968 research outputs found
Anomaly Cancellation in Supergravity with Fayet-Iliopoulos Couplings
We review and clarify the cancellation conditions for gauge anomalies which
occur when N=1, D=4 supergravity is coupled to a Kahler non-linear sigma-model
with gauged isometries and Fayet-Iliopoulos couplings. For a flat sigma-model
target space and vanishing Fayet-Iliopoulos couplings, consistency requires
just the conventional anomaly cancellation conditions. A consistent model with
non-vanishing Fayet-Iliopoulos couplings is unlikely unless the Green-Schwarz
mechanism is used. In this case the U(1) gauge boson becomes massive and the
D-term potential receives corrections. A Green-Schwarz mechanism can remove
both the abelian and certain non-abelian anomalies in models with a gauge
non-invariant Kahler potential.Comment: 27 page
Diffractive Higgs Production from Intrinsic Heavy Flavors in the Proton
We propose a novel mechanism for exclusive diffractive Higgs production in which the Higgs boson carries a significant fraction of the
projectile proton momentum. This mechanism will provide a clear experimental
signal for Higgs production due to the small background in this kinematic
region. The key assumption underlying our analysis is the presence of intrinsic
heavy flavor components of the proton bound state, whose existence at high
light-cone momentum fraction has growing experimental and theoretical
support. We also discuss the implications of this picture for exclusive
diffractive quarkonium and other channels.Comment: 30 pages, 5 figure
Helical vs. fundamental solitons in optical fibers
We consider solitons in a nonlinear optical fiber with a single polarization
in a region of parameters where it carries exactly two distinct modes, the
fundamental one and the first-order helical mode. From the viewpoint of
applications to dense-WDM communication systems, this opens way to double the
number of channels carried by the fiber. Aside from that, experimental
observation of helical (spinning) solitons and collisions between them and with
fundamental solitons are issues of fundamental interest. We introduce a system
of coupled nonlinear Schroedinger equations for fundamental and helical modes,
which have nonstandard values of the cross-phase-modulation coupling constants,
and investigate, analytically and numerically, results of "complete" and
"incomplete" collisions between solitons carried by the two modes. We conclude
that the collision-induced crosstalk is partly attenuated in comparison with
the usual WDM system, which sometimes may be crucially important, preventing
merger of the colliding solitons into a breather. The interaction between the
two modes is found to be additionally strongly suppressed in comparison with
that in the WDM system in the case when a dispersion-shifted or
dispersion-compensated fiber is used.Comment: a plain latex file with the text and two ps files with figures.
Physica Scripta, in pres
Orthocomplementation and compound systems
In their 1936 founding paper on quantum logic, Birkhoff and von Neumann
postulated that the lattice describing the experimental propositions concerning
a quantum system is orthocomplemented. We prove that this postulate fails for
the lattice L_sep describing a compound system consisting of so called
separated quantum systems. By separated we mean two systems prepared in
different ``rooms'' of the lab, and before any interaction takes place. In that
case the state of the compound system is necessarily a product state. As a
consequence, Dirac's superposition principle fails, and therefore L_sep cannot
satisfy all Piron's axioms. In previous works, assuming that L_sep is
orthocomplemented, it was argued that L_sep is not orthomodular and fails to
have the covering property. Here we prove that L_sep cannot admit and
orthocomplementation. Moreover, we propose a natural model for L_sep which has
the covering property.Comment: Submitted for the proceedings of the 2004 IQSA's conference in
Denver. Revised versio
Estudio electrocardiografía en estación y de cúbito lateral derecho en crías de alpaca (Vicugna pacos)
The aim of the study was to determine the electrocardiographic parameters in both station and right lateral decubitus positions in baby alpacas. The work was done in 30 alpacas (17 males and 13 females) of 60 days old, from the communities alpaqueras Maranganí, Canchis in Cusco. The electrocardiographic values in station and right lateral decubitus were: heart rate 124.83 and 114.16, P wave duration 0.04 and 0.04 s, P wave amplitude 0.180 and 0.173 mV, duration and PQ 0.101 s 0.102, 0.039 and 0.038 QRS duration s, QRS complex 0.643 and 0.557 mV, duration and QT 0.225 0.2370.040 s, T wave amplitude 0.393 and 0.413 mV. The values of ECG parameters showed no significant differences between the two positions. We conclude that is possible to use any positions for the clinic examen in alpacas.El presente estudio tuvo por objetivo determinar los parámetros electrocardiográficos en las posiciones estación y decúbito lateral derecha en crías de alpacas. El trabajo se hizo en 30 alpacas (17 machos y 13 hembras) menores de 60 días de edad, provenientes de las comunidades alpaqueras de Maranganí, Canchis, en Cusco. Los valores electrocardiográficos en estación y en decúbito lateral derecho fueron: Frecuencia cardiaca 124.83 y 114.16, Duración onda P 0.04 y 0.04 s, amplitud onda P 0.180 y 0.173 mV, duración PQ 0.102 y 0.101 s, duración QRS 0.039 y 0.038 s, complejo QRS 0.643 y 0.557 mV, duración QT 0.225 y 0.2370.040 s, amplitud onda T 0.393 y 0.413 mV, los valores no mostraron diferencias significativas al comparalos entre ambas posiciones. Se concluye que en alpacas se puede usar indiferentemente cualquiera de las dos posiciones electrocardiográficas para fines clínico
Tur\'an numbers for -free graphs: topological obstructions and algebraic constructions
We show that every hypersurface in contains a large grid,
i.e., the set of the form , with . We use this to
deduce that the known constructions of extremal -free and
-free graphs cannot be generalized to a similar construction of
-free graphs for any . We also give new constructions of
extremal -free graphs for large .Comment: Fixed a small mistake in the application of Proposition
Double-loop hysteresis of multisite dilute Sr(YDy)O single crystal Kramers paramagnets: electron-phonon interaction, quantum tunneling and cross-relaxation
Experimental and theoretical studies of the dynamic magnetization in swept
magnetic fields of the orthorhombic SrYO single-crystals doped with the
Dy Kramers ions (0.01 and 0.5 at.%) with natural abundances of even and
odd Dy isotopes are presented. Impurity ions substitute for Y ions at
two nonequivalent crystallographic sites with the same local symmetry but
strongly different crystal fields. Well pronounced double-loop hysteresis is
observed at temperatures 2, 4, 5 and 6 K for sweeping rates of 5 and 1 mT/s.
The microscopic model of spectral, magnetic and kinetic properties of Dy
ions is developed based on the results of EPR, site selective optical spectra
and magnetic relaxation measurements. The derived approach to the dynamic
magnetization in the sweeping field based on the numerical solution of
generalized master equations with time-dependent transition probabilities
induced by the electron-phonon interaction, quantum tunneling and
cross-relaxation allowed us to reproduce successfully the evolution of the
hysteresis loop shape with temperature, sweeping rate and concentration of
paramagnetic ions.Comment: 11 pages, 6 figures, 2 tables, 52 reference
Scanning the Quark-Gluon Plasma with Charmonium
We suggest the variation of charmonium suppression with Feynman x_F in heavy
ion collisions as a novel and sensitive probe for the properties of the matter
created in such reactions. In contrast to the proton-nucleus case where nuclear
suppression is weakest at small x_F, final state interactions with the comoving
matter create a minimum at x_F=0, which is especially deep and narrow if a
quark-gluon plasma is formed. While a particularly strong effect is predicted
at SPS, at the higher RHIC energy it overlaps with the expected sharp variation
with x_F of nuclear effects and needs comparison with proton-nucleus data. If
thermal enhancement of J/\Psi production takes over at the energies of RHIC and
LHC, it will form an easily identified peak, rather than dip in x_F dependence.
We predict a steep dependence on centrality and suggest that this new probe is
complementary to the dependence on transverse energy, and is more sensitive to
a scenario of final state interactions.Comment: 5 pages including 3 figures. Stylistic and clarifying corrections are
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Nonequilibrium Cooper pairing in the nonadiabatic regime
We obtain a complete solution for the mean-field dynamics of the BCS paired
state with a large, but finite number of Cooper pairs in the non-adiabatic
regime. We show that the problem reduces to a classical integrable Hamiltonian
system and derive a complete set of its integrals of motion. The condensate
exhibits irregular multi-frequency oscillations ergodically exploring the part
of the phase-space allowed by the conservation laws. In the thermodynamic limit
however the system can asymptotically reach a steady state.Comment: 4 pages, no figure
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