12,382 research outputs found
Spin and pseudospin symmetries in the antinucleon spectrum of nuclei
Spin and pseudospin symmetries in the spectra of nucleons and antinucleons
are studied in a relativistic mean-field theory with scalar and vector
Woods-Saxon potentials, in which the strength of the latter is allowed to
change. We observe that, for nucleons and antinucleons, the spin symmetry is of
perturbative nature and it is almost an exact symmetry in the physical region
for antinucleons. The opposite situation is found in the pseudospin symmetry
case, which is better realized for nucleons than for antinucleons, but is of
dynamical nature and cannot be viewed in a perturbative way both for nucleons
and antinucleons. This is shown by computing the spin-orbit and
pseudospin-orbit couplings for selected spin and pseudospin partners in both
spectra.Comment: 8 figures, uses revtex 4.1 macro
Deterministic Secure Communications using Two-Mode Squeezed States
We propose a scheme for quantum cryptography that uses the squeezing phase of
a two-mode squeezed state to transmit information securely between two parties.
The basic principle behind this scheme is the fact that each mode of the
squeezed field by itself does not contain any information regarding the
squeezing phase. The squeezing phase can only be obtained through a joint
measurement of the two modes. This, combined with the fact that it is possible
to perform remote squeezing measurements, makes it possible to implement a
secure quantum communication scheme in which a deterministic signal can be
transmitted directly between two parties while the encryption is done
automatically by the quantum correlations present in the two-mode squeezed
state.Comment: 10 pages, 4 figure
On the relativistic L-S coupling
The fact that the Dirac equation is linear in the space and time derivatives
leads to the coupling of spin and orbital angular momenta that is of a pure
relativistic nature. We illustrate this fact by computing the solutions of the
Dirac equation in an infinite spherical well, which allows to go from the
relativistic to the non-relativistic limit by just varying the radius of the
well.Comment: LateX2e, 12 pages, 1 figure, accepted in Eur. J. Phy
A note on a third order curvature invariant in static spacetimes
We consider here the third order curvature invariant
in static spacetimes
for which is conformally flat. We evaluate
explicitly the invariant for the -dimensional Majumdar-Papapetrou multi
black-holes solution, confirming that does indeed vanish on the event
horizons of such black-holes. Our calculations show, however, that solely the
vanishing of is not sufficient to locate an event horizon in
non-spherically symmetric spacetimes. We discuss also some tidal effects
associated to the invariant .Comment: 5 pages, 3 figures. Extra material available at
http://vigo.ime.unicamp.br/in
Time-optimal Unitary Operations in Ising Chains II: Unequal Couplings and Fixed Fidelity
We analytically determine the minimal time and the optimal control laws
required for the realization, up to an assigned fidelity and with a fixed
energy available, of entangling quantum gates () between
indirectly coupled qubits of a trilinear Ising chain. The control is coherent
and open loop, and it is represented by a local and continuous magnetic field
acting on the intermediate qubit. The time cost of this local quantum operation
is not restricted to be zero. When the matching with the target gate is perfect
(fidelity equal to one) we provide exact solutions for the case of equal Ising
coupling. For the more general case when some error is tolerated (fidelity
smaller than one) we give perturbative solutions for unequal couplings.
Comparison with previous numerical solutions for the minimal time to generate
the same gates with the same Ising Hamiltonian but with instantaneous local
controls shows that the latter are not time-optimal.Comment: 11 pages, no figure
Kinetic description of charmonium production in high-energy nuclear collisions
We study the evolution of charmonia as they collide with the constituents of
the fireball produced in high-energy nucleus-nucleus collisions. The latter
evolves in a manner controlled by the equation of state as given by lattice
QCD, and is constructed in such a way that the observed hadronic spectra are
correctly reproduced. A kinetic description of charmonium interactions with
both quark-gluon and hadronic degrees of freedom allows to study in detail the
evolution in different regimes, controlled by collision energy, kinematics and
geometry. The data collected at the CERN-SPS accelerator are well described and
new estimates for J/psi production at BNL-RHIC are presented.Comment: 19 pages, LaTeX, 13 .eps figure
Closed-loop input impedance of PWM buck-derived DC-DC convertersProceedings of IEEE International Symposium on Circuits and Systems - ISCAS '94
Errors on the inverse problem solution for a noisy spherical gravitational wave antenna
A single spherical antenna is capable of measuring the direction and
polarization of a gravitational wave. It is possible to solve the inverse
problem using only linear algebra even in the presence of noise. The simplicity
of this solution enables one to explore the error on the solution using
standard techniques. In this paper we derive the error on the direction and
polarization measurements of a gravitational wave. We show that the solid angle
error and the uncertainty on the wave amplitude are direction independent. We
also discuss the possibility of determining the polarization amplitudes with
isotropic sensitivity for any given gravitational wave source.Comment: 13 pages, 4 figures, LaTeX2e, IOP style, submitted to CQ
Non-linear unbalanced Bessel beams: Stationary conical waves supported by nonlinear losses
Nonlinear losses accompanying Kerr self-focusing substantially impacts the
dynamic balance of diffraction and nonlinearity, permitting the existence of
localized and stationary solutions of the 2D+1 nonlinear Schrodinger equation
which are stable against radial collapse. These are featured by linear conical
tails that continually refill the nonlinear, central spot. An experiment shows
that the discovered solution behaves as strong attractor for the self-focusing
dynamics in Kerr media.Comment: 4 pages, 2 figures; experimental verification adde
Reconstructing the massive black hole cosmic history through gravitational waves
The massive black holes we observe in galaxies today are the natural
end-product of a complex evolutionary path, in which black holes seeded in
proto-galaxies at high redshift grow through cosmic history via a sequence of
mergers and accretion episodes. Electromagnetic observations probe a small
subset of the population of massive black holes (namely, those that are active
or those that are very close to us), but planned space-based gravitational-wave
observatories such as the Laser Interferometer Space Antenna (LISA) can measure
the parameters of ``electromagnetically invisible'' massive black holes out to
high redshift. In this paper we introduce a Bayesian framework to analyze the
information that can be gathered from a set of such measurements. Our goal is
to connect a set of massive black hole binary merger observations to the
underlying model of massive black hole formation. In other words, given a set
of observed massive black hole coalescences, we assess what information can be
extracted about the underlying massive black hole population model. For
concreteness we consider ten specific models of massive black hole formation,
chosen to probe four important (and largely unconstrained) aspects of the input
physics used in structure formation simulations: seed formation, metallicity
``feedback'', accretion efficiency and accretion geometry. For the first time
we allow for the possibility of ``model mixing'', by drawing the observed
population from some combination of the ``pure'' models that have been
simulated. A Bayesian analysis allows us to recover a posterior probability
distribution for the ``mixing parameters'' that characterize the fractions of
each model represented in the observed distribution. Our work shows that LISA
has enormous potential to probe the underlying physics of structure formation.Comment: 24 pages, 16 figures, submitted to Phys. Rev.
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