane,
which then zippers with the v-SNARE on the vesicle to drive
membrane fusion. However, the t-SNARE complex readily misfolds
and its structure, stability, and dynamics are elusive. Using
single-molecule force spectroscopy, we modeled synaptic t-SNARE
complex as a parallel three-helix bundle with a small frayed Cterminus.
The helical bundle sequentially folded in an N-terminal
domain (NTD) and a C-terminal domain (CTD) separated by a
central ionic layer, with total unfolding energy of ∼17 kBT. Peptide
binding to the CTD activated the t-SNARE complex to initiate
NTD zippering with the v-SNARE, a mechanism likely shared by
Munc18-1. The NTD zippering then dramatically stabilized the CTD,
facilitating further SNARE zippering. The subtle bidirectional tSNARE
conformational switch was mediated by the ionic layer.
Thus, the t-SNARE complex acts as a switch to enable fast and
controlled SNARE zippering required for synaptic vesicle fusion
and neurotransmission
Probing canonical geometrical objects by digital spiral imaging
We recently proposed a novel concept to remotely acquire information of objects, based on the discrete orbital angular momentum of ligh. Here we use two different experimental schemes for implementing the technique. We use a canonical phase jump as a target to test the methods and to compare the results
Quasienergy Spectroscopy of Excitons
We theoretically study nonlinear optics of excitons under intense THz
irradiation. In particular, the linear near infrared absorption and resonantly
enhanced nonlinear sideband generation are described. We predict a rich
structure in the spectra which can be interpreted in terms of the quasienergy
spectrum of the exciton, via a remarkably transparent expression for the
susceptibility, and show that the effects of strongly avoided quasienergy
crossings manifest themselves directly, both in the absorption and transmitted
sidebands.Comment: 4 pages RevTex, 3 eps figs included, as publishe
Two Disease-Causing SNAP-25B Mutations Selectively Impair SNARE C-terminal Assembly
Synaptic exocytosis relies on assembly of three soluble N-ethylmaleimide-sensitive factor attachment receptor (SNARE) proteins into a parallel four-helix bundle to drive membrane fusion. SNARE assembly occurs by stepwise zippering of the vesicle-associated SNARE (v-SNARE) onto a binary SNARE complex on the target plasma membrane (t-SNARE). Zippering begins with slow N-terminal association followed by rapid C-terminal zippering, which serves as a power stroke to drive membrane fusion. SNARE mutations have been associated with numerous diseases, especially neurological disorders. It remains unclear how these mutations affect SNARE zippering, partly due to difficulties to quantify the energetics and kinetics of SNARE assembly. Here, we used single-molecule optical tweezers to measure the assembly energy and kinetics of SNARE complexes containing single mutations I67T/N in neuronal SNARE synaptosomal-associated protein of 25 kDa (SNAP-25B), which disrupt neurotransmitter release and have been implicated in neurological disorders. We found that both mutations significantly reduced the energy of C-terminal zippering by ~ 10 kBT, but did not affect N-terminal assembly. In addition, we observed that both mutations lead to unfolding of the C-terminal region in the t-SNARE complex. Our findings suggest that both SNAP-25B mutations impair synaptic exocytosis by destabilizing SNARE assembly, rather than stabilizing SNARE assembly as previously proposed. Therefore, our measurements provide insights into the molecular mechanism of the disease caused by SNARE mutations
Measurement of the t(t)over-bar production cross section in the dilepton channel in pp collisions at √s=8 TeV
The top-antitop quark (t (t) over bar) production cross section is measured in proton-proton collisions at root s = 8 TeV with the CMS experiment at the LHC, using a data sample corresponding to an integrated luminosity of 5.3 fb(-1). The measurement is performed by analysing events with a pair of electrons or muons, or one electron and one muon, and at least two jets, one of which is identified as originating from hadronisation of a bottom quark. The measured cross section is 239 +/- 2 (stat.) +/- 11 (syst.) +/- 6 (lum.) pb, for an assumed top-quark mass of 172.5 GeV, in agreement with the prediction of the standard model
On the Theory of Vibronic Superradiance
The Dicke superradiance on vibronic transitions of impurity crystals is
considered. It is shown that parameters of the superradiance (duration and
intensity of the superradiance pulse and delay times) on each vibronic
transition depend on the strength of coupling of electronic states with the
intramolecular impurity vibration (responsible for the vibronic structure of
the optical spectrum in the form of vibrational replicas of the pure electronic
line) and on the crystal temperature through the Debye-Waller factor of the
lattice vibrations. Theoretical estimates of the ratios of the time delays, as
well as of the superradiance pulse intensities for different vibronic
transitions well agree with the results of experimental observations of
two-color superradiance in the polar dielectric KCl:O2-. In addition, the
theory describes qualitatively correctly the critical temperature dependence of
the superradiance effect.Comment: 8 pages, 1 figur
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