1,690 research outputs found
Dimensionful deformations of Poincare' symmetries for a Quantum Gravity without ideal observers
Quantum Mechanics is revisited as the appropriate theoretical framework for
the description of the outcome of experiments that rely on the use of classical
devices. In particular, it is emphasized that the limitations on the
measurability of (pairs of conjugate) observables encoded in the formalism of
Quantum Mechanics reproduce faithfully the ``classical-device limit'' of the
corresponding limitations encountered in (real or gedanken) experimental
setups. It is then argued that devices cannot behave classically in Quantum
Gravity, and that this might raise serious problems for the search of a class
of experiments described by theories obtained by ``applying Quantum Mechanics
to Gravity.'' It is also observed that using heuristic/intuitive arguments
based on the absence of classical devices one is led to consider some candidate
Quantum-Gravity phenomena involving dimensionful deformations of the Poincare'
symmetries.Comment: 7 pages, Latex. (This essay received an ``honorable mention'' from
the Gravity Research Foundation, 1998-Ed.
Tidal Waves -- a non-adiabatic microscopic description of the yrast states in near-spherical nuclei
The yrast states of nuclei that are spherical or weakly deformed in their
ground states are described as quadrupole waves running over the nuclear
surface, which we call "tidal waves". The energies and E2 transition
probabilities of the yrast states in nuclides with = 44, 46, 48 and are calculated by means of the cranking model in a microscopic
way. The nonlinear response of the nucleonic orbitals results in a strong
coupling between shape and single particle degrees of freedom
On the area operators of the Husain-Kuchar-Rovelli model and Canonical/Loop Quantum Gravity
I investigate the relation between an operative definition of the area of a
surface specified by matter fields and the area operators recently introduced
in the canonical/loop approach to Quantum Gravity and in Rovelli's variant of
the Husain-Kuchar Quantum-Gravity toy model. The results suggest that the
discreteness of the spectra of the area operators might not be observable.Comment: LaTex, 8 page
Proof of Gravity and Yang-Mills Amplitude Relations
Using BCFW on-shell recursion techniques, we prove a sequence of explicit
n-point Kawai-Lewellen-Tye relations between gravity and Yang-Mills amplitudes
at tree level.Comment: 17 pages, no figures, JHE
Spontaneous magnetization in high-density quark matter
It is shown that the spontaneous magnetization occurs due to the anomalous
magnetic moments of quarks in the high-density quark matter under the
tensor-type four-point interaction. The spin polarized condensate for each
flavor of quark appears at high baryon density, which leads to the spontaneous
magnetization due to the anomalous magnetic moments of quarks. The implications
to the strong magnetic field in the compact stars is discussed.Comment: 19 pages, 3 figure
Spin-triplet pairing in large nuclei
The nuclear pairing condensate is expected to change character from
spin-singlet to spin-triplet when the nucleus is very large and the neutron and
proton numbers are equal. We investigate the transition between these two
phases within the framework of the Hartree-Fock-Bogoliubov equations, using a
zero-range interaction to generate the pairing. We confirm that extremely large
nucleus would indeed favor triplet pairing condensates, with the Hamiltonian
parameters taken from known systematics. The favored phase is found to depend
on the specific orbitals at the Fermi energy. The smallest nuclei with a
well-developed spin-triplet condensate are in the mass region A ~ 130-140.Comment: 8 pages, 2 figures, 2 table
Spin Polarization versus Color-Flavor-Locking in High Density Quark Matter
It is shown that spin polarization with respect to each flavor in
three-flavor quark matter occurs instead of the color-flavor locking at high
baryon density by using the Nambu-Jona-Lasinio model with four-point
tensor-type interaction. Also, it is indicated that the order of phase
transition between the color-flavor locked phase and the spin polarized phase
is the first order by means of the second order perturbation theory.Comment: 23 pages, 4 figure
One-loop SYM-supergravity relation for five-point amplitudes
We derive a linear relation between the one-loop five-point amplitude of N=8
supergravity and the one-loop five-point subleading-color amplitudes of N=4
supersymmetric Yang-Mills theory.Comment: 17 pages, 2 figures; v2: very minor correction
Comment on "Limits of the measurability of the local quantum electromagnetic-field amplitude"
It is argued that the findings of a recent reanalysis by Compagno and Persico
[Phys. Rev. A 57, 1595 (1998)] of the Bohr--Rosenfeld procedure for the
measurement of a single space-time-averaged component of the electromagnetic
field are incorrect when the field measurement time is shorter than that
required for light to traverse the measurement's test body. To this end, the
time-averaged "self-force" on the test body, assumed for simplicity to be of a
spherical shape, is evaluated in terms of a one-dimensional quadrature for the
general trajectory allowed for the test body by Compagno and Persico, and in
closed form for the limiting steplike trajectory used by Bohr and Rosenfeld.Comment: 5 pages, REVTe
- …