12,826 research outputs found
NNLO QCD Corrections to t-channel Single Top-Quark Production and Decay
We present a fully differential next-to-next-to-leading order calculation of
t-channel single top-quark production and decay at the LHC under narrow-width
approximation and neglecting cross-talk between incoming protons. We focus on
the fiducial cross sections at 13 TeV, finding that the next-to-next-to-leading
order QCD corrections can reach the level of -6%. The scale variations are
reduced to the level of a percent. Our results can be used to improve
experimental acceptance estimates and the measurements of the single top-quark
production cross section and the top-quark electroweak couplings.Comment: 6 pages, 4 figures, version appear on PRD rapid communicatio
Can the Lepton Flavor Mixing Matrix Be Symmetric?
Current neutrino oscillation data indicate that the 3x3 lepton flavor mixing
matrix V is likely to be symmetric about its V_{e3}-V_{\mu 2}-V_{\tau 1} axis.
This off-diagonal symmetry corresponds to three pairs of {\it congruent}
unitarity triangles in the complex plane. Terrestrial matter effects can
substantially modify the genuine CP-violating parameter and off-diagonal
asymmetries of V in realistic long-baseline experiments of neutrino
oscillations.Comment: RexTex 14 pages (4 PS figures). More discussions adde
Universal Conductance Fluctuations in Mesoscopic Systems with Superconducting Leads: Beyond the Andreev Approximation
We report our investigation of the sample to sample fluctuation in transport
properties of phase coherent normal metal-superconductor hybrid systems.
Extensive numerical simulations were carried out for quasi-one dimensional and
two dimensional systems in both square lattice (Fermi electron) as well as
honeycomb lattice (Dirac electron). Our results show that when the Fermi energy
is within the superconducting energy gap , the Andreev conductance
fluctuation exhibits a universal value (UCF) which is approximately two times
larger than that in the normal systems. According to the random matrix theory,
the electron-hole degeneracy (ehD) in the Andreev reflections (AR) plays an
important role in classifying UCF. Our results confirm this. We found that in
the diffusive regime there are two UCF plateaus, one corresponds to the
complete electron-hole symmetry (with ehD) class and the other to conventional
electron-hole conversion (ehD broken). In addition, we have studied the Andreev
conductance distribution and found that for the fixed average conductance
the Andreev conductance distribution is a universal function that depends only
on the ehD. In the localized regime, our results show that ehD continues to
serve as an indicator for different universal classes. Finally, if normal
transport is present, i.e., Fermi energy is beyond energy gap , the AR
is suppressed drastically in the localized regime by the disorder and the ehD
becomes irrelevant. As a result, the conductance distribution is that same as
that of normal systems
Anomalous elasticity of nematic elastomers
We study the anomalous elasticity of nematic elastomers by employing the
powers of renormalized field theory. Using general arguments of symmetry and
relevance, we introduce a minimal Landau-Ginzburg-Wilson elastic energy for
nematic elastomers. Performing a diagrammatic low temperature expansion, we
analyze the fluctuations of the displacement fields at and below the upper
critical dimension 3. Our analysis reveals an anomaly of certain elastic moduli
in the sense that they depend on the length scale. In this dependence
is logarithmic and below it is of power law type with anomalous scaling
exponents. One of the 4 relevant shear moduli vanishes at long length scales
whereas the only relevant bending modulus diverges.Comment: 4 page
The Poisson-Boltzmann Theory for Two Parallel Uniformly Charged Plates
We solve the nonlinear Poisson-Boltzmann equation for two parallel and likely
charged plates both inside a symmetric elecrolyte, and inside a 2 : 1
asymmetric electrolyte, in terms of Weierstrass elliptic functions. From these
solutions we derive the functional relation between the surface charge density,
the plate separation, and the pressure between plates. For the one plate
problem, we obtain exact expressions for the electrostatic potential and for
the renormalized surface charge density, both in symmetric and in asymmetric
electrolytes. For the two plate problems, we obtain new exact asymptotic
results in various regimes.Comment: 17 pages, 9 eps figure
Scale Setting Using the Extended Renormalization Group and the Principle of Maximum Conformality: the QCD Coupling Constant at Four Loops
A key problem in making precise perturbative QCD predictions is to set the
proper renormalization scale of the running coupling. The extended
renormalization group equations, which express the invariance of physical
observables under both the renormalization scale- and scheme-parameter
transformations, provide a convenient way for estimating the scale- and
scheme-dependence of the physical process. In this paper, we present a solution
for the scale-equation of the extended renormalization group equations at the
four-loop level. Using the principle of maximum conformality (PMC) /
Brodsky-Lepage-Mackenzie (BLM) scale-setting method, all non-conformal
terms in the perturbative expansion series can be summed into the
running coupling, and the resulting scale-fixed predictions are independent of
the renormalization scheme. Different schemes lead to different effective
PMC/BLM scales, but the final results are scheme independent. Conversely, from
the requirement of scheme independence, one not only can obtain
scheme-independent commensurate scale relations among different observables,
but also determine the scale displacements among the PMC/BLM scales which are
derived under different schemes. In principle, the PMC/BLM scales can be fixed
order-by-order, and as a useful reference, we present a systematic and
scheme-independent procedure for setting PMC/BLM scales up to NNLO. An explicit
application for determining the scale setting of up to four
loops is presented. By using the world average , we obtain the asymptotic scale for the 't Hooft associated
with the scheme, MeV, and
the asymptotic scale for the conventional scheme,
MeV.Comment: 9 pages, no figures. The formulas in the Appendix are correcte
Thermal Fluctuations and Rubber Elasticity
The effects of thermal elastic fluctuations in rubber materials are examined.
It is shown that, due to an interplay with the incompressibility constraint,
these fluctuations qualitatively modify the large-deformation stress-strain
relation, compared to that of classical rubber elasticity. To leading order,
this mechanism provides a simple and generic explanation for the peak structure
of Mooney-Rivlin stress-strain relation, and shows a good agreement with
experiments. It also leads to the prediction of a phonon correlation function
that depends on the external deformation.Comment: 4 RevTeX pages, 1 figure, submitted to PR
More Straightforward Extraction of the Fundamental Lepton Mixing Parameters from Long-Baseline Neutrino Oscillations
We point out the simple reversibility between the fundamental neutrino mixing
parameters in vacuum and their effective counterparts in matter. The former can
therefore be expressed in terms of the latter, allowing more straightforward
extraction of the genuine lepton mixing quantities from a variety of
long-baseline neutrino oscillation experiments. In addition to the
parametrization-independent results, we present the formulas based on the
standard parametrization of the lepton flavor mixing matrix and give a typical
numerical illustration.Comment: RevTex 10 pages. Minor changes. Phys. Rev. D in printin
Phases and Transitions in Phantom Nematic Elastomer Membranes
Motivated by recently discovered unusual properties of bulk nematic
elastomers, we study a phase diagram of liquid-crystalline polymerized phantom
membranes, focusing on in-plane nematic order. We predict that such membranes
should enerically exhibit five phases, distinguished by their conformational
and in-plane orientational properties, namely isotropic-crumpled,
nematic-crumpled, isotropic-flat, nematic-flat and nematic-tubule phases. In
the nematic-tubule phase, the membrane is extended along the direction of {\em
spontaneous} nematic order and is crumpled in the other. The associated
spontaneous symmetries breaking guarantees that the nematic-tubule is
characterized by a conformational-orientational soft (Goldstone) mode and the
concomitant vanishing of the in-plane shear modulus. We show that long-range
orientational order of the nematic-tubule is maintained even in the presence of
harmonic thermal luctuations. However, it is likely that tubule's elastic
properties are ualitatively modified by these fluctuations, that can be studied
using a nonlinear elastic theory for the nematic tubule phase that we derive at
the end of this paper.Comment: 12 pages, 4 eps figures. To appear in PR
Polymeric forms of carbon in dense lithium carbide
The immense interest in carbon nanomaterials continues to stimulate intense
research activities aimed to realize carbon nanowires, since linear chains of
carbon atoms are expected to display novel and technologically relevant
optical, electrical and mechanical properties. Although various allotropes of
carbon (e.g., diamond, nanotubes, graphene, etc.) are among the best known
materials, it remains challenging to stabilize carbon in the one-dimensional
form because of the difficulty to suitably saturate the dangling bonds of
carbon. Here, we show through first-principles calculations that ordered
polymeric carbon chains can be stabilized in solid LiC under moderate
pressure. This pressure-induced phase (above 5 GPa) consists of parallel arrays
of twofold zigzag carbon chains embedded in lithium cages, which display a
metallic character due to the formation of partially occupied carbon lone-pair
states in \emph{sp}-like hybrids. It is found that this phase remains the
most favorable one in a wide range of pressure. At extreme pressure (larger the
215 GPa) a structural and electronic phase transition towards an insulating
single-bonded threefold-coordinated carbon network is predicted.Comment: 10 pages, 6 figure
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