76,588 research outputs found
Conformal Symmetry and Pion Form Factor: Soft and Hard Contributions
We discuss a constraint of conformal symmetry in the analysis of the pion
form factor. The usual power-law behavior of the form factor obtained in the
perturbative QCD analysis can also be attained by taking negligible quark
masses in the nonperturbative quark model analysis, confirming the recent
AdS/CFT correspondence. We analyze the transition from soft to hard
contributions in the pion form factor considering a momentum-dependent
dynamical quark mass from a nonnegligible constituent quark mass at low
momentum region to a negligible current quark mass at high momentum region. We
find a correlation between the shape of nonperturbative quark distribution
amplitude and the amount of soft and hard contributions to the pion form
factor.Comment: 7 pages, 6 figures, extensively revised, to appear in Phys. Rev.
Intersecting Brane World from Type I Compactification
We elaborate that general intersecting brane models on orbifolds are obtained
from type I string compactifications and their T-duals. Symmetry breaking and
restoration occur via recombination and parallel separation of branes,
preserving supersymmetry. The Ramond-Ramond tadpole cancelation and the toron
quantization constrain the spectrum as a branching of the adjoints of SO(32),
up to orbifold projections. Since the recombination changes the gauge coupling,
the single gauge coupling of type I could give rise to different coupling below
the unification scale. This is due to the nonlocal properties of the
Dirac-Born-Infeld action. The weak mixing angle sin^2 theta_W = 3/8 is
naturally explained by embedding the quantum numbers to those of SO(10).Comment: 31 pages, 5 figure
Time-dependent coupled oscillator model for charged particle motion in the presence of a time varyingmagnetic field
The dynamics of time-dependent coupled oscillator model for the charged
particle motion subjected to a time-dependent external magnetic field is
investigated. We used canonical transformation approach for the classical
treatment of the system, whereas unitary transformation approach is used when
managing the system in the framework of quantum mechanics. For both approaches,
the original system is transformed to a much more simple system that is the sum
of two independent harmonic oscillators which have time-dependent frequencies.
We therefore easily identified the wave functions in the transformed system
with the help of invariant operator of the system. The full wave functions in
the original system is derived from the inverse unitary transformation of the
wave functions associated to the transformed system.Comment: 16 page
Topological quantization and degeneracy in Josephson-junction arrays
We consider the conductivity quantization in two-dimensional arrays of
mesoscopic Josephson junctions, and examine the associated degeneracy in
various regimes of the system. The filling factor of the system may be
controlled by the gate voltage as well as the magnetic field, and its
appropriate values for quantization is obtained by employing the Jain hierarchy
scheme both in the charge description and in the vortex description. The
duality between the two descriptions then suggests the possibility that the
system undergoes a change in degeneracy while the quantized conductivity
remains fixed.Comment: To appear in Phys. Rev.
A QCD Axion from Higher Dimensional Gauge Field
We point out that a QCD axion solving the strong CP problem can arise
naturally from parity-odd gauge field C_M in 5-dimensional (5D) orbifold field
theory. The required axion coupling to the QCD anomaly comes from the 5D
Chern-Simons coupling, and all other unwanted U(1)_{PQ} breaking axion
couplings can be avoided naturally by the 5D gauge symmetry of C_M and the 5D
locality. If the fifth dimension is warped, the resulting axion scale is
suppressed by small warp factor compared to the Planck scale, thereby the model
can generate naturally an intermediate axion scale f_a=10^{10} - 10^{12}GeV.Comment: 5 pages, Revtex
Extremal extensions of entanglement witnesses: Unearthing new bound entangled states
In this paper, we discuss extremal extensions of entanglement witnesses based
on Choi's map. The constructions are based on a generalization of the Choi map
due to Osaka, from which we construct entanglement witnesses. These extremal
extensions are powerful in terms of their capacity to detect entanglement of
positive under partial transpose (PPT) entangled states and lead to unearthing
of entanglement of new PPT states. We also use the Cholesky-like decomposition
to construct entangled states which are revealed by these extremal entanglement
witnesses.Comment: 8 pages 6 figures revtex4-
Sudden death of effective entanglement
Sudden death of entanglement is a well-known effect resulting from the finite
volume of separable states. We study the case when the observer has a limited
measurement capability and analyse the effective entanglement, i.e.
entanglement minimized over the output data. We show that in the well defined
system of two quantum dots monitored by single electron transistors, one may
observe a sudden death of effective entanglement when real, physical
entanglement is still alive. For certain measurement setups, this occurs even
for initial states for which sudden death of physical entanglement is not
possible at all. The principles of the analysis may be applied to other
analogous scenarios, such as etimation of the parameters arising from quantum
process tomography.Comment: final version, 5 pages, 3 figure
Can real-time visual feedback during gait retraining reduce metabolic demand for individuals with transtibial amputation?
The metabolic demand of walking generally increases following lower extremity amputation. This study used real-time visual feedback to modify biomechanical factors linked to an elevated metabolic demand of walking in individuals with transtibial amputation. Eight persons with unilateral, traumatic transtibial amputation and 8 uninjured controls participated. Two separate bouts of real-time visual feedback were provided during a single session of gait retraining to reduce 1) center of mass sway and 2) thigh muscle activation magnitudes and duration. Baseline and post-intervention data were collected. Metabolic rate, heart rate, frontal plane center of mass sway, quadriceps and hamstrings muscle activity, and co-contraction indices were evaluated during steady state walking at a standardized speed. Visual feedback successfully decreased center of mass sway 12% (p = 0.006) and quadriceps activity 12% (p = 0.041); however, thigh muscle co-contraction indices were unchanged. Neither condition significantly affected metabolic rate during walking and heart rate increased with center-of-mass feedback. Metabolic rate, center of mass sway, and integrated quadriceps muscle activity were all not significantly different from controls. Attempts to modify gait to decrease metabolic demand may actually adversely increase the physiological effort of walking in individuals with lower extremity amputation who are young, active and approximate metabolic rates of able-bodied adults
The definability criterions for convex projective polyhedral reflection groups
Following Vinberg, we find the criterions for a subgroup generated by
reflections \Gamma \subset \SL^{\pm}(n+1,\mathbb{R}) and its finite-index
subgroups to be definable over where is an integrally
closed Noetherian ring in the field . We apply the criterions for
groups generated by reflections that act cocompactly on irreducible properly
convex open subdomains of the -dimensional projective sphere. This gives a
method for constructing injective group homomorphisms from such Coxeter groups
to \SL^{\pm}(n+1,\mathbb{Z}). Finally we provide some examples of
\SL^{\pm}(n+1,\mathbb{Z})-representations of such Coxeter groups. In
particular, we consider simplicial reflection groups that are isomorphic to
hyperbolic simplicial groups and classify all the conjugacy classes of the
reflection subgroups in \SL^{\pm}(n+1,\mathbb{R}) that are definable over
. These were known by Goldman, Benoist, and so on previously.Comment: 31 pages, 8 figure
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