670 research outputs found
A solution of a problem of Sophus Lie: Normal forms of 2-dim metrics admitting two projective vector fields
We give a complete list of normal forms for the 2-dimensional metrics that
admit a transitive Lie pseudogroup of geodesic-preserving transformations and
we show that these normal forms are mutually non-isometric. This solves a
problem posed by Sophus Lie.Comment: This is an extended version of the paper that will appear in Math.
Annalen. Some typos were corrected, references were updated, title was
changed (as in the journal version). 31 page
Some remarks on off-shell scattering in the eikonal approximation
Using the Abel inversion for the eikonal phase as function of the interaction
we derive simple integral relations between half and on-shell eikonal phases. A
frequently used short-range approximation for the half off-shell phase and
profile appears supported by the above-mentioned relation. We work out some
examples and also address the half off-shell eikonal phase pertinent to a
diffractive amplitude. The latter is relevant for a calculation of selected
transparencies of nuclei for a proton, knocked-out in selected
semi-inclusive (SI) reactions. Some numerical results for are given.Comment: 12 pages, uuencoded PS files for text and fig
The Superparticle and the Lorentz Group
We present a unified group-theoretical framework for superparticle theories.
This explains the origin of the ``twistor-like'' variables that have been used
in trading the superparticle's -symmetry for worldline supersymmetry.
We show that these twistor-like variables naturally parametrise the coset space
, where is the Lorentz group
and is its maximal subgroup. This space is a compact manifold, the
sphere . Our group-theoretical construction gives the proper
covariantisation of a fixed light-cone frame and clarifies the relation between
target-space and worldline supersymmetries.Comment: 33 page
A twistor-like D=10 superparticle action with manifest N=8 world-line supersymmetry
We propose a new formulation of the Brink-Schwarz superparticle which
is manifestly invariant under both the target-space super-Poincar\'e group and
the world-line local superconformal group. This twistor-like construction
naturally involves the sphere as a coset space of the Lorentz
group. The action contains only a finite set of auxiliary fields, but they
appear in unusual trilinear combinations. The origin of the on-shell
fermionic symmetry of the standard Brink-Schwarz formulation is
explained. The coupling to a super-Maxwell background requires a new
mechanism, in which the electric charge appears only on shell as an integration
constant.Comment: 22pages, standard LATEX fil
Performance of a fine-sampling electromagnetic calorimeter prototype in the energy range from 1 to 19 GeV
The fine-sampling electromagnetic calorimeter prototype has been
experimentally tested using the 1-19 GeV/c tagged beams of negatively charged
particles at the U70 accelerator at IHEP, Protvino. The energy resolution
measured by electrons is Delta{E}/E=2.8%/\sqrt{E} + 1.3%. The position
resolution for electrons is Delta{x}=3.1 + 15.4/sqrt{E} mm in the center of the
cell. The lateral non-uniformity of the prototype energy response to electrons
and MIPs has turned out to be negligible. Obtained experimental results are in
a good agreement with Monte-Carlo simulations.Comment: Article is prepared for pdflatex using the class elsart. 13 pages, 9
figures in 11 PDF file
Events in a Non-Commutative Space-Time
We treat the events determined by a quantum physical state in a
noncommutative space-time, generalizing the analogous treatment in the usual
Minkowski space-time based on positive-operator-valued measures (POVMs). We
consider in detail the model proposed by Snyder in 1947 and calculate the POVMs
defined on the real line that describe the measurement of a single coordinate.
The approximate joint measurement of all the four space-time coordinates is
described in terms of a generalized Wigner function (GWF). We derive lower
bounds for the dispersion of the coordinate observables and discuss the
covariance of the model under the Poincare' group. The unusual transformation
law of the coordinates under space-time translations is interpreted as a
failure of the absolute character of the concept of space-time coincidence. The
model shows that a minimal length is compatible with Lorents covariance.Comment: 13 pages, revtex. Introductory part shortened and some arguments made
more clea
Endothelial miR-30c suppresses tumor growth via inhibition of TGF-β–induced Serpine1
In tumors, extravascular fibrin forms provisional scaffolds for endothelial cell (EC) growth and motility during angiogenesis. We report that fibrin-mediated angiogenesis was inhibited and tumor growth delayed following postnatal deletion of Tgfbr2 in the endothelium of Cdh5-CreERT2 Tgfbr2fl/fl mice (Tgfbr2iECKOmice). ECs from Tgfbr2iECKO mice failed to upregulate the fibrinolysis inhibitor plasminogen activator inhibitor 1 (Serpine1, also known as PAI-1), due in part to uncoupled TGF-β–mediated suppression of miR-30c. Bypassing TGF-β signaling with vascular tropic nanoparticles that deliver miR-30c antagomiRs promoted PAI-1–dependent tumor growth and increased fibrin abundance, whereas miR-30c mimics inhibited tumor growth and promoted vascular-directed fibrinolysis in vivo. Using single-cell RNA-Seq and a NanoString miRNA array, we also found that subtypes of ECs in tumors showed spectrums of Serpine1 and miR-30c expression levels, suggesting functional diversity in ECs at the level of individual cells; indeed, fresh EC isolates from lung and mammary tumor models had differential abilities to degrade fibrin and launch new vessel sprouts, a finding that was linked to their inverse expression patterns of miR-30c and Serpine1 (i.e., miR-30chi Serpine1lo ECs were poorly angiogenic and miR-30clo Serpine1hi ECs were highly angiogenic). Thus, by balancing Serpine1 expression in ECs downstream of TGF-β, miR-30c functions as a tumor suppressor in the tumor microenvironment through its ability to promote fibrin degradation and inhibit blood vessel formation
Running coupling in electroweak interactions of leptons from f(R)-gravity with torsion
The f(R)-gravitational theory with torsion is considered for one family of
leptons; it is found that the torsion tensor gives rise to interactions having
the structure of the weak forces while the intrinsic non-linearity of the f(R)
function provides an energy-dependent coupling: in this way, torsional f(R)
gravity naturally generates both structure and strength of the electroweak
interactions among leptons. This implies that the weak interactions among the
lepton fields could be addressed as a geometric effect due to the interactions
among spinors induced by the presence of torsion in the most general f(R)
gravity. Phenomenological considerations are addressed.Comment: 9 pages. arXiv admin note: text overlap with arXiv:1012.5529 by other
author
Deriving the mass of particles from Extended Theories of Gravity in LHC era
We derive a geometrical approach to produce the mass of particles that could
be suitably tested at LHC. Starting from a 5D unification scheme, we show that
all the known interactions could be suitably deduced as an induced symmetry
breaking of the non-unitary GL(4)-group of diffeomorphisms. The deformations
inducing such a breaking act as vector bosons that, depending on the
gravitational mass states, can assume the role of interaction bosons like
gluons, electroweak bosons or photon. The further gravitational degrees of
freedom, emerging from the reduction mechanism in 4D, eliminate the hierarchy
problem since generate a cut-off comparable with electroweak one at TeV scales.
In this "economic" scheme, gravity should induce the other interactions in a
non-perturbative way.Comment: 30 pages, 1 figur
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